Field of invention

The present invention relates to a method for printing an Organic Light Emitting Diode (OLED), an OLED printed by this method and a printing device adjusted to carry out this method.

State of the art

An OLED is a light emitting diode in which the emissive

electroluminescent layer is a film of organic compounds which emits light in response to an electric current. This layer of organic semiconductors is situated between two electrodes. The typical OLED comprises a layer of organic materials situated between the two electrodes, the anode and cathode, all placed on a substrate. The organic molecules are electrically semiconductive. The most basic polymeric OLEDs comprise a single organic layer, but multilayer OLEDs are common nowadays. These layers are usually printed via an appropriate printing device filled with an appropriate ink. When preparing OLED devices usually printing techniques are used to apply the active layer. Suitable and preferred deposition methods include liquid coating and printing techniques. Preferred deposition methods include, without limitation, dip coating, spin coating, spray coating, aerosol jetting, ink jet printing, nozzle printing, gravure printing, doctor blade coating, roller printing, reverse-roller printing, flexographic printing, web printing, screen printing, stencil printing, spray coating, dip coating, curtain coating, kiss coating, meyer bar coating, 2 roll nip fed coating, anilox coaters, knife coating or slot dye coating. Preferably, the OSC layer is applied with gravure printing, doctor blade coating, roller printing, reverse-roller printing, flexographic printing, web printing, anilox coaters or ink jet printing, more preferably with ink jet printing. Gravure and flexographic printing and variants of these printing methods are preferred. These include but or not limited to, micro gravure, reverse gravure, offset gravure, reverse roll etc. Both web fed (roll to roll) and sheetfed in both flatbed and the more conventional On the round' configurations can be used.

Based on the low solubility of the most of the present organic compounds useful as emitting materials and/or charge transport materials, these techniques need the use of solvents in high amounts.

For example, WO 201 1/076325 A1 discloses compositions comprising light emitting materials and/or charge transport materials and a polymeric binder, as well as their use as inks for the preparation of OLED devices.

EP 1 883 124 A1 describes a formulation of light-emitting materials particularly suitable for forming displays and lamps via printing techniques comprising organic-light emitting material housed in a protective porous matrix material, a binder and a solvent. However, the OLED material encompasses also polymeric materials.

US 2007/0103059 discloses compositions comprising an OLED material and a polymer having very specific repeating units. The polymer having specific repeating units is added to improve the emitting efficiency of the OLED. Also polymeric OLED materials can be employed.

US 5,952,778 relates to an encapsulated organic light emitting device having an improved protective covering comprising a first layer of passivating metal, a second layer of an inorganic dielectric material and a third layer of polymer. The organic light emitting material can be of high molecular weight or of low molecular weight.

Thus, the printing of OLEDs and the respectively used inks are known in the art. To print the OLEDs on a substrate, common ink-jet printers are used and provided with the above mentioned

appropriate inks.

Nevertheless, it is important that the printers are adjusted in view of the ink to be used, because every ink has certain characteristics which can influence the shape, image and appearance of the printed OLED. It is of critical importance that no ink is misplaced into neighboring pixels as this would contaminate the color and be deleterious to the electrical properties.

Therefore, it is generally not desirable that multiple droplets (of radically different sizes, commonly referred to as satellites) are formed, because these smaller droplets can be caught-up within airflows in the printer and deposited in undesired locations. During the ejection process a filament of ink is produced, the velocity of the leading edge of the filament decreases, allowing the 'tail' to catch up and form a single drop. Frequently with a poor formulation and/or waveform a single drop is formed with a very small droplet (satellite) formed behind the first with a considerably lower velocity. In particular since the separated droplets usually are different in size, and typically smaller than 3 μιτι in diameter, the separated droplets are displaced on the substrate and, thus, deteriorate the printed image. For example, the piezo-electric printers used for printing OLEDs are adjusted such that the actuation waveform in

combination with the size of the single droplet ejected by the printing head and in combination with the properties of the used ink prevents the formation of multiple droplets. In Fig. 2 such a waveform is shown for a 10 pi Fujifilm Dimatix SQ print-head droplet that is used for an ink having a viscosity of 0.975 cP at 20°C.

Another possibility to avoid generation of separated droplets is described in US 2006/0028497 A1 . This document relates to an inkjet recording method of using comparative high viscous inks which are hardened by ultraviolet rays. Particularly, this method outputs high-definition images and is capable of suppressing the generation of ink mists, i.e. suppressing generation of satellites or separated droplets that can be displaced by airflows. According to US 20006/0028497 A1 , it is preferred if there is no generation of satellites at all. For this, it is proposed to use an ink with a viscosity between 5 and 20 cP and that the jetted-out droplets have a velocity of 5 m/s in a distance of 1 mm away from the nozzle. In this way, the satellites stay closer than 500 μιτι to the main droplet so that the satellites are not misplaced.

Summary of the invention

In the OLED business, there is an ever increasing demand for printing at higher resolution, i.e. printing more droplets on a certain area (pixels per inch (ppi)). However, the size or volume of an ejected droplet is determined by the printing head used for ejecting the droplets. Thus, decreasing the size or volume of the droplet requires construction of a printing head capable of ejecting smaller droplets. One of the smallest droplets available at presents is produced by a 1 picoliter (pi) print head and high ink concentration. High concentration is desirable in order to reduce the film thickness of the film in the pixel thus avoiding overspill in the neighboring pixels. This is more ideally suited to small molecule OLEDs, due to both rheological and solubility considerations. Additionally, when printing within pixels it is important that the drop size of the ink droplet does not exceed the dimensions of the pixel. Thus, it is an object of the present invention to provide a method for printing an OLED by using a commonly known printer but improving the resulting resolution. This object is solved by a method including the features of claim 1 and by a piezo-printing device according to claim 12. Further preferred embodiments are depicted in the dependent claims.

Surprisingly, it has been found that using an ink with a viscosity lower than 5 cP will cause the formation of two smaller droplets of essentially the same size. For this, the waveform of the actuation of the piezo-printer has to be adjusted accordingly.

Thus, the method according to the present invention comprises the manufacturing of one or more layers of an OLED, wherein the one or more layers containing at least one organic semiconducting material, comprising the step printing a solution with a piezo-electric printing device, the solution containing at least one organic solvent and at least one organic semiconducting material onto a substrate and the step drying the printed solution, wherein the solution has a viscosity lower than 5 cP, preferably lower than 4 cP, more preferably lower than 2 cP and most preferably lower than 1 cP, and the electric impulse for actuating the piezo-electric printing device is appropriately controlled corresponding to the used printing head, in particular controlled such, that at least two smaller but essentially equally sized droplets are formed. Preferably 2, 3, 4, 5, 6, 7, 8, 9 or 10 droplets, and more preferably 2, 3, 4, 5, 6 or 7 droplets, are formed. The expression "essentially equally sized droplets", as used in the present application, means that the diameter difference of the droplet having the largest diameter and the droplet having the lowest diameter is < 20%, preferably < 10% and more preferably < 5%.

By using this method, the surprising effect has occurred that the resolution of the printed OLED significantly improves. This is because at least two droplets with essentially the same size are formed. In particular the diameter of the two resulting droplets are reduced in comparison to a single ejected droplet. E.g., if the ejected droplet has a volume of 10 pi (which depends on the printing head) which would normally be about 26.7 μιτι (micrometer) in diameter will decrease into two droplets of approximately 21 μιτι in diameter. Similarly, with a 1 pi droplet having a diameter of about 12.4 μιτι, two droplets of about 9.8 μιτι are formed. Similarly if more drops are formed then the size of the drops becomes increasingly smaller. Thus, by using a common printer and merely adjusting the waveform of the printing device and the viscosity of the ink, a printing method capable of printing in an improved resolution can be achieved. As a result of the improved printing method also an OLED having a better resolution can be manufactured having smaller drop diameters than the print-head would normally produce. These

OLEDs can be distinguished from commonly printed OLEDs since their droplet diameter can only be achieved with the inventive method. The printing is preferably carried out with a printing head generating droplets of a size of 30 pi or lower, more preferably a size of 10 pi or lower and most preferably a size of 3 pi or lower. Using these printing heads improves the general resolution. In combination with the inventive method, this effect can be enhanced.

In one embodiment, the solution comprises a concentration of small molecule organic semiconducting material (small molecule OLED (SMOLED)) of at least 1 .0 %, preferably at least 2.5 %, and more preferably at least 5 %. This can include the hole injection layer, the hole transport layer, the emissive layer and the electron transport layer. By using SMOLED, a further enhanced resolution can be obtained.

In another embodiment, the solution comprises a concentration of a polymeric organic semiconducting material (polymeric OLED (POLED)) of at most 2.5 %, preferably at most 1 .5 %, and more preferably at most 0.5 %. Again, this can include the hole injection layer, the hole transport layer, the emissive layer and the electron transport layer. The added polymers do not affect the device performance, but increase the film formation potential which is advantageously. In addition binders can also be added to aid film formation.

Preferably, the solution comprises at least two organic solvents with a resultant viscosity lower than 5 cP, preferably lower than 4 cP, more preferably lower than 2 cP, and most preferably lower than 1 cP. By using at least two organic solvents the drying and fluid properties of the solution can be better controlled. In particular, if the second or more solvents used for the solution should provide good solubility to the emissive layer. These solvents should also preferably have boiling points that differ within a minimum range of 10°C, preferably at least 30°C and more preferably at least 50°C. With these minimum differences in boiling points of the at least two solvents it is easier to adjust the preferred characteristics of the resulting solution/ink. Furthermore, the boiling point of the at least two solvents should preferably be in the range of 150°C to 300°C, more preferably in the range of 200°C to 300°C and most preferably in the range of 250°C to 290°C. In this range the most preferred solvents for the invention are found. Generally, similar characteristics of the different solvents provide a good solubility. Thus, using two solvents with similar characteristics enhance forming a homogenous film and avoid the crystallization of the different organic semiconducting materials.

The step of drying the solution can comprise a vacuum drying process after printing the OLED. The drying process is carried out after printing of every layer of the OLED device. Of course, the vacuum drying process can be applied to every drying process of the different layers. However, it is also possible that only for certain layers the vacuum drying process is carried out. The vacuum drying process is preferably carried out at a temperature at or above 20°C. Since the pressure in the vacuum drying process is very low, the solvent evaporates quickly and improves the drying.

Another aspect of the invention is an OLED that is manufactured with the method according to the present invention. Since the resulting diameter of the separated droplet is distinguishable from the droplets which are ordinary printed by size, the particular resolution cannot be achieved solely by a print-head, but only by using the method of the present invention.

