FIELD

The present disclosure relates to electroactive materials such as hole transport materials (HTMs) for use in solar cells, for example solid state organic/hybrid solar cells such as solid state perovskite solar cells. The present disclosure also relates to dye sensitized solar cells and bulk heterojunction solar cells comprising HTMs. The present disclosure also relates to printing compositions comprising HTMs, such as printing ink formulations, and methods of manufacturing solar cells comprising roll-to- roll processes involving printing or coating of the compositions.

BACKGROUND

Solar cells are commonly made from various silicon based semi-conductors providing p-n type junctions; although in the last 20 years there has been extensive development in providing a range of new types of solar cells including dye-sensitized solar cells (DSSC), quantum dot solar cells (QDSCs), organic polymer solar cells (OPSCs) and perovskite solar cells (PSCs).

Perovskite solar cells (PSCs) are the most recent developments in the solar cell area, and perovskite materials were first used in solar cells in 2009 (Miyasaka et al "Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells". JACS 131 (17): 6050-6051 ). In typical PSCs, both electron transporting materials (ETMs) and hole transporting materials (HTMs) are necessary.

ETMs allow many types of conductive metal oxides in order to transport electrons, such as mesoporous Ti0 ₂ layer (Lee et al, "Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites", 4 October 2012, Science 338 (6107): 643-647), as well as planar ZnO layer (Kelly et al, "Perovskite solar cells with a planar heterojunction structure prepared using room-temperature solution processing techniques", 22 December 2013, Nature Photonics 8, 133-138). Whereas HTMs, commonly spiro-OMeTAD, have also been used in the PSCs which demonstrated over 10% efficiencies by using the 'sensitized' Ti0 ₂ architecture with solid-state hole transport material of spiro-OMeTAD, although higher efficiencies, above 10%, have been attained by replacing the Ti0 ₂ scaffold with an inert scaffold.

Hole transport materials (HTMs) provide one of many types of electroactive materials commonly used in various types of solar cells and other photovoltaic devices to facilitate the transport of holes toward the cathode by acting as electron donors to assist flow of electrons toward the anode originating from a UV absorber material. There are a large variety of HTMs used in OLEDs, other types of organic solar cells and photovoltaic devices, including triphenylene-fused triazatruxene derivatives, triphenylam ine derivatives, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, vinyl naphthalene derivatives, poly(copper phthalocyanine) , molybdenum trioxide, nickel oxide, copper thiocyanate and tungsten trioxide based materials.

However, even with the numerous candidates for HTMs available, they still present various problems in the operation of solar cells including providing incomplete pore filling of sensitized solar cells, oxidation problems, and unpredictable low hole mobility. Furthermore, identifying suitable HTMs for use in sensitized PSCs is particularly problematic and difficult, since in comparison to HTMs suitable for OLEDs or other types of organic solar cells and other photovoltaic devices, PSCs have relatively narrow bandgap requirements. Many HTMs that are suitable for OLEDs or other types of organic solar cells and photovoltaic devices, which might have been considered suitable for PSCs even after considering the narrow band gap

requirements, in practice are not suitable. For OLEDs or other types of organic solar cells and photovoltaic devices, there are thousands of light emitting materials/UV absorbing materials available, each with different HOMO levels, so it is less problematic to find a suitable HTM for a corresponding emitting layer in an OLED. As a result, this accounts for the wide variety of HTMs available for use in conventional OLED, or other types of organic solar cells and photovoltaic device development

It is therefore a difficult task to identify appropriate HTMs that can provide a suitable HOMO for matching bandgap requirements of perovskite absorbers, and that also provide other properties suitable for use in the manufacture and operation of solar cell devices, such as suitable pore filling and hole mobility properties whilst being suitably resilient to any problematic oxidation.

In addition , laboratory scale fabrication techniques such as spin coating processes have been used to achieve the flatness and uniform ity required from thin film solar cells, such as organic solar cells and PSCs. However, large scale industrial manufacture of solar cells also requires different fabrication techniques, and laboratory scale fabrication techniques such as spin coating processes are not cost-effective. Large industrial scale fabrication processes, such roll-to-roll processing and printing techniques, require HTMs with particularly suitable properties that allow them to be incorporated into formulations for application across a broader processing window while still providing appropriate mechanical (e.g. flatness and uniformity) and charge transport properties in the solar cell devices.

Accordingly, there is a need for identifying HTMs, electron donor or p-type semiconductor compounds, which can be used in sensitized solar cell devices, such as solid state perovskite sensitized solar cells (PSSC), and possess mechanical and charge transport properties that are suitable for industrial scale fabrication of solar cells.

SUMMARY

The present inventors have identified a selection of compounds that are surprisingly advantageous for use in solar cells as hole transport, electron donor or p- type semiconductor compounds or materials (HTMs), and in particular for solid state sensitized solar cells such as solid state perovskite sensitized solar cells (PSSC). The compounds according to at least some embodiments as described herein can also provide mechanical and charge transport properties suitable for industrial scale based fabrication of solar cells, for example printing and roll-to-roll processing techniques. There is also provided printing compositions comprising the HTMs and methods of manufacturing solar cells comprising roll-to-roll processing and application of the compositions onto a layered solar cell substrate.

In one aspect, there is provided a solar cell comprising:

a first electrode;

a second electrode; and

one or more electroactive layer(s) in electrical connection with the first and second electrodes, wherein at least one electroactive layer comprises a photoactive sensitizer material and at least one electroactive layer comprises a hole transport material, the hole transport material comprising a compound according to Formula 1 :

A ⁸ A ² A ³ A ⁵

Formula 1

wherein

T _c is selected from Ge, C=C, CH-CH, N-N, C=C-CH, CH-O-CH, CH-S-CH, CH- S(0)-CH, CH-S(0) ₂ -CH, CH-C=C-CH, CH-C≡C-CH;

A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are each independently selected from hydrogen or a diphenylamine group of -N(phenyl) ₂ , providing at least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are independently selected from the diphenylamine group, and wherein the diphenylamine group is substituted with one or more electron donating groups selected from d- ₅ alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , and R ¹ and R ² are each independently selected from hydrogen, C _{1 -5} alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, wherein each alkyl, alkenyl, alkynyl and phenyl is optionally substituted; and

X ¹ and X ² are each independently absent to represent a single covalent bond between two phenyl rings or are each independently selected from O and S.

