Technical Field

The present invention relates to novel light emitting device architectures for application in displays, light panels and other optoelectronic devices, and in particular to stacked blue light emitting devices that comprise two or more emissive units that emit blue light having substantially different chromaticity.

Background

Organic Light Emitting Diode (OLED) technology is advancing rapidly, with recent innovations enabling thinner and lighter displays with higher resolution, improved frame rate and enhanced contrast ratio. OLED technology is now considered state-of- the-art for small-area displays and is widely adopted in flagship smartphones such as the Samsung Galaxy S20 Ultra, iPhone 11 Pro Max and One Plus 8 Pro, which all comprise efficient, bight and colourful OLED displays.

Despite the ongoing success of OLED technology in the small-area display market, relatively few large-area displays such as televisions comprise OLED technology. The majority of televisions are still manufactured using adapted liquid crystal display (LCD) architectures. This disparity can be explained by the difference in display architectures for small-area OLED smartphone displays and large-area OLED television displays.

OLED smartphones comprise an RGB OLED display architecture where red, green and blue organic light emitting materials are patterned into separate red, green and blue sub-pixels that emit red, green and blue light. An exemplary RGB OLED display architecture is depicted by arrangement 1800 in FIG. 18. The device of the red sub pixel 1805 comprises a red emissive layer 1840. The device of the green sub-pixel 1815 comprises a green emissive layer 1850. The device of the blue sub-pixel 1825 comprises a blue emissive layer 1860. The red, green and blue emissive layers are disposed between a first electrode 1820 and a second electrode 1830. All layers are disposed on a substrate 1810. The exemplary RGB OLED display architecture of arrangement 1800 may include optional additional device layers that are not depicted in FIG. 18. Patterning of red, green and blue emissive layers is achieved by depositing red, green and blue organic light emitting materials by vapour thermal evaporation through fine metal masks with openings that are precisely aligned to the respective red, green and blue sub-pixels. The RGB OLED display architecture delivers high performance because each of the red, green and blue sub-pixels may be individually optimized to emit efficient, bright and colourful light. The RGB OLED display architecture is also relatively low cost because each of the red, green and blue sub pixels typically comprises a simple OLED device stack of approximately 6-7 evaporated layers. Unfortunately, the RGB OLED display architecture used so successfully in smartphones has not been successfully scaled for application in televisions. The problem is that manufacturing televisions requires larger glass substrates (e.g. 3130 mm x 2880 mm Gen 10 substrates) than manufacturing smartphones (e.g. 1800 mm x 1500 mm Gen 6 substrates). The fine metal masks required to pattern red, green and blue organic light emitting material into red, green and blue sub-pixels then have the tendency to sag over the larger substrate area leading to misalignment and undesirable shadowing effects.

OLED televisions instead comprise an RGBW OLED display architecture where each sub-pixel of the display comprises a white OLED. Individual patterning of different sub pixels is not required. An exemplary RGBW OLED display architecture is depicted by arrangement 1900 in FIG. 19. Colour filters of red, green and blue are patterned over three-out-of-four of the white OLED sub-pixels. The device of the red sub-pixel 1905 comprises a white OLED optically coupled to a red colour filter 1985. The device of the green sub-pixel 1915 comprises a white OLED optically coupled to a green colour filter 1990. The device of the blue sub-pixel 1925 comprises a white OLED optically coupled to a blue colour filter 1995. The device of the white sub-pixel 1935 comprises a white OLED without a colour filter. Each white OLED comprises a stacked light emitting device having three emissive units comprising a red emissive layer 1930, a green emissive layer 1950 and a blue emissive layer 1970 all disposed between a first electrode 1920 and a second electrode 1980. The red emissive layer 1930 is separated from the green emissive layer 1950 by a first charge generation layer 1940. The green emissive layer 1950 is separated from the blue emissive layer 1970 by a second charge generation layer 1960. All layers are disposed on a substrate 1910. The exemplary RGBW OLED display architecture of arrangement 1900 may include optional additional device layers that are not depicted in FIG. 19.

Unfortunately, the RGBW OLED display architecture used in OLED televisions delivers reduced performance compared to the RGB OLED display architecture used in OLED smartphones. The is because the majority of light emitted from the white OLEDs in the red, green and blue sub-pixels is filtered out. This reduces the efficiency and brightness of the display. The colourfulness of an RGBW OLED display is also limited because there is a trade-off between using stronger colour filters to extend the colour gamut of the display and reducing brightness by filtering out more white light. The RGBW OLED display architecture is also relatively expensive because each of the red, green and blue sub-pixels typically comprises a white OLED device stack of approximately 15-20 evaporated layers.

OLED televisions with an RGBW OLED display architecture are therefore less efficient, less bright, less colourful and relatively more expensive than OLED smartphones with an RGB OLED display architecture. This is why OLED technology is widely adopted in smartphones but not in televisions. To address this challenge, a novel QD-OLED display architecture was recently proposed by Samsung. An exemplary QD-OLED display architecture is depicted by arrangement 2000 in FIG. 20. In the QD-OLED display architecture, each sub-pixel of the display comprises a blue OLED. Colour conversion layers of red and green are then patterned over two-out-of-three of the blue OLED sub-pixels. The device of the red sub-pixel 2005 comprises a blue emissive layer 2040 optically coupled to a red colour conversion layer 2050. The device of the green sub pixel 2015 comprises a blue emissive layer 2040 optically coupled to a green colour conversion layer 2060. The device of the blue sub-pixel 2025 comprises a blue emissive layer 2040 without a colour conversion layer. The blue emissive layers are disposed between a first electrode 2020 and a second electrode 2030. All layers are disposed on a substrate 2010. The exemplary QD-OLED display architecture of arrangement 2000 may include optional additional device layers that are not depicted in FIG. 20.

Samsung propose that the red and green colour conversion layers comprise quantum dot (QD) material which gives rise to the name of QD-OLED for this display architecture.

The QD-OLED display architecture is expected to be an improvement over the RGBW OLED display architecture. This is because converting blue light to red light or green light using colour conversion layers is a more efficient process than filtering white light to red, green or blue light using colour filters. QD-OLED displays are therefore expected to be more efficient, brighter and more colourful than RGBW OLED displays. Furthermore, the blue OLED device stack in a QD-OLED display may be simpler and may comprise fewer layers than the white OLED stack in an RGBW OLED display. This reduces costs. These improvements may all be achieved without fine metal mask technology because as for RGBW OLED displays, QD-OLED displays may be manufactured without individual patterning of light-emitting materials for the different sub-pixels.

However, the proposed QD-OLED display architecture does suffer from drawbacks. In particular, one significant drawback is that the lifetime of blue OLED devices is typically shorter than for red and green OLED devices, and in the QD-OLED display architecture blue OLEDs are used to provide light for the red and green sub-pixels as well as for the blue sub-pixels. This is expected to limit the lifetime of a QD-OLED display. Furthermore, blue light emitted by the blue OLEDs must be highly saturated to enable the display to render deep blue colours and an extended colour gamut. The problem is that deep blue phosphorescent emitters that have higher efficiency are relatively unstable and unsuitable for commercial applications. It is therefore expected that deep blue fluorescent emitters that have lower efficiency, but relatively improved stability will be required. This will reduce the efficiency and brightness of the QD-OLED display. Furthermore, blue light emitted by the blue OLEDs must be simultaneously optimized to match the absorption of the red and green colour conversion materials and to be deep enough to enable a display to render deep blue colours for an extended colour gamut. There is likely a trade-off that will result in reduced performance.

The present invention addresses these problems by proposing a stacked blue light emitting device architecture comprising two or more emissive units that emit blue light having substantially different chromaticity for application in displays, light panels and other optoelectronic devices. Optionally, at least one emissive unit may emit deeper blue light and at least one emissive unit may emit lighter blue light.

The proposed architecture is depicted by exemplary arrangement 2100 in FIG. 21 for a stacked blue light emitting device having two emissive units. The device of the red sub pixel 2105 comprises a first blue emissive unit 2130 and a second blue emissive unit 2150 separated by a first charge generation layer 2140 and optically coupled to a red colour conversion layer 2170. The device of the green sub-pixel 2115 comprises a first blue emissive unit 2130 and a second blue emissive unit 2150 separated by a first charge generation layer 2140 and optically coupled to a green colour conversion layer 2180. The device of the blue sub-pixel 2125 comprises a first blue emissive unit 2130 and a second blue emissive unit 2150 separated by a first charge generation layer 2140. The layers of the first and second blue emissive units and first charge generation layer are all disposed between a first electrode 2120 and a second electrode 2160. All layers are disposed on a substrate 2110. At least one of the first blue emissive unit 2130 and the second blue emissive unit 2150 may emit a lighter blue light, and at least one of the first blue emissive unit 2130 and the second blue emissive unit 2150 may emit a deeper blue light.

Optionally, the stacked blue light emitting device architecture of the present invention may comprise a third emissive unit 2220 and a second charge generation layer 2210. This is depicted by exemplary arrangement 2200 in FIG. 22 for a stacked blue light emitting device having three emissive units. The third emissive unit 2220 may emit a lighter blue light or a deeper blue light.

Optionally, the emissive units may be addressed independently and may emit light independently of each other. Optionally, the emissive units may be commonly addressed and may not emit light independently of each other.

Such stacked blue light emitting devices may be incorporated into the red, green and blue sub-pixels of an OLED display. When the blue sub-pixel of such a display is required to emit a relatively saturated blue light that is more saturated than light that may be emitted from the lighter blue emissive units, but less saturated than light that may be emitted from the deeper blue emissive units, the emissive unit that emits deeper blue light may be individually addressed and may emit light to generate the display image while the emissive unit that emits lighter blue light may remain inactive. However, when the blue sub-pixel of such a display is only required to emit a relatively unsaturated blue light that is less saturated than light that may be emitted from the lighter blue emissive units, the emissive unit that emits lighter blue light may be individually addressed and may emit light to generate the display image while the emissive unit that emits deeper blue light may remain inactive. Light may be emitted from the relatively more efficient and/or stable lighter blue emissive unit to render the majority of display images, with light emitted from the relatively less efficient and/or stable deeper blue emissive unit only required to render a small proportion of images. The efficiency and/or lifetime of the display may therefore be enhanced. Furthermore, the lighter blue emissive unit may be used on its own or in combination with the deeper blue emissive unit to provide light to the red and green colour conversion layers in the red and green sub-pixels.

Optionally, the lighter blue emissive unit may comprise a phosphorescent organic light emitting material or a fluorescent organic light emitting material. Optionally, the deeper blue emissive unit may comprise a phosphorescent organic light emitting material or a fluorescent organic light emitting material. Optionally, the lighter blue emissive unit may comprise a fluorescent organic light emitting material and the deeper blue emissive unit may comprise a fluorescent organic light emitting material. Optionally, the lighter blue emissive unit may comprise a phosphorescent organic light emitting material and the deeper blue emissive unit may comprise a phosphorescent organic light emitting material. Optionally, the lighter blue emissive unit may comprise a phosphorescent organic light emitting material and the deeper blue emissive unit may comprise a fluorescent organic light emitting material.

The proposed novel device architecture is ideally suited to OLED devices and displays. The proposed novel device architecture is also ideally suited to quantum dot light emitting diode (QLED) displays comprising quantum dot light emitting material and perovskite light emitting diode (PeLED) displays comprising perovskite light emitting material. Inherent properties of organic light emitting materials, quantum dot light emitting materials and perovskite light emitting materials render them well-suited to the herein disclosed stacked blue light emitting device architecture. These properties include optical band gaps that are readily tunable across the visible, ultra-violet and infra-red spectra, high colour saturation that enables displays with wide colour gamut, excellent charge transport properties and low non-radiative rates.

The proposed novel device architecture has several advantages over the related art, as demonstrated by the following exemplary related art:

WO 2019/224546 A1 discloses a stacked light emitting device comprising at least one PeLED emissive unit and at least one PeLED, OLED or QLED emissive unit. The emissive units may be of any colour and may be commonly or independently addressable. The emissive units may be optically coupled to one or more colour conversion layers. This has the benefit of enabling different classes of emissive materials, such as OLED, QLED and PeLED to be combined in a stacked light emitting device. However, unlike the present disclosure, WO 2019/224546 A1 does not disclose details of how such a stacked light emitting device architecture may be implemented in one or more sub pixels of a display. Furthermore, it does not disclose any embodiments where the emissive units may be of different chromaticity or describe any applications or advantages of having emissive units of different chromaticity. It only discloses chromaticity data for exemplary emissive units comprising different classes of emissive materials. Unlike the present disclosure, WO 2019/224546 A1 is also limited to stacked light emitting devices where one or more PeLED emissive units and combined with one or more PeLED, OLED or QLED emissive units. It does not include stacked light emitting devices comprising only OLED, only QLED or only PeLED emissive units, which would be simpler to manufacture.

US 2019/0043407 A1 discloses a pixel layout for a display comprising a blue sub-pixel that comprises a stacked blue light emitting device having two blue emissive units of different chromaticities that are independently addressable, and (as disclosed in paragraph [0043] and [0057]) red and green sub-pixels that are single junction (not stacked) light emitting devices. Unlike the present disclosure, the pixel layout disclosed in US 2019/0043407 A1 does not comprise red and green colour conversion layers, and requires that red, green and blue emissive units be individually patterned into their respective sub-pixels. This may add complexity and cost to the manufacturing process and may be difficult to scale to larger area substrates.

EP 3188272 A1 discloses a stacked blue light emitting device comprising a first emissive unit and a second emissive unit separated by a charge generation layer. The first emissive unit comprises a first emissive layer that emits blue light, and the second emissive unit comprises a second emissive layer that emits blue light, wherein the first and second emissive layers emit light of different chromaticity. Also disclosed is an example with three emissive units comprising three emissive layers. Also included is a display architecture, wherein there are colour conversion materials over the red and green sub-pixels. Unlike the present disclosure, the emissive units disclosed in EP 3188272 A1 in FIG. 7 and FIG. 8 are commonly addressable and the charge generation layer is common to all sub-pixels. There is no disclosure of independently addressable emissive units. Unlike the present disclosure, it is therefore impossible to select and independently address different emissive units and different emissive layers of different chromaticities to render an image depending on the image content. Equivalent reduced power consumption and increased device lifetime therefore cannot be achieved.

WO 2020/030042 A1 discloses an OLED display comprising at least a first blue emissive layer and one or more additional blue emissive layers disposed over the entire display area of a substrate, and a quantum dot colour film disposed on the light-emitting side of the substrate. Paragraphs [0065] and [0066] describe that the blue emissive layers emit blue light of different chromaticity, with one emitting at 400-440 nm, and the other emitting at 440-490 nm. The quantum dot film may comprise red quantum dots for the red sub-pixel and green quantum dots for the green sub-pixel. The blue sub pixel may or may not comprise quantum dots. The blue emissive layers may be connected in series by a charge generation layer as in a standard stacked device, or there may be separate anode and cathodes for each emissive unit that are electrically connected in series. Unlike the present disclosure, the emissive layers disclosed in WO 2020/030042 A1 are described as being connected in series. There is no disclosure of independently addressable emissive units. Unlike the present disclosure, it is therefore impossible to select and independently address different emissive units and different emissive layers of different chromaticities to render an image depending on the image content. Equivalent reduced power consumption and increased device lifetime therefore cannot be achieved.

As an overview, several OLED materials and configurations are described in Uoyama et al. and in European patent EP 0423283 B1 and United States patents US 6303238 B1 and US 7279704 B2. Several QLED materials and configurations are described in Kathirgamanathan et al. Several PeLED materials and configurations are described in Adjokatse et al. All of these references are included herein by reference in their entirety.

As used herein, the term "organic" includes polymeric materials as well as small molecule organic materials that may be used to fabricate optoelectronic devices, such as OLEDs. As used herein, the term small molecule refers to any organic material that is not a polymer, and small molecules may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the small molecule class. Small molecules may also be incorporated into polymers, for example as a pendant group on a polymer backbone or as part of the backbone. A dendrimer may be a small molecule and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein the term "organic light emitting material" includes fluorescent and phosphorescent organic light emitting materials, as well as organic materials that emit light through mechanisms such as triplet-triplet annihilation (TTA) or thermally activated delayed fluorescence (TADF) or hyperfluorescence. As used herein, organic materials that emit light through mechanisms such as TADF or hyperfluorescence are considered fluorescent organic light emitting materials. One example of organic light emitting material that emits red light is bis(2-(3,5-dimethylphenyl)quinoline-C2,N') (acetylacetonato) iridium(lll) lr(dmpq)2(acac). One example of organic light emitting material that emits green light is tris(2-phenylpyridine)iridium (lr(ppy)3). One example of organic light emitting material that emits blue light is bis[2-(4,6- difluorophenyl)pyridinato-C2,N](picolinato)iridium(lll) (Flrpic).

In general, OLED devices may be photoluminescent or electroluminescent. The term "OLED" may be used to describe single emissive unit electroluminescent devices that comprise electroluminescent organic light emitting material. The term "OLED" may also be used to describe one or more emissive units of stacked electroluminescent devices that comprise electroluminescent organic light emitting material. This nomenclature may differ slightly from that used by other sources.

As used herein, the term "quantum dot" includes quantum dot material, quantum rod material and other luminescent nanocrystal material, with the exception of "perovskite" material, which is defined separately herein. Quantum dots may generally be considered as semiconductor nanoparticles that exhibit properties that are intermediate between bulk semiconductors and discrete molecules. Quantum dots may comprise lll-V semiconductor material, such as gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), indium phosphide (InP) and indium arsenide (InAs), or ll-VI semiconductor material, such as zinc oxide (ZnO), zinc sulfide (ZnS), cadmium sulfide (CdS), cadmium selenide (CdSe) and cadmium telluride (CdTe), or combinations thereof. In general, as a result of quantum confinement effects, optoelectronic properties of quantum dots may change as a function of size or shape of the quantum dot.