A further aspect of the invention relates to a piezo-electric printing device having a printing head of 30 pi or less, wherein the piezoelectric printing device is provided with a printing solution containing at least one organic solvent and at least one organic semiconducting material. Such a printer is ideally suited to carry out the method according to the present invention. Although the structure of the common print heads is sufficient to achieve a better resolution since the generated rows of droplets have a smaller size, it is preferred to additionally adjust the angle of the print-head. This allows the nozzle to nozzle pitch to be reduced. In this way, the small gap between the droplet-rows can be avoided. However, if suggested to a skilled person such an adjustment of the nozzles is easily carried out.

Brief description of the Figures

Figure 1 shows the concept of multiple drop usage in a channel

(single, dual and multi drops).

Figures 2 and 3 show a waveform that is used in the prior art for printing with an ink having a low viscosity, and the corresponding printing result.

Figures 4 and 5 show a waveform according to the present

invention with a dual drop approach, and the

corresponding printed result.

Figures 6 and 7 show a waveform according to the present

invention with a multiple drop approach, and the corresponding printed result.

Detailed description of preferred embodiments

In the following, the terms "solution" and "solvent" are used.

"Solution" means in the following the ink ready to be printed on an substrate for an OLED, whereas "solvent" is meant as being a agent or liquid. Thus, several solvents can be mixed together with to be combined into a solution, i.e. a solution can comprise one or more solvents. The solution can additionally comprise different additives.

Furthermore, the viscosity is usually measured at a temperature of 25°C and can be measured by common methods and apparatuses, for example a rotational viscometer, oscillation type viscometer or capillary type viscometer. The present invention can be carried out with common inks meeting the necessary characteristics as stated below and can be printed with common printers which are correspondingly adjusted. Basically, usable solutions are disclosed in the prior art documents listed in the introduction. However, in general there are some characteristics the solution used for the present invention should have. Most important, the solution should have a viscosity below 5 cP, preferably below 4 cP, more preferably below 2 cP and most preferably below 1 cP. Other characteristics concern the surface tension and the density of the solution, but the common ranges of these characteristics with the commonly used inks/solutions are less important as long as the viscosity is in the inventive range.

In addition to the viscosity of the solution, the printing head for the piezo-electric printing device and the waveform for actuating the piezo-electric printing device are important. By adjusting the waveform of the actuation signal in correspondence to the printing head and combining it with the appropriate solution as described above, the three parameters are defined that serve as basic features for the present invention. The actuation waveform should be adjusted such that the ejection process forms at least two droplets and these droplets should have essentially the same size to avoid different flying characteristics of the different droplets.

Additionally, by having the same size, it also can be secured that the offset will not cause the droplets to exceed the dimensions of the pixels.

The waveform is controlled by adjusting rise, drop, maximum voltage and/or maintaining time of the maximum voltage in accordance to the used printing head, in addition with some printers multiple stages (>3) within the waveform can be created. This can be done by simple testing of different waveforms for a certain solution with a particular printing head.

As a printer common printers can be used. As an example a Pixdro LP-50 printer with a print head of Fujifilm Dimatix SQ is used that has a drop volume of 10 pi. This printer is a piezo-electric printing device that is actuated by a correspondingly adjusted electric signal with a respective waveform. The Pixdro LP-50 has very limited waveform generation and can only be used with a single rise time, a peak hold at a certain voltage and a drop time (only these three segments are achievable with this printer). With other printers more segments can be added, which provides greater flexibility for controlling the waveform. As such the same effect can be achieved by using different parameters. Fig. 2 shows a waveform according to the invention for the 10 pi Fujifilm Dimatix SQ print head on a

Pixdro LP50 printer that has been mentioned in the introduction of this application. For this waveform of the impulse for actuating the piezo-electric printing device, a voltage of 52 V has been chosen. The rise to the maximum voltage takes 7 s (microseconds).

The maximum voltage of the actuation waveform is maintained for 10 s. The drop time of the impulse is 17 s. Under this waveform the ink described in example 1 produces a single droplet.

In the present examples, in Figure 4 the waveform has been optimized for the above-mentioned 10 pi printing head of Fujifilm Dimatix SQ and results in printing two droplets instead of only one single droplet. The maximum voltage of 40 V has been maintained for 9 s and the rise and drop are carried out within 2 s. This reliably results in two smaller droplets of essentially the same size.

As to Figure 6 the maximum voltage of 35 V is maintained for 2.5 [is, the rise and drop last 2 s. As a result, 7 discrete droplets have been formed, further decreasing the size of the single droplets and improving the resolution.

This means, having a solution with a viscosity of 5 cP or lower, using a certain printing head with a particular droplet size and having an actuation waveform of the piezo printing head adjusted in accordance to the printing head, two or more droplets of essentially the same size can be formed. It is important that the separated droplets have essentially the same size, because differently sized droplets could deteriorate the resulting image on the printed OLED layer, although small tolerances of the droplet size will always occur. Figure 1 shows a simplified comparison between a single droplet printed with a common waveform and/or an ink having a viscosity higher than 5 cP (Fig. 1 A) and double droplets according to the invention. As can be seen, the two drops in Fig. 1 B have a smaller size and, thus, result in more but smaller drops, increasing the resulting resolution. The droplets printed in Figure 1 correspond to a 10 pi printing head that eject single droplets with a diameter of about 27 μιτι and decrease to about 20 μιτι if they separate.

In a printing device, usually a plurality of printing nozzles is arranged adjacent to each other in single or multiple rows. When printing into a pixelated substrate it is important to line the centre of the nozzles (or drops) with the pixel pattern. This can be acheived by angling the print head, if the nozzle pitch (gap between nozzles) is different to the native resolution of the pixelated substrate.

After printing a layer of the OLED in this way, the printed layer is dried, in particular in a vacuum drying process with or without heat during the drying phase. However, alternatively or additionally also drying with a radiation can be carried out. Then, another layer can be printed until the OLED is manufactured and finished. As to the ink, the solution contains at least one organic solvent and at least one organic semiconducting material. The at least one organic semiconducting material could either be a small molecule organic semiconducting material or a polymeric organic

semiconducting material.

The organic semiconducting material is selected from the group consisting of fluorescent emitters, phosphorescent emitters, host materials, matrix materials, exciton-blocking materials, electron- transport materials, electron-injection materials, hole-conductor materials, hole-injection materials, n-dopants, p-dopants, wideband-gap materials, electron-blocking materials and hole-blocking materials.

Preferred embodiments of organic semiconducting materials are disclosed in detail in WO 201 1/076314 A1 , where this document is incorporated into the present application by way of reference. In a preferred embodiment, the organic semiconducting material is an organic semiconductor selected from the group consisting of hole-injecting, hole-transporting, emitting, electron-transporting and electron-injecting materials. More preferably, the organic semiconducting material is an organic semiconductor selected from the group consisting of hole-injecting and hole-transporting materials.

The organic semiconducting material can be a compound having a low molecular weight, a polymer, an oligomer or a dendrimer, where the organic functional material may also be in the form of a mixture. Thus, the formulations according to the present invention may comprise two different compounds having a low molecular weight, one compound having a low molecular weight and one polymer or two polymers (blend). Organic semiconducting materials are frequently described via the properties of the frontier orbitals, which are described in greater detail below. Molecular orbitals, in particular also the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), their energy levels and the energy of the lowest triplet state Ti or of the lowest excited singlet state Si of the materials are determined via quantum-chemical calculations. In order to calculate organic substances without metals, firstly a geometry optimisation is carried out using the "Ground State/Semi- empirical/Default Spin/AM1 /Charge 0/Spin Singlet" method. An energy calculation is subsequently carried out on the basis of the optimised geometry. The "TD-SCF/DFT/Default Spin/B3PW91 " method with the "6-31 G(d)" base set (charge 0, spin singlet) is used here. For metal-containing compounds, the geometry is optimised via the "Ground State/Hartree-Fock/Default Spin/l_anl_2MB/Charge 0/Spin Singlet" method. The energy calculation is carried out analogously to the above-described method for the organic substances, with the difference that the "Lanl_2DZ" base set is used for the metal atom and the "6-31 G(d)" base set is used for the ligands. The energy calculation gives the HOMO energy level HEh or LUMO energy level LEh in hartree units. The HOMO and LUMO energy levels in electron volts calibrated with reference to cyclic voltammetry measurements are determined therefrom as follows:

HOMO(eV) = ((HEh ^* 27.212)-0.9899)/1 .1206

LUMO(eV) = ((LEh ^* 27.212)-2.0041 )/1 .385 For the purposes of the present application, these values are to be regarded as HOMO and LUMO energy levels respectively of the materials. The lowest triplet state Ti is defined as the energy of the triplet state having the lowest energy which arises from the quantum-chemical calculation described.

The lowest excited singlet state Si is defined as the energy of the excited singlet state having the lowest energy which arises from the quantum-chemical calculation described.

The method described herein is independent of the software package used and always gives the same results. Examples of frequently used programs for this purpose are "GaussianO W" (Gaussian Inc.) and Q-Chem 4.1 (Q-Chem, Inc.).

Compounds having hole-injection properties, also called hole- injection materials herein, simplify or facilitate the transfer of holes, i.e. positive charges, from the anode into an organic layer. In general, a hole-injection material has an HOMO level which is in the region of or above the level of the anode, i.e. in general is at least -5.3 eV. Compounds having hole-transport properties, also called hole- transport materials herein, are capable of transporting holes, i.e. positive charges, which are generally injected from the anode or an adjacent layer, for example a hole-injection layer. A hole-transport material generally has a high HOMO level of preferably at least -5.4 eV. Depending on the structure of an electronic device, it may also be possible to employ a hole-transport material as hole-injection material. The preferred compounds which have hole-injection and/or hole- transport properties include, for example, triarylamine, benzidine, tetraaryl-para-phenylenediamine, triarylphosphine, phenothiazine, phenoxazine, dihydrophenazine, thianthrene, dibenzo-para-dioxin, phenoxathiyne, carbazole, azulene, thiophene, pyrrole and furan derivatives and further O-, S- or N-containing heterocycles having a high HOMO (HOMO = highest occupied molecular orbital). As compounds which have hole-injection and/or hole-transport properties, particular mention may be made of phenylenediamine derivatives (US 3615404), arylamine derivatives (US 3567450), amino-substituted chalcone derivatives (US 3526501 ),

styrylanthracene derivatives (JP-A-56-46234), polycyclic aromatic compounds (EP 1009041 ), polyarylalkane derivatives (US

3615402), fluorenone derivatives (JP-A-54-1 10837), hydrazone derivatives (US 3717462), acylhydrazones, stilbene derivatives (JP- A-61 -210363), silazane derivatives (US 4950950), polysilanes (JP- A-2-204996), aniline copolymers (JP-A-2-282263), thiophene oligomers (JP Heisei 1 (1989) 21 1399), polythiophenes, poly(N- vinylcarbazole) (PVK), polypyrroles, polyanilines and other electrically conducting macromolecules, porphyrin compounds (JP- A-63-2956965, US 4720432), aromatic dimethylidene-type compounds, carbazole compounds, such as, for example, CDBP, CBP, mCP, aromatic tertiary amine and styrylamine compounds (US 4127412), such as, for example, triphenylamines of the benzidine type, triphenylamines of the styrylamine type and

triphenylamines of the diamine type. It is also possible to use arylamine dendrimers (JP Heisei 8 (1996) 193191 ), monomeric triarylamines (US 3180730), triarylamines containing one or more vinyl radicals and/or at least one functional group containing active hydrogen (US 3567450 and US 3658520), or tetraaryldiamines (the two tertiary amine units are connected via an aryl group). More triarylamino groups may also be present in the molecule. Phthalo- cyanine derivatives, naphthalocyanine derivatives, butadiene derivatives and quinoline derivatives, such as, for example, dipyrazino[2,3-f:2',3'-h]quinoxalinehexacarbonitrile, are also suitable.