In some embodiments, T _c may be selected from Ge, C=C, CH-CH, N-N, or CH-

O-CH. T _c may be selected from C=C or N-N. T _c may be selected from C=C.

Each phenyl group of each diphenylamine may be substituted with one or more electron donating groups selected from Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and Ci- ₅ alkyl. The electron donating group may be OC^alkyl, for example OCH ₃ . The electron donating group may be located at the ortho and/or para positions of the phenyl group. The electron donating group may be located at the para position of each phenyl group.

At least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be independently selected from the same diphenylamine group. For example, four of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be independently selected from the same diphenylamine group. In an embodiment, at least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. For example, the compound of Formula 1 may have one or more axis of symmetry. One advantage of symmetry can be to facilitate synthesis of the compounds. In another embodiment, at least one of A ¹ , A ² , A ⁷ , and A ⁸ , and at least one of A ³ , A ⁴ , A ⁵ , and A ⁶ , are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. In another embodiment, at least one of A ¹ and A ² , and at least one of A ³ and A ⁴ are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. . In another embodiment, both A ¹ and A ² , and both A ³ and A ⁴ are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. In another embodiment, two of A ¹ , A ² , A ⁷ , and A ⁸ , and two of A ³ , A ⁴ , A ⁵ , and A ⁶ , may be independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical.

A ¹ , A ² , A ³ , and A ⁴ , may be each selected from hydrogen and A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be each selected from the diphenylamine group as described above. A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be each selected from hydrogen and A ¹ , A ² , A ³ , and A ⁴ , may be each selected from the diphenylamine group as described above.

It will be appreciated that the solar cell is a photoactive optoelectronic device that can generate an electrical current in response to electromagnetic radiation. The solar cell may be a solid state sensitized solar cell. The solid state sensitized solar cell may be a solid state perovskite sensitized solar cell (PSSC).

The one or more one electroactive layers may comprise or consist of a layer comprising a photoactive sensitizer material and a hole transport material. The hole transport material comprises a compound of Formula 1 as described herein. The one or more electroactive layers may comprise an electroactive layer comprising a hole blocking, electron transport or n-type semiconductor material. It will be appreciated that at least one electrode is transparent, for example a transparent conducting support layer. The photoactive sensitizer material may be a perovskite material.

In another aspect, there is provided a compound according to Formula 1 :

Formula 1 wherein

T _c is selected from Ge, C=C, CH-CH, N-N, C=C-CH, CH-O-CH, CH-S-CH, CH- S(0)-CH, CH-S(0) ₂ -CH, CH-C=C-CH, CH-C≡C-CH;

A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are each independently selected from hydrogen or a diphenylamine group of -N(phenyl) ₂ , providing at least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are independently selected from the diphenylamine group, and wherein the diphenylamine group is substituted with one or more electron donating groups selected from Ci _-5 alkyl, C ₂ - ₅ alkenyl, C ₂ - ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , and R ¹ and R ² are each independently selected from hydrogen, C _{1 -5} alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and each alkyl, alkenyl, alkynyl and phenyl is optionally substituted; and

X ¹ and X ² are each independently absent to represent a single covalent bond between two phenyl rings or are each independently selected from O and S.

In some embodiments, T _c may be selected from Ge, C=C, CH-CH, N-N, or CH- O-CH. T _c may be selected from C=C or N-N. T _c may be selected from C=C.

Each phenyl group of each diphenylamine may be substituted with one or more electron donating groups selected from d- ₅ alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and C _h alky!. The electron donating group may be OCi- ₅ alkyl. The electron donating group may be OCH ₃ . The electron donating groups may be located at the ortho and/or para positions of the phenyl group. The electron donating group may be located at the para position of each phenyl group.

At least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be independently selected from the same diphenylamine group. For example, four of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be independently selected from the same diphenylamine group. In an embodiment, at least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. For example, the compound of Formula 1 may have one or more axis of symmetry. One advantage of symmetry can be to facilitate synthesis of the compounds. In another embodiment, at least one of A ¹ , A ² , A ⁷ , and A ⁸ , and at least one of A ³ , A ⁴ , A ⁵ , and A ⁶ , are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. In another embodiment, at least one of A ¹ and A ² , and at least one of A ³ and A ⁴ are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. . In another embodiment, both A ¹ and A ² , and both A ³ and A ⁴ are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. In another embodiment, two of A ¹ , A ² , A ⁷ , and A ⁸ , and two of A ³ , A ⁴ , A ⁵ , and A ⁶ , may be independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical.

A ¹ , A ² , A ³ , and A ⁴ , may be each selected from hydrogen and A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be each selected from the diphenylamine group as described above. A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be each selected from hydrogen and A ¹ , A ² , A ³ , and A ⁴ , may be each selected from the diphenylamine group as described above.

The solar cell as described above may be a printed solar cell sheet. The sheet may be a flexible sheet comprising a flexible substrate (e.g. PET). The sheet may be a continuous roll-to-roll sheet. The printed solar cell sheet may comprise a substrate sheet, a first electrode, an electron transport layer, a photoactive sensitizer layer, a hole transport layer comprising a compound of Formula 1 as described herein, and a second electrode. The photoactive sensitizer layer may be a perovskite layer.

In another aspect, there is provided an electroactive layer comprising a photoactive sensitizer material and a hole transport material, the hole transport material comprising a compound according to Formula 1 as described herein. The photoactive sensitizer material may be a perovskite material. It will be appreciated that the perovskite material and hole transport material provide a heterojunction for use in a solar cell such as a PSSC. The light absorbing electroactive layer may be provided on a support layer, such as transparent conducting support that may be optionally coated with a hole blocking, electron transport or n-type semiconductor material.