Several types of quantum dot may be stimulated to emit light in response to optical or electrical excitation. That is to say that quantum dot light emitting material may be photoluminescent or electroluminescent. This nomenclature may differ slightly from that used by other sources.

As used herein, the term "quantum dot" does not include "perovskite" material. Several types of perovskite material, such as perovskite nanocrystals, 2D perovskite materials and Quasi-2D perovskite materials, are semiconducting materials that exhibit properties intermediate between bulk semiconductors and discrete molecules, where in a similar manner to quantum dots, quantum confinement may affect optoelectronic properties. However, as used herein, such materials are referred to as "perovskite" materials and not "quantum dot" materials. A first reason for this nomenclature is that perovskite materials and quantum dot materials, as defined herein, generally comprise different crystal structures. A second reason for this nomenclature is that perovskite materials and quantum dot materials, as defined herein, generally comprise different material types within their structures. A third reason for this nomenclature is that emission from perovskite material is generally independent of the structural size of the perovskite material, whereas emission from quantum dot material is generally dependent on the structural size (e.g. core and shell) of the quantum dot material. This nomenclature may differ slightly from that used by other sources.

In general, quantum dot light emitting materials comprise a core. Optionally, the core may be surrounded by one or more shells. Optionally, the core and one or more shells may be surrounded by a passivation structure. Optionally, the passivation structure may comprise ligands bonded to the one or more shells. The size of the of the core and shell(s) may influence the optoelectronic properties of quantum dot light emitting material. Generally, as the size of the core and shell(s) is reduced, quantum confinement effects become stronger, and electroluminescent emission may be stimulated at shorter wavelength. For display applications, the diameter of the core and shell(s) structure is typically in the range of 1 - 10 nm. Quantum dots that emit blue light are typically the smallest, with core-shell(s) diameter in the approximate range of 1 - 2.5 nm. Quantum dots that emit green light are typically slightly larger, with core-shell(s) diameter in the approximate range of 2.5 - 4 nm. Quantum dots that emit red light are typically larger, with core-shell(s) diameter in the approximate range of 5-7 nm. It should be understood that these ranges are provided by way of example and to aid understanding and are not intended to be limiting.

Examples of quantum dot light emitting materials include materials comprising a core of CdSe. CdSe has a bulk bandgap of 1.73 eV, corresponding to emission at 716nm. However, the emission spectrum of CdSe may be adjusted across the visible spectrum by tailoring the size of the CdSe quantum dot. Quantum dot light emitting materials comprising a CdSe core may further comprise one or more shells, comprising CdS, ZnS or combinations thereof. Quantum dot light emitting materials comprising CdSe may further comprise a passivation structure, which may include ligands bonded to the shell(s). Quantum dot light emitting materials comprising CdSe/CdS or CdSe/ZnS core shell structures may be tuned to emit red, green or blue light for application in displays and/or light panels.

Examples of quantum dot light emitting materials further include materials comprising a core of InP. InP has a bulk bandgap of 1.35 eV, corresponding to emission at 918nm. However, the emission spectrum of InP may be adjusted across the visible spectrum by tailoring the size of the InP quantum dot. Quantum dot light emitting materials comprising an InP core may further comprise one or more shells of CdS, ZnS or combinations thereof. Quantum dot light emitting materials comprising InP may further comprise a passivation structure, which may include ligands bonded to the shell(s). Quantum dot light emitting materials comprising InP/CdS or InP/ZnS core-shell structures may be tuned to emit red, green or blue light for application in displays and/or light panels.

In general, QLED devices may be photoluminescent or electroluminescent. The term "QLED" may be used to describe single emissive unit electroluminescent devices that comprise electroluminescent quantum dot light emitting material. The term "QLED" may also be used to describe one or more emissive units of stacked electroluminescent devices that comprise electroluminescent quantum dot light emitting material. This nomenclature may differ slightly from that used by other sources.

As used herein, the term "perovskite" includes any perovskite material that may be used in an optoelectronic device. Any material that may adopt a three-dimensional (3D) structure of ABX ₃ , where A and B are cations and X is an anion, may be considered a perovskite material. FIG. 3 depicts an example of a perovskite material with a 3D structure of ABX ₃ . The A cations may be larger than the B cations. The B cations may be in 6-fold coordination with surrounding X anions. The A anions may be in 12-fold coordination with surrounding X anions.

Perovskite materials are becoming increasingly attractive for application in optoelectronic devices. Many of the perovskite materials used to make such devices are earth-abundant and relatively inexpensive, so perovskite optoelectronic devices have the potential for cost advantages. There are many classes of perovskite material. One class of perovskite material that has shown particular promise for optoelectronic devices is the metal halide perovskite material class. For metal halide perovskite material, the A component may be a monovalent organic cation, such as methylammonium (CHsNh ) or formamidinium (CH(NH ₂ ) ₂ ⁺ ), an inorganic atomic cation, such as caesium (Cs ⁺ ), or a combination thereof, the B component may be a divalent metal cation, such as lead (Pb ⁺ ), tin (Sn ⁺ ), copper (Cu ⁺ ), europium (Eu ⁺ ) or a combination thereof, and the X component may be a halide anion, such as I , Br, Cl , or a combination thereof. Where the A component is an organic cation, the perovskite material may be defined as an organic metal halide perovskite material. CH ₃ NH ₃ PbBr ₃ and CH(NH ₂ ) ₂ Pbl ₃ are non-limiting examples of metal halide perovskite materials with a 3D structure. Where the A component is an inorganic cation, the perovskite material may be defined as an inorganic metal halide perovskite material. CsPbU, CsPbCh and CsPbBr ₃ are non-limiting examples of inorganic metal halide perovskite materials.

As used herein, the term "perovskite" further includes any material that may adopt a layered structure of I_ ₂ (ABC ₃ ) _h -iBC ₄ (which may also be written as L ₂ A _n -iB _n X _3n+i ), where L, A and B are cations, X is an anion, and n is the number of BX ₄ monolayers disposed between two layers of cation L. FIG. 4 depicts examples of perovskite materials with a layered structure of I_ ₂ (ABC ₃ ) _h -iBC ₄ having different values for n. For metal halide perovskite material, the A component may be a monovalent organic cation, such as methylammonium (CH ₃ NH ₃ ⁺ ) or formamidinium (CH(NH ₂ ) ₂ ⁺ ), an atomic cation, such as caesium (Cs ⁺ ), or a combination thereof, the L component may be an organic cation such as 2-phenylethylammonium (C ₆ H ₅ C ₂ H ₄ NH ₃ ⁺ ) or 1-napthylmethylammonium (CI _O H7CH2NH3 ⁺ ), the B component may be a divalent metal cation, such as lead (Pb ⁺ ), tin (Sn ⁺ ), copper (Cu ⁺ ), europium (Eu ⁺ ) or a combination thereof, and the X component may be a halide anion, such as I , Br, Cl , or a combination thereof. (C6H ₅ C2H ₄ NH3)2(CH(NH2)2PbBr3)n-iPbBr4 and (CioHyChkNHs iCHsNHsPbbBrJn-iPblsBr are non-limiting examples of metal halide perovskite material with a layered structure.

Where the number of layers n is large, for example n greater than approximately 10, perovskite material with a layered structure of I_ ₂ (ABC ₃ ) _h -iBC ₄ adopts a structure that is approximately equivalent to perovskite material with a 3D structure of ABX ₃ . As used herein, and as would generally be understood by one skilled in the art, perovskite material having a large number of layers may be referred to as a 3D perovskite material, even though it is recognized that such perovskite material has reduced dimensionality from n = . Where the number of layers n = 1, perovskite material with a layered structure of I_ ₂ (ABC ₃ ) _h -iBC ₄ adopts a two-dimensional (2D) structure of L ₂ BX ₄ . Perovskite material having a single layer may be referred to as a 2D perovskite material. Where n is small, for example n in the range of approximately 2-10, perovskite material with a layered structure of I_2(ABC3) _h- iBC4 adopts a quasi-two- dimensional (Quasi-2D) structure. Perovskite material having a small number of layers may be referred to as a Quasi-2D perovskite material. Owing to quantum confinement effects, the energy band gap is lowest for layered perovskite material structures where n is highest.

Perovskite material may have any number of layers. Perovskites may comprise 2D perovskite material, Quasi-2D perovskite material, 3D perovskite material or a combination thereof. For example, perovskites may comprise an ensemble of layered perovskite materials having different numbers of layers. For example, perovskites may comprise an ensemble of Quasi-2D perovskite materials having different numbers of layers.

As used herein, the term "perovskite" further includes films of perovskite material. Films of perovskite material may be crystalline, polycrystalline or a combination thereof, with any number of layers and any range of grain or crystal size.

As used herein, the term "perovskite" further includes nanocrystals of perovskite material that have structure equivalent to or resembling the 3D perovskite structure of ABX ₃ or the more general layered perovskite structure of I_ ₂ (ABC ₃ ) _h -iBC ₄ . Nanocrystals of perovskite material may include perovskite nanoparticles, perovskite nanowires, perovskite nanoplatelets, or a combination thereof. Nanocrystals of perovskite material may be of any shape or size, with any number of layers and any range of grain or crystal sizes. FIG. 5 depicts an example of nanocrystal of perovskite material with a layered structure that resembles I_2(ABC3) _h- iBC4, where n = 5 and L cations are arranged at the surface of the perovskite nanocrystal. The term "resembles" is used because for a nanocrystal of perovskite material, the distribution of L cations may differ from that of perovskite material with a formal layered structure of I_2(ABC3) _h- iBC4. For example, in a nanocrystal of perovskite material, there may be a greater proportion of L cations arranged along the sides of the nanocrystal.

Several types of perovskite material may be stimulated to emit light in response to optical or electrical excitation. That is to say that perovskite light emitting material may be photoluminescent or electroluminescent. This nomenclature may differ slightly from that used by other sources. One example of a perovskite light emitting material that emits red light is methylammonium lead iodide (CF NHsPbls).

One example of a perovskite light emitting material that emits green light is formamidinium lead bromide (CHiNFh PbBrs). One example of a perovskite light emitting material that emits blue light is methylammonium lead chloride (CHsNHsPbCIs).

In general, PeLED devices may be photoluminescent or electroluminescent. The term "PeLED" may be used to describe single emissive unit electroluminescent devices that comprise electroluminescent perovskite light emitting material. The term "PeLED" may also be used to describe one or more emissive units of stacked electroluminescent devices that comprise electroluminescent perovskite light emitting material. This nomenclature may differ slightly from that used by other sources.

As used herein, "top" means furthest away from the substrate, while "bottom" means closest to the substrate. Where a first layer is described as "disposed over" a second layer, the first layer is disposed further away from the substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is "in contact with" the second layer.

As used herein, "solution processible" means capable of being dissolved, dispersed or transported in and/or deposited from a liquid medium, either in solution or suspension form.

As used herein, and as would be generally understood by one skilled in the art, a first "Highest Occupied Molecular Orbital" (HOMO) or "Lowest Unoccupied Molecular Orbital" (LUMO) energy level is "greater than" or "higher than" a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) and electron affinities (EA) are measured as negative energies relative to a vacuum level, a higher HOMO energy level corresponds to an IP that is less negative. Similarly, a higher LUMO energy level corresponds to an EA that is less negative. On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A "higher" HOMO or LUMO energy level appears closer to the top of such a diagram than a "lower" HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is "greater than" or "higher than" a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a "higher" work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a "higher" work function is illustrated as further away from the vacuum level in the downward direction. The definitions of HOMO and LUMO energy levels therefore follow a different convention than work functions.

As used herein, and as would be generally understood by one skilled in the art, a light emitting device, such as a PeLED, OLED or QLED may be referred to as a "stacked" light emitting device if two or more emissive units are separated by one or more charge generation layers within the layer structure of the light emitting device. In some sources, a stacked light emitting device may be referred to as a tandem light emitting device. It should be understood that the terms "stacked" and "tandem" may be used interchangeably, and as used herein, a tandem light emitting device is also considered to be a stacked light emitting device. This nomenclature may differ slightly from that used by other sources.

As used herein, the terms "OLED", "QLED" and "PeLED" may be used to describe single emissive unit electroluminescent devices that respectively comprise electroluminescent organic, quantum and perovskite light emitting materials. The terms "OLED", "QLED" and "PeLED" may also be used to describe one or more emissive units of stacked electroluminescent devices that respectively comprise electroluminescent organic, quantum dot and perovskite light emitting materials.

As used herein, the term "optically coupled" refers to one or more elements of a device or structure that are arranged such that light may impart between the one or more elements. The one or more elements may be in contact or may be separated by a gap or any connection, coupling, link or the like that allows for imparting of light between the one or more elements. For example, one or more sub-pixels within a pixel arrangement of a display may be optically coupled to one or more colour altering layers such as colour conversion layers and colour filters.

Summary

A device is provided. In one embodiment, the device comprises a stacked blue light emitting device comprising: a first electrode; a second electrode; a first emissive unit comprising a first emissive layer; a second emissive unit comprising a second emissive layer; and a first charge generation layer; wherein the first emissive unit, the second emissive unit and the first charge generation layer are all disposed between the first electrode and the second electrode; the first emissive unit is disposed over the first electrode; the first charge generation layer is disposed over the first emissive unit; the second emissive unit is disposed over the first charge generation layer; the second electrode is disposed over the second emissive unit; the first emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the first peak wavelength; the first emissive unit emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (xl, yl); the second emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the second peak wavelength; the second emissive unit emits blue light having a second chromaticity having second CIE 1931 (x, y) colour space chromaticity coordinates of (x2, y2); the second chromaticity is substantially different to the first chromaticity; and the first emissive layer and the second emissive layer comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material. In one embodiment, the second chromaticity coordinates (x2, y2) are not contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). In one embodiment, the second chromaticity coordinates (x2, y2) are not contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). In one embodiment, the second peak wavelength is at least 4 nm greater than or at least 4 nm less than the first peak wavelength. In one embodiment, the first CIE 1931 (x, y) colour space chromaticity coordinates (xl, yl) may be converted to first CIE 1976 (u', v') colour space chromaticity coordinates (ul, vl); and the second CIE 1931 (x, y) colour space chromaticity coordinates (x2, y2) may be converted to second CIE 1976 (u', v') colour space chromaticity coordinates (u2, v2); wherein the first chromaticity coordinates (ul, vl) and the second chromaticity coordinates (u2, v2) are sufficiently different such that the difference in chromaticity as defined by Auv is 0.010 or more.

In one embodiment, the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm.

In one embodiment, the first emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the second emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080. In one embodiment, the first emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080; and the second emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less.

In one embodiment, the first emissive layer and the second emissive layer comprise organic light emitting material. In one embodiment, at least one of the first emissive layer and the second emissive layer comprise phosphorescent organic light emitting material; and at least one of the first emissive layer and the second emissive layer comprise fluorescent organic light emitting material. In one embodiment, the first emissive layer and the second emissive layer comprise quantum dot light emitting material. In one embodiment, the first emissive layer and the second emissive layer comprise perovskite light emitting material. In one embodiment, the first emissive layer comprises a first class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; the second emissive layer comprises a second class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; and the second class of light emitting material is not the same as the first class of light emitting material. In one embodiment, the first emissive unit and the second emissive unit are independently addressable and may emit light independently of each other. In one embodiment, the first emissive unit and the second emissive unit are commonly addressable and may not emit light independently of each other.

In one embodiment, the stacked blue light emitting device further comprises: a third emissive unit comprising a third emissive layer; and a second charge generation layer; wherein the third emissive unit and the second charge generation layer are disposed between the second emissive unit and the second electrode; the second charge generation layer is disposed over the second emissive unit; the third emissive unit is disposed over the second charge generation layer; the second electrode is disposed over the third emissive unit; the third emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the third peak wavelength; the third emissive unit emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (x3, y3); and the third emissive layer comprises organic light emitting material, quantum dot light emitting material or perovskite light emitting material.

In one embodiment, the third chromaticity is substantially the same as one of the first chromaticity and the second chromaticity; and the third chromaticity is substantially different to one of the first chromaticity and the second chromaticity. In one embodiment, the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; and the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit. In one embodiment, the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit; wherein the emissive unit which is commonly addressed with the third emissive unit has substantially the same chromaticity as the third emissive unit; and the emissive unit which is addressed independently of the third emissive unit has substantially different chromaticity to the third emissive unit.

In one embodiment, the device is part of a light panel. In one embodiment, the device is part of a display.

A display is provided. In one embodiment, the display comprises: a first sub-pixel configured to emit red light with a peak wavelength in the visible spectrum in the range of 580 nm to 780 nm; a second sub-pixel configured to emit green light with a peak wavelength in the visible spectrum in the range of 500 nm to 580 nm; and a third sub-pixel configured to emit blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm; wherein the first sub-pixel comprises a first stacked blue light emitting device optically coupled to a red colour conversion layer; the second sub-pixel comprises a second stacked blue light emitting device optically coupled to a green colour conversion layer; and the third sub-pixel comprises a third stacked blue light emitting device; wherein all of the first, second and third stacked blue light emitting devices comprise: a first electrode; a second electrode; a first emissive unit comprising a first emissive layer; a second emissive unit comprising a second emissive layer; and a first charge generation layer; wherein the first emissive unit, the second emissive unit and the first charge generation layer are all disposed between the first electrode and the second electrode; the first emissive unit is disposed over the first electrode; the first charge generation layer is disposed over the first emissive unit; the second emissive unit is disposed over the first charge generation layer; the second electrode is disposed over the second emissive unit; the first emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the first peak wavelength; the first emissive unit emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (xl, yl); the second emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the second peak wavelength; the second emissive unit emits blue light having a second chromaticity having second CIE 1931 (x, y) colour space chromaticity coordinates of (x2, y2); the second chromaticity is substantially different to the first chromaticity; and the first emissive layer and the second emissive layer comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material.