Preference is given to aromatic tertiary amines containing at least two tertiary amine units (US 2008/010231 1 A1 , US 4720432 and US 5061569), such as, for example, NPD (a-NPD = 4,4'-bis[N-(1 - naphthyl)-N-phenylamino]biphenyl) (US 5061569), TPD 232 (= N,N'-bis-(N,N'-diphenyl-4-aminophenyl)-N,N-diphenyl-4,4'-dia mino- 1 ,1 '-biphenyl) or MTDATA (MTDATA or m-MTDATA = 4,4',4"-tris[3- methylphenyl)phenylamino]triphenylamine) (JP-A-4-308688), TBDB (= N,N,N',N'-tetra(4-biphenyl)diaminobiphenylene), TAPC (= 1 ,1 - bis(4-di-p-tolylaminophenyl)cyclohexane), TAPPP (= 1 ,1 -bis(4-di-p- tolylaminophenyl)-3-phenylpropane), BDTAPVB (= 1 ,4-bis[2-[4- [N,N-di(p-tolyl)amino]phenyl]vinyl]benzene), TTB (= Ν,Ν,Ν',Ν'-tetra- p-tolyl-4,4'-diaminobiphenyl), TPD (= 4,4'-bis[N-3-methylphenyl]-N- phenylamino)biphenyl), N,N,N',N'-tetraphenyl-4,4"'-diamino-

1 ,1 ',4',1 ",4",1 '"-quaterphenyl, likewise tertiary amines containing carbazole units, such as, for example, TCTA (= 4-(9H-carbazol-9- yl)-N,N-bis[4-(9H-carbazol-9-yl)phenyl]benzenamine). Preference is likewise given to hexaazatriphenylene compounds in accordance with US 2007/0092755 A1 and phthalocyanine derivatives (for example h Pc, CuPc (= copper phthalocyanine), CoPc, NiPc, ZnPc, PdPc, FePc, MnPc, CIAIPc, CIGaPc, CllnPc, CISnPc, CI ₂ SiPc, (HO)AIPc, (HO)GaPc, VOPc, TiOPc, MoOPc, GaPc-O-GaPc). Particular preference is given to the following triarylamine

compounds of the formulae (TA-1 ) to (TA-12), which are disclosed in EP 1 162193 B1 , EP 650 955 B1 , Synth.Metals 1997, 91 (1 -3), 209, DE 196461 19 A1 , WO 2006/122630 A1 , EP 1 860 097 A1 , EP 1834945 A1 , JP 08053397 A, US 6251531 B1 , US

2005/0221 124, JP 08292586 A, US 7399537 B2, US 2006/0061265 A1 , EP 1 661 888 and WO 2009/041635. The said compounds of the formulae (TA-1 ) to (TA-12) may also be substituted:

formula TA-1 1 formula TA-12

Further compounds which can be employed as hole-injection materials are described in EP 0891 121 A1 and EP 1029909 A1 , injection layers in general in US 2004/01741 16 A1 .

These arylamines and heterocycles which are generally employed as hole-injection and/or hole-transport materials preferably result in an HOMO in the polymer of greater than -5.8 eV (vs. vacuum level), particularly preferably greater than -5.5 eV.

Compounds which have electron-injection and/or electron-transport properties are, for example, pyridine, pyrimidine, pyridazine, pyrazine, oxadiazole, quinoline, quinoxaline, anthracene, benz- anthracene, pyrene, perylene, benzimidazole, triazine, ketone, phosphine oxide and phenazine derivatives, but also triarylboranes and further O-, S- or N-containing heterocycles having a low LUMO (LUMO = lowest unoccupied molecular orbital).

Particularly suitable compounds for electron-transporting and electron-injecting layers are metal chelates of 8-hydroxyquinoline (for example LiQ, AIQ ₃ , GaQ ₃ , MgQ ₂ , ZnQ ₂ , lnQ ₃ , ZrQ ₄ ), BAIQ, Ga oxinoid complexes, 4-azaphenanthren-5-ol-Be complexes (US

5529853 A, cf. formula ET-1 ), butadiene derivatives (US 4356429), heterocyclic optical brighteners (US 4539507), benzimidazole derivatives (US 2007/0273272 A1 ), such as, for example, TPBI (US 5766779, cf. formula ET-2), 1 ,3,5-triazines, for example

spirobifluorenyltriazine derivatives (for example in accordance with DE 102008064200), pyrenes, anthracenes, tetracenes, fluorenes, spirofluorenes, dendrimers, tetracenes (for example rubrene derivatives), 1 ,10-phenanthroline derivatives (JP 2003-1 15387, JP 2004- 31 1 184, JP 2001 -267080, WO 02/043449), silacyclopentadiene derivatives (EP 1480280, EP 1478032, EP 1469533), borane derivatives, such as, for example, triarylborane derivatives containing Si (US 2007/0087219 A1 , cf. formula ET-3), pyridine derivatives (JP 2004-200162), phenanthrolines, especially 1 ,10- phenanthroline derivatives, such as, for example, BCP and Bphen, also several phenanthrolines connected via biphenyl or other aromatic groups (US 2007-0252517 A1 ) or phenanthrolines connected to anthracene (US 2007-0122656 A1 , cf. formulae ET-4 and ET-5).

TPBI

2,2',2"-(1,3,5-benzenetriyl)tris(1-p enyl-1H-benzimidazole) formula ET-1 formula ET-2

formula ET-3 formula ET-4

formula ET-5

Likewise suitable are heterocyclic organic compounds, such as, for example, thiopyran dioxides, oxazoles, triazoles, imidazoles or oxadiazoles. Examples of the use of five-membered rings

containing N, such as, for example, oxazoles, preferably 1 ,3,4- oxadiazoles, for example compounds of the formulae ET-6, ET-7, ET-8 and ET-9, which are disclosed, inter alia, in US 2007/0273272 A1 ; thiazoles, oxadiazoles, thiadiazoles, triazoles, inter alia, see US 2008/010231 1 A1 and Y.A. Levin, M.S. Skorobogatova, Khimiya Geterotsiklicheskikh Soedinenii 1967 (2), 339-341 , preferably compounds of the formula ET-10, silacyclopentadiene derivatives. Preferred compounds are the following of the formulae (ET-6) to (ET-10):

formula ET-6

formula ET-7

formula ET-8

formula ET-9

formula ET-10

It is also possible to employ organic compounds, such as derivatives of fluorenone, fluorenylidenemethane,

perylenetetracarbonic acid, anthraquinonedimethane,

diphenoquinone, anthrone and anthraquinonediethylenediamine. Preference is given to 2,9,10-substituted anthracenes (with 1 - or 2-naphthyl and 4- or 3-biphenyl) or molecules which contain two anthracene units (US 2008/0193796 A1 , cf. formula ET-1 1 ). Also very advantageous is the connection of 9,10-substituted anthracene units to benzimidazole derivatives (US 2006/147747 A and EP 1551206 A1 , cf. formulae ET-12 and ET-13).

formula ET-12 formula ET-13

The compounds which are able to generate electron-injection and/or electron-transport properties preferably result in an LUMO of less than -2.5 eV (vs. vacuum level), particularly preferably less than -2.7 eV.

The present formulations may comprise emitters. The term emitter denotes a material which, after excitation, which can take place by transfer of any type of energy, allows a radiative transition into a ground state with emission of light. In general, two classes of emitter are known, namely fluorescent and phosphorescent emitters. The term fluorescent emitter denotes materials or compounds in which a radiative transition from an excited singlet state into the ground state takes place. The term phosphorescent emitter preferably denotes luminescent materials or compounds which contain transition metals.

Emitters are frequently also called dopants if the dopants cause the properties described above in a system. A dopant in a system comprising a matrix material and a dopant is taken to mean the component whose proportion in the mixture is the smaller.

Correspondingly, a matrix material in a system comprising a matrix material and a dopant is taken to mean the component whose proportion in the mixture is the greater. Accordingly, the term phosphorescent emitter can also be taken to mean, for example, phosphorescent dopant.

Compounds which are able to emit light include, inter alia, fluorescent emitters and phosphorescent emitters. These include, inter alia, compounds containing stilbene, stilbenamine, styrylamine, coumarine, rubrene, rhodamine, thiazole, thiadiazole, cyanine, thiophene, paraphenylene, perylene, phtalocyanine, porphyrin, ketone, quinoline, imine, anthracene and/or pyrene structures.

Particular preference is given to compounds which are able to emit light from the triplet state with high efficiency, even at room temperature, i.e. exhibit electrophosphorescence instead of electro- fluorescence, which frequently causes an increase in the energy efficiency. Suitable for this purpose are firstly compounds which contain heavy atoms having an atomic number of greater than 36. Preference is given to compounds which contain d- or f-transition metals which satisfy the above-mentioned condition. Particular preference is given here to corresponding compounds which contain elements from group 8 to 10 (Ru, Os, Rh, Ir, Pd, Pt). Suitable functional compounds here are, for example, various complexes, as described, for example, in WO 02/068435 A1 , WO 02/081488 A1 , EP 1239526 A2 and WO 2004/026886 A2. Preferred compounds which can serve as fluorescent emitters are described by way of example below. Preferred fluorescent emitters are selected from the class of the monostyrylamines, the distyryl- amines, the tristyrylamines, the tetrastyrylamines, the styryl- phosphines, the styryl ethers and the arylamines.