In another aspect, there is provided a printing composition comprising a solvent and a compound of Formula 1 as described herein.

The printing composition may be formulated for a roll-to-roll fabrication process. The printing composition may be a printing ink formulation. The printing composition may be formulated for application from a slot-die printing or coating apparatus.

The printing composition may be formulated to achieve a predetermined thickness as a printed thin film, for example having a printed thin film thickness of between 0.1 μιη and 1000 μιη, 1 μιη and 500 μιη, or between 10 μιη and 200 μιη.

The solvent may be an organic solvent. The organic solvent may be selected from a hydrocarbon, halogenated hydrocarbon, ether, ketone, alcohol, nitrile, ester, carbonate, and mixtures thereof. The organic solvent may be selected from benzene, o-xylene, toluene, diethyl ether, tetrahydrofuran, diphenyl ether, anisole,

dimethoxybenzene, methylene chloride, chloroform, chlorobenzene, acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, ethanol, propanol, isopropanol, n-butyl alcohol, tert-butyl alcohol, acetonitrile, propionitrile, benzonitrile, ethyl acetate, butyl acetate, ethylene carbonate, propylene carbonate, and mixtures thereof. The organic solvent may be selected from benzene, o-xylene, toluene, methylene chloride, chloroform, chlorobenzene, and mixtures thereof.

The compositions may comprise one or more additives, such as a dopant, electrolyte, binder, polymer, rheological modifier, surfactant, or mixtures thereof. An additive may be a polymer, for example poly(thiophenes) and poly(phenylene vinylenes). An additive may be an electrolyte, for example

bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine.

In another aspect, there is provided a method of manufacturing a hole transport layer on a layered solar cell sheet comprising a step of printing a hole transport composition comprising a solvent and a compound of Formula 1 as described herein onto a photoactive sensitizer layer of the layered solar cell sheet to form a hole transport layer thereon. The step of printing may involve a slot die printer.

In another aspect, there is provided a method of manufacturing a solar cell may comprise the steps of:

providing a layered solar cell sheet comprising a substrate sheet, a first electrode layer, optionally an electron transport layer, and a photoactive sensitizer layer;

printing a hole transport composition comprising a solvent and a compound of

Formula 1 as described herein onto the photoactive sensitizer layer of the layered solar cell sheet to form a hole transport layer; and

providing a second electrode on the hole transport layer to form the solar cell. The printing may be slot die printing.

In another aspect, there is provided a method of manufacturing a hole transport layer on a layered solar cell sheet by roll-to-roll processing comprising a step of printing a hole transport composition comprising a solvent and a compound of Formula 1 as described herein onto a photoactive sensitizer layer of the layered solar cell sheet to form a hole transport layer thereon. The step of printing may involve a slot die printer. In another aspect, there is provided a method of manufacturing one or more layers of a solar cell may comprise the steps of:

providing a layered solar cell sheet comprising a substrate sheet, a first electrode layer, optionally an electron transport layer, and a photoactive sensitizer layer;

delivering the layered solar cell sheet through a roll-to-roll fabrication process that comprises applying to the photoactive sensitizer layer of the layered solar cell sheet, a hole transport layer composition comprising a solvent and a compound of Formula 1 as described herein to form a hole transport layer on the layered solar cell sheet; and

providing a second electrode on the hole transport layer to form the solar cell. The solar cell may be a solid state sensitized solar cell. The photoactive sensitizer layer may comprise or consist of a perovskite material to provide a solid state perovskite sensitized solar cell (PSSC).

Applying the hole transport layer composition to the layered solar cell sheet may comprise a printing or coating technique, for example a slot-die printer configured for cooperation with the roll-to-roll fabrication process. The roll-to-roll fabrication process may comprise a slot-die printer for applying the composition to the sheet.

One or more other layers of the solar cell may be applied to the substrate in the roll-to-roll fabrication process. For example, the layered solar cell sheet may comprise a substrate layer and a first electrode layer, and prior to formation of the hole transport layer, an optional electron transport layer and a photoactive sensitizer layer may be sequentially applied onto the layered solar cell sheet in the roll-to-roll fabrication process. The roll-to-roll fabrication process may comprise further heating or sintering steps. The photoactive sensitizer layer may be formed in situ on the solar cell sheet during the fabrication process. One or more layers may be thermally annealed.

In another aspect, there is provided use of a compound of Formula 1 as described herein as a hole transport material for a solar cell. The solar cell may be a solid state sensitized solar cell. The solid state sensitized solar cell may be a solid state perovskite sensitized solar cell (PSSC).

In another aspect, there is provided a hole transport material for a solar cell comprising a compound of Formula 1 as described herein. The solar cell may be a solid state sensitized solar cell. The solid state sensitized solar cell may be a solid state perovskite sensitized solar cell (PSSC).

In another aspect, there is provided a compound of Formula 1 as described herein for use as a hole transport material for a solar cell. The solar cell may be a solid state sensitized solar cell. The solid state sensitized solar cell may be a solid state perovskite sensitized solar cell (PSSC). BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present disclosure will now be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a general bilayer heterojunction configuration of a perovskite solar cell device according to one embodiment of the present disclosure;

Figure 2 shows a general meso-superstructured heterojunction configuration of a perovskite solar cell device according to one embodiment of the present disclosure, wherein an electroactive layer comprises hole transport material encompassing a perovskite coated scaffold material, which is in connection with the electron transport layer;

Figure 3 shows a general mesoscopic heterojunction configuration of a perovskite solar cell device according to one embodiment of the present disclosure, providing a modified bilayer type configuration comprising a first electroactive layer comprising a hole transport material and a second electroactive layer comprising perovskite coated scaffold material, which is in connection with the electron transport layer;

Figure 4 shows a cyclic voltammogram of Compound 1 as described herein compared to Spiro-OMe-TAD;

Figures 5a and 5b show a photoelectron spectrum in air (PESA) of Compound 1 compared to Spiro-OMe-TAD, respectively;

Figures 6a to 6c show various arrangements of roll-to-roll processes configured with one or more slot die apparatus;

Figure 7 shows an arrangement of layering in a perovskite solar cell; and Figure 8 shows the performance of current density vs voltage of a perovskite solar cell comprising Compound 1 as described herein.