In one embodiment, for all of the first, second and third stacked blue light emitting devices, the second chromaticity coordinates (x2, y2) are not contained within a one- step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). In one embodiment, for all of the first, second and third stacked blue light emitting devices, the second chromaticity coordinates (x2, y2) are not contained within a three- step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). In one embodiment, for all of the first, second and third stacked blue light emitting devices, the second peak wavelength is at least 4 nm greater than or at least 4 nm less than the first peak wavelength. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first CIE 1931 (x, y) colour space chromaticity coordinates (xl, yl) may be converted to first CIE 1976 (u', v') colour space chromaticity coordinates (ul, vl); and the second CIE 1931 (x, y) colour space chromaticity coordinates (x2, y2) may be converted to second CIE 1976 (u', v') colour space chromaticity coordinates (u2, v2); wherein the first chromaticity coordinates (ul, vl) and the second chromaticity coordinates (u2, v2) are sufficiently different such that the difference in chromaticity as defined by Auv is 0.010 or more. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm.

In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the second emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080; and the second emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less.

In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive layer and the second emissive layer comprise organic light emitting material. In one embodiment, for all of the first, second and third stacked blue light emitting devices, at least one of the first emissive layer and the second emissive layer comprise phosphorescent organic light emitting material; and at least one of the first emissive layer and the second emissive layer comprise fluorescent organic light emitting material. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive layer and the second emissive layer comprise quantum dot light emitting material. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive layer and the second emissive layer comprise perovskite light emitting material. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive layer comprises a first class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; the second emissive layer comprises a second class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; and the second class of light emitting material is not the same as the first class of light emitting material.

In one embodiment, the first stacked blue light emitting device, the second stacked blue light emitting device and the third stacked blue light emitting device all have the same device architecture.

In one embodiment, for any of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are independently addressable and may emit light independently of each other. In one embodiment, for any of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are commonly addressable and may not emit light independently of each other.

In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are independently addressable and may emit light independently of each other. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are commonly addressable and may not emit light independently of each other.

In one embodiment, the first emissive unit and the second emissive unit of the third stacked blue light emitting device are independently addressable and may emit light independently of each other; and the first emissive unit and the second emissive unit of the first stacked blue light emitting device are commonly addressable and may not emit light independently of each other; and the first emissive unit and the second emissive unit of the second stacked blue light emitting device are commonly addressable and may not emit light independently of each other.

In one embodiment, all of the first, second and third stacked blue light emitting devices further comprise: a third emissive unit comprising a third emissive layer; and a second charge generation layer; wherein the third emissive unit and the second charge generation layer are disposed between the second emissive unit and the second electrode; the second charge generation layer is disposed over the second emissive unit; the third emissive unit is disposed over the second charge generation layer; and the second electrode is disposed over the third emissive unit; and the third emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the third peak wavelength; the third emissive unit emits blue light having a third chromaticity having third CIE 1931 (x, y) colour space chromaticity coordinates of (x3, y3); and the third emissive layer comprises organic light emitting material, quantum dot light emitting material or perovskite light emitting material.

In one embodiment, for all of the first, second and third stacked blue light emitting devices, the third chromaticity is substantially the same as one of the first chromaticity and the second chromaticity; and the third chromaticity is substantially different to one of the first chromaticity and the second chromaticity. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; and the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit. In one embodiment, for all of the first, second and third stacked blue light emitting devices, the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit; wherein the emissive unit which is commonly addressed with the third emissive unit has substantially the same chromaticity as the third emissive unit; and the emissive unit which is addressed independently of the third emissive unit has substantially different chromaticity to the third emissive unit.

In one embodiment, the display is part of a consumer product.

Description of the Drawings

The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those in the art will understand that the drawings are not to scale.

In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non- underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing. Embodiments of the present disclosure will now be described, by way of example only, with reference to the following:

FIG. 1 depicts a light emitting device.

FIG. 2 depicts an inverted light emitting device.

FIG. 3 depicts 3D perovskite light emitting material with structure ABX3.

FIG. 4 depicts layered perovskite light emitting material with structure I_2(ABC3) _h- iBC4, where n = 1, 3, 5, 10 and .

FIG. 5 depicts an example of a nanocrystal of perovskite material with a layered structure that resembles I_2(ABC3) _h- iBC4, where n = 5.

FIG. 6 depicts a stacked light emitting device having two emissive units.

FIG. 7 depicts a stacked light emitting device having three emissive units. FIG. 8 depicts layers of a stacked light emitting device having two emissive units.

FIG. 9 depicts layers of a stacked light emitting device having three emissive units.

FIG. 10 depicts a rendition of the CIE 1931 (x, y) colour space chromaticity diagram.

FIG. 11 depicts a rendition of the CIE 1931(x, y) colour space chromaticity diagram that also shows colour gamut for (a) DCI-P3 and (b) Rec. 2020 colour spaces.

FIG. 12 depicts a rendition of the CIE 1931 (x, y) colour space chromaticity diagram that also shows colour gamut for (a) DCI-P3 and (b) Rec. 2020 colour spaces with colour coordinates for exemplary blue devices.

FIG. 13 depicts a rendition of the CIE 1931 (x, y) colour space chromaticity diagram that also shows 10-step MacAdam ellipses.

FIG. 14 depicts exemplary electroluminescence emission spectra for blue light emitting devices plotted against the photopic luminous efficiency function.

FIG. 15 depicts various configurations of emissive units for a stacked blue light emitting device having two blue emissive units.

FIG. 16 depicts various configurations of emissive units for a stacked blue light emitting device having three blue emissive units.

FIG. 17 depicts exemplary designs of red, green and blue sub-pixels for application in a display.

FIG. 18 depicts an exemplary RGB OLED display architecture.

FIG. 19 depicts an exemplary RGBW OLED display architecture.

FIG. 20 depicts an exemplary QD-OLED display architecture.

FIG. 21 depicts an exemplary QD-OLED display architecture comprising two blue emissive units.

FIG. 22 depicts an improved QD-OLED display architecture comprising three blue emissive units.

Description of Embodiments

The present invention relates to OLEDs, QLEDs and PeLEDs. Device architectures and operating principles for OLEDs, QLEDs and PeLEDs are substantially similar. Each of these light emitting devices comprises at least one emissive layer disposed between and electrically connected to an anode and a cathode. For an OLED, the emissive layer comprises organic light emitting material. For a QLED, the emissive layer comprises quantum dot light emitting material. For a PeLED, the emissive layer comprises perovskite light emitting material. For each of these light emitting devices, when a current is applied, the anode injects holes and the cathode injects electrons into the emissive layer(s). The injected holes and electrons each migrate towards the oppositely charged electrode. When an electron and a hole localize, an exciton, which is a localized electron-hole pair having an excited energy state, may be formed. Light is emitted if the exciton relaxes via a photo-emissive mechanism. Non-radiative mechanisms, such as thermal radiation and/or Auger recombination may also occur but are generally considered undesirable. Substantial similarity between device architectures and working principles required for OLEDs, QLEDs and PeLEDs, facilitates the combination of organic light emitting material, quantum dot light emitting material and perovskite light emitting material in a single light emitting device.

FIG. 1 shows a light emitting device 100 with a single emissive unit. The light emitting device 100 may be an OLED, QLED or PeLED. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120, a hole transport layer 125, an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a cathode 155 and a barrier layer 160. Device 100 may be fabricated by depositing the layers described in order. As the device 100 has anode 115 disposed under cathode 155, device 100 may be referred to as a "standard" device architecture. For an OLED, the emissive layer comprises organic light emitting material. For a QLED, the emissive layer comprises quantum dot light emitting material. For a PeLED, the emissive layer comprises perovskite light emitting material.

FIG. 2 shows an inverted light emitting device 200 with a single emissive unit. The light emitting device 200 may be an OLED, QLED or PeLED. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described in order. As the device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an "inverted" device architecture. For an OLED, the emissive layer comprises organic light emitting material. For a QLED, the emissive layer comprises quantum dot light emitting material. For a PeLED, the emissive layer comprises perovskite light emitting material. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of an OLED, QLED or PeLED.

The simple layered structures illustrated in FIGS. 1 and 2 are provided by way of non limiting examples, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs, QLEDs and PeLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on factors such as performance, design and cost. Other layers, not specifically described, may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in a device, the hole transport layer may transport and inject holes into the emissive layer and may be described as a hole transport layer or a hole injection layer.

OLEDs, PeLEDs and QLEDs are generally intended to emit light through at least one of the electrodes, and one or more transparent electrodes may be useful in such optoelectronic devices. For example, a transparent electrode material, such as indium tin oxide (ITO), may be used for the bottom electrode, while a transparent electrode material, such as a thin metallic layer of a blend of magnesium and silver (Mg:Ag), may be used for the top electrode. For a device intended to emit light only through the bottom electrode, the top electrode does not need to be transparent, and may be comprised of an opaque and/or reflective layer, such as a metal layer having a high reflectivity. Similarly, for a device intended only to emit light through the top electrode, the bottom electrode may be opaque and/or reflective, such as a metal layer having a high reflectivity. Where an electrode does not need to be transparent, using a thicker layer may provide better conductivity and may reduce voltage drop and/or Joule heating in the device, and using a reflective electrode may increase the amount of light emitted through the other electrode by reflecting light back towards the transparent electrode. A fully transparent device may also be fabricated, where both electrodes are transparent.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise a substrate 110. The substrate 110 may comprise any suitable material that provides the desired structural and optical properties. The substrate 110 may be rigid or flexible. The substrate 110 may be flat or curved. The substrate 110 may be transparent, translucent or opaque. Preferred substrate materials are glass, plastic and metal foil. Other substrates, such as fabric and paper may be used. The material and thickness of the substrate 110 may be chosen to obtain desired structural and optical properties.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise an anode 115. The anode 115 may comprise any suitable material or combination of materials known to the art, such that the anode 115 is capable of conducting holes and injecting them into the layers of the device. Preferred anode 115 materials include conductive metal oxides, such as indium tin oxide (ITO), indium zinc oxide (IZO) and aluminum zinc oxide (AIZnO), metals such as silver (Ag), aluminum (Al), aluminum-neodymium (AI:Nd), gold (Au) and alloys thereof, or a combination thereof. Other preferred anode 115 materials include graphene, carbon nanotubes, nanowires or nanoparticles, silver nanowires or nanoparticles, organic materials, such as poly(3,4- ethylenedioxythiophene) : polystyrene sulfonate (PEDOT:PSS) and derivatives thereof, or a combination thereof. Compound anodes comprising one or more anode materials in a single layer may be preferred for some devices. Multilayer anodes comprising one or more anode materials in one or more layers may be preferred for some devices. One example of a multilayer anode is ITO/Ag/ITO. In a standard device architecture for OLEDs, QLEDs and PeLEDs, the anode 115 may be sufficiently transparent to create a bottom-emitting device, where light is emitted through the substrate. One example of a transparent anode commonly used in a standard device architecture is a layer of ITO. Another example of a transparent anode commonly used in a standard device architecture is ITO/Ag/ITO, where the Ag thickness is less than approximately 25 nm. By including a layer of silver of thickness less than approximately 25 nm, the anode may be transparent as well as partially reflective. When such a transparent and partially reflective anode is used in combination with a reflective cathode, such as LiF/AI, this may have the advantage of creating a microcavity within the device. A microcavity may provide one or more of the following advantages: an increased total amount of light emitted from device, and therefore higher efficiency and brightness; an increased proportion of light emitted in the forward direction, and therefore increased apparent brightness at normal incidence; and spectral narrowing of the emission spectrum, resulting in light emission with increased colour saturation. The anode 115 may be opaque and/or reflective. In a standard device architecture for OLEDs, QLEDs and PeLEDs, a reflective anode 115 may be preferred for some top- emitting devices to increase the amount of light emitted from the top of the device. One example of a reflective anode commonly used in a standard device architecture is a multilayer anode of ITO/Ag/ITO, where the Ag thickness is greater than approximately 80 nm. When such a reflective anode is used in combination with a transparent and partially reflective cathode, such as Mg:Ag, this may have the advantage of creating a microcavity within the device. The material and thickness of the anode 115 may be chosen to obtain desired conductive and optical properties. Where the anode 115 is transparent, there may be a range of thicknesses for a particular material that is thick enough to provide the desired conductivity, yet thin enough to provide the desired degree of transparency. Other materials and structures may be used.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise a hole transport layer 125. The hole transport layer 125 may include any material capable of transporting holes. The hole transport layer 125 may be deposited by a solution process or by a vacuum deposition process. The hole transport layer 125 may be doped or undoped. Doping may be used to enhance conductivity.

Examples of undoped hole transport layers are N,N'-Di(l-naphthyl)-N,N'-diphenyl- (l,l'-biphenyl)-4,4'-diamine (NPD), poly[(9,9-dioctylfluorenyl-2,7-diyl)-co -(4,4'-(N -(4- sec-butylphenyl) diphenylamine (TFB), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)- benzidine] (poly-TPD), poly(9-vinylcarbazole) (PVK), 4,4'-Bis(N-carbazolyl)-l,l'-biphenyl (CBP), Spiro-OMeTAD and molybdenum oxide (M0O ₃ ). One example of a doped hole transport layer is 4,4',4"-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA) doped with F4-TCNQ at a molar ratio of 50:1. One example of a solution-processed hole transport layer is PEDOT:PSS. Other hole transport layers and structures may be used.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise an emissive layer 135. The emissive layer 135 may include any material capable of emitting light when a current is passed between anode 115 and cathode 155.

Several examples of fluorescent organic light emitting materials are described in European patent EP 0423283 Bl. Several examples of phosphorescent organic light emitting materials are described in United States patent US 6303238 Bl and United States patent US 7279704 B2. Several examples of organic light emitting materials that emit through a TADF mechanism are described in Uoyama et al.

Several examples of quantum dot light emitting materials are described in Kathirgamanathan et al. All of these citations are included herein by reference in their entirety.

Examples of perovskite light-emitting materials include 3D perovskite materials, such as methylammonium lead iodide (CHsNHsPbU), methylammonium lead bromide (CH ₃ NH ₃ PbBr ₃ ), methylammonium lead chloride (CHsNHsPbCh), formamidinium lead iodide (CH(NH ₂ ) ₂ Pbl ₃ ), formamidinium lead bromide (CH(NH ₂ ) ₂ PbBr ₃ ), formamidinium lead chloride (CH(NH ₂ ) ₂ PbCl ₃ ), caesium lead iodide (CsPbU), caesium lead bromide (CsPbBrs) and caesium lead chloride (CsPbCh). Examples of perovskite light-emitting materials further include 3D perovskite materials with mixed halides, such as CHsNHsPbls- _x Cl _x , CHsNHsPbls- _x Br _x , CHsNHsPbCIs- _x Br _x , CH(NH ₂ ) ₂ Pbl _3-x Br _x , CH(NH ₂ ) ₂ Pbl ₃ - _x Cl _x , CH(NH ₂ ) ₂ PbCl _{3 x} Br _x , CsPbU- _x Cl _x , CsPbl _3-x Br _x and CsPbCl _3-x Br _x , where x is in the range of 0-3. Examples of perovskite light-emitting materials further include 2D perovskite materials such as (Ci ₀ H ₇ CH ₂ NH ₃ ) ₂ Pbl ₄ , (Ci ₀ H ₇ CH ₂ NH ₃ ) ₂ PbBr ₄ , (Ci ₀ H ₇ CH ₂ NH ₃ ) ₂ PbCI ₄ , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ Pbl ₄ , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbBr ₄ and (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbCI ₄ , 2D perovskite materials with mixed halides, such as (CioH ₇ CH ₂ NH ₃ ) ₂ Pbl _4-x Cl _x , (CioH ₇ CH ₂ NH ₃ ) ₂ Pbl _4-x Br _x , (CioH ₇ CH ₂ NH ₃ ) ₂ PbCI _4-x Br _x , (CeHsCzFUNHs PbU- _x Cl _x , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ Pbl _4-x Br _x and (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ PbCI _4-x Br _x , where x is in the range of 0-4. Examples of perovskite light- emitting materials further include Quasi-2D perovskite materials, such as (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ (CH(NH ₂ ) ₂ PbBr ₃ ) _n -iPbl ₄ , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ (CH(NH ₂ ) ₂ PbBr ₃ ) _n -iPbBr ₄ ,

(C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ (CH(NH ₂ ) ₂ PbBr ₃ ) _n -iPbCI ₄ , (Ci ₀ H ₇ CH ₂ NH ₃ ) ₂ (CH ₃ NH ₃ Pbl ₂ Br) _n -iPbl ₄ ,

(CioH ₇ CH ₂ NH ₃ ) ₂ (CH ₃ NH ₃ Pbl ₂ Br) _n -iPbBr ₄ and (Ci ₀ H ₇ CH ₂ NH ₃ ) ₂ (CH ₃ NH ₃ Pbl ₂ Br) _n -iPbCI ₄ , where n is the number of layers, and, optionally, n may be in the range of about 2-10. Examples of perovskite light-emitting materials further include Quasi-2D perovskite materials with mixed halides, such as (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ (CH(NH ₂ ) ₂ PbBr ₃ ) _n -iPbl _4-x Cl _x , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ (CH(NH ₂ ) ₂ PbBr ₃ ) _n -iPbl _4-x Br _x , (C ₆ H ₅ C ₂ H ₄ NH ₃ ) ₂ (CH(NH ₂ ) ₂ PbBr ₃ ) _n -iPbCI _4-x Br _x , (CioH ₇ CH ₂ NH ₃ ) ₂ (CH ₃ NH ₃ Pbl ₂ Br) _n -iPbl _4-x Cl _x , (CioH ₇ CH ₂ NH ₃ ) ₂ (CH ₃ NH ₃ Pbl ₂ Br) _n -iPbl _4-x Br _x and (CioH CH NH ) (CH NH Pbl Br) _n -iPbCl - _x Br _x , where n is the number of layers, and, optionally, n may be in the range of about 2-10, and x is in the range of 0-4. Examples of perovskite light-emitting materials further include any of the aforementioned examples, where the divalent metal cation lead (Pb ⁺ ) may be replaced with tin (Sn ⁺ ), copper (Cu ⁺ ) or europium (Eu ⁺ ). Examples of perovskite light-emitting materials further include perovskite light-emitting nanocrystals with structures that closely resemble Quasi-2D perovskite materials.