A monostyrylamine is taken to mean a compound which contains one substituted or unsubstituted styryl group and at least one, preferably aromatic, amine. A distyrylamine is taken to mean a compound which contains two substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. A tristyrylamine is taken to mean a compound which contains three substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. A tetrastyrylamine is taken to mean a compound which contains four substituted or unsubstituted styryl groups and at least one, preferably aromatic, amine. The styryl groups are particularly preferably stilbenes, which may also be further substituted.

Corresponding phosphines and ethers are defined analogously to the amines. An arylamine or an aromatic amine in the sense of the present invention is taken to mean a compound which contains three substituted or unsubstituted aromatic or heteroaromatic ring systems bonded directly to the nitrogen. At least one of these aromatic or heteroaromatic ring systems is preferably a condensed ring system, preferably having at least 14 aromatic ring atoms.

Preferred examples thereof are aromatic anthracenamines, aro- matic anthracenediamines, aromatic pyrenamines, aromatic pyrene- diamines, aromatic chrysenamines or aromatic chrysenediamines. An aromatic anthracenamine is taken to mean a compound in which one diarylamino group is bonded directly to an anthracene group, preferably in the 9-position. An aromatic anthracenediamine is taken to mean a compound in which two diarylamino groups are bonded directly to an anthracene group, preferably in the 2,6- or 9,10- position. Aromatic pyrenamines, pyrenediamines, chrysenamines and chrysenediamines are defined analogously thereto, where the diarylamino groups are preferably bonded to the pyrene in the 1 -position or in the 1 ,6-position. Further preferred fluorescent emitters are selected from indeno- fluorenamines or indenofluorenediamines, which are described, inter alia, in WO 2006/122630; benzoindenofluorenamines or benzoindenofluorenediamines, which are described, inter alia, in WO 2008/006449; and dibenzoindenofluorenamines or dibenzo- indenofluorenediamines, which are described, inter alia, in

WO 2007/140847.

Examples of compounds from the class of the styrylamines which can be employed as fluorescent emitters are substituted or un- substituted tristilbenamines or the dopants described in

WO 2006/000388, WO 2006/058737, WO 2006/000389, WO 2007/065549 and WO 2007/1 15610. Distyrylbenzene and distyrylbiphenyl derivatives are described in US 5121029. Further styrylamines can be found in US 2007/0122656 A1 .

Particularly preferred styrylamine compounds are the compounds of the formula EM-1 described in US 7250532 B2 and the compounds of the formula EM-2 described in DE 10 2005 058557 A1 :

Particularly preferred triarylannine compounds are compounds of the formulae EM-3 to EM-15 disclosed in CN 1583691 A, JP 08/053397 A and US 6251531 B1 , EP 1957606 A1 , US 2008/01 13101 A1 , US 2006/210830 A , WO 2008/006449 and DE 102008035413 and derivatives thereof:

formula EM-3 formula EM-4

formula EM-15 Further preferred compounds which can be employed as

fluorescent emitters are selected from derivatives of naphthalene, anthracene, tetracene, benzanthracene, benzophenanthrene (DE 10 2009 005746), fluorene, fluoranthene, periflanthene,

indenoperylene, phenanthrene, perylene (US 2007/0252517 A1 ), pyrene, chrysene, decacyclene, coronene, tetraphenylcyclopenta- diene, pentaphenylcyclopentadiene, fluorene, spirofluorene, rubrene, coumarine (US 4769292, US 6020078, US 2007/0252517 A1 ), pyran, oxazole, benzoxazole, benzothiazole, benzimidazole, pyrazine, cinnamic acid esters, diketopyrrolopyrrole, acridone and quinacridone (US 2007/0252517 A1 ).

Of the anthracene compounds, particular preference is given to 9,10-substituted anthracenes, such as, for example, 9,10- diphenylanthracene and 9,10-bis(phenylethynyl)anthracene. 1 ,4- Bis(9'-ethynylanthracenyl)benzene is also a preferred dopant.

Preference is likewise given to derivatives of rubrene, coumarine, rhodamine, quinacridone, such as, for example, DMQA (= Ν,Ν'- dimethylquinacridone), dicyanomethylenepyran, such as, for example, DCM (= 4-(dicyanoethylene)-6-(4-dimethylaminostyryl-2- methyl)-4H-pyran), thiopyran, polymethine, pyrylium and

thiapyrylium salts, periflanthene and indenoperylene.

Blue fluorescent emitters are preferably polyaromatic compounds, such as, for example, 9,10-di(2-naphthylanthracene) and other anthracene derivatives, derivatives of tetracene, xanthene, perylene, such as, for example, 2,5,8,1 1 -tetra-f-butylperylene, phenylene, for example 4,4'-bis(9-ethyl-3-carbazovinylene)-1 ,1 '- biphenyl, fluorene, fluoranthene, arylpyrenes (US 2006/0222886 A1 ), arylenevinylenes (US 5121029, US 5130603), bis(azinyl)imine- boron compounds (US 2007/0092753 A1 ), bis(azinyl)methene compounds and carbostyryl compounds.

Further preferred blue fluorescent emitters are described in C.H. Chen et al.: "Recent developments in organic electroluminescent materials" Macromol. Symp. 125, (1997) 1 -48 and "Recent progress of molecular organic electroluminescent materials and devices" Mat. Sci. and Eng. R, 39 (2002), 143-222. Further preferred blue-fluorescent emitters are the hydrocarbons disclosed in DE 102008035413.

Preferred compounds which can serve as phosphorescent emitters are described below by way of example.

Examples of phosphorescent emitters are revealed by

WO 00/70655, WO 01/41512, WO 02/02714, WO 02/15645, EP 1 191613, EP 1 191612, EP 1 191614 and WO 2005/033244. In general, all phosphorescent complexes as are used in accordance with the prior art for phosphorescent OLEDs and as are known to the person skilled in the art in the area of organic electroluminescence are suitable, and the person skilled in the art will be able to use further phosphorescent complexes without inventive step. Phosphorescent metal complexes preferably contain Ir, Ru, Pd, Pt, Os or Re, more preferably Ir.

Preferred ligands are 2-phenylpyridine derivatives, 7,8- benzoquinoline derivatives, 2-(2-thienyl)pyridine derivatives, 2-(1 - naphthyl)pyridine derivatives, 1 -phenylisoquinoline derivatives,

3-phenylisoquinoline derivatives or 2-phenylquinoline derivatives. All these compounds may be substituted, for example by fluoro, cyano and/or trifluoromethyl substituents for blue. Auxiliary ligands are preferably acetylacetonate or picolinic acid.

In particular, complexes of Pt or Pd with tetradentate ligands of the formula EM-16 are suitable

The compounds of the formula EM-16 are described in greater detail in US 2007/0087219 A1 , where, for an explanation of the substituents and indices in the above formula, reference is made to this specification for disclosure purposes. Furthermore, Pt-porphyrin complexes having an enlarged ring system (US 2009/0061681 A1 ) and Ir complexes, for example 2,3,7,8,12,13,17,18-octaethyl-21 H, 23H-porphyrin-Pt(ll), tetraphenyl-Pt(ll) tetrabenzoporphyrin (US 2009/0061681 A1 ), c/s-bis(2-phenylpyridinato-N,C ² ')Pt(ll), c/s-bis(2- (2'-thienyl)pyridinato-N,C ³ ')Pt(ll), c/ ^' s-bis(2-(2'-thienyl)quinolinato- N,C ⁵ ')Pt(ll), (2-(4,6-difluorophenyl)pyridinato-N,C ² ')Pt(ll) (acetylacetonate), or tris(2-phenylpyridinato-N,C ² ')lr(lll) (= lr(ppy)3, green), bis(2-phenylpyridinato-N,C ² )lr(lll) (acetylacetonate) (= lr(ppy)2 acetylacetonate, green, US 2001/0053462 A1 , Baldo, Thompson et al. Nature 403, (2000), 750-753), bis(1 -phenylisoquinolinato- N,C ² ')(2-phenylpyridinato-N,C ² ')iridium(lll), bis(2-phenylpyridinato- N,C ² ')(1 -phenylisoquinolinato-N,C ² ')iridium(lll), bis(2-(2'- benzothienyl)pyridinato-N,C ³ ')iridium(lll) (acetylacetonate), bis(2- (4',6'-difluorophenyl)pyndinato-N,C ² ')iridium(lll) (piccolinate) (FIrpic, blue), bis(2-(4',6'-difluorophenyl)pyridinato-N,C ² ')lr(lll) (tetrakis(1 - pyrazolyl)borate), tris(2-(biphenyl-3-yl)-4-tert-butylpyridine)- iridium(lll), (ppz) ₂ lr(5phdpym) (US 2009/0061681 A1 ), (45ooppz) ₂ - lr(5phdpym) (US 2009/0061681 A1 ), derivatives of 2-phenyl- pyridine-lr complexes, such as, for example, PQIr (= iridium(lll) bis(2-phenylquinolyl-N,C ² ')acetylacetonate), tris(2-phenylisoquino- linato-N,C)lr(lll) (red), bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C ³ )- lr (acetylacetonate) ([Btp2lr(acac)], red, Adachi et al. Appl. Phys. Lett. 78 (2001 ), 1622-1624).

Likewise suitable are complexes of trivalent lanthanides, such as, for example, Tb ³⁺ and Eu ³⁺ (J. Kido et al. Appl. Phys. Lett. 65 (1994), 2124, Kido et al. Chem. Lett. 657, 1990, US 2007/0252517 A1 ), or phosphorescent complexes of Pt(ll), lr(l), Rh(l) with maleonitrile dithiolate (Johnson et al., JACS 105, 1983, 1795), Re(l) tricarbonyl-diimine complexes (Wrighton, JACS 96, 1974, 998, inter alia), Os(ll) complexes with cyano ligands and bipyridyl or phenanthroline ligands (Ma et al., Synth. Metals 94, 1998, 245).

Further phosphorescent emitters having tridentate ligands are described in US 6824895 and US 10/729238. Red-emitting phosphorescent complexes are found in US 6835469 and US 6830828.

Particularly preferred compounds which are used as phosphorescent dopants are, inter alia, the compounds of the formula EM-17 described, inter alia, in US 2001/0053462 A1 and Inorg. Chem. 2001 , 40(7), 1704-171 1 , JACS 2001 , 123(18), 4304-4312, and derivatives thereof.

formula EM-17

Derivatives are described in US 7378162 B2, US 6835469 B2 and JP 2003/253145 A.