DETAILED DESCRIPTION

The present disclosure is described in the following various non-limiting embodiments, which relate to investigations undertaken to identify organic compounds for advantageous use as hole transport, electron donor or p-type semiconductor materials for solid state sensitized solar cells, for example perovskite sensitized solar cells (PSSC). It was surprisingly found that a range of organic compounds are useful as hole transport materials in solid state sensitized solar cells, and in particular for perovskite sensitized solar cells (PSSC), and possess mechanical and charge transport properties that are suitable for large industrial scale based fabrication of solar cells, such as printing or roll-to-roll fabrication processes.

GENERAL TERMS

The term "electroactive material" refers to any electrically active material suitable for use in various types of solar cells. For example, electroactive materials may include photoactive sensitizer materials, hole transport materials, electron transport materials, and nanomaterials.

The terms "photoactive sensitizer material", "photoactive sensitizer", "sensitizer" or like term, refers to any material suitable for use in solar cells capable of absorbing electromagnetic radiation. For example, suitable photoactive sensitizer materials may include semiconductor materials, semiconductor nanomaterials, light absorbing dyes, and perovskite materials.

The term "photoactive sensitizer layer" refers to a layer comprising any one or more photoactive sensitizer materials.

The terms "hole transport", "hole transport material" or like term, refers to materials used in various types of solar cells to facilitate the transport of holes toward the cathode by acting as electron donors to assist flow of electrons toward the anode originating from a sensitizer material. The hole-transport material may also be referred to as an electron blocking material or p-type semiconductor.

The terms "electron transport", "electron transport material" or like term, refers to materials used in various types of solar cells to facilitate the transport of electrons toward the anode by acting as electron acceptors to assist flow of electrons toward the anode originating from a sensitizer material. The electron-transport material may also be referred to as a hole blocking material or n-type semiconductor. The term "scaffold" refers to any material suitable for use in a solar cell that is capable of providing a support surface, structure or medium for a photoactive sensitizer material. The scaffold may facilitate increasing the surface area of photoactive sensitizer material and electron transfer, such as transfer to the electron transport layer or anode. The scaffold material may be an electron transport material, for example titanium dioxide, or an insulating material for example aluminium oxide.

Throughout this specification, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e. one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. For example, reference to "a" includes a single as well as two or more; reference to "an" includes a single as well as two or more; reference to "the" includes a single as well as two or more and so forth.

Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.

Each example of the present disclosure described herein is to be applied mutatis mutandis to each and every other example unless specifically stated otherwise. The present disclosure is not to be limited in scope by the specific examples described herein, which are intended for the purpose of exemplification only. Functionally- equivalent products, compositions and methods are within the scope of the disclosure as described herein.

The term "and/or", e.g., "X and/or Y" shall be understood to mean either "X and Y" or "X or Y" and shall be taken to provide explicit support for both meanings or for either meaning.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents forms part of the common general knowledge in the art, in Australia or in any other country.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. SPECI FIC TERMS

"Aryl" whether used alone, or in compound words such as arylalkyl, aryloxy or arylthio, represents: (i) an optionally substituted mono- or polycyclic aromatic carbocyclic moiety, e.g., of about 6 to about 30 carbon atoms, such as phenyl, naphthyl or fluorenyl; or, (ii) an optionally substituted partially saturated polycyclic carbocyclic aromatic ring system in which an aryl and a cycloalkyl or cycloalkenyl group are fused together to form a cyclic structure such as a tetrahydronaphthyl, indenyl jndanyl or fluorene ring.

The term "optionally substituted" means that a group is either substituted or unsubstituted, at any available position. Substitution can be with one or more groups selected from, e.g., alkyl, alkenyl, alkynyl, aryl, alkanoyl, alkoxycarbonyl, alkoxy, aryloxy, alkanoate, aryloate, hydroxyl, halo, haloalkyi, haloary, and haloalkoxy. It will be appreciated that other groups not specifically described may also be used.

In addition to the disclosure herein, in a certain embodiment, a group that is substituted has 1 , 2, 3, or 4 substituents, 1 , 2, or 3 substituents, 1 or 2 substituents, or 1 substituent.

The term "halo" or "halogen" whether employed alone or in compound words such as haloalkyi or haloalkoxy represents fluorine, chlorine, bromine or iodine.

Further, when used in compound words such as haloalkyi or haloalkoxy, the alkyl may be partially halogenated or fully substituted with halogen atoms which may be independently the same or different. Examples of haloalkyi include, without limitation, - CH ₂ CH ₂ F, -CF ₂ CF ₃ and -CH ₂ CHFCI. Examples of haloalkoxy include, without limitation, -OCHF ₂ , -OCF ₃ , -OCH ₂ CCI ₃ , -OCH ₂ CF ₃ and -OCH ₂ CH ₂ CF ₃ .

"Alkyl" whether used alone, or in compound words such as alkoxy, alkylthio, alkylamino, dialkylamino or haloalkyi, represents straight or branched chain hydrocarbons ranging in size from one to about 10 carbon atoms, or more. Thus alkyl moieties include, unless explicitly limited to smaller groups, moieties ranging in size, for example, from one to about 5 carbon atoms or greater, such as, methyl, ethyl, n- propyl, iso-propyl and/or butyl, pentyl.

"Alkenyl" whether used alone, or in compound words such as alkenyloxy or haloalkenyl, represents straight or branched chain hydrocarbons containing at least one carbon-carbon double bond, including, unless explicitly limited to smaller groups, moieties ranging in size from two to about 10 carbon atoms or greater, such as, methylene, ethylene, 1 -propenyl, 2-propenyl, and/or butenyl, pentenyl.