Perovskite light emitting material may comprise organic metal halide perovskite material, such as methylammonium lead iodide (CHsNHsPbls), methylammonium lead bromide (CHsNHsPbBrs), methylammonium lead chloride (CHsNHsPbCh), where the materials comprises an organic cation. Perovskite light emitting material may comprise inorganic metal halide perovskite material, such as caesium lead iodide (CsPbU), caesium lead bromide (CsPbBrs) and caesium lead chloride (CsPbCh), where the material comprises an inorganic cation. Furthermore, perovskite light emitting material may comprise perovskite light emitting material where there is a combination of organic and inorganic cations. The choice of an organic or inorganic cation may be determined by several factors, including desired emission colour, efficiency of electroluminescence, stability of electroluminescence and ease of processing. Inorganic metal halide perovskite material may be particularly well-suited to perovskite light-emitting materials with a nanocrystal structure, such as those depicted in FIG. 5, wherein an inorganic cation may enable a compact and stable perovskite light-emitting nanocrystal structure.

Perovskite light emitting material may be included in the emissive layer 135 in a number of ways. For example, the emissive layer may comprise 2D perovskite light- emitting material, Quasi-2D perovskite light-emitting material or 3D perovskite light- emitting material, or a combination thereof. Optionally, the emissive layer may comprise perovskite light emitting nanocrystals. Optionally, the emissive layer 135 may comprise an ensemble of Quasi-2D perovskite light emitting materials, where the Quasi-2D perovskite light emitting materials in the ensemble may comprise a different number of layers. An ensemble of Quasi-2D perovskite light emitting materials may be preferred because there may be energy transfer from Quasi-2D perovskite light emitting materials with a smaller number of layers and a larger energy band gap to Quasi-2D perovskite light emitting materials with a larger number of layers and a lower energy band gap. This energy funnel may efficiently confine excitons in a PeLED device and may improve device performance. Optionally, the emissive layer 135 may comprise perovskite light emitting nanocrystal materials. Perovskite light emitting nanocrystal materials may be preferred because nanocrystal boundaries may be used to confine excitons in a PeLED device, and surface cations may be used to passivate the nanocrystal boundaries. This exciton confinement and surface passivation may improve device performance. Other emissive layer materials and structures may be used.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise an electron transport layer 145. The electron transport layer 145 may include any material capable of transporting electrons. The electron transport layer 145 may be deposited by a solution process or by a vacuum deposition process. The electron transport layer 145 may be doped or undoped. Doping may be used to enhance conductivity.

Examples of undoped electron transport layers are tris(8- hydroxyquinolinato)aluminum (Alqs), 2,2',2"-(l,B,5-Benzinetnyl)-tris(l-phenyl-l-H- benzimidazole) (TPBi), 2,9-Dimethyl-4,7-diphenyl-l,10-phenanthroline (BCP), zinc oxide (ZnO) and titanium dioxide (T1O3). One example of a doped electron transport layer is 4,7-diphenyl-l,10-phenanthroline (BPhen) doped with lithium (Li) at a molar ratio of 1:1. One example of a solution-processed electron transport layer is [6, 61- Phenyl C61 butyric acid methyl ester (PCBM). Other electron transport layers and structures may be used.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise a cathode 155. The cathode 155 may comprise any suitable material or combination of materials known to the art, such that the cathode 155 is capable of conducting electronics and injecting them into the layers of the device. Preferred cathode 155 materials include metal oxides, such as indium tin oxide (ITO), indium zinc oxide (IZO) and fluorine tin oxide (FTO), metals, such as calcium (Ca), barium (Ba), magnesium (Mg) and ytterbium (Yb) or a combination thereof. Other preferred cathode 155 materials include metals such as silver (Ag), aluminum (Al), aluminum-neodymium (Al: Nd), gold (Au) and alloys thereof, or a combination thereof. Compound cathodes comprising one or more cathode materials in a single layer may be preferred from some devices. One example of a compound cathode is Mg:Ag. Multilayer cathodes comprising one or more cathode materials in one or more layers may be preferred for some devices. One example of a multilayer cathode is Ba/AI. In a standard device architecture for OLEDs, QLEDs and PeLEDs, the cathode 155 may be sufficiently transparent to create a top-emitting device, where light is emitted from the top of the device. One example of a transparent cathode commonly used in a standard device architecture is a compound layer of Mg:Ag. By using a compound of Mg:Ag, the cathode may be transparent as well as partially reflective. When such a transparent and partially reflective cathode is used in combination with a reflective anode, such as ITO/Ag/ITO, where the Ag thickness is greater than approximately 80 nm, this may have the advantage of creating a microcavity within the device. The cathode 155 may be opaque and/or reflective. In a standard device architecture for OLEDs, QLEDs and PeLEDs, a reflective cathode 155 may be preferred for some bottom-emitting devices to increase the amount of light emitted through the substrate from the bottom of the device. One example of a reflective cathode commonly used in a standard device architecture is a multilayer cathode of LiF/AI. When such a reflective cathode is used in combination with a transparent and partially reflective anode, such as ITO/Ag/ITO, where the Ag thickness is less than approximately 25 nm, this may have the advantage of creating a microcavity within the device.

The material and thickness of the cathode 155 may be chosen to obtain desired conductive and optical properties. Where the cathode 155 is transparent, there may be a range of thicknesses for a particular material that is thick enough to provide the desired conductivity, yet thin enough to provide the desired degree of transparency. Other materials and structures may be used.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise one or more blocking layers. Blocking layers may be used to reduce the number of charge carriers (electrons or holes) and/or excitons exiting the emissive layer. An electron blocking layer 130 may be disposed between the emissive layer 135 and the hole transport layer 125 to block electrons from leaving the emissive layer 135 in the direction of the hole transport layer 125. Similarly, a hole blocking layer 140 may be disposed between the emissive layer 135 and the electron transport layer 145 to block holes from leaving the emissive layer 135 in the direction of the electron transport layer 145. Blocking layers may also be used to block excitons from diffusing from the emissive layer. As used herein, and as would be understood by one skilled in the art, the term "blocking layer" means that the layer provides a barrier that significantly inhibits transport of charge carriers and/or excitons, without suggesting that the layer completely blocks the charge carriers and/or excitons. The presence of such a blocking layer in a device may result in substantially higher efficiencies as compared to a similar device lacking a blocking layer. A blocking layer may also be used to confine emission to a desired region of a device.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise one or more injection layers. Generally, injection layers are comprised of one or more materials that may improve the injection of charge carriers from one layer, such as an electrode, into an adjacent layer. Injection layers may also perform a charge transport function.

In device 100, the hole injection layer 120 may be any layer that improves the injection of holes from the anode 115 into the hole transport layer 125. Examples of materials that may be used as a hole injection layer are Copper(ll)phthalocyanine (CuPc) and 1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile (HATCN), which may be vapor deposited, and polymers, such as PEDOT:PSS, which may be deposited from solution. Another example of a material that may be used as a hole injection layer is molybdenum oxide (M0O3). A hole injection layer (HIL) 120 may comprise a charge carrying component having HOMO energy level that favourably matches, as defined by their herein-described relative IP energies, with the adjacent anode layer on one side of the HIL, and the hole transporting layer on the opposite side of the HIL. The "charge carrying component" is the material responsible for the HOMO energy level that actually transports the holes. This material may be the base material of the HIL, or it may be a dopant. Using a doped HIL allows the dopant to be selected for its electrical properties, and the host to be selected for morphological properties, such as ease of deposition, wetting, flexibility, toughness, and others. Preferred properties of the HIL material are such that holes can be efficiently injected from the anode into the HIL material. The charge carrying component of the HIL 120 preferably has an IP not more than about 0.5 eV greater than the IP of the anode material. Similar conditions apply to any layer into which holes are being injected. HIL materials are further distinguished from conventional hole transporting materials that are typically used in the hole transporting layer of an OLED, QLED or PeLED in that such HIL materials may have a hole conductivity that is substantially less than the hole conductivity of conventional hole transporting materials. The thickness of the HIL 120 of the present invention may be thick enough to planarize the anode and enable efficient hole injection, but thin enough not to hinder transportation of holes. For example, an HIL thickness of as little as 10 nm may be acceptable. However, for some devices, an HIL thickness of up to 50 nm may be preferred.

In device 100, the electron injection layer 150 may be any layer that improves the injection of electrons from the cathode 155 into the electron transport layer 145. Examples of materials that may be used as an electron injection layer are inorganic salts, such as lithium fluoride (LiF), sodium fluoride (NaF), barium fluoride (BaF), caesium fluoride (CsF), and caesium carbonate (CSCO3). Other examples of materials that may be used as an electron injection layer are metal oxides, such as zinc oxide (ZnO) and titanium oxide (T1O2), and metals, such as calcium (Ca), barium (Ba), magnesium (Mg) and ytterbium (Yb). Other materials or combinations of materials may be used for injection layers. Depending on the configuration of a particular device, injection layers may be disposed at locations different than those shown in device 100.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise a barrier layer 160. One purpose of the barrier layer 160 is to protect device layers from damaging species in the environment, including moisture, vapour and/or gasses. Optionally, the barrier layer 160 may be deposited over, under or next to the substrate, electrode, or any other parts of the device, including an edge. Optionally, the barrier layer 160 may be a bulk material such as glass or metal, and the bulk material may be affixed over, under of next to the substrate, electrode, or any other parts of the device. Optionally, the barrier layer 160 may be deposited onto a film, and the film may be affixed over, under of next to the substrate, electrode, or any other parts of the device. Where the barrier layer 160 is deposited onto a film, preferred film materials comprise glass, plastics, such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) and metal foils. Where the barrier layer 160 is a bulk material or deposited onto a film, preferred materials used to affix the film or bulk material to the device include thermal or UV-curable adhesives, hot-melt adhesives and pressure sensitive adhesives.

The barrier layer 160 may be a bulk material or formed by various known deposition techniques, including sputtering, vacuum thermal evaporation, electron-beam deposition and chemical vapour deposition (CVD) techniques, such as plasma- enhanced chemical vapour deposition (PECVD) and atomic layer deposition (ALD). The barrier layer 160 may include compositions having a single phase as well as compositions having multiple phases. Any suitable material or combination of materials may be used for the barrier layer 160. The barrier layer 160 may incorporate organic or inorganic compounds or both. Preferred inorganic barrier layer materials include aluminum oxides such as AI2O3, silicon oxides such as SiC>2, silicon nitrides such as SiN _x and bulk materials such as glasses and metals. Preferred organic barrier layer materials include polymers. The barrier layer 160 may comprise a single layer or multiple layers. Multilayer barriers comprising one or more barrier materials in one or more layers may be preferred for some devices. One preferred example of a multilayer barrier is a barrier comprising alternating layers of SiN _x and a polymer, such as in the multilayer barrier SiN _x /polymer/SiN _x .

FIG. 6 shows a stacked light emitting device 600 having two emissive units. The light emitting device 600 may comprise one or more OLED, QLED or PeLED emissive units or a combination thereof. Device 600 may include a first electrode 610, a first emissive unit 620, a first charge generation layer 630, a second emissive unit 640, and a second electrode 650. The first electrode 610 may be directly connected to an external electrical source El. The second electrode 650 may be directly connected to an external electrical source E2. The first charge generation layer 630 may be directly connected to an external electrical source E3. Device 600 may be fabricated by depositing the layers described in order.

FIG. 8 depicts a layer structure for a stacked light emitting device 800 having two emissive units. The light emitting device 800 may comprise one or more OLED, QLED or PeLED emissive units or a combination thereof. Device 800 may include a substrate 805, an anode 810, a first hole injection layer 815, a first hole transport layer 820, a first emissive layer 825, a first hole blocking layer 830, a first electron transport layer 835, a first charge generation layer 840, a second hole injection layer 845, a second hole transport layer 850, a second emissive layer 855, a second hole blocking layer 860, a second electron transport layer 865, a first electron injection layer 870, and a cathode 875. The first emissive unit 880 may comprise the first hole injection layer 815, the first hole transport layer 820, the first emissive layer 825, the first hole blocking layer 830, and the first electron transport layer 835. The second emissive unit 885 may comprise the second hole injection layer 845, the second hole transport layer 850, the second emissive layer 855, the second hole blocking layer 860, the second electron transport layer 865, and the first electron injection layer 870. Device 800 may be fabricated by depositing the layers described in order.

FIG. 7 shows a stacked light emitting device 700 having three emissive units. The light emitting device 700 may comprise one or more OLED, QLED or PeLED emissive units or a combination thereof. Device 700 may include a first electrode 710, a first emissive unit 720, a first charge generation layer 730, a second emissive unit 740, a second charge generation layer 750, a third emissive unit 760, and a second electrode 770. The first electrode 710 may be directly connected to an external electrical source El. The second electrode 770 may be directly connected to an external electrical source E2. The first charge generation layer 730 may be directly connected to an external electrical source E3. The second charge generation layer 750 may be connected to an external electrical source E4. Device 700 may be fabricated by depositing the layers described in order.

FIG. 9 depicts a layer structure for a stacked light emitting device 900 having three emissive units. The light emitting device 900 may comprise one or more OLED, QLED or PeLED emissive units or a combination thereof. Device 900 may include a substrate 905, an anode 910, a first hole injection layer 915, a first hole transport layer 920, a first emissive layer 925, a first electron transport layer 930, a first charge generation layer 935, a second hole transport layer 940, a second emissive layer 945, a second electron transport layer 950, a second charge generation layer 955, a third hole transport layer 960, a third emissive layer 965, a third electron transport layer 970, a first electron injection layer 975, and a cathode 980. The first emissive unit 985 may comprise the first hole injection layer 915, the first hole transport layer 920, the first emissive layer 925, and the first electron transport layer 930. The second emissive unit 990 may comprise the second hole transport layer 940, the second emissive layer 945, and the second electron transport layer 950. The third emissive unit 995 may comprise the third hole transport layer 960, the third emissive layer 965, the third electron transport layer 970, and the first electron injection layer 975. Device 900 may be fabricated by depositing the layers described in order.

The simple layered structures illustrated in FIGS. 8 and 9 are provided by way of non limiting examples, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional light emitting devices may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on factors such as performance, design and cost. Other layers, not specifically described, may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in a device, the electron transport layer may transport electrons into the emissive layer, and also block holes from exiting the emissive layer, and may be described as an electron transport layer or a hole blocking layer.

Stacked light emitting device architectures, as depicted in FIGS. 6, 7, 8 and 9, may provide one or more of the following advantages: (1) light from multiple emissive units may be combined within the same surface area of the device thereby increasing the brightness of the device; (2) multiple emissive units may be connected electrically in series with substantially the same current passing through each emissive unit thereby allowing the device to operate at increased brightness without substantial increase in current density thereby extending the operation lifetime of the device; and (3) the light emitted from separate emissive units may be separately controlled, thereby allowing the brightness and/or colour of the device to be tuned according to the exact needs of the application.

Generally, the operational lifetime (LT) of an OLED, QLED or PeLED at luminance (L) may be expressed as LT2 = LTi x (Li / L2) ^AF where LTi is the measured lifetime of the device at (high) luminance Li, LT2 is the predicted lifetime at (low) luminance L2 and AF is the acceleration factor. Approximate acceleration factors to convert measured lifetimes at higher luminance to predicted lifetimes at lower luminance have been determined to be in the approximate range of 1.5 - 2.0 for OLEDs, QLEDs and PeLEDs.

For a stacked light emitting device comprising two emissive units, for the same total device luminance, each emissive unit may operate with luminance L2 that is two times lower than the luminance Li required for an equivalent light emitting device with a single emissive unit. If an acceleration factor of 2.0 is assumed, then the expected operational lifetime for a stacked light emitting device with two emissive units is 2 ² = 4 times longer than that of an equivalent light emitting device with a single emissive unit. Furthermore, for a stacked light emitting device comprising three emissive units, for the same total device luminance each emissive unit may operate with luminance L2 that is three times lower than the luminance Li required for an equivalent light emitting device with a single emissive unit. If an acceleration factor of 2.0 is assumed, then the expected operational lifetime for a stacked light emitting device with three emissive units is 3 ² = 9 times longer than that of an equivalent light emitting device with a single emissive unit.

Examples of stacked light emitting devices that include organic light emitting materials are described in United States patent US 5707745 Bl, Forrest et al., Frobel et al. and Jung et al. All of these citations are included herein by reference in their entirety. United States patent US 5707745 Bl describes a multicolour stacked organic light emitting device. Forrest et al. and Frobel et al. describe stacked organic light emitting devices comprising red, green and blue emissive units that are independently addressable. Jung et al. describes a top emitting stacked organic light emitting device comprising three emissive units, where light from the three emissive units may be combined to generate emission of white light from the device.

Performance advantages of such stacked light emitting devices are well-understood. However, until now there has been no demonstration of a stacked blue OLED, QLED or PeLED device that comprises two or more emissive units that emit blue light with substantially different chromaticity. The novel device architecture presented herein is therefore different from and an improvement over the existing state-of-the-art.

The present invention relates to a stacked blue light emitting device architecture comprising two or more emissive units that emit blue light having substantially different chromaticity for application in displays, light panels and other optoelectronic devices. Optionally, at least one emissive unit may emit a deeper blue light and at least one emissive unit may emit a lighter blue light. Optionally, emissive units may be addressed independently and may emit light independently of each other. Optionally, emissive units may be commonly addressed and may not emit light independently of each other.