Furthermore, the compounds of the formulae EM-18 to EM-21 described in US 7238437 B2, US 2009/008607 A1 and

EP 134871 1 , and derivatives thereof, can be employed as emitters.

formula EM-18 formula EM-19

Quantum dots can likewise be employed as emitters, these materials being disclosed in detail in WO 201 1/076314 A1 . Compounds which are employed as host materials, in particular together with emitting compounds, include materials from various classes of substances.

Host materials generally have larger band gaps between HOMO and LUMO than the emitter materials employed. In addition, preferred host materials exhibit properties of either a hole- or electron-transport material. Furthermore, host materials can have both electron- and hole-transport properties.

Host materials are in some cases also called matrix material, in particular if the host material is employed in combination with a phosphorescent emitter in an OLED.

Preferred host materials or co-host materials, which are employed, in particular, together with fluorescent dopants, are selected from the classes of the oligoarylenes (for example 2, 2', 7,7'- tetraphenylspirobifluorene in accordance with EP 676461 or dinaphthylanthracene), in particular the oligoarylenes containing condensed aromatic groups, such as, for example, anthracene, benzanthracene, benzophenanthrene (DE 10 2009 005746, WO 2009/069566), phenanthrene, tetracene, coronene, chrysene, fluo- rene, spirofluorene, perylene, phthaloperylene, naphthaloperylene, decacyclene, rubrene, the oligoarylenevinylenes (for example

DPVBi = 4,4'-bis(2,2-diphenylethenyl)-1 ,1 '-biphenyl or spiro-DPVBi in accordance with EP 676461 ), the polypodal metal complexes (for example in accordance with WO 04/081017), in particular metal complexes of 8-hydroxyquinoline, for example AIQ3 (= aluminium(lll) tris(8-hydroxyquinoline)) or bis(2-methyl-8-quinolinolato)-4-

(phenylphenolinolato)aluminium, also with imidazole chelate (US 2007/0092753 A1 ) and the quinoline-metal complexes, amino- quinoline-metal complexes, benzoquinoline-metal complexes, the hole-conducting compounds (for example in accordance with WO 2004/05891 1 ), the electron-conducting compounds, in particular ketones, phosphine oxides, sulfoxides, etc. (for example in accordance with WO 2005/084081 and WO 2005/084082), the atropisomers (for example in accordance with WO 2006/048268), the boronic acid derivatives (for example in accordance with

WO 2006/1 17052) or the benzanthracenes (for example in accordance with WO 2008/145239).

Particularly preferred compounds which can serve as host materials or co-host materials are selected from the classes of the

oligoarylenes, comprising anthracene, benzanthracene and/or pyrene, or atropisomers of these compounds. An oligoarylene in the sense of the present invention is intended to be taken to mean a compound in which at least three aryl or arylene groups are bonded to one another. Preferred host materials are selected, in particular, from compounds of the formula (H-1 ),

Ar^Ar Ar ⁶ (H-1 ) where Ar ⁴ , Ar ⁵ , Ar ⁶ are on each occurrence, identically or differently, an aryl or heteroaryl group having 5 to 30 aromatic ring atoms, which may optionally be substituted, and p represents an integer in the range from 1 to 5; the sum of the π electrons in Ar ⁴ , Ar ⁵ and Ar ⁶ is at least 30 if p = 1 and at least 36 if p = 2 and at least 42 if p = 3.

In the compounds of the formula (H-1 ), the group Ar ⁵ particularly preferably stands for anthracene, and the groups Ar ⁴ and Ar ⁶ are bonded in the 9- and 10-position, where these groups may optionally be substituted. Very particularly preferably, at least one of the groups Ar ⁴ and/or Ar ⁶ is a condensed aryl group selected from 1 - or 2-naphthyl, 2-, 3- or 9-phenanthrenyl or 2-, 3-, 4-, 5-, 6- or 7-benzanthracenyl. Anthracene-based compounds are described in US 2007/0092753 A1 and US 2007/0252517 A1 , for example 2-(4- methylphenyl)-9,10-di-(2-naphthyl)anthracene, 9-(2-naphthyl)-10- (1 ,1 '-biphenyl)anthracene and 9,10-bis[4-(2,2-diphenylethenyl)- phenyl]anthracene, 9,10-diphenylanthracene, 9,10-bis(phenyl- ethynyl)anthracene and 1 ,4-bis(9'-ethynylanthracenyl)benzene.

Preference is also given to compounds containing two anthracene units (US 2008/0193796 A1 ), for example 10,10'-bis[1 ,1 ',4',1 "]ter- phenyl-2-yl-9,9'-bisanthracenyl. Further preferred compounds are derivatives of arylamine, styrylamine, fluorescein, diphenylbutadiene, tetraphenylbutadiene, cyclopentadiene, tetraphenylcyclopentadiene, pentaphenylcyclo- pentadiene, coumarine, oxadiazole, bisbenzoxazoline, oxazole, pyridine, pyrazine, imine, benzothiazole, benzoxazole,

benzimidazole (US 2007/0092753 A1 ), for example 2,2',2"-(1 ,3,5- phenylene)tris[1 -phenyl-1 H-benzimidazole], aldazine, stilbene, styrylarylene derivatives, for example 9,10-bis[4-(2,2-diphenyl- ethenyl)phenyl]anthracene, and distyrylarylene derivatives (US 5121029), diphenylethylene, vinylanthracene, diaminocarbazole, pyran, thiopyran, diketopyrrolopyrrole, polymethine, cinnamic acid esters and fluorescent dyes.

Particular preference is given to derivatives of arylamine and styrylamine, for example TNB (= 4,4'-bis[N-(1 -naphthyl)-N-(2- naphthyl)amino]biphenyl). Metal-oxinoid complexes, such as LiQ or AIQ3, can be used as co-hosts. Preferred compounds with oligoarylene as matrix are disclosed in US 2003/0027016 A1 , US 7326371 B2, US 2006/043858 A, WO 2007/1 14358, WO 2008/145239, JP 3148176 B2, EP 1009044, US 2004/018383, WO 2005/061656 A1 , EP 0681019B1 , WO

2004/013073A1 , US 5077142, WO 2007/065678 and DE

102009005746, where particularly preferred compounds are described by the formulae H-2 to H-8.

formula H-6 formula H-7

formula H-8

Furthermore, compounds which can be employed as host or matrix include materials which are employed together with phosphorescent emitters.

These compounds, which can also be employed as structural elements in polymers, include CBP (N,N-biscarbazolylbiphenyl), carbazole derivatives (for example in accordance with

WO 2005/039246, US 2005/0069729, JP 2004/288381 , EP

1205527 or WO 2008/086851 ), azacarbazoles (for example in accordance with EP 1617710, EP 161771 1 , EP 1731584 or

JP 2005/347160), ketones (for example in accordance with

WO 2004/093207 or in accordance with DE 102008033943), phosphine oxides, sulfoxides and sulfones (for example in

accordance with WO 2005/003253), oligophenylenes, aromatic amines (for example in accordance with US 2005/0069729), bipolar matrix materials (for example in accordance with WO 2007/137725), silanes (for example in accordance with WO 2005/1 1 1 172), 9,9- diarylfluorene derivatives (for example in accordance with

DE 102008017591 ), azaboroles or boronic esters (for example in accordance with WO 2006/1 17052), triazine derivatives (for example in accordance with DE 102008036982), indolocarbazole derivatives (for example in accordance with WO 2007/063754 or WO 2008/056746), indenocarbazole derivatives (for example in accordance with DE 102009023155 and DE 102009031021 ), diazaphosphole derivatives (for example in accordance with DE 102009022858), triazole derivatives, oxazoles and oxazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, distyrylpyrazine derivatives, thiopyran dioxide derivatives, phenylenediamine derivatives, tertiary aromatic amines, styrylamines, amino-substituted chalcone derivatives, indoles, hydrazone derivatives, stilbene derivatives, silazane derivatives, aromatic dimethylidene compounds, carbodiimide derivatives, metal complexes of 8-hydroxyquinoline derivatives, such as, for example, AIQ3, which may also contain

triarylaminophenol ligands (US 2007/0134514 A1 ), metal complex/polysilane compounds, and thiophene, benzothiophene and dibenzothiophene derivatives.

Examples of preferred carbazole derivatives are mCP (= 1 ,3-N,N- dicarbazolylbenzene (= 9,9'-(1 ,3-phenylene)bis-9H-carbazole)) (formula H-9), CDBP (= 9,9'-(2,2'-dimethyl[1 ,1 '-biphenyl]-4,4'- diyl)bis-9H-carbazole), 1 ,3-bis(N,N'-dicarbazolyl)benzene (= 1 ,3- bis(carbazol-9-yl)benzene), PVK (polyvinylcarbazole), 3,5-di(9H- carbazol-9-yl)biphenyl and CMTTP (formula H-10). Particularly referred compounds are disclosed in US 2007/0128467 A1 and US 2005/0249976 A1 (formulae H-1 1 and H-13).

formula H-9 formula H-10

-1 1 formula H-12

formula H-13

Preferred tetraaryl-Si compounds are disclosed, for example, in US 2004/02091 15, US 2004/02091 16, US 2007/0087219 A1 and in H. Gilman, E.A. Zuech, Chemistry & Industry (London, United

Kingdom), 1960, 120.

Particularly preferred tetraaryl-Si compounds are described by the formulae H-14 to H-21 .

formula H-14 formula H-15

Triphenyl-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]silane formula H-16 formula H-17

formula H-18 formula H-19

formula H-20 formula H-21

Particularly preferred compounds from group 4 for the preparation of the matrix for phosphorescent dopants are disclosed, inter alia, in DE 102009022858, DE 102009023155, EP 652273 B1 , WO

2007/063754 and WO 2008/056746, where particularly preferred compounds are described by the formulae H-22 to H-25.

formula H-22 formula H-23

formula H-24 formula H-25

With respect to the semiconducting compounds which can be employed in accordance with the invention and which can serve as host material, especial preference is given to substances which contain at least one nitrogen atom. These preferably include aromatic amines, triazine derivatives and carbazole derivatives. Thus, carbazole derivatives in particular exhibit surprisingly high efficiency. Triazine derivatives result in unexpectedly long lifetimes of the electronic devices.

It may also be preferred to employ a plurality of different matrix materials as a mixture, in particular at least one electron-conducting matrix material and at least one hole-conducting matrix material. Preference is likewise given to the use of a mixture of a charge- transporting matrix material and an electrically inert matrix material which is not in involved in the charge transport to a significant extent, if at all, as described, for example, in WO 2010/108579.