"Alkynyl" whether used alone, or in compound words such as alkynyloxy, represents straight or branched chain hydrocarbons containing at least one carbon- carbon triple bond, including, unless explicitly limited to smaller groups, moieties ranging in size from, e.g., two to about 10 carbon atoms or greater, such as, ethynyl, 1 - propynyl, 2-propynyl, and/or butynyl, pentynyl.

"Hydroxyl" represents a -OH moiety.

"Alkoxy" represents an -O-alkyl group in which the alkyl group is as defined supra. Examples include methoxy, ethoxy, n-propoxy, iso-propoxy, and the different butoxy, pentoxy.

"Aryloxy" represents an -O-aryl group in which the aryl group is as defined supra. Examples include, without limitation, phenoxy and naphthoxy.

"Alkenyloxy" represents an -O-alkenyl group in which the alkenyl group is as defined supra. An example is allyloxy.

"Alkanoate" represents an -OC(=0)-R group in which R is an alkyl group as defined supra.

"Aryloate" represents a -OC(=0)-R group in which R is an aryl group as defined supra.

"Amino" represents an -NH ₂ moiety.

"Alkylamino" represents an -NHR or -NR ₂ group in which R is an alkyl group as defined supra. Examples include, without limitation, methylamino, ethylamino, n- propylamino, isopropylamino, and the different butylamino, pentylamino, hexylamino and higher isomers.

"Arylamino" represents an -NHR or -NR ₂ group in which R is an aryl group as defined supra. An example is phenylamino or diphenylamino.

"Carbonylamino" represents a carboxylic acid amide group -NHC(=0)R that is linked to the rest of the molecule through a nitrogen atom. "Alkylcarbonylamino" represents a -NHC(=0)R group in which R is an alkyl group as defined supra.

"Arylcarbonylamino" represents an -NHC(=0)R group in which R is an aryl group as defined supra.

In addition to the disclosure herein, the term "substituted," when used to modify a specified group or radical, can also mean that one or more hydrogen atoms of the specified group or radical are each, independently of one another, replaced with the same or different substituent groups as defined below.

SOLAR CELLS

Hole transport materials and compounds thereof as described herein can be advantageously used in solar cells, such as solid state sensitized solar cells, and associated photoactive optoelectronic devices incorporating such solar cells.

Solid state sensitized solar cells generally comprise a light absorbing electroactive material in electrical connection with a first and second electrode that comprises a heterojunction. The heterojunction may be provided by an interface between an electron donor material and an electron acceptor material. In a solid state perovskite solar cell the heterojunction may be provided by the interface between the perovskite material and a hole transport material or hole blocking material. It will be appreciated that in a photovoltaic device, an electroactive material is arranged such that the device generates an electrical current upon the absorption of the photons.

Solar cells may be prepared in the form of a bilayer heterojunction

configuration, a meso-superstructured hereojunction configuration or a mesoscopic heterojunction configuration.

The configuration of a bilayer heterojunction solar cell is shown in Figure 1 , where a bilayer heterojunction solar cell (1 ) may generally comprise an anode (2), for example as a transparent layer of indium tin oxide, covered by a transparent thin film support (3), and a cathode (7), for example in the form of an adjacent metal cathode. Between the anode and cathode are layers of an optional hole blocking material (4) (or electron transport material or n-conductor), a perovskite material (5), and a hole transport material (6) (or electron blocking material or p-conductor). The hole blocking material, if present, is located on the anode side of the cell or device, and the hole transport material is located on the cathode side of the device. The perovskite material may be provided as its own layer (Figure 1 ) or may be incorporated into a layer comprising a hole transport material (see Figure 2). It will be appreciated that the configuration provides a heterojunction where the perovskite material is at least insulated from one of the electrodes, typically by a region of hole transport material being located between the cathode and the perovskite material. The device may contain multiple layers, and the term "bilayer" should be interpreted as encompassing 2 or more layers.

Another configuration of the solar cell device is a meso superstructured heterojunction configuration shown in Figure 2, where a meso-superstructured solar cell (8) may generally comprise an anode (2), for example a transparent layer of indium tin oxide covered by a transparent thin film support (3), and a cathode (7), for example in the form of an adjacent metal cathode. An optional hole blocking material (4) (or electron transport material or n-conductor) may be provided on the anode. An active material comprising a hole transport material (6) (or electron blocking material or p- conductor) is typically provide on the cathode and may comprise perovskite material (5) on an suitable insulating scaffold material (9), for example Al ₂ 0 ₃ . The perovskite material may partially coat the scaffold material, which may provide an increased surface area of perovskite and/or facilitate electron transfer to the optional hole blocking material or anode. In some embodiments the electroactive layer comprises hole transport material encompassing a perovskite coated scaffold material, which is in connection with the electron transport layer.

Another configuration of the solar cell is a mesoscopic heterojunction configuration shown in Figure 3, where a mesoscopic solar cell (10) may generally comprise an anode (2), for example a transparent layer of indium tin oxide covered by a transparent thin film support (3), and a cathode (7), for example in the form of an adjacent metal cathode. An optional hole blocking material (4) (or electron transport material or n-conductor) may be provided on the anode. An active material comprising a hole transport material (6) (or electron blocking material or p-conductor) is typically provide on the cathode and may comprise perovskite material (5) on an suitable conducting scaffold material (1 1 ), for example Ti0 ₂ . In some embodiments there is provided a modified bilayer type configuration comprising a first electroactive layer comprising a hole transport material and a second electroactive layer comprising perovskite coated scaffold material, which is in connection with the electron transport layer.

The hole transport layer is typically configured to provide a region of hole transport material between the cathode and the perovskite material.

The above devices of Figures 1 -3 may be in the form of a single cell, or multiple cells connected in parallel and/or series. The device typically further comprises positive and negative terminals (not illustrated) for connection to an energy storage device or other electrical component(s) or circuit(s). The solar cell may comprise an electrode, on which a suitable scaffold material is preferably provided, wherein a perovskite layer may be provided on said scaffold material, and wherein a counter electrode, is provided in electrical contact with said perovskite layer. According to an embodiment, the anode, the scaffold structure, the perovskite layer and the cathode are present in this order from one side to the other of the solar cell. Protective electron and/or hole transport layers may or may not be present, for example at appropriate positions between the electrodes and the scaffold material and perovskite layer, respectively.