Such stacked blue light emitting devices may be incorporated into the red, green and blue sub-pixels of an OLED display. When the blue sub-pixel of such a display is required to emit a relatively saturated blue light, the emissive unit that emits deeper blue light may be individually addressed and may emit light to generate the display image while the emissive unit that emits lighter blue light may remain inactive. However, when the blue sub-pixel of such a display is only required to emit a relatively unsaturated blue light, the emissive unit that emits lighter blue light may be individually addressed and may emit light to generate the display image while the emissive unit that emits deeper blue light may remain inactive. Light may be emitted from the relatively more efficient and/or stable lighter blue emissive unit to render the majority of display images, with light emitted from the relatively less efficient and/or stable deeper blue emissive unit only required to render a small proportion of images. The efficiency and/or lifetime of the display may therefore be enhanced. Furthermore, the lighter blue emissive unit may be used on its own or in combination with the deeper blue emissive unit to provide light to the red and green colour conversion layers in the red and green sub-pixels.

Optionally, devices fabricated in accordance with embodiments of the present invention may comprise two emissive layers. Optionally, devices fabricated in accordance with embodiments of the present invention may comprise three emissive layers. Optionally, devices fabricated in accordance with embodiments of the present invention may comprise four or more emissive layers. Optionally, devices fabricated in accordance with embodiments of the present invention may comprise two emissive units. Optionally, devices fabricated in accordance with embodiments of the present invention may comprise three emissive units. Optionally, devices fabricated in accordance with embodiments of the present invention may comprise four or more emissive units.

Optionally, an emissive unit may comprise an emissive layer. Optionally, an emissive unit may further comprise one or more additional layers, such as a hole injection layer, a hole transport layer, an electron blocking layer, a hole blocking layer, an electron transport layer and/or an electron injection layer. Optionally, some of these additional layers may be included within an emissive unit, and some of these additional layers may be excluded.

Devices fabricated in accordance with embodiments of the present invention may optionally comprise one or more charge generation layers. Optionally, a charge generation layer may be used to separate two or more emissive units within a stacked light emitting device. Stacked light emitting device 600, depicted in FIG. 6, comprises a first charge generation layer 630, which separates a first emissive unit 620 from a second emissive unit 640. Stacked light emitting device 700, depicted in FIG. 7, comprises a first charge generation layer 730, which separates a first emissive unit 720 from a second emissive unit 740. Stacked light emitting device 700, depicted in FIG. 7, further comprises a second charge generation layer 750, which separates a second emissive unit 740 from a third emissive unit 760.

A charge generation layer 630, 730 or 750 may comprise a single layer or multiple layers. Optionally, a charge generation layer 630, 730 or 750 may comprise an n-doped layer for the injection of electrons, and a p-doped layer for the injection of holes. Optionally, a charge generation layer 630, 730 or 750 may include a hole injection layer (HIL). Optionally, a p-doped layer of a charge generation layer 630, 730 or 750 may function as a hole injection layer (HIL). FIG. 9 depicts a stacked light emitting device 900 having three emissive units, where a first charge generation layer 935 includes a hole injection layer (not shown), and a second charge generation layer 955 includes a hole injection layer (not shown). Optionally, a charge generation layer 630, 730 or 750 may be positioned adjacent to and in contact with a separate hole injection layer. FIG. 8 depicts a stacked light emitting device 800 having two emissive units, where a first charge generation layer 840 is adjacent to and in contact with a second hole injection layer 845.

Optionally, a charge generation layer 630, 730 or 750 may include an electron injection layer (EIL). Optionally, an n-doped layer of a charge generation layer 630, 730 or 750 may function as an electron injection layer (EIL). FIG. 9 depicts a stacked light emitting device 900 having three emissive units, where a first charge generation layer 935 includes an electron injection layer (not shown), and a second charge generation layer 955 includes an electron injection layer (not shown). Optionally, a charge generation layer 630, 730 or 750 may be positioned adjacent to and in contact with a separate electron injection layer.

Optionally, a charge generation layer 630, 730 or 750 may include a layer for conducting holes and/or injecting them into the layers of the device. Such a layer may comprise any suitable material or combination of materials known to the art, such that the layer is capable of conducting holes and/or injecting them into the layers of the device. Such a layer may be referred to as an anode layer. Optionally, a charge generation layer 630, 730 or 750 may include a layer for conducting electrons and/or injecting them into the layers of the device. Such a layer may comprise any suitable material or combination of materials known to the art, such that the layer is capable of conducting electrons and/or injecting them into the layers of the device. Such a layer may be referred to as a cathode layer. Optionally, a charge generation layer 630, 730 or 750 may comprise an anode and cathode layer that are electrically connected to each other.

A charge generation layer 630, 730 or 750 may be deposited by a solution process or by a vacuum deposition process. A charge generation layer 630, 730 or 750 may be composed of any applicable materials that enable injection of electrons and holes. A charge generation layer 630, 730 or 750 may be doped or undoped. Doping may be used to enhance conductivity.

One example of vapour process charge generation layer is a dual layer structure consisting of lithium doped BPhen (Li-BPhen) as the n-doped layer for electron injection, in combination with of 1,4,5,8,9,11-Hexaazatriphenylenehexacarbonitrile (HATCN) as the p-doped layer for hole injection. One example of a solution process charge generation layer is a dual layer structure consisting of polyethylenimine (PEI) surface modified zinc oxide (ZnO) as the n-doped layer for electron injection, in combination with molybdenum oxide (M0O3) or tungsten trioxide (WO3) as the p- doped layer for hole injection. Other materials or combinations of materials may be used for charge generation layers. Depending on the configuration of a particular device, charge generation layers may be disposed at locations different than those shown in device 800 and device 900.

Optionally, one or more charge generation layers within a stacked light emitting device may be directly connected to one or more external electrical sources. Optionally, one or more emissive units of a stacked light emitting may be independently addressable and may emit light independently of each other. Connecting one or more charge generation layers to one or more external electrical sources may be of advantage in that light emission from separate emissive units of a stacked light emitting device may be selected and separately controlled according to the needs of the application. In the present invention, connecting one or more charge generation layers to one or more external electrical sources may allow the chromaticity of blue light from a stacked light emitting device to be controlled. Unless otherwise specified, any one of the layers of the various embodiments may be deposited by any suitable method. Methods include vacuum thermal evaporation, sputtering, electron beam physical vapour deposition, organic vapor phase deposition and organic vapour jet printing. Other suitable methods include spincoating and other solution-based processes. Substantially similar processes can be used to deposit materials used in OLED, QLED and PeLED devices, which facilitates the combination of these materials in a light emitting device.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide range of consumer products. Optionally, devices may be used in displays for televisions, computer monitors, tablets, laptop computers, smart phones, cell phones, digital cameras, video recorders, smartwatches, fitness trackers, personal digital assistants, vehicle displays and other electronic devices. Optionally, devices may be used for micro-displays or heads-up displays. Optionally, devices may be used in light panels for interior or exterior illumination and/or signaling, in smart packaging or in billboards.

Optionally, various control mechanisms may be used to control light emitting devices fabricated in accordance with the present invention, including passive matrix and active matrix address schemes.

The materials and structures described herein may have applications in devices other than light emitting devices. For example, other optoelectronic devices such as solar cells, photodetectors, transistors or lasers may employ the materials and structures.

The present invention relates to novel light emitting device architectures for application in devices, such as displays, light panels and other optoelectronic devices, and in particular to stacked blue light emitting devices that comprise two or more emissive units that emit blue light having substantially different chromaticity.

A device is provided. The device may be understood with reference to arrangement 600 in FIG. 6 that depicts an exemplary stacked light emitting device having two emissive units. In one embodiment, the device comprises a stacked blue light emitting device 600 comprising: a first electrode 610; a second electrode 650; a first emissive unit 620 comprising a first emissive layer (not shown); a second emissive unit 640 comprising a second emissive layer (not shown); and a first charge generation layer 630; wherein the first emissive unit 620, the second emissive unit 640 and the first charge generation layer 630 are all disposed between the first electrode 610 and the second electrode 650; the first emissive unit 620 is disposed over the first electrode 610; the first charge generation layer 630 is disposed over the first emissive unit 620; the second emissive unit 640 is disposed over the first charge generation layer 630; the second electrode 650 is disposed over the second emissive unit 640; the first emissive unit 620 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the first peak wavelength; the first emissive unit 620 emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (xl, yl); the second emissive unit 640 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the second peak wavelength; the second emissive unit 640 emits blue light having a second chromaticity having second CIE 1931 (x, y) colour space chromaticity coordinates of (x2, y2); the second chromaticity is substantially different to the first chromaticity; and the first emissive layer and the second emissive layer comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material.

As used herein, "red", "green" and "blue" refer to the degree to which light emitted by a light emitting material, emissive layer, emissive unit, region or device can be described as similar to or different from the hues of red, green and blue. Materials, layers, regions, units and devices may be described herein in reference to the hue of light they emit. As used herein, a red material, layer, region, unit or device, refers to one that emits light with a red hue that has an emission spectrum with a peak wavelength in the visible spectrum in the range of 580 nm to 780 nm; a green material, layer, region, unit or device, refers to one that emits light with a green hue that has an emission spectrum with a peak wavelength in the visible spectrum in the range of 500 nm to 580 nm; and a blue material, layer, region, unit or device, refers to one that emits light with a blue hue that has an emission spectrum with a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm.

Similarly, any reference to a colour altering layer refers to a layer that converts or modifies another hue of light to light having a wavelength as specified for that hue. In general, there are two classes of colour altering layers: colour filters that modify a spectrum by removing unwanted wavelengths of light, and colour conversion layers that convert photons of higher energy to photons of lower energy. A red color filter refers to a filter that results in light having an emission spectrum with a peak wavelength in the range of 580 nm to 780 nm. A green color filter refers to a filter that results in light having an emission spectrum with a peak wavelength in the range of 500 nm to 580 nm. A blue color filter refers to a filter that results in light having an emission spectrum with a peak wavelength in the range of 380 nm to 500 nm. A red colour conversion layer refers to a conversion layer that results in light having an emission spectrum with a peak wavelength in the range of 580 nm to 780 nm. A green colour conversion layer refers to a conversion layer that results in light having an emission spectrum with a peak wavelength in the range of 500 nm to 580 nm. FIG. 19 depicts an arrangement 1900 for an exemplary RGBW OLED display comprising red 1985, green 1990 and blue 1995 colour filters that modify a white spectrum. FIG. 20 depicts an arrangement 2000 for an exemplary QD-OLED display comprising red 2050 and green 2060 colour conversion layers that convert photons of blue light to photons of red and green light. As used herein, light emitted from materials, layers, units, regions or devices may be referred to herein as "deep" or "deeper" or "light" or "lighter", which refers to the relative saturation of the light. In one embodiment, as used herein, "deep-blue" light refers to blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, and "light-blue" light refers to blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, as used herein, "deeper" blue light refers to blue light with relatively shorter peak wavelength, and "lighter" blue light refers to blue light with relatively longer peak wavelength.

Chromaticity refers to an objective specification of the quality of colour regardless of its luminance. As used herein, the "chromaticity" of light and may be visualized and quantified using the CIE 1931 (x, y) chromaticity diagram which depicts the CIE 1931 XYZ colour space. The chromaticity of light emitted from a material, layer, unit, region or device may be quantified by its CIE 1931 (x, y) coordinates on the CIE 1931 (x, y) chromaticity diagram.

As used herein, light emitted from materials, layers, units, regions or devices may be considered to have "substantially different" chromaticity if the light emitted is noticeably different to the average human eye. As used herein, light emitted from materials, layers, units, regions or devices may be considered to have "substantially the same" chromaticity if the light emitted is indistinguishable to the average human eye.

One suitable technique to quantify the chromaticity and difference of chromaticity of light is to use MacAdam ellipses. This may be visualized with reference to FIG. 13, which depicts MacAdam ellipses superimposed on the CIE 1931 (x, y) colour space chromaticity diagram. Within the CIE 1931 (x, y) colour space chromaticity diagram, a one-step MacAdam ellipse contains all chromaticity coordinates which are indistinguishable to the average human eye from the chromaticity coordinates at the center of the ellipse. That is to say to the average human eye any light with chromaticity coordinates outside of a 1-step ellipse is noticeably different in chromaticity from the chromaticity at the centre of the ellipse. Tolerance may be introduced by extending the ellipses. For example, a two-step MacAdam ellipse has axes that are two times as large as for a one-step ellipse, and a ten-step MacAdam ellipse has axes that are ten times as large as for a one-step ellipse. All the MacAdam ellipses depicted in FIG. 13 are ten-step MacAdam ellipses.

In one embodiment, the second chromaticity coordinates (x2, y2) measured for light emitted from the second emissive unit 640 are not contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl) measured for light emitted from the first emissive unit 620. In one embodiment, the second chromaticity coordinates (x2, y2) measured for light emitted from the second emissive unit 640 are not contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl) measured for light emitted from the first emissive unit 620.

One further suitable technique to characterize the difference in chromaticity of light emitted from materials, layers, units, regions or devices is to quantify the absolute difference in CIE 1976 (u', v') chromaticity coordinates. The CIE 1976 (u', v') color space is used in preference over the CIE 1931 (x, y) colour space because unlike the CIE 1931 (x, y) colour space, in the CIE 1976 (u', v') colour space, distance is approximately proportional to perceived difference in colour. The conversion between the colour spaces is simple: u' = 4x / (-2x + 12y + 3) and v' = 9y / (-2x + 12y +3). Difference in chromaticity can be quantified as: Auv = V(Au' ² + Dn' ² ) = V((ul - u2) ² + (vl - v2) ² ), which is the distance in the CIE 1976 (u', v') colour space of first chromaticity coordinates (ul, vl) from second chromaticity coordinates (u2, v2). As used herein, light emitted from a first material, region, unit or device with first chromaticity coordinates (ul, vl) may be considered to have a substantially different chromaticity to light emitted from a second material, region, unit or device with second chromaticity coordinates (u2, v2) if the difference in chromaticity as defined by Auv is 0.010 or more. In one embodiment, the first CIE 1931 (x, y) colour space chromaticity coordinates (xl, yl) may be converted to CIE 1976 (u', v') colour space chromaticity coordinates (ul, vl); and the second CIE 1931 (x, y) colour space chromaticity coordinates (x2, y2) may be converted to second CIE 1976 (u', v') colour space chromaticity coordinates (u2, v2); wherein the first chromaticity coordinates (ul, vl) of light emitted from the first blue emissive layer 620 and the second chromaticity coordinates (u2, v2) of light emitted from the second blue emissive layer 640 are sufficiently different such that the difference in chromaticity as defined by Auv is 0.010 or more.

One further suitable technique to characterize the difference in chromaticity of light emitted from materials, layers, units, regions or devices is to measure the emission spectrum and compare peak emission wavelength. In one embodiment, the second peak wavelength of light emitted from the second emissive unit 640 is at least 4 nm greater than or at least 4 nm less than the first peak wavelength of light emitted from the first emissive unit 620.

The proposed novel device architecture is ideally suited to OLED, QLED and PeLED displays. One or more advantages of including organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material in the first emissive layer of the first emissive unit 620 and in the second emissive layer of the second emissive unit 640 of a stacked blue light emitting device may be demonstrated using the data shown in Table 1 and FIG. 12. The data in Table 1 and FIG. 12 may also be used to demonstrate one or more advantages of combining emissive layers comprising different types of light emitting material in a stacked blue light emitting device. Table 1 shows CIE 1931 (x, y) colour coordinates for single emissive unit blue OLED, QLED and PeLED devices. Also included in Table 1 are CIE 1931 (x, y) colour coordinates for DCI-P3 and Rec. 2020 colour gamut standards and for a commercial OLED display. Generally, for blue light a lower CIE y value corresponds to deeper emission. This can be understood with reference FIG. 12, which depicts data from Table 1 for light blue OLEDs (squares), deep blue OLEDs (pentagons), deep blue QLEDs (triangles) and deep blue PeLEDs (circles) as well as data for a commercial OLED display (stars) and the primary colours of the DCI-P3 colour gamut in FIG. 12a and for the Rec. 2020 colour gamut in FIG. 12b.

Table 1: CIE 1931 (x, y) colour coordinates for exemplary single emissive unit blue OLEDs, QLEDs and PeLEDs and for a commercial OLED display. Also included are colour coordinates for DCI-P3 and Rec. 2020 colour gamut standards.

The CIE 1931 (x, y) colour coordinate data reported for single emissive unit blue OLED, QLED and PeLED devices in Table 1 are exemplary. Commercial OLED data are taken from the Apple iPhone X, which fully supports the DCI-P3 colour gamut. This data set is available from Raymond Soneira at DisplayMate Technologies Corporation (Soneira et al.). The other data are taken from a selection of peer-reviewed scientific journals: Light-blue OLED data are taken from Zanoni et al. Deep-blue OLED data are taken from Takita et al. Deep-blue QLED data are taken from Wang et al. Deep-blue PeLED data are taken from Kumar et al. Data from these sources are used by way of example, and should be considered non-limiting. Data from other peer-reviewed scientific journals, simulated data and/or experimental data collected from laboratory devices may also be used to demonstrate the aforementioned advantages of the claimed device architecture.

The presented chromaticity data can be further understood with reference to emission spectra. FIG. 14 depicts exemplary normalized electroluminescence emission spectra for the single emissive unit blue OLEDs summarized in Table 1. The spectrum depicted using a dashed line corresponds to the spectrum for an OLED that emits light-blue light with an emission peak at 470 nm. The spectrum depicted using a solid line corresponds to the spectrum for an OLED that emits deep-blue light with an emission peak at 451 nm. Note that the shapes of the emission spectra have been simplified to bell curves for ease of understanding. OLEDs are used by way of example in FIG. 14, but the same principles may also be applied to QLEDs and PeLEDs.