It is furthermore possible to employ compounds which improve the transition from the singlet state to the triplet state and which, employed in support of the functional compounds having emitter properties, improve the phosphorescence properties of these compounds. Suitable for this purpose are, in particular, carbazole and bridged carbazole dimer units, as described, for example, in WO 2004/070772 A2 and WO 2004/1 13468 A1 . Also suitable for this purpose are ketones, phosphine oxides, sulfoxides, sulfones, silane derivatives and similar compounds, as described, for example, in WO 2005/040302 A1 . n-Dopants herein are taken to mean reducing agents, i.e. electron donors. Preferred examples of n-dopants are W(hpp) ₄ and other electron-rich metal complexes in accordance with WO 2005/086251 A2, P=N compounds (for example WO 2012/175535 A1 , WO 2012/175219 A1 ), naphthylenecarbodiimides (for example WO 2012/168358 A1 ), fluorenes (for example WO 2012/031735 A1 ), free radicals and diradicals (for example EP 1837926 A1 , WO 2007/107306 A1 ), pyridines (for example EP 2452946 A1 , EP 2463927 A1 ), N-heterocyclic compounds (for example WO

2009/000237 A1 ) and acridines as well as phenazines (for example US 2007/145355 A1 ).

Furthermore, the formulations may comprise a wide-band-gap material as functional material. Wide-band-gap material is taken to mean a material in the sense of the disclosure content of US 7,294,849. These systems exhibit particularly advantageous performance data in electroluminescent devices. The compound employed as wide-band-gap material can preferably have a band gap of 2.5 eV or more, preferably 3.0 eV or more, particularly preferably 3.5 eV or more. The band gap can be calculated, inter alia, by means of the energy levels of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO).

Furthermore, the formulations may comprise a hole-blocking material (HBM) as functional material. A hole-blocking material denotes a material which prevents or minimises the transmission of holes (positive charges) in a multilayer system, in particular if this material is arranged in the form of a layer adjacent to an emission layer or a hole-conducting layer. In general, a hole-blocking material has a lower HOMO level than the hole-transport material in the adjacent layer. Hole-blocking layers are frequently arranged between the light-emitting layer and the electron-transport layer in OLEDs.

It is basically possible to employ any known hole-blocking material. In addition to other hole-blocking materials described elsewhere in the present application, advantageous hole-blocking materials are metal complexes (US 2003/0068528), such as, for example, bis(2- methyl-8-quinolinolato)(4-phenylphenolato)aluminium(lll) (BAIQ).

Fac-tris(1 -phenylpyrazolato-N,C2)iridium(lll) (lr(ppz)3) is likewise employed for this purpose (US 2003/0175553 A1 ). Phenanthroline derivatives, such as, for example, BCP, or phthalimides, such as, for example, TMPP, can likewise be employed.

Furthermore, advantageous hole-blocking materials are described in WO 00/70655 A2, WO 01/41512 and WO 01/93642 A1 . Furthermore, the formulations may comprise an electron-blocking material (EBM) as functional material. An electron-blocking material denotes a material which prevents or minimises the transmission of electrons in a multilayer system, in particular if this material is arranged in the form of a layer adjacent to an emission layer or an electron-conducting layer. In general, an electron-blocking material has a higher LUMO level than the electron-transport material in the adjacent layer. It is basically possible to employ any known electron-blocking material. In addition to other electron-blocking materials described elsewhere in the present application, advantageous electron- blocking materials are transition-metal complexes, such as, for example, lr(ppz) ₃ (US 2003/0175553).

The electron-blocking material can preferably be selected from amines, triarylamines and derivatives thereof.

Furthermore, the organic semiconducting materials in the

formulations preferably have, if they are low-molecular-weight compounds (i.e. "small molecules"), a molecular weight of < 3,000 g/mol, more preferably < 2,000 g/mol and most preferably < 1 ,000 g/mol. Of particular interest are furthermore semiconducting compounds which are distinguished by a high glass-transition temperature. In this connection, particularly preferred functional compounds which can be employed as organic semiconducting material in the formulations are those which have a glass-transition temperature of ≥ 70°C, preferably > 100°C, more preferably > 125°C and most preferably > 150°C, determined in accordance with DIN 51005. The formulations may also comprise polymers as organic

semiconducting materials. The compounds described above as organic semiconducting materials, which frequently have a relatively low molecular weight, can also be mixed with a polymer. It is likewise possible to incorporate these compounds covalently into a polymer. This is possible, in particular, with compounds which are substituted by reactive leaving groups, such as bromine, iodine, chlorine, boronic acid or boronic acid ester, or by reactive, polymerisable groups, such as olefins or oxetanes. These can be used as monomers for the production of corresponding oligomers, dendrimers or polymers. The oligomerisation or polymerisation here preferably takes place via the halogen functionality or the boronic acid functionality or via the polymerisable group. It is furthermore possible to crosslink the polymers via groups of this type. The compounds and polymers according to the invention can be employed as crosslinked or uncrosslinked layer.

Polymers which can be employed as organic semiconducting materials frequently contain units or structural elements which have been described in the context of the compounds described above, inter alia those as disclosed and extensively listed in WO 02/077060 A1 , in WO 2005/014689 A2 and in WO 201 1 /076314 A1 . These are incorporated into the present application by way of reference. The functional materials can originate, for example, from the following classes:

Group 1 : structural elements which are able to generate hole- injection and/or hole-transport properties; Group 2: structural elements which are able to generate

electron-injection and/or electron-transport properties; Group 3: structural elements which combine the properties described in relation to groups 1 and 2; structural elements which have light-emitting

properties, in particular phosphorescent groups; structural elements which improve the transition from the so-called singlet state to the triplet state; structural elements which influence the morphology or also the emission colour of the resultant polymers; structural elements which are typically used as backbone.

The structural elements here may also have various functions, so that a clear assignment need not be advantageous. For example, a structural element of group 1 may likewise serve as backbone.

The polymer having hole-transport or hole-injection properties employed as organic semiconducting material, containing structural elements from group 1 , may preferably contain units which correspond to the hole-transport or hole-injection materials described above.

Further preferred structural elements of group 1 are, for example, triarylamine, benzidine, tetraaryl-para-phenylenediamine, carbazole, azulene, thiophene, pyrrole and furan derivatives and further O-, S- or N-containing heterocycles having a high HOMO. These

arylamines and heterocycles preferably have an HOMO of above - 5.8 eV (against vacuum level), particularly preferably above -5.5 eV. Preference is given, inter alia, to polymers having hole-transport or hole-injection properties, containing at least one of the following recurring units of the formula HTP-1 :

HTP-1 in which the symbols have the following meaning:

Ar ¹ is, in each case identically or differently for different recurring units, a single bond or a monocyclic or polycyclic aryl group, which may optionally be substituted;

Ar ² is, in each case identically or differently for different recurring units, a monocyclic or polycyclic aryl group, which may optionally be substituted; is, in each case identically or differently for different recurring units, a monocyclic or polycyclic aryl group, which may optionally be substituted; m is 1 , 2 or 3.

Particular preference is given to recurring units of the formula HTP-1 which are selected from the group consisting of units of the formulae HTP-1 A to HTP-1 C:

HTP-1A

HTP-1 B

HTP-1 C in which the symbols have the following meaning:

R ^a is on each occurrence, identically or differently, H, a substituted or unsubstituted aromatic or heteroaromatic an alkyl, cycloalkyl, alkoxy, aralkyl, aryloxy, arylthio, alkoxycarbonyl, silyl or carboxyl group, a halogen atom, cyano group, a nitro group or a hydroxyl group; r is 0, 1 , 2, 3 or 4, and s is 0, 1 , 2, 3, 4 or 5.

Preference is given, inter alia, to polymers having hole-transport or hole-injection properties, containing at least one of the following recurring units of the formula HTP-2: in which the symbols have the following meaning:

T ¹ and T ² are selected independently from thiophene, selenophene, thieno[2,3-b]thiophene, thieno[3,2-b]thiophene, dithienothiophene, pyrrole and aniline, where these groups may be substituted by one or more radicals R ^b ;

R ^b is selected independently on each occurrence from halogen, -CN, -NC, -NCO, -NCS, -OCN, -SCN, -C(=O)NR°R ⁰⁰ , -C(=O)X, -C(=O)R°, -NH ₂ , -NR°R ⁰⁰ , -SH, -SR°, -SO ₃ H, -SO ₂ R°, -OH, -NO ₂ , -CF3, -SF5, an optionally substituted silyl, carbyl or hydrocarbyl group having 1 to 40 carbon atoms, which may optionally be substituted and may optionally contain one or more heteroatoms;

R° and R ⁰⁰ are each independently H or an optionally substituted carbyl or hydrocarbyl group having 1 to 40 carbon atoms, which may optionally be substituted and may optionally contain one or more heteroatoms;

Ar ⁷ and Ar ⁸ represent, independently of one another, a monocyclic or polycyclic aryl or heteroaryl group, which may optionally be substituted and may optionally be bonded to the 2,3-position of one or both adjacent thiophene or selenophene groups; c and e are, independently of one another, 0, 1 , 2, 3 or 4, where 1 < c + e < 6; d and f are, independently of one another, 0, 1 , 2, 3 or 4.

Preferred examples of polymers having hole-transport or hole- injection properties are described, inter alia, in WO 2007/131582 A1 and WO 2008/009343 A1 .

The polymer having electron-injection and/or electron-transport properties employed as organic semiconducting material, containing structural elements from group 2, may preferably contain units which correspond to the electron-injection and/or electron-transport materials described above.

Further preferred structural elements of group 2 which have electron-injection and/or electron-transport properties are derived, for example, from pyridine, pyrimidine, pyridazine, pyrazine, oxadiazole, quinoline, quinoxaline and phenazine groups, but also triarylborane groups or further O-, S- or N-containing heterocycles having a low LUMO level. These structural elements of group 2 preferably have an LUMO of below -2.7 eV (against vacuum level), particularly preferably below -2.8 eV.

The organic semiconducting material can preferably be a polymer which contains structural elements from group 3, where structural elements which improve the hole and electron mobility (i.e.

structural elements from groups 1 and 2) are connected directly to one another. Some of these structural elements can serve as emitters here, where the emission colours may be shifted, for example, into the green, red or yellow. Their use is therefore advantageous, for example, for the generation of other emission colours or a broad-band emission by polymers which originally emit in blue. The polymer having light-emitting properties employed as organic semiconducting material, containing structural elements from group 4, may preferably contain units which correspond to the emitter materials described above. Preference is given here to polymers containing phosphorescent groups, in particular the emitting metal complexes described above which contain corresponding units containing elements from groups 8 to 10 (Ru, Os, Rh, Ir, Pd, Pt).