The electrode may be in the form of an anode, for example as a transparent layer of indium tin oxide or molybdenum oxide treated silver, covered by a transparent thin film support. "Transparent" means transparent to at least a part, or a major part of the visible light. The anode maybe substantially transparent to all wavelengths or types of visible light. Furthermore, the anode may be transparent to non-visible light, such as UV and IR radiation.

The anode may provide the support layer of the solar cell. The solar cell may be built on the anode. The support of the solar cell may be provided on the side of the counter electrode. The anode does not necessarily provide the support of the device, but may simply be or comprise a current collector, for example a metal foil. The anode may function and/or comprise a current collector, collecting the current obtained from the solar cell.

For example, the anode may comprise a material selected from indium doped tin oxide (ITO), fluorine doped tin oxide (FTO), ZnO-Ga ₂ 0 ₃ , ZnO-AI ₂ 0 ₃ , tin-oxide, antimony doped tin oxide (ATO), molybdenum oxide treated silver, SrGe0 ₃ and zinc oxide, which may be coated on a transparent substrate, such as plastic or glass. The plastic or glass may provide the support structure of the anode. Such support layers are generally known as conductive glass and conductive plastic, respectively, which may provide support layers for the anode. The anode may comprise a conducting transparent layer, which may be selected from conducting glass and from conducting plastic.

The current collector may be provided by a conductive metal foil, such as a titanium or zinc foil, for example. Non-transparent conductive materials may be used as current collectors in particular on the side of the device that is not exposed to the light to be captured by the device.

A surface-increasing scaffold material may be provided on the anode. The scaffold material may be nanostructured and/or nanoporous. The scaffold structure therefore may be structured on a nanoscale. The structures of the scaffold material may increase the effective surface compared to the surface of the anode. The scaffold material may be made from any one or combinations selected from of a large variety of different materials. The surface-increasing scaffold structure of the solar cell, active material layer and/or heterojunction may comprise or consist of a semiconductor material, a conducting material, a non-conducting material, or combinations thereof. Suitable scaffold materials are well known in the art. For example, the material of the scaffold may be selected from semiconducting materials, such as Si, Ti0 ₂ , Sn0 ₂ , Fe ₂ 0 ₃ , ZnO, W0 ₃ , Nb ₂ 0 ₅ , CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, CdTe, SrTi0 ₃ , GaP, InP, GaAs, CulnS ₂ , CulnSe ₂ , and combinations thereof. The semiconductor materials may be selected from Si, Ti0 ₂ , Sn0 ₂ , ZnO, W0 ₃ , Nb ₂ 0 ₅ and SrTi0 ₃ . The scaffold material may be made from a non-conducting and/or insulating material, for example plastics such as plastic nanoparticles by heating and/or cross-linking.

Where the scaffold material is made from and/or comprises a non-conducting material, an electrical connection between the following layer, for example the perovskite layer and the anode should be warranted. This may be achieved by allowing the perovskite layer being in direct contact with the anode. The scaffold structure may cover region of the conductive support surface. The scaffold material may also be coated with a layer of an electrically conducting and/or semiconducting material. The coating is sufficiently thin so as to substantially retain the original nanostructured and/or nanoporous structure of the scaffold material.

The scaffold structure may comprise and/or be prepared from nanoparticles, or nanosheets, which nanoparticleas and/or nanosheets may be further annealed. The nanoparticles may have dimensions and/or sizes in the range of 2 to 300 nm, 3 to 200 nm, 4 to 150 nm, or 5 to 100 nm. "Dimension" or "size" with respect to the

nanoparticles means here maximum extensions in any direction of space, including the diameter in case of substantially spherical or ellipsoid particles, or length and thickness in case of nanosheets. The size of the nanoparticles may be determined by transmission electron microscopy (TEM) and selected area electron diffraction (SAED).

The surface-increasing scaffold material may be nanostructured and/or nanoporous. The surface area per gram ratio of said scaffold material may be in the range of 20 to 200 m ² /g, 30 to 150 m ² /g, or 60 to 120 m ² /g. The surface per gram ratio may be determined via the BET gas adsorption method.

The scaffold material may form a continuous and/or complete, or, alternatively, a non-continuous and/or non-complete layer on said anode. The scaffold material may form a layer having a thickness selected from but not limited to 10 to 2000 nm, 15 to 1000 nm, 20 to 500 nm, 50 to 400 nm or 100 to 300 nm. For the purpose of this specification, a "continuous layer" or a "complete layer" is a layer that covers the anode completely so that there can be no contact between the perovskite layer and the anode. If the scaffold material is non-continuously and/or non-completely provided on said anode, the perovskite layer could get in direct contact with said anode or optional protective electron transport layer. A further layer may be provided between a, for example, non-continuous, scaffold layer and the anode, for example an optional protective electron transport layer as disclosed elsewhere in this specification. In this case, a direct contact of the perovskite layer and the anode is avoided.

The surface-increasing scaffold material may be provided on said anode. There may be one or more intermediate layers between the scaffold material and the conductive support. Such intermediate layers, if present, may be conducting and/or semiconducting.

The counter electrode may be in the form of a cathode, and may be in direct contact with the perovskite layer and/or not separated by any further layer or medium from the perovskite layer. A hole transport material or layer, as described herein, may be provided between the perovskite layer and the cathode. The hole transport layer may be provided by a compound of Formula 1 as described herein. If there are several perovskite layers, the hole transport layer may be provided between the outermost perovskite layer and the cathode. In other words, the cathode is either directly in contact with the (outermost) perovskite layer or with the hole transport layer towards the inside of the solar cell.