Emission spectra with peaks located closer to the peak of the photopic luminous efficiency function at 555 nm generally have greater overlap with the photopic luminous efficiency function. FIG. 14 shows that the light-blue emission spectrum has greater overlap with the photopic luminous efficiency function than the respective deep-blue emission spectrum. This means that fewer photos are required for the same perceived brightness for light-blue light than for deep-blue light. Emissive units that emit light-blue light may therefore have greater efficiency than emissive units that emit deep-blue light.

The stacked blue light emitting device of the present invention comprising lighter and deeper blue emissive units having substantially different chromaticity may therefore enable devices such as displays to operate with improved efficiency. This is because the more efficient lighter blue emissive unit may be used to render the majority of images, with the less efficient deeper blue emissive unit used only to render a minority of images where extended colour gamut is required. The energy savings are substantial because the majority of images rendered by a display in day-to-day use do not require extended colour gamut.

To demonstrate such a stacked blue light emitting device, the two or more emissive units may be required to be independently addressable so that they may emit light independently of each other. In one embodiment, the first emissive unit 620 and the second emissive unit 640 are independently addressable and may emit light independently of each other. As depicted in FIG. 6, this may be achieved if one or more charge generation layers 630 are directly connected to an external electrical source.

In one embodiment, as depicted in arrangement 600 in FIG. 6, the first electrode 610 is directly connected to an external electrical source El, the second electrode 650 is directly connected to an external electrical source E2, and the first charge generation layer 630 is directly connected to an external electrical source E3. The first emissive unit may be independently addressed putting El on a positive potential with respect to E3 for a standard device architecture, or by putting El on a negative potential with respect to E3 for an inverted device architecture. The second emissive unit may be independently addressed putting E3 on a positive potential with respect to E2 for a standard device architecture, or by putting E3 on a negative potential with respect to E2 for an inverted device architecture. In one embodiment, the device comprises a stacked blue light emitting device comprising at least two blue emissive units. FIG. 15 depicts various configurations of emissive units for a stacked blue light emitting device having two blue emissive units. In each configuration, the stacked blue light emitting device comprises a first electrode 610, a first blue emissive unit 620 comprising a first blue emissive layer (not shown), a first charge generation layer 630, a second blue emissive unit 640 comprising a second blue emissive layer (not shown) and a second electrode 650. The first blue emissive unit 620, the first charge generation layer 630 and the second blue emissive unit 640 are all disposed between the first electrode 610 and the second electrode 650. The first blue emissive unit 620 is disposed over the first electrode 610. The first charge generation layer 630 is disposed over the first blue emissive unit 620. The second blue emissive unit 640 is disposed over the first charge generation layer 630. The second electrode 650 is disposed over the second blue emissive unit 640. In each configuration, the first blue emissive layer and the second blue emissive layer each comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material.

In one embodiment, the first blue emissive unit 620 may emit blue light and the second blue emissive unit 640 may emit blue light. In one embodiment, the first blue emissive unit 620 and the second blue emissive unit 640 may both emit blue light with peak wavelength in the visible spectrum in the range of 380 nm to 500 nm. In one embodiment, as depicted by device 1510 in FIG. 15a, the first blue emissive unit 620 may emit lighter blue light and the second blue emissive unit 640 may emit deeper blue light. In one embodiment, as depicted by device 1520 in FIG. 15b, the first blue emissive unit 620 may emit deeper blue light and the second blue emissive unit 640 may emit lighter blue light.

In one embodiment, the first blue emissive unit 620 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the second blue emissive unit 640 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, the first blue emissive unit 620 emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the second blue emissive unit 640 emits blue light with a CIE 1931 y coordinate of more than 0.080. In one embodiment, the second blue emissive unit 640 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the first blue emissive unit 620 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, the second blue emissive unit 640 emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the blue first emissive unit 620 emits blue light with a CIE 1931 y coordinate of more than 0.080.

Such exemplary embodiments may all be realized using any suitable combination of light emitting materials from the light-blue OLED, deep-blue OLED, deep-blue QLED and/or deep-blue PeLED devices described in Table 1. In one embodiment, the first emissive unit 620 and the second emissive unit 640 are commonly addressable and may not emit light independently of each other.

Inherent properties of organic light emitting materials, quantum dot light emitting materials and perovskite light emitting materials render them well-suited to the herein disclosed stacked blue light emitting device architecture. These properties include optical band gaps that are readily tunable across the visible, ultra-violet and infra-red spectra, high colour saturation that enables displays with wide colour gamut, excellent charge transport properties and low non-radiative rates.

In one preferred embodiment, the first blue emissive layer and the second blue emissive layer comprise organic light emitting material. In one embodiment, the first blue emissive layer and the second blue emissive layer comprise fluorescent organic light emitting material. In one embodiment, the first blue emissive layer and the second blue emissive layer comprise phosphorescent organic light emitting material.

In one embodiment, at least one of the first emissive layer and the second emissive layer comprise phosphorescent organic light emitting material; and at least one of the first emissive layer and the second emissive layer comprise fluorescent organic light emitting material. In one preferred embodiment, the first blue emissive layer is a light- blue emissive layer comprising phosphorescent organic light emitting material; and the second blue emissive layer is a deep-blue emissive layer comprising fluorescent organic light emitting material. In one preferred embodiment, the first blue emissive layer is a deep-blue emissive layer comprising fluorescent organic light emitting material; and the second blue emissive layer is a light-blue emissive layer comprising phosphorescent organic light emitting material. Such stacked blue light emitting device architectures may be of advantage because a more efficient but less stable phosphorescent organic material may emit light-blue light to render light-blue colours, whereas a less efficient but more stable fluorescent organic material may emit deep- blue light to render deep-blue colours.

In one embodiment, the first blue emissive layer and the second blue emissive layer comprise quantum dot light emitting material. In one embodiment, the first blue emissive layer and the second blue emissive layer comprise perovskite light emitting material.

In one embodiment, the first blue emissive layer comprises a first class of blue light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; and the second blue emissive layer comprises a second class of blue light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; wherein the second class of blue light emitting material is not the same as the first class of blue light emitting material. In one preferred embodiment, the first blue emissive layer comprises organic light emitting material and the second blue emissive layer comprises quantum dot light emitting material or perovskite light emitting material.

In one embodiment, by combining a first blue emissive unit 620 comprising organic light emitting material with a second blue emissive unit 640 comprising organic light emitting material, a stacked light emitting device that may render the blue primary colour of the DCI-P3 or Rec. 2020 colour gamut may be demonstrated. In one embodiment, by combining a first emissive unit 620 comprising organic light emitting material with a second emissive unit 640 comprising quantum dot light emitting materials or perovskite light emitting material, a stacked blue light emitting device that may render the blue primary colour of the DCI-P3 or Rec. 2020 colour gamut may be demonstrated. Such devices may be of advantage in that when implemented in one or more sub-pixels of a display, the display may render a broader range of colours experienced in everyday life, thereby improving functionality and user experience. Such a device may be of further advantage in that it may provide the display with further advantages such as improved efficiency, higher brightness, improved operational lifetime, lower voltage and/or reduced cost.

In one embodiment, the first blue emissive unit 620 comprises one and not more than one emissive layer. In one embodiment, the first blue emissive unit 620 comprises two or more emissive layers. In one embodiment, the second blue emissive unit 640 comprises one and not more than one emissive layer. In one embodiment, the second blue emissive unit 640 comprises two or more emissive layers. In one embodiment, the first emissive layer comprises one and not more than one light emitting material. In one embodiment, the first emissive layer comprises two or more light emitting materials. In one embodiment, the second emissive layer comprises one and not more than one light emitting material. In one embodiment, the second emissive layer comprises two or more light emitting materials.

The present invention may be further understood with reference to arrangement 700 in FIG. 7 that depicts an exemplary stacked light emitting device having three emissive units. In one embodiment, the device comprises a stacked blue light emitting device 700 comprising: a first electrode 710; a second electrode 770; a first emissive unit 720 comprising a first emissive layer (not shown); a second emissive unit 740 comprising a second emissive layer (not shown); and a first charge generation layer 730; wherein the first emissive unit 720, the second emissive unit 740 and the first charge generation layer 730 are all disposed between the first electrode 710 and the second electrode 770; the first emissive unit 720 is disposed over the first electrode 710; the first charge generation layer 730 is disposed over the first emissive unit 720; the second emissive unit 740 is disposed over the first charge generation layer 730; the second electrode 770 is disposed over the second emissive unit 740; the first emissive unit 720 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the first peak wavelength; the first emissive unit 720 emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (xl, yl); the second emissive unit 740 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the second peak wavelength; the second emissive unit 740 emits blue light having a second chromaticity having second CIE 1931 (x, y) colour space chromaticity coordinates of (x2, y2); the second chromaticity is substantially different to the first chromaticity; and the first emissive layer and the second emissive layer comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material.

The stacked blue light emitting device 700 further comprises: a third emissive unit 760 comprising a third emissive layer (not shown); and a second charge generation layer 750; wherein the third emissive unit 760 and the second charge generation layer 750 are disposed between the second emissive unit 740 and the second electrode 770; the second charge generation layer 750 is disposed over the second emissive unit 740; the third emissive unit 760 is disposed over the second charge generation layer 750; the second electrode 770 is disposed over the third emissive unit 760; the third emissive unit 760 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the third peak wavelength; the third emissive unit 760 emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (x3, y3); and the third emissive layer comprises organic light emitting material, quantum dot light emitting material or perovskite light emitting material.

FIG. 16 depicts various configurations of blue emissive units for a stacked blue light emitting device having three blue emissive units. In each configuration, the stacked blue light emitting device comprises a first electrode 710, a first blue emissive unit 720 comprising a first blue emissive layer (not shown), a first charge generation layer 730, a second blue emissive unit 740 comprising a second blue emissive layer (not shown), a second charge generation layer 750, a third blue emissive unit 760 comprising a third blue emissive layer (not shown), and a second electrode 770. The first blue emissive unit 720, the first charge generation layer 730, the second blue emissive unit 740, the second charge generation layer 750 and the third blue emissive unit 760 are all disposed between the first electrode 710 and the second electrode 770. The first blue emissive unit 720 is disposed over the first electrode 710. The first charge generation layer 730 is disposed over the first blue emissive unit 720. The second blue emissive unit 740 is disposed over the first charge generation layer 730. The second charge generation layer 750 is disposed over the second emissive unit 740. The third blue emissive unit 760 is disposed over the second charge generation layer 750. The second electrode 770 is disposed over the third blue emissive unit 760. In each configuration, the first blue emissive layer, the second blue emissive layer and the third blue emissive layer each comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material. In one embodiment, the first blue emissive unit 720 may emit blue light, the second blue emissive unit 740 may emit blue light and the third blue emissive unit 760 may emit blue light. In one embodiment, the first blue emissive unit 720, the second blue emissive unit 740 and the third blue emissive unit 760 may all emit blue light with peak wavelength in the visible spectrum in the range of 380 nm to 500 nm.

In one embodiment, as depicted by device 1610 in FIG. 16a, the first blue emissive unit 720 may emit lighter blue light, the second blue emissive unit 740 may emit deeper blue light and the third blue emissive unit 760 may emit deeper blue light. In one embodiment, as depicted by device 1620 in FIG. 16b, the first blue emissive unit 720 may emit deeper blue light, the second blue emissive unit 740 may emit deeper blue light and the third blue emissive unit 760 may emit lighter blue light. In one embodiment, as depicted by device 1630 in FIG. 16c, the first blue emissive unit 720 may emit deeper blue light, the second blue emissive unit 740 may emit lighter blue light and the third blue emissive unit 760 may emit deeper blue light. In one embodiment, as depicted by device 1640 in FIG. 16d, the first blue emissive unit 720 may emit lighter blue light, the second blue emissive unit 740 may emit lighter blue light and the third blue emissive unit 760 may emit deeper blue light. In one embodiment, as depicted by device 1650 in FIG. 16e, the first blue emissive unit 720 may emit deeper blue light, the second blue emissive unit 740 may emit lighter blue light and the third blue emissive unit 760 may emit lighter blue light. In one embodiment, as depicted by device 1660 in FIG. 16f, the first blue emissive unit 720 may emit lighter blue light, the second blue emissive unit 740 may emit deeper blue light and the third blue emissive unit 760 may emit lighter blue light.

In one embodiment, the first blue emissive unit 720 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm, the second blue emissive unit 740 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, and the third blue emissive unit 760 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm. In one embodiment, the first blue emissive unit 720 emits blue light with a CIE 1931 y coordinate of more than 0.080, the second blue emissive unit 740 emits blue light with a CIE 1931 y coordinate of 0.080 or less, and the third blue emissive unit 760 emits blue light with a CIE 1931 y coordinate of 0.080 or less.

In one embodiment, the first blue emissive unit 720 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, the second blue emissive unit 740 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, and the third blue emissive unit 760 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, the first blue emissive unit 720 emits blue light with a CIE 1931 y coordinate of 0.080 or less, the second blue emissive unit 740 emits blue light with a CIE 1931 y coordinate of 0.080 or less, and the third blue emissive unit 760 emits blue light with a CIE 1931 y coordinate of more than 0.080.

In one embodiment, the first blue emissive unit 720 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, the second blue emissive unit 740 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm, and the third blue emissive unit 760 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm. In one embodiment, the first blue emissive unit 720 emits blue light with a CIE 1931 y coordinate of 0.080 or less, the second blue emissive unit 740 emits blue light with a CIE 1931 y coordinate of more than 0.080, and the third blue emissive unit 760 emits blue light with a CIE 1931 y coordinate of 0.080 or less.

In one embodiment, the first blue emissive unit 720 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm, the second blue emissive unit 740 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm, and the third blue emissive unit 760 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm. In one embodiment, the first blue emissive unit 720 emits blue light with a CIE 1931 y coordinate of more than 0.080, the second blue emissive unit 740 emits blue light with a CIE 1931 y coordinate of more than 0.080, and the third blue emissive unit 760 emits blue light with a CIE 1931 y coordinate of 0.080 or less.

In one embodiment, the first blue emissive unit 720 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, the second blue emissive unit 740 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm, and the third blue emissive unit 760 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, the first blue emissive unit 720 emits blue light with a CIE 1931 y coordinate of 0.080 or less, the second blue emissive unit 740 emits blue light with a CIE 1931 y coordinate of more than 0.080, and the third blue emissive unit 760 emits blue light with a CIE 1931 y coordinate of more than 0.080.

In one embodiment, the first blue emissive unit 720 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm, the second blue emissive unit 740 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm, and the third blue emissive unit 760 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. In one embodiment, the first blue emissive unit 720 emits blue light with a CIE 1931 y coordinate of more than 0.080, the second blue emissive unit 740 emits blue light with a CIE 1931 y coordinate of 0.080 or less, and the third blue emissive unit 760 emits blue light with a CIE 1931 y coordinate of more than 0.080. Such exemplary embodiments may all be realized using any suitable combination of light emitting materials from the light-blue OLED, deep-blue OLED, deep-blue QLED and/or deep-blue PeLED devices described in Table 1.

In one embodiment, the third chromaticity is substantially the same as one of the first chromaticity and the second chromaticity; and the third chromaticity is substantially different to one of the first chromaticity and the second chromaticity. In one embodiment, the third chromaticity is substantially the same as the first chromaticity and substantially different to the second chromaticity. In one embodiment, the third chromaticity is substantially the same as the second chromaticity and substantially different to the first chromaticity.

To demonstrate such a stacked blue light emitting device, the three or more emissive units may be required to be independently addressable so that they may emit light independently of each other. In one embodiment, the first emissive unit, the second emissive unit and the third emissive unit are independently addressable and may emit light independently of each other. As depicted in FIG. 7, this may be achieved if one or more charge generation layers are directly connected to an external electrical source.

In one embodiment, as depicted in arrangement 700 in FIG. 7, the first electrode 710 is directly connected to an external electrical source El, the second electrode 770 is directly connected to an external electrical source E2, the first charge generation layer 730 is directly connected to an external electrical source E3, and the second charge generation layer 750 is directly connected to an external electrical source E4. The first emissive unit may be independently addressed putting El on a positive potential with respect to E3 for a standard device architecture, or by putting El on a negative potential with respect to E3 for an inverted device architecture. The second emissive unit may be independently addressed putting E3 on a positive potential with respect to E4 for a standard device architecture, or by putting E3 on a negative potential with respect to E4 for an inverted device architecture. The third emissive unit may be independently addressed putting E4 on a positive potential with respect to E2 for a standard device architecture, or by putting E4 on a negative potential with respect to E2 for an inverted device architecture.

In one embodiment, the first blue emissive unit 720, the second blue emissive unit 740 and the third blue emissive unit 760 may all be commonly addressable and may not emit light independently of each other. In one embodiment, the first blue emissive unit 720, the second blue emissive unit 740 and the third blue emissive unit 760 may all be independently addressable and may all emit light independently of each other. In one embodiment, at least one emissive unit may be independently addressable and may emit light independently of the other two emissive units, whereas the other two emissive units may be commonly addressable and may not emit light independently of each other. In one embodiment, the third emissive unit 760 is commonly addressed with one of the first emissive unit 720 and the second emissive unit 740 and may not emit light independently of one of the first emissive unit 720 and the second emissive unit 740; and the third emissive unit 760 is addressed independently of one of the first emissive unit 720 and the second emissive unit 740 and may emit light independently of one of the first emissive unit 720 and the second emissive unit 740. In one embodiment, the third emissive unit 760 is commonly addressed with one of the first emissive unit 720 and the second emissive unit 740 and may not emit light independently of one of the first emissive unit 720 and the second emissive unit 740; the third emissive unit 760 is addressed independently of one of the first emissive unit 720 and the second emissive unit 740 and may emit light independently of one of the first emissive unit 720 and the second emissive unit 740; wherein the emissive unit which is commonly addressed with the third emissive unit 760 has substantially the same chromaticity as the third emissive unit 760; and the emissive unit which is addressed independently of the third emissive unit 760 has substantially different chromaticity to the third emissive unit 760.