The polymer employed as organic semiconducting material containing units of group 5 which improve the transition from the so- called singlet state to the triplet state can preferably be employed in support of phosphorescent compounds, preferably the polymers containing structural elements of group 4 described above. A polymeric triplet matrix can be used here. Suitable for this purpose are, in particular, carbazole and connected carbazole dimer units, as described, for example, in DE 10304819 A1 and DE 10328627 A1 . Also suitable for this purpose are ketone, phosphine oxide, sulfoxide, sulfone and silane derivatives and similar compounds, as described, for example, in DE 10349033 A1 . Furthermore, preferred structural units can be derived from compounds which have been described above in connection with the matrix materials employed together with phosphorescent compounds. The further organic semiconducting material is preferably a polymer containing units of group 6 which influence the morphology and/or the emission colour of the polymers. Besides the polymers mentioned above, these are those which have at least one further aromatic or another conjugated structure which do not count amongst the above-mentioned groups. These groups accordingly have only little or no effect on the charge-carrier mobilities, the non- organometallic complexes or the singlet-triplet transition.

Structural units of this type are able to influence the morphology and/or the emission colour of the resultant polymers. Depending on the structural unit, these polymers can therefore also be used as emitters.

In the case of fluorescent OLEDs, preference is therefore given to aromatic structural elements having 6 to 40 C atoms or also tolan, stilbene or bisstyrylarylene derivative units, each of which may be substituted by one or more radicals. Particular preference is given here to the use of groups derived from 1 ,4-phenylene, 1 ,4- naphthylene, 1 ,4- or 9,10-anthrylene, 1 ,6-, 2,7- or 4,9-pyrenylene, 3,9- or 3,10-perylenylene, 4,4'-biphenylene, 4,4"-terphenylylene, 4,4'-bi-1 ,1 '-naphthylylene, 4,4'-tolanylene, 4,4'-stilbenylene or 4,4"- bisstyrylarylene derivatives.

The polymer employed as organic semiconducting material preferably contains units of group 7, which preferably contain aromatic structures having 6 to 40 C atoms which are frequently used as backbone.

These include, inter alia, 4,5-dihydropyrene derivatives, 4,5,9,10- tetrahydropyrene derivatives, fluorene derivatives, which are disclosed, for example, in US 5962631 , WO 2006/052457 A2 and WO 2006/1 18345 A1 , 9,9-spirobifluorene derivatives, which are disclosed, for example, in WO 2003/020790 A1 , 9,10-phenanthrene derivatives, which are disclosed, for example, in WO 2005/104264 A1 , 9,10-dihydrophenanthrene derivatives, which are disclosed, for example, in WO 2005/014689 A2, 5,7-dihydrodibenzoxepine derivatives and cis- and trans-indenofluorene derivatives, which are disclosed, for example, in WO 2004/041901 A1 and WO 2004/ 1 13412 A2, and binaphthylene derivatives, which are disclosed, for example, in WO 2006/063852 A1 , and further units which are disclosed, for example, in WO 2005/056633 A1 , EP 1344788 A1 , WO 2007/043495 A1 , WO 2005/033174 A1 , WO 2003/099901 A1 and DE 102006003710.

Particular preference is given to structural units of group 7 which are selected from fluorene derivatives, which are disclosed, for example, in US 5,962,631 , WO 2006/052457 A2 and

WO 2006/1 18345 A1 , spirobifluorene derivatives, which are disclosed, for example, in WO 2003/020790 A1 , benzofluorene, dibenzofluorene, benzothiophene and dibenzofluorene groups and derivatives thereof, which are disclosed, for example, in

WO 2005/056633 A1 , EP 1344788 A1 and WO 2007/043495 A1 . Especially preferred structural elements of group 7 are represented by the general formula PB-1 :

formula PB-1 in which the symbols and indices have the following meanings A, B and B' are each, also for different recurring units, identically or differently, a divalent group, which is preferably selected from

-CR ^c R ^d -, -NRS -PRS -O-, -S-, -SO-, -SO2-, -CO-, -CS-, -CSe-, -P(=O)R ^c -, -P(=S)R ^C - and -SiR ^c R ^d -;

R ^c and R ^d are selected on each occurrence, independently, from H, halogen, -CN, -NC, -NCO, -NCS, -OCN, -SCN, -C(=O)NR°R ⁰⁰ , -C(=O)X, -C(=O)R°, -NH2, -NR°R ⁰⁰ , -SH, -SR°, -SO3H, -SO2R ⁰ , -OH, -NO2, -CF3, -SF5, an optionally substituted silyl, carbyl or

hydrocarbyl group having 1 to 40 carbon atoms, which may optionally be substituted and may optionally contain one or more heteroatoms, where the groups R ^c and R ^d may optionally form a spiro group with a fluorene radical to which they are bonded; X is halogen;

R° and R ⁰⁰ are each, independently, H or an optionally substituted carbyl or hydrocarbyl group having 1 to 40 carbon atoms, which may optionally be substituted and may optionally contain one or more heteroatoms; g is in each case, independently, 0 or 1 and h is in each case, independently, 0 or 1 , where the sum of g and h in a sub-unit is preferably 1 ; m is an integer > 1 ;

Ar ¹ and Ar ² represent, independently of one another, a monocyclic or polycyclic aryl or heteroaryl group, which may optionally be substituted and may optionally be bonded to the 7,8-position or the 8,9-position of an indenofluorene group; and a and b are, independently of one another, 0 or 1

If the groups R ^c and R ^d form a spiro group with the fluorene group to which these groups are bonded, this group preferably represents a spirobifluorene.

Particular preference is given to recurring units of the formula PB-1 which are selected from the group consisting of units of the formulae PB-1 A to PB-1 E:

formula PB-1 C

formula PB-1 D

formula PB-1 E where R ^c has the meaning described above for formula PB-1 , 1 , 2, 3 or 4, and R ^e has the same meaning as the radical R ^c .

R ^e is preferably -F, -CI, -Br, -I, -CN, -NO ₂ , -NCO, -NCS, -OCN, -SCN, -C(=O)NR°R ⁰⁰ , -C(=O)X, -C(=O)R°, -NR°R ⁰⁰ , an optionally substituted silyl, aryl or heteroaryl group having 4 to 40, preferably 6 to 20, C atoms, or a straight-chain, branched or cyclic alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or

alkoxycarbonyloxy group having 1 to 20, preferably 1 to 12, C atoms, where one or more hydrogen atoms may optionally be substituted by F or CI, and the groups R°, R ⁰⁰ and X have the meaning described above for formula PB-1 .

Particular preference is given to recurring units of the formula PB-1 which are selected from the group consisting of units of the formulae PB-1 F to PB-1 1:

formula PB-1 1 in which the symbols have the following meaning L is H, halogen or an optionally fluorinated, linear or branched alkyl or alkoxy group having 1 to 12 C atoms and preferably stands for H, F, methyl, i-propyl, t-butyl, n-pentoxy or trifluoromethyl; and L' is an optionally fluorinated, linear or branched alkyl or alkoxy group having 1 to 12 C atoms and preferably stands for n-octyl or n-octyloxy.

For carrying out the present invention, preference is given to polymers which contain more than one of the structural elements of groups 1 to 7 described above. It may furthermore be provided that the polymers preferably contain more than one of the structural elements from one group described above, i.e. comprise mixtures of structural elements selected from one group.

Particular preference is given, in particular, to polymers which, besides at least one structural element which has light-emitting properties (group 4), preferably at least one phosphorescent group, additionally contain at least one further structural element of groups 1 to 3, 5 or 6 described above, where these are preferably selected from groups 1 to 3.

The proportion of the various classes of groups, if present in the polymer, can be in broad ranges, where these are known to the person skilled in the art. Surprising advantages can be achieved if the proportion of one class present in a polymer, which is in each case selected from the structural elements of groups 1 to 7 described above, is preferably in each case > 5 mol%, particularly preferably in each case > 10 mol%.

The preparation of white-emitting copolymers is described in detail, inter alia, in DE 10343606 A1 . In order to improve the solubility, the polymers may contain corresponding groups. It may preferably be provided that the polymers contain substituents, so that on average at least 2 non- aromatic carbon atoms, particularly preferably at least 4 and especially preferably at least 8 non-aromatic carbon atoms are present per recurring unit, where the average relates to the number average. Individual carbon atoms here may be replaced, for example, by O or S. However, it is possible for a certain proportion, optionally all recurring units, to contain no substituents which contain non-aromatic carbon atoms. Short-chain substituents are preferred here, since long-chain substituents can have adverse effects on layers which can be obtained using organic functional materials. The substituents preferably contain at most 12 carbon atoms, preferably at most 8 carbon atoms and particularly preferably at most 6 carbon atoms in a linear chain.

The polymer employed in accordance with the invention as organic semiconducting material can be a random, alternating or

regioregular copolymer, a block copolymer or a combination of these copolymer forms.

In a further embodiment, the polymer employed as organic semiconducting material can be a non-conjugated polymer having side chains, where this embodiment is particularly important for phosphorescent OLEDs based on polymers. In general,

phosphorescent polymers can be obtained by free-radical copolymerisation of vinyl compounds, where these vinyl compounds contain at least one unit having a phosphorescent emitter and/or at least one charge-transport unit, as is disclosed, inter alia, in US

7250226 B2. Further phosphorescent polymers are described, inter alia, in JP 2007/21 1243 A2, JP 2007/197574 A2, US 7250226 B2 and JP 2007/059939 A.

In a further preferred embodiment, the non-conjugated polymers contain backbone units, which are connected to one another by spacer units. Examples of such triplet emitters which are based on non-conjugated polymers based on backbone units are disclosed, for example, in DE 102009023154. In a further preferred embodiment, the non-conjugated polymer can be designed as fluorescent emitter. Preferred fluorescent emitters which are based on non-conjugated polymers having side chains contain anthracene or benzanthracene groups or derivatives of these groups in the side chain, where these polymers are disclosed, for example, in JP 2005/108556, JP 2005/285661 and

JP 2003/338375.

These polymers can frequently be employed as electron- or hole- transport materials, where these polymers are preferably designed as non-conjugated polymers.

Furthermore, the organic semiconducting materials in the

formulations preferably have, in the case of polymeric organic semiconducting materials, a molecular weight M _w of > 10,000 g/mol, particularly preferably > 20,000 g/mol and especially preferably > 50,000 g/mol.