Schematically, the solar cell may comprise and/or consist of the following layers as shown in Figure 1 :

(2) anode and (3) transparent substrate

(4) optional electron transport material;

(5) perovskite layer(s);

(6) optional hole transport material;

(7) cathode

The above layer (5) may optionally include a scaffold material.

The method of preparing a solar cell may comprise a step of applying one or more organic-inorganic perovskite layers on anode, optional electron transport material or scaffold therein. The perovskite layer may be applied by any suitable process. The method may comprise, consist essentially of or consist of the steps of providing an anode, applying an optional inclusion of a protective electron transport material layer, on which an optional inclusion of a surface-increasing scaffold material is provided; applying one or more organic-inorganic perovskite layer on any one of the

aforementioned layers; applying a hole transport material layer, and, applying a counter electrode. These steps may be conducted in this order, with further or other steps being conducted before, after or within these steps without changing the order of the steps.

The counter electrode may be applied on the perovskite layer, or, if there are several such layers, on the outermost of said perovskite layers. The hole conducting material used may be provided between the outermost perovskite layer and the counter electrode. There may comprise the step of applying a counter electrode on the hole conductor layer.

In preparing a solar cell, single layers of the organic materials may be deposited sequentially, for example by thermal evaporation at reduced pressures (e.g. below 2x 10 ^"6 mbar). Organic layers may be dissolved in a solvent, such as an organic solvent for example chlorobenezene and 1 ,2-dichlorobenezene. Thin films can be further thermally annealed, for example at 120 for 1 0 minutes.

A layer of Ca can also be deposited by thermal evaporation at reduced pressures, for example below 2x 10 ^"7 mbar. A metal layer, such as an Al layer, can be deposited, for example by Angstrom Engineering evaporator at pressures below 2x 1 0 ^{" 7} mbar. The devices can be annealed, for example on a hotplate in a glovebox.

A small amount of silver paint (Silver Print II, GC electronics, Part no. : 22-023) can also be deposited onto the connection points of the electrodes. Completed devices can be encapsulated with glass and a UV-cured epoxy, for example by using Lens Bond type J-91 and exposing to 254nm UV-light inside a glovebox (H ₂ 0 and 0 ₂ levels both < 1 ppm) for 10 minutes.

In another configuration the structure of the device can be inverted and the device fabrication process can commence with a cathode and be completed by the addition of a top anode. In both configurations either or both electrodes may be transparent to the electromagnetic radiation, for example light, that is being detected.

PRINTED SOLAR CELL SHEETS

There is also provided a printed solar cell sheet comprising a compound of

Formula 1 as described herein. The sheet may be a flexible sheet comprising a flexible substrate (e.g. PET). The sheet may be a continuous roll-to-roll sheet.

The printed solar cell sheet may comprise a substrate sheet, a first electrode, an electron transport layer, a photoactive sensitizer layer, a hole transport layer comprising a compound of Formula 1 as described herein, and a second electrode.

The printed solar cell sheet may comprise a solar cell as described herein, for example a perovskite solar cell (PSC). The substrate sheet may be transparent film, for example glass or polyethylene terephthalate (e.g. flexible PET). The first electrode may for example comprise indium tin oxide (ITO). The electron transport layer may for example comprise ZnO. The photoactive sensitizer layer may be a perovskite layer.

HOLE TRANSPORT MATERIALS

Hole transport materials that can be used in the solar cells (or layers thereof) as described by the present disclosure may comprise or consist of one or more compounds of Formula 1 as described herein. It will be appreciated that other electroactive materials including various hole transport materials may be used in the solar cells, or layers thereof, as described by the present disclosure, either in separate layers or together with compounds of Formula 1 .

A compound of Formula 1 may be represented by:

Formula 1

wherein

T _c is selected from Si, Ge, C=C, CH-CH, N-N, C=C-CH, CH-O-CH, CH-S-CH, CH-S(0)-CH, CH-S(0) ₂ -CH, CH-C=C-CH, CH-C≡C-CH;

A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are each independently selected from hydrogen and a diphenylamine group of -N(phenyl) ₂ , wherein the diphenylamine group is substituted with an electron donating group selected from Ci _-5 alkyl, C ₂ - ₅ alkenyl, C ₂ . salkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , and wherein R ¹ and R ² are each independently selected from hydrogen, C _{1 -5} alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted; and

X ¹ and X ² are each independently absent to represent a single covalent bond between two phenyl rings or are each independently selected from O and S. A compound of Formul :

Formula 1

wherein

Tc is selected from Ge, C=C, CH-CH, N-N, C=C-CH, CH-O-CH, CH-S-CH, CH-

S(0)-CH, CH-S(0) ₂ -CH, CH-C=C-CH, CH-C≡C-CH;

A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are each independently selected from hydrogen or a diphenylamine group of -N(phenyl) ₂ , providing at least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are independently selected from the diphenylamine group, and wherein the diphenylamine group is substituted with one or more electron donating groups selected from Ci _-5 alkyl, C ₂ - ₅ alkenyl, C ₂ - ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , and R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, wherein each alkyl, alkenyl, alkynyl and phenyl is optionally substituted; and

X ¹ and X ² are each independently absent to represent a single covalent bond between two phenyl rings or are each independently selected from O and S.

In some embodiments, T _c may be selected from Ge, C=C, CH-CH, N-N, or CH- O-CH. T _c may be selected from C=C, CH-CH, or N-N. T _c may be selected from C=C or N-N. T _c may be selected from C=C.

The hole transport material may comprise a compound according to

Formula 1 a:

Formula 1 a

wherein X ¹ , X ² , A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be selected from or more embodiments as described herein for Formula 1 .

The hole transport material may comprise a compound according to Formula 1 a(i):

i o Formula 1 a(i)

wherein A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be selected from any one or more embodiments as described herein for Formula 1 .