In one embodiment, a lighter blue emissive unit may be commonly addressed with another lighter blue emissive unit and may not emit light independently of another lighter blue emissive unit. In one embodiment, a deeper blue emissive unit may be commonly addressed with another deeper blue emissive unit and may not emit light independently of another deeper blue emissive unit. In one embodiment, a lighter blue emissive unit may be addressed independently from a deeper blue emissive unit and may emit light independently from the deeper blue emissive unit. In one embodiment, a deeper blue emissive unit may be addressed independently from a lighter blue emissive unit and may emit light independently from the lighter blue emissive unit.

For example, in device 1610 in FIG. 16a the lighter blue first emissive unit 720 may emit light independently of both the deeper blue second emissive unit 740 and the deeper blue third emissive unit 760, whereas the deeper blue second emissive unit 740 and the deeper blue third emissive unit 760 may be commonly addressable and may not emit light independently of each other.

In one embodiment, the third chromaticity coordinates (x3, y3) are not contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl), but are contained within a one-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2). In one embodiment, the third chromaticity coordinates (x3, y3) are not contained within a one-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2), but are contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). In one embodiment, the third chromaticity coordinates (x3, y3) are not contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl), but are contained within a three-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2). In one embodiment, the third chromaticity coordinates (x3, y3) are not contained within a three-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2), but are contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl).

In one embodiment, the third CIE 1931 (x, y) colour space chromaticity coordinates (x3, y3) may be converted to third CIE 1976 (u', v') colour space chromaticity coordinates (u3, v3). In one embodiment, the third chromaticity coordinates (u3, v3) and the first chromaticity coordinates (ul, vl) are sufficiently different such that the difference in chromaticity as defined by Auv = V((u3 - ul) ² + (v3 - vl) ² ) is 0.010 or more; but the third chromaticity coordinates (u3, v3) and the second chromaticity coordinates (u2, v2) are sufficiently similar such that the difference in chromaticity as defined by Auv = V((u3 - u2) ² + (v3 - v2) ² ) is less than 0.010. In one embodiment, the third chromaticity coordinates (u3, v3) but the second chromaticity coordinates (u2, v2) are sufficiently different such that the difference in chromaticity as defined by Auv = V((u3 - u2) ² + (v3 - v2) ² ) is 0.010 or more; and the third chromaticity coordinates (u3, v3) and the first chromaticity coordinates (ul, vl) are sufficiently similar such that the difference in chromaticity as defined by Auv = V((u3 - ul) ² + (v3 - vl) ² ) is less than 0.010.

In one embodiment, the third peak wavelength is at least 4 nm greater than or less than the first peak wavelength; but the third peak wavelength is within 4 nm of the second peak wavelength. In one embodiment, the third peak wavelength is at least 4 nm greater than or less than the second peak wavelength; but the third peak wavelength is within 4 nm of the first peak wavelength.

Such a device comprising three or more blue emissive units within a stacked blue light emitting device architecture may be of advantage in that light from more blue emissive units may be combined within the same surface area of the device thereby increasing the brightness of the device; and multiple emissive units may be connected electrically in series with substantially the same current passing through each emissive unit thereby allowing the device to operate at increased brightness without substantial increase in current density thereby extending the operation lifetime of the device.

In one embodiment, the stacked blue light emitting device may include a microcavity structure. Optionally, as described herein, a microcavity structure may be created where a transparent and partially reflective electrode is used in combination with an opposing reflective electrode. Optionally, in a standard device architecture, a bottom- emission microcavity structure may be created using a transparent and partially reflective multilayer anode such as ITO/Ag/ITO, where the Ag thickness is less than approximately 25 nm, in combination with a reflective multilayer cathode such as LiF/AI. In this architecture, light emission is through the anode. Optionally, in a standard device architecture, a top-emission microcavity structure may be created using a transparent and partially reflective compound cathode such as Mg:Ag in combination with a reflective multilayer anode such as ITO/Ag/ITO, where the Ag thickness is greater than approximately 80 nm. In this architecture, light emission is through the cathode.

Such a device may be of advantage in that such a microcavity structure may increase the total amount of light emitted from the device, thereby increasing the efficiency and brightness of the device. Such a device may further be of advantage in that such a microcavity structure may increase the proportion of light emitted in the forward direction from the device, thereby increasing the apparent brightness of the device to a user positioned at normal incidence. Such a device may further be of advantage in that such a microcavity structure may narrow the spectrum of emitted light from the device, thereby increasing the colour saturation of the emitted light. Application of such a microcavity structure to the device may thereby enable the device to render a primary colour of the DCI-P3 colour gamut. Application of such a microcavity structure to the device may thereby enable the device to render a primary colour of the Rec. 2020 colour gamut.

In one embodiment, the device is part of a display. In one embodiment, the device may be included in a sub-pixel of a display. Optionally, the display may be incorporated into a wide range of consumer products. Optionally, the display may be used in televisions, computer monitors, tablets, laptop computers, smart phones, cell phones, digital cameras, video recorders, smartwatches, fitness trackers, personal digital assistants, vehicle displays and other electronic devices. Optionally, the display may be used for micro-displays or heads-up displays. Optionally, the display may be used in light sources for interior or exterior illumination and/or signaling, in smart packaging or in billboards.

FIG. 17 depicts exemplary designs of sub-pixels. Included in FIG. 17 is an arrangement 1700 of three adjacent sub-pixels, each of length L and width W. The first sub-pixel 1710 may comprise a red sub-pixel, wherein such a red sub-pixel may comprise a stacked blue light emitting device such as depicted in FIG. 6 or FIG. 7 that is optically coupled to a red colour conversion layer. The second sub-pixel 1720 may comprise a green sub-pixel, wherein such a green sub-pixel may comprise a stacked blue light emitting device such as depicted in FIG. 6 or FIG. 7 that is optically coupled to a green colour conversion layer. The third sub-pixel 1730 may comprise a blue sub-pixel, wherein such a blue sub-pixel may comprise a stacked blue light emitting device such as depicted in FIG. 6 or FIG. 7. A typical pixel arrangement of a commercial display may comprise a sub-pixel arrangement such as 1700.

A display is provided. In one embodiment, the display comprises sub-pixels that may be arranged as depicted in arrangement 1700 in FIG. 17. The display may be further understood with reference to arrangement 2100 depicted in FIG. 21. In one embodiment the display comprises: a first sub-pixel 1710 configured to emit red light with a peak wavelength in the visible spectrum of 580 nm to 780 nm; a second sub-pixel 1720 configured to emit green light with a peak wavelength in the visible spectrum of 500 nm to 580 nm; and a third sub-pixel 1730 configured to emit blue light with a peak wavelength in the visible spectrum of 380 nm to 500 nm; wherein the first sub-pixel 1710 comprises a first stacked blue light emitting device 2105 optically coupled to a red colour conversion layer 2170; the second sub-pixel 1720 comprises a second stacked blue light emitting device 2115 optically coupled to a green colour conversion layer 2180; and the third sub-pixel 1730 comprises a third stacked blue light emitting device 2125; wherein all of the first 1705, second 1715 and third 1725 stacked blue light emitting devices comprise: a first electrode 2120; a second electrode 2160; a first emissive unit 2130 comprising a first emissive layer (not shown); a second emissive unit 2150 comprising a second emissive layer (not shown); and a first charge generation layer 2140; wherein the first emissive unit 2130, the second emissive unit 2150 and the first charge generation layer 2140 are all disposed between the first electrode 2120 and the second electrode 2160; the first emissive unit 2130 is disposed over the first electrode 2120; the first charge generation layer 2140 is disposed over the first emissive unit 2130; the second emissive unit 2150 is disposed over the first charge generation layer 2140; the second electrode 2160 is disposed over the second emissive unit 2150; the first emissive unit 2130 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the first peak wavelength; the first emissive unit 2130 emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (xl, yl); the second emissive unit 2150 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the second peak wavelength; the second emissive unit 2150 emits blue light having a second chromaticity having second CIE 1931 (x, y) colour space chromaticity coordinates of (x2, y2); the second chromaticity is substantially different to the first chromaticity; and the first emissive layer and the second emissive layer comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material.

In one embodiment, the second chromaticity coordinates (x2, y2) measured for light emitted from the second emissive unit 2150 are not contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl) measured for light emitted from the first emissive unit 2130 for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the second chromaticity coordinates (x2, y2) measured for light emitted from the second emissive unit 2150 are not contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl) measured for light emitted from the first emissive unit 2130 for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the first CIE 1931 (x, y) colour space chromaticity coordinates (xl, yl) may be converted to first CIE 1976 (u', v') colour space chromaticity coordinates (ul, vl); and the second CIE 1931 (x, y) colour space chromaticity coordinates (x2, y2) may be converted to second CIE 1976 (u', v') colour space chromaticity coordinates (u2, v2); wherein the first chromaticity coordinates (ul, vl) of light emitted from the first blue emissive unit 2130 and the second chromaticity coordinates (u2, v2) of light emitted from the second blue emissive unit 2150 are sufficiently different such that the difference in chromaticity as defined by Auv is 0.010 or more for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices.

In one embodiment, the second peak wavelength of light emitted from the second emissive unit 2150 is at least 4 nm greater than or at least 4 nm less than the first peak wavelength of light emitted from the first emissive unit 2130 for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices.

In one embodiment, the first blue emissive unit 2130 may emit blue light and the second blue emissive unit 2150 may emit blue light for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 and the second blue emissive unit 2150 may both emit blue light with peak wavelength in the visible spectrum in the range of 380 nm to 500 nm for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 may emit lighter blue light and the second blue emissive unit 2150 may emit deeper blue light for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 may emit deeper blue light and the second blue emissive unit 2150 may emit lighter blue light for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices.

In one embodiment, the first blue emissive unit 2130 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the second blue emissive unit 2150 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the second blue emissive unit 2150 emits blue light with a CIE 1931 y coordinate of more than 0.080 for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the second blue emissive unit 2150 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the first blue emissive unit 2130 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices. In one embodiment, the second blue emissive unit 2150 emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the blue first emissive unit 2130 emits blue light with a CIE 1931 y coordinate of more than 0.080 for all of the first 2105, second 2115 and third 2125 stacked blue light emitting devices.

Such exemplary embodiments may be realized using any suitable combination of light emitting materials from the light-blue OLED, deep-blue OLED, deep-blue QLED and/or deep-blue PeLED devices described in Table 1.

In one embodiment, the first stacked blue light emitting device 2105, the second stacked blue light emitting device 2115 and the third stacked blue light emitting device 2125 all have the same device architecture. That is to say that the first 2105, second 2115 and third 2125 stacked light blue emitting devices all comprise the same device layers arranged in the same configuration and comprising the same materials in the same proportions. That is to say that the first 2105, second 2115 and third 2125 stacked light blue emitting devices all have the same optoelectronic performance.

In one embodiment, the first emissive unit 2130 and the second emissive unit 2150 of any of the first 2105, second 2125 and third 2125 blue stacked light emitting devices are commonly addressable and may not emit light independently of each other. In one embodiment, the first emissive unit 2130 and the second emissive unit 2150 of any of the first 2105, second 2125 and third 2125 blue stacked light emitting devices are independently addressable and may emit light independently of each other.

In one embodiment, the first emissive unit 2130 and the second emissive unit 2150 of all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices are commonly addressable and may not emit light independently of each other. In one embodiment, the first emissive unit 2130 and the second emissive unit 2150 of all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices are independently addressable and may emit light independently of each other.

In one embodiment, the first emissive unit 2130 and the second emissive unit 2150 of the third stacked blue light emitting device 2125 are independently addressable and may emit light independently of each other, and the first emissive unit 2130 and the second emissive unit 2150 of the first stacked blue light emitting device 2105 are commonly addressable and may not emit light independently of each other, and the first emissive unit 2130 and the second emissive unit 2150 of the second stacked blue light emitting device 2115 are commonly addressable and may not emit light independently of each other.

In one preferred embodiment, the first blue emissive layer and the second blue emissive layer comprise organic light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices. In one embodiment, the first blue emissive layer and the second blue emissive layer comprise fluorescent organic light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices. In one embodiment, the first blue emissive layer and the second blue emissive layer comprise phosphorescent organic light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices.

In one embodiment, at least one of the first emissive layer and the second emissive layer comprise phosphorescent organic light emitting material; and at least one of the first emissive layer and the second emissive layer comprise fluorescent organic light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices. In one preferred embodiment, the first blue emissive layer is a light-blue emissive layer comprising phosphorescent organic light emitting material; and the second blue emissive layer is a deep-blue emissive layer comprising fluorescent organic light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices. In one preferred embodiment, the first blue emissive layer is a deep-blue emissive layer comprising fluorescent organic light emitting material; and the second blue emissive layer is a light-blue emissive layer comprising phosphorescent organic light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices. Such stacked blue light emitting device architectures may be of advantage because a more efficient but less stable phosphorescent organic material may emit light-blue light to render light-blue colours, whereas a less efficient but more stable fluorescent organic material may emit deep-blue light to render deep-blue colours.

In one embodiment, the first blue emissive layer and the second blue emissive layer comprise quantum dot light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices. In one embodiment, the first blue emissive layer and the second blue emissive layer comprise perovskite light emitting material for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices.

In one embodiment, for all of the first 2105, second 2125 and third 2125 blue stacked light emitting devices, the first blue emissive layer comprises a first class of blue light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; and the second blue emissive layer comprises a second class of blue light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; wherein the second class of blue light emitting material is not the same as the first class of blue light emitting material. In one preferred embodiment, the first blue emissive layer comprises organic light emitting material and the second blue emissive layer comprises quantum dot light emitting material or perovskite light emitting material.

In one embodiment, as depicted by arrangement 2200 in FIG. 22, all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices further comprise: a third emissive unit 2220 comprising a third emissive layer (not shown); and a second charge generation layer 2210; wherein the third emissive unit 2220 and the second charge generation layer 2210 are disposed between the second emissive unit 2150 and the second electrode 2160; the second charge generation layer 2210 is disposed over the second emissive unit 2150; the third emissive unit 2220 is disposed over the second charge generation layer 2210; the second electrode 2160 is disposed over the third emissive unit 2220; the third emissive unit 2220 emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the third peak wavelength; the third emissive unit 2220 emits blue light having a third chromaticity having third CIE 1931 (x, y) colour space chromaticity coordinates of (x3, y3); and the third emissive layer comprises organic light emitting material, quantum dot light emitting material or perovskite light emitting material.

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity is substantially the same as the first chromaticity and substantially different to the second chromaticity. In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity is substantially the same as the second chromaticity and substantially different to the first chromaticity.

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity coordinates (x3, y3) are not contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl), but are contained within a one-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2). In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity coordinates (x3, y3) are not contained within a one-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2), but are contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity coordinates (x3, y3) are not contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl), but are contained within a three-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2). In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity coordinates (x3, y3) are not contained within a three-step MacAdam ellipse that is centralized on the second chromaticity coordinates (x2, y2), but are contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl).

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third CIE 1931 (x, y) colour space chromaticity coordinates (x3, y3) may be converted to third CIE 1976 (u', v') colour space chromaticity coordinates (u3, v3). In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity coordinates (u3, v3) and the first chromaticity coordinates (ul, vl) are sufficiently different such that the difference in chromaticity as defined by Auv = V((u3 - ul) ² + (v3 - vl) ² ) is 0.010 or more; but the third chromaticity coordinates (u3, v3) and the second chromaticity coordinates (u2, v2) are sufficiently similar such that the difference in chromaticity as defined by Auv = V((u3 - u2) ² + (v3 - v2) ² ) is less than 0.010. In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third chromaticity coordinates (u3, v3) and the second chromaticity coordinates (u2, v2) are sufficiently different such that the difference in chromaticity as defined by Auv = V((u3 - u2) ² + (v3 - v2) ² ) is 0.010 or more; but the third chromaticity coordinates (u3, v3) and the first chromaticity coordinates (ul, vl) are sufficiently similar such that the difference in chromaticity as defined by Auv = V((u3 - ul) ² + (v3 - vl) ² ) is less than 0.010.

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third peak wavelength is at least 4 nm greater than or less than the first peak wavelength; but the third peak wavelength is within 4 nm of the second peak wavelength. In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third peak wavelength is at least 4 nm greater than or less than the second peak wavelength; but the third peak wavelength is within 4 nm of the first peak wavelength.

In one embodiment, the first blue emissive unit 2130, the second blue emissive unit 2150 and the third blue emissive unit 2220 may emit blue light for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130, the second blue emissive unit 2150 and the third blue emissive unit 2220 may emit blue light with peak wavelength in the visible spectrum in the range of 380 nm to 500 nm for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 may emit deeper blue light, the second blue emissive unit 2150 may emit deeper blue light and the third blue emissive unit 2220 may emit lighter blue light for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 may emit lighter blue light, the second blue emissive unit 2150 may emit lighter blue light and the third blue emissive unit 2220 may emit deeper blue light for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. Other combinations of lighter and deeper blue emissive units are also envisaged for any or all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices.

In one embodiment, the first blue emissive unit 2130 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; the second blue emissive unit 2150 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the third blue emissive unit 2220 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 emits blue light with a CIE 1931 y coordinate of 0.080 or less; the second blue emissive unit 2150 emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the third blue emissive unit 2220 emits blue light with a CIE 1931 y coordinate of more than 0.080 for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm; the second blue emissive unit 2150 emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm; and the third blue emissive unit 2220 emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. In one embodiment, the first blue emissive unit 2130 emits blue light with a CIE 1931 y coordinate of more than 0.080; the second blue emissive unit 2150 emits blue light with a CIE 1931 y coordinate of more than 0.080; and the third blue emissive unit 2220 emits blue light with a CIE 1931 y coordinate of 0.080 or less for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices. Other combinations of lighter and deeper blue emissive units are also envisaged for any or all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices.