The molecular weight M _w of the polymers here is preferably in the range from 10,000 to 2,000,000 g/mol, particularly preferably in the range from 20,000 to 1 ,000,000 g/mol and very particularly preferably in the range from 50,000 to 300,000 g/mol. The molecular weight M _w is determined by means of GPC (= gel permeation chromatography) against an internal polystyrene standard.

The publications cited above for description of the semiconducting compounds are incorporated into the present application by way of reference for disclosure purposes.

The formulations according to the invention may comprise all organic semiconducting materials which are necessary for the production of the respective functional layer of the electronic device. If, for example, a hole-transport, hole-injection, electron-transport or electron-injection layer is built up precisely from one functional compound, the formulation comprises precisely this compound as organic semiconducting material. If an emission layer comprises, for example, an emitter in combination with a matrix or host material, the formulation comprises, as organic semiconducting material, precisely the mixture of emitter and matrix or host material, as described in greater detail elsewhere in the present application. Besides the said components, the formulation according to the invention may comprise further additives and processing assistants. These include, inter alia, surface-active substances (surfactants), lubricants and greases, additives which modify the viscosity, additives which increase the conductivity, dispersants,

hydrophobicising agents, adhesion promoters, flow improvers, antifoams, deaerating agents, diluents, which may be reactive or unreactive, fillers, assistants, processing assistants, dyes, pigments, stabilisers, sensitisers, nanoparticles and inhibitors. It is further preferred that the solution contains at least two or more solvents to control the drying and fluid properties of the solution. The second or more solvents used should provide good solubility to the materials of the layer to be printed or a blend of solvents with similar boiling points. If the solubility is not good, then the film will have a tendency to crystallize instead of forming an even

homogenous film.

It is also possible to further include a small quantity of a polymer in order to enhance the film formation without a affecting the device performance. Addition of surfactants or volatile surfactants to the ink at a level that does not impair the device performance is also possible. Furthermore, film formers can be added to the solution.

The solution may be a hot-melt type, i.e. a liquid at printing

temperature with a viscosity of lower than 5 cP at 10°C above the melting point of the solvent, but solid at room temperature.

The solvent must be capable of being evaporated or sublimed at atmospheric pressure or reduced pressure (down to 10 ^"7 torr) with heat up to 200°C as required to leave essentially no solvent residue.

In the following, several exemplary solvents are listed which are usable for the solution of the present invention. However, also WO 201 1/076325 A1 and the other prior art documents list possible solvents usable for the solution, as long as the solution has a resulting viscosity of 5 cP or lower.

Solvent Bp [°C] VP at 25°C RER

Methyl benzoate 200 0.353 2.036 o-Ethylphenol 200 0.196 1 .132

1 -Methyl-2-lsobutylbenzene 201 0.833 6.682

Pentylbenzene 204 0.297 2.362

1 -Ethyl-3-Propylbenzene 204 0.307 2.433

1 ,2-Dimethyl-3-Propylbenzene 204 0.316 2.492 Isopinocamphone 206 0.25 1 .822 p-n-Butyltoluene 207 0.289 2.298

1 ,2,3-Trimethyl-4-Ethylbenzene 208 0.334 2.591

1 ,2,4-Trinnethyl-3-Ethylbenzene 208 0.334 2.591

Butylphenylether 209 0.202 1 .519

Cyclohexylethylalcohol 21 1 0.044 0.282

Ethyl benzoate 213 0.168 1 .1 17

Pentamethylbenzene 213 0.176 1 .344

Terpineol 214 0.051 0.39 a-Terpineol 217 0.018 0.133

1 ,2,3-Triethylbenzene 220 0.1 19 1 .025

2,3-Dimethoxytoluene 223 0.083 0.563

Hexylbenzene 224 0.093 0.81 1

Pentylphenylether 227 0.065 0.535

Benzylacetone 234 0.035 0.243

2-Decalinol 234 0.009 0.069

Isobutyl benzoate 236 0.04 0.33

Bicyclohexyl 239 0.068 0.592

Cyclohexyl benzene 240 0.066 0.516

2,3-Diethylphenol 241 0.01 1 0.08

Methyl Cinnamate 241 0.015 0.106

Methyl (E)-Cinnamate 241 0.015 0.106

Heptylbenzene 241 0.031 0.29

Valerophenone 243 0.029 0.223

N-N-Butyl Pyrrolidone 244 0.007 0.048

Ethyl Hydrocinnamate 244 0.012 0.099

Para-lsopropyl Acetophenone 245 0.026 0.2

3-Phenylpropylacetate 247 0.009 0.07

1 -Phenyl-2-Pentanol 250 0.002 0.016

Butyl benzoate 250 0.006 0.3

Isopentyl benzoate 252 0.01 1 0.098 3-Phenyl-4-Pentenal 252 0.014 0.102

1 -Ethylnaphthalene 253 0.019 0.136

Benzylvalerate 254 0.006 0.056

2-Methylbutylbenzoate 254 0.01 1 0.095

1 , 2, 3,4-Tetraethyl benzene 256 0.017 0.174

1 ,2, 3, 5-Tetraethyl benzene 256 0.017 0.174

1 ,2,4, 5-Tetraethyl benzene 256 0.017 0.174

1 ,1 ,3,3,5-Pentannethylindan 257 0.03 0.281

Amylbenzoate 259 0.008 0.075

Isoamylphenylacetate 262 0.002 0.022

1 ,2-Dimethylnaphthalene 263 0.012 0.087

Dicyclohexylmethane 264 0.017 0.162

Isopropylcinnamate 265 0.003 0.022

Octylbenzene 265 0.009 0.094

1 -Butyl-[1 ,2,3,4-

267 0.01 0.094 Tetrahydronaphthalene]

2-lsopropylnaphthalene 268 0.009 0.073

Benzylhexanoate 269 0.002 0.018

Ethylcinnamate 271 0.002 0.019

2-Cyclohexylcyclohexanone 272 0.007 0.063

1 -Propylnaphthalene 273 0.006 0.049

3-Phenoxytoluene 273 0.001 0.01

2,2,5,7-Tetrannethyltetraline 274 0.012 0.1 12

Hexylbenzoate 276 0.002 0.021

Cyclododecanone 277 0.007 0.066

Nonylbenzene 280 0.003 0.032

3-Benzyl-4-Heptanone 282 0.001 0.01

Benzylheptanoate 284 0.001 0.006

1 -Sec-Butylnaphthalene 287 0.003 0.023

Heptylbenzoate 291 0.001 0.006

Isopropylquinoline 292 0.002 0.014 1 -Butylnaphthalene 292 0.002 0.02

Pentaethyl benzene 293 0.001 0.009

Decylbenzene 294 0.001 0.01 1

Benzyloctanoate 299 0.001 0.002

2,6-Diethylnaphthalene 299 0.004 0.037

Bp = Boiling point; VP = Vapor Pressure; RER = Relative Evaporation Rate

The invention will now be described in more detail by reference to the following examples, which are illustrative only and do not limit the scope of the present invention.

Working Examples

Example 1

A printing ink was prepared by the following procedure.

0.10 g of a hole-transport polymer HTM-001 was weighted into a glass vial. To this 20 ml of mesitylene was added. A small magnetic stirrer bar was added and the glass vial was sealed. This was warmed to 35 to 40°C and stirred for 2 hours to ensure complete dissolution of the solid materials. After dissolving the lid was removed and helium was bubbled through for 20 minutes in order to de-gas, after this the container was placed in a vacuum desicator and left overnight to remove the Helium.

Structure of the hole-transport polymer HTM-001

5 ml of the ink was filtered using a 0.45 μ filter (25 mm diameter ex Millipore) into the ink reservoir on the Pixdro LP50 and then purged through the Fujifilm SQ print-head.

A further 10 ml of ink was filtered and placed in the ink reservoir. A full ink jet test was performed to assess the print performance of the ink, ink-jet behaviour was observed and commented on. Ink-jet waveform was optimised, and the effects of changing the

voltage/frequency and pulse width on droplet velocity were also assessed. Using a standard waveform 1 or 2 drops could easily be obtained, by further manipulation it was also possible to obtain many droplets.

Print-head: Fujifilm Dimatix SQ

Drop volume: 10 pi drop volume

Drop Diameter: -27 μ

Temperature: 25°C

Formulation: 0.5% HTM-001 in Mesitylene

Viscosity: 0.975 cp @ 20°C

Pixel width: 23 μ

Bank Width: 5 μ

The viscosity is determined at a temperature of 25°C by measuring on AR-G2 rheometer manufactured by TA Instruments. This measurement can be done over a shear range of 10 to 1000 s ^"1 using 40 mm parallel plate geometry.

Printing single drops

Figure 2 shows the optimised waveform and resultant drops for single drop printing. Delay on this image was 200 ps, so the drop velocity is around 2 m s ^"1 .

After initial alignment was performed, the print with single drops is shown in Figure 3. In this case the alignment is good, with the drops placed in the centers of the channels. Overspill is evident in every case.

It was concluded that using single 10 pi drops, it is not possible to print single channels and overspill will always be present. Example 2

Printing 2 drops

An ink was prepared in the manner as described in Example 1 . The print parameters used were very standard with both the initial rise and fall being the same time duration. As can be seen two approximately even sized drops are formed.

Figure 4 shows the optimised waveform and resulting drop formation for printing two drops. The strobe delay was 200 ps, so the speed of the faster drop was around 3 m s ^"1 .

Figure 5 shows the result of the prints using double drops. Again it can be seen that it is not possible to obtain single channel printing.

These will have a drop volume of 4 to 6 pi resulting in a diameter of approximately 20 to 23 microns, this is extremely close to the size of the channel that is being printed into. It is therefore not surprising that these drops did not land within the confines of one pixel width, in addition the accuracy of the printer is +/- 5 micron so any slight deviation from printing along the center line could mean that the position of the ink is in the neighbouring channel.

Example 3

Printing many drops

The final test is to print many drops. When examining the effect of the print parameters on the drop formation it was observed that under certain conditions a relatively stable string of drops was formed of similar sizes. The print parameters were optimised to give as many small drops as possible, with the furthest separation. Figure 6 shows the waveform and resultant droplet formation of obtaining many drops.

Figure 6 shows that a string of drops of approximately equal size can be achieved. In this case there are 7 discrete drops. The volume of these drops should be around 1 .45 pi, with a diameter of around 14 urn. This is now significantly smaller than the channel.

Example 7 shows that it is possible to achieve printing using multiple drops, in this case 7 drops.

This clearly shows that by modifying the waveform it is possible to obtain multiple drops and therefore obtain successful printing.