Such exemplary embodiments may all be realized using any suitable combination of light emitting materials from the light-blue OLED, deep-blue OLED, deep-blue QLED and/or deep-blue PeLED devices described in Table 1.

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the first blue emissive unit 2130, the second blue emissive unit 2150 and the third blue emissive unit 2220 may all be commonly addressable and may not emit light independently of each other. In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the first blue emissive unit 2130, the second blue emissive unit 2150 and the third blue emissive unit 2220 may all be independently addressable and may all emit light independently of each other. In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, at least one emissive unit may be independently addressable and may emit light independently of the other two emissive units, whereas the other two emissive units may be commonly addressable and may not emit light independently of each other.

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third emissive unit 2220 is commonly addressed with one of the first emissive unit 2130 and the second emissive unit 2150 and may not emit light independently of one of the first emissive unit 2130 and the second emissive unit 2150; and the third emissive unit 2220 is addressed independently of one of the first emissive unit 2130 and the second emissive unit 2150 and may emit light independently of one of the first emissive unit 2130 and the second emissive unit

2150.

In one embodiment, for all of the first 2205, second 2215 and third 2225 stacked blue light emitting devices, the third emissive unit 2220 is commonly addressed with one of the first emissive unit 2130 and the second emissive unit 2150 and may not emit light independently of one of the first emissive unit 2130 and the second emissive unit 2150; the third emissive unit 2220 is addressed independently of one of the first emissive unit 2130 and the second emissive unit 2150 and may emit light independently of one of the first emissive unit 2130 and the second emissive unit 2150; wherein the emissive unit which is commonly addressed with the third emissive unit 2220 has substantially the same chromaticity as the third emissive unit 2220; and the emissive unit which is addressed independently of the third emissive unit 2220 has substantially different chromaticity to the third emissive unit 2220.

In one embodiment, a lighter blue emissive unit may be commonly addressed with another lighter blue emissive unit and may not emit light independently of another lighter blue emissive unit. In one embodiment, a deeper blue emissive unit may be commonly addressed with another deeper blue emissive unit and may not emit light independently of another deeper blue emissive unit. In one embodiment, a lighter blue emissive unit may be addressed independently from a deeper blue emissive unit and may emit light independently from the deeper blue emissive unit. In one embodiment, a deeper blue emissive unit may be addressed independently from a lighter blue emissive unit and may emit light independently from the lighter blue emissive unit.

When implemented in a display, stacked blue light emitting devices comprising two or more emissive units that emit light having substantially different chromaticity as disclosed herein are expected to enable the display to operate with improved efficiency and extended lifetime compared to a display comprising single emissive unit devices that can render the same colour gamut. This is because when the blue sub pixel of such a display is required to emit a relatively saturated blue light, the emissive unit that emits deeper blue light may be individually addressed and may emit light to generate the display image while the emissive unit that emits lighter blue light may remain inactive. However, when the blue sub-pixel of such a display is only required to emit a relatively unsaturated blue light, the emissive unit that emits lighter blue light may be individually addressed and may emit light to generate the display image while the emissive unit that emits deeper blue light may remain inactive. Light may be emitted from the relatively more efficient and/or stable lighter blue emissive unit to render the majority of display images, with light emitted from the relatively less efficient and/or stable deeper blue emissive unit only required to render a small proportion of images. The efficiency and/or lifetime of the display may therefore be enhanced. Furthermore, the lighter blue emissive unit may be used on its own or in combination with the deeper blue emissive unit to provide light to the red and green colour conversion layers in the red and green sub-pixels.

This can be demonstrated by modelling the power consumption of a display when rendering a set of typical display images. An example of such modelling is described in United States patent US 9559151 B2, which discloses a device that may be used as a multi-colour pixel, wherein the device comprises a first OLED, a second OLED, a third OLED and a fourth OLED. This reference is included herein by reference in its entirety. Note that the present invention is a significant improvement over US 9559151 B2 because equivalent energy savings and lifetime enhancement can be achieved without the need for an additional fourth sub-pixel in the display that reduces aperture ratio, efficiency and lifetime, and adds complexity and cost. Furthermore, the present invention is compatible with the use of different types of light emitting materials, including organic light emitting material, quantum dot light emitting materials and perovskite light emitting materials.

In one embodiment, the stacked light emitting device may be included in a light panel. Optionally, the light panel may be included in a wide range of consumer products. Optionally the light panel may be used for interior or exterior illumination and/or signaling, in smart packaging or in billboards.

A person skilled in the art will understand that only a few examples of use are described, but that they are in no way limiting.

Modifications to embodiments of the invention described in the foregoing are possible without departing from the scope of the invention as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "consisting of", "have", "is" used to describe and claim the present invention are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. Any numerals included within parentheses in the accompanying claims are intended to assist understanding of the claims and should not be construed in any way to limit subject matter claimed by these claims.

Certain embodiments of the invention are as follows:

1. A device comprising: a stacked blue light emitting device comprising: a first electrode; a second electrode; a first emissive unit comprising a first emissive layer; a second emissive unit comprising a second emissive layer; and a first charge generation layer; wherein the first emissive unit, the second emissive unit and the first charge generation layer are all disposed between the first electrode and the second electrode; the first emissive unit is disposed over the first electrode; the first charge generation layer is disposed over the first emissive unit; the second emissive unit is disposed over the first charge generation layer; the second electrode is disposed over the second emissive unit; the first emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the first peak wavelength; the first emissive unit emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (xl, yl); the second emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the second peak wavelength; the second emissive unit emits blue light having a second chromaticity having second CIE 1931 (x, y) colour space chromaticity coordinates of (x2, y2); the second chromaticity is substantially different to the first chromaticity; and the first emissive layer and the second emissive layer comprise organic light emitting material, quantum dot light emitting material and/or perovskite light emitting material. The device of embodiment 1, wherein the second chromaticity coordinates (x2, y2) are not contained within a one- step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). The device of embodiment 1, wherein the second chromaticity coordinates (x2, y2) are not contained within a three- step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yl). The device of any one of embodiments 1 to 3, wherein the second peak wavelength is at least 4 nm greater than or at least 4 nm less than the first peak wavelength. The device of any one of embodiments 1 to 3, wherein the first CIE 1931 (x, y) colour space chromaticity coordinates (xl, yl) may be converted to first CIE 1976 (u', v') colour space chromaticity coordinates (ul, vl); and the second CIE 1931 (x, y) colour space chromaticity coordinates (x2, y2) may be converted to second CIE 1976 (u', v') colour space chromaticity coordinates (u2, v2); wherein the first chromaticity coordinates (ul, vl) and the second chromaticity coordinates (u2, v2) are sufficiently different such that the difference in chromaticity as defined by Auv is 0.010 or more. The device of any one of embodiments 1 to 5, wherein the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. The device of any one of embodiments 1 to 5, wherein the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm. The device of any one of embodiments 1 to 5, wherein the first emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the second emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080. The device of any one of embodiments 1 to 5, wherein the first emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080; and the second emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less. The device of any one of embodiments 1 to 9, wherein the first emissive layer and the second emissive layer comprise organic light emitting material. The device of embodiment 10, wherein at least one of the first emissive layer and the second emissive layer comprise phosphorescent organic light emitting material; and at least one of the first emissive layer and the second emissive layer comprise fluorescent organic light emitting material. The device of any one of embodiments 1 to 9, wherein the first emissive layer and the second emissive layer comprise quantum dot light emitting material. The device of any one of embodiments 1 to 9, wherein the first emissive layer and the second emissive layer comprise perovskite light emitting material. The device of any one of embodiments 1 to 9, wherein the first emissive layer comprises a first class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; the second emissive layer comprises a second class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; and the second class of light emitting material is not the same as the first class of light emitting material. The device of any one of embodiments 1 to 14, wherein the first emissive unit and the second emissive unit are independently addressable and may emit light independently of each other. The device of any one of embodiments 1 to 14, wherein the first emissive unit and the second emissive unit are commonly addressable and may not emit light independently of each other. The device of any one of embodiments 1 to 16, wherein the stacked blue light emitting device further comprises: a third emissive unit comprising a third emissive layer; and a second charge generation layer; wherein the third emissive unit and the second charge generation layer are disposed between the second emissive unit and the second electrode; the second charge generation layer is disposed over the second emissive unit; the third emissive unit is disposed over the second charge generation layer; the second electrode is disposed over the third emissive unit; the third emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the third peak wavelength; the third emissive unit emits blue light having first CIE 1931 (x, y) colour space chromaticity coordinates of (x3, y3); and the third emissive layer comprises organic light emitting material, quantum dot light emitting material or perovskite light emitting material. The device of embodiment 17, wherein the third chromaticity is substantially the same as one of the first chromaticity and the second chromaticity; and the third chromaticity is substantially different to one of the first chromaticity and the second chromaticity. The device of embodiment 17, wherein the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; and the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit. The device of embodiment 17, wherein the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit; wherein the emissive unit which is commonly addressed with the third emissive unit has substantially the same chromaticity as the third emissive unit; and the emissive unit which is addressed independently of the third emissive unit has substantially different chromaticity to the third emissive unit. The device of any one of embodiments 1 to 20, wherein the device is part of a light panel. The device of any one of embodiments 1 to 20, wherein the device is part of a display. A display is provided, wherein the display comprises: a first sub-pixel configured to emit red light with a peak wavelength in the visible spectrum in the range of 580 nm to 780 nm; a second sub-pixel configured to emit green light with a peak wavelength in the visible spectrum in the range of 500 nm to 580 nm; and a third sub-pixel configured to emit blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm; wherein the first sub-pixel comprises a first stacked blue light emitting device optically coupled to a red colour conversion layer; the second sub-pixel comprises a second stacked blue light emitting device optically coupled to a green colour conversion layer; and the third sub-pixel comprises a third stacked blue light emitting device; wherein all of the first, second and third stacked blue light emitting devices comprises the stacked blue light emitting device of embodiment 1. The display of embodiment 23, wherein for all of the first, second and third stacked blue light emitting devices, the second chromaticity coordinates (x2, y2) are not contained within a one-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yi)· The display of embodiment 23, wherein for all of the first, second and third stacked blue light emitting devices, the second chromaticity coordinates (x2, y2) are not contained within a three-step MacAdam ellipse that is centralized on the first chromaticity coordinates (xl, yi)· The display of any one of embodiments 23 to 25, wherein for all of the first, second and third stacked blue light emitting devices, the second peak wavelength is at least 4 nm greater than or at least 4 nm less than the first peak wavelength. The display of any one of embodiments 23 to 25, wherein for all of the first, second and third stacked blue light emitting devices: the first CIE 1931 (x, y) colour space chromaticity coordinates (xl, yl) may be converted to first CIE 1976 (u', v') colour space chromaticity coordinates (ul, vl); and the second CIE 1931 (x, y) colour space chromaticity coordinates (x2, y2) may be converted to second CIE 1976 (u', v') colour space chromaticity coordinates (u2, v2); wherein the first chromaticity coordinates (ul, vl) and the second chromaticity coordinates (u2, v2) are sufficiently different such that the difference in chromaticity as defined by Auv is 0.010 or more. The display of any one of embodiments 23 to 27, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm. The display of any one of embodiments 23 to 27, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 465 nm to 500 nm; and the second emissive unit emits blue light with a peak wavelength in the visible spectrum in the range of 380 nm to 465 nm. The display of any one of embodiments 23 to 27, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less; and the second emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080. The display of any one of embodiments 23 to 27, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive unit emits blue light with a CIE 1931 y coordinate of more than 0.080; and the second emissive unit emits blue light with a CIE 1931 y coordinate of 0.080 or less. The display of any one of embodiments 23 to 31, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive layer and the second emissive layer comprise organic light emitting material. The display of embodiment 32, wherein for all of the first, second and third stacked blue light emitting devices: at least one of the first emissive layer and the second emissive layer comprise phosphorescent organic light emitting material; and at least one of the first emissive layer and the second emissive layer comprise fluorescent organic light emitting material. The display of any one of embodiments 23 to 31, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive layer and the second emissive layer comprise quantum dot light emitting material. The display of any one of embodiments 23 to 31, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive layer and the second emissive layer comprise perovskite light emitting material. The display of any one of embodiments 23 to 31, wherein for all of the first, second and third stacked blue light emitting devices: the first emissive layer comprises a first class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; the second emissive layer comprises a second class of light emitting material that is either organic light emitting material, quantum dot light emitting material or perovskite light emitting material; and the second class of light emitting material is not the same as the first class of light emitting material. The display of any one of embodiments 23 to 36, wherein the first stacked blue light emitting device, the second stacked blue light emitting device and the third stacked blue light emitting device all have the same device architecture. The display of any one of embodiments 23 to 37, wherein for any of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are independently addressable and may emit light independently of each other. The display of any one of embodiments 23 to 37, wherein for any of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are commonly addressable and may not emit light independently of each other. The display of any one of embodiments 23 to 37, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are independently addressable and may emit light independently of each other. The display of any one of embodiments 23 to 37, wherein for all of the first, second and third stacked blue light emitting devices, the first emissive unit and the second emissive units are commonly addressable and may not emit light independently of each other. The display of any one of embodiments 23 to 41, wherein the first emissive unit and the second emissive unit of the third stacked blue light emitting device are independently addressable and may emit light independently of each other; and the first emissive unit and the second emissive unit of the first stacked blue light emitting device and the second stacked blue light emitting device are commonly addressable and may not emit light independently of each other. The display of any one of embodiments 23 to 42, wherein all of the first, second and third stacked blue light emitting devices further comprise: a third emissive unit comprising a third emissive layer; and a second charge generation layer; wherein the third emissive unit and the second charge generation layer are disposed between the second emissive unit and the second electrode; the second charge generation layer is disposed over the second emissive unit; the third emissive unit is disposed over the second charge generation layer; and the second electrode is disposed over the third emissive unit; and the third emissive unit emits blue light having a peak wavelength in the visible spectrum in the range of 380 nm to 500 nm that is defined as the third peak wavelength; the third emissive unit emits blue light having a third chromaticity having third CIE 1931 (x, y) colour space chromaticity coordinates of (x3, y3); and the third emissive layer comprises organic light emitting material, quantum dot light emitting material or perovskite light emitting material.

44. The display of embodiment 43, wherein for all of the first, second and third stacked blue light emitting devices: the third chromaticity is substantially the same as one of the first chromaticity and the second chromaticity; and the third chromaticity is substantially different to one of the first chromaticity and the second chromaticity.

45. The display of embodiment 43, wherein for all of the first, second and third stacked blue light emitting devices: the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; and the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit.

46. The display of embodiment 43, wherein for all of the first, second and third stacked blue light emitting devices: the third emissive unit is commonly addressed with one of the first emissive unit and the second emissive unit and may not emit light independently of one of the first emissive unit and the second emissive unit; the third emissive unit is addressed independently of one of the first emissive unit and the second emissive unit and may emit light independently of one of the first emissive unit and the second emissive unit; wherein the emissive unit which is commonly addressed with the third emissive unit has substantially the same chromaticity as the third emissive unit; and the emissive unit which is addressed independently of the third emissive unit has substantially different chromaticity to the third emissive unit.

47. The display of any one of embodiments 23 to 46, wherein the display is part of a consumer product.

Patent References

EP 0423283 Bl, Friend et al., Electroluminescent Devices

US 5707745 Bl, Forrest et al., Multicolor Organic Light Emitting Devices

US 6303238 Bl, Thompson et al., OLEDs Doped with Phosphorescent Compounds US 7279704 B2, Walters et al., Complexes with Tridentate Ligands US 9559151 B2, Hack et al., OLED Display Architecture WO 2019/224546 Al WO 2020/030042A1 US 2019/0043407 Al

EP 3188272 Al

Other References

S. Adjokatse et al.. Broadly tunable metal halide perovskites for solid-state light- emission applications, Materials Today, Vol. 20, Issue 8, Pages 413-424 (2017).

Forrest et al., The stacked OLED (SOLED): a new type of organic device for achieving high-resolution full-color displays, Synthetic Metals, Vol. 91, Issues 1-3, Pages 9-13 (1997).

Frobel et al., Three-terminal RGB full-colour OLED pixels for ultrahigh density displays, Nature Scientific Reports, Vol. 8, Article 9684 (2018).

Jung et al., 3 Stacked Top Emitting White OLED for High Resolution OLED TV, SID Symposium Digest of Technical Papers 2016, Vol. 47, Pages 707-710 (2016).

Kathirgamanathan et al., Electroluminescent Organic and Quantum Dot LEDs: The State of the Art, Journal of Display Technology, Vol. 11, Number 5, Pages 480-493 (2015).

Kumar et al., Efficient Blue Electroluminescence Using Quantum-Confined Two- Dimensional Perovskites, ACS Nano, Vol. 10, Pages 9720-9729 (2016).

Soneira et al., iPhone X OLED Display Technology Shoot-Out, DisplayMate Technologies Corporation

Takita et al., Highly efficient deep-blue fluorescent dopant for achieving low-power OLED display satisfying BT.2020 chromaticity, Journal of the SID 2018 (2018).

Uoyama et al., Highly efficient organic light-emitting diodes from delayed fluorescence, Nature, Vol. 492, Pages 234-238 (2012).

Wang et al., Blue Quantum Dot Light-Emitting Diodes with High Electroluminescent Efficiency, ACS Applied Materials & Interfaces, Vol. 9, Pages 38755-38760 (2017).

Zanoni et al., Sky-blue OLED through PVK:[lr(Fppy)2(Mepic)] active layer, Synthetic Metals, Vol. 222, Part B, Pages 393-396 (2016)