At least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be independently selected from the same diphenylamine group. For example, four of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and 15 A ⁸ , may be independently selected from the same diphenylamine group. In an

embodiment, at least two of A ¹ , A ² , A ³ , A ⁴ , A ⁵ , A ⁶ , A ⁷ , and A ⁸ , are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. For example, the compound of Formula 1 may have one or more axis of symmetry. One advantage of symmetry can be to facilitate synthesis of 20 the compounds. In another embodiment, at least one of A ¹ , A ² , A ⁷ , and A ⁸ , and at least one of A ³ , A ⁴ , A ⁵ , and A ⁶ , are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. In another embodiment, at least one of A ¹ and A ² , and at least one of A ³ and A ⁴ are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. . In another embodiment, both A ¹ and A ² , and both A ³ and A ⁴ are independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical. In another embodiment, two of A ¹ , A ² , A ⁷ , and A ⁸ , and two of A ³ , A ⁴ , A ⁵ , and A ⁶ , may be independently selected from the same diphenylamine group such that the compound according to Formula 1 is symmetrical.

In relation to further embodiments of the diphenylamine group, one or more electron donating groups may be located at the ortho and/or para positions of the phenyl group. An electron donating group may be located at the para position of each phenyl group. It will be appreciated that the "ortho" and "para" terminology is relative to the nitrogen atom of the diphenylamine group. Each phenyl group of each

diphenylamine may be substituted with an electron donating group selected from Ci_ ₅ alkyl, C ₂ - ₅ alkenyl, C ₂ - ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, C^alkyl, C ₂ - ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from d_ ₅ alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, C^alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from d_ ₅ alkyl, OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and C _h alky!. The electron donating group may be selected from OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and Ci_ ₅ alkyl. The electron donating group may be OC^salkyl. The electron donating group may be OCH ₃ .

A ¹ , A ² , A ³ , and A ⁴ , may be each selected from hydrogen and A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be each selected from the diphenylamine group of -N(phenyl) ₂ , wherein the diphenylamine group is substituted with an electron donating group selected from Ci_ ₅ alkyl, C ₂ _ ₅ alkenyl, C ₂ _ ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , and wherein R ¹ and R ² are each independently selected from hydrogen, d-salkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. Each phenyl group of each diphenylamine may be substituted with an electron donating group selected from C _{1 -5} alkyl, C ₂ _ ₅ alkenyl, C ₂ _ salkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ - ₅ alkenyl, C ₂ - ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from C _{1 -5} alkyl, C ₂ . ₅ alkenyl, C ₂ _ ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from C _{1 -5} alkyl, OR ¹ or

NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and ₅ alkyl. The electron donating group may be selected from OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and C^alkyl. The electron donating group may be OCi _-5 alkyl. The electron donating group may be OCH ₃ . The electron donating group may be substituted at the ortho and/or para positions of the phenyl group. The electron donating group may be substituted at the para position of the phenyl group.

A ⁵ , A ⁶ , A ⁷ , and A ⁸ , may be each selected from hydrogen and A ¹ , A ² , A ³ , and A ⁴ , may be each selected from the diphenylamine group of -N(phenyl) ₂ , wherein the diphenylamine group is substituted with an electron donating group selected from d_ ₅ alkyl, C ₂ _ ₅ alkenyl, C ₂ _ ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , and wherein R ¹ and R ² are each independently selected from hydrogen, C^alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. Each phenyl group of each diphenylamine may be substituted with an electron donating group selected from Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . salkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ _ ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci- ₅ alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from Ci _-5 alkyl, OR ¹ or

NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and Ci_ ₅ alkyl. The electron donating group may be selected from OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and d- ₅ alkyl. The electron donating group may be OC _{1 -5} alkyl. The electron donating group may be OCH ₃ . The electron donating group may be substituted at the ortho and/or para positions of the phenyl group. The electron donating group may be substituted at the para position of the phenyl group.

Diphenylamine Groups

In some embodiments of compounds of Formula 1 , the diphenylamine groups may be provided by a grou

Formula 2

wherein

R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , and R ⁸ , are each independently selected from hydrogen, Ci_ ₅ alkyl, C ₂ - ₅ alkenyl, C ₂ - ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² ; wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ - ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted.

In some embodiments, R ³ , R ⁵ , R ⁶ and R ⁸ , are each hydrogen, and R ⁴ and R ⁷ are each an electron donating group selected from Ci- ₅ alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, phenyl, OC(0)R ¹ , OR ¹ , NHC(0)R ¹ , or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen, Ci _-5 alkyl, C ₂ . ₅ alkenyl, C ₂ . ₅ alkynyl, and phenyl, and wherein each alkyl, alkenyl, alkynyl and phenyl may be further optionally substituted. The electron donating group may be selected from Ci _-5 alkyl, OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and ₅ alkyl. The electron donating group may be selected from OR ¹ or NR ¹ R ² , wherein R ¹ and R ² are each independently selected from hydrogen and C^alkyl. The electron donating group may be OCi- ₅ alkyl. The electron donating group may be OCH ₃ . Various non-limiting further examples of compounds according to the present disclosure are provided as follows:

It will be appreciated that compounds known to be suitable as HTMs in any electronic device such as OLEDs cannot be expected to be suitable as HTMs in solid state sensitized solar cells, and particularly so for HTMs in solid state perovskite solar cells (PSSC). The inventors tested a large number of compounds and many that might have been expected to be suitable as HTMs from suitability with other electronic devices, were proven repeatedly not to work in solid state sensitized solar cells of PSSCs. To function in PSSCs the HTM compounds must have a specific 'matching' HOMO level, be stable during operation of the device and then interact in the operating environment of electroactive layers of the device to provide acceptable properties. Such multifaceted properties result in very few compounds being suitable as HTMs in PSSCs, even when those compounds are known to be suitable HTMs in other types of electronic devices.

The properties of Compound 1 were compared with a known compound Spiro- OMeTAD (SHT-263 livilux® Merck) to confirm its efficiency as use as an HTM. The cyclic voltammogram of Compound 1 compared to the cyclic voltammogram of Spiro- OMe-TAD confirmed there is a significant difference in electrochemical properties between the two compounds (see Figure 4). This was also confirmed by the photoelectron spectrum in air (PESA) of Compound 1 that shows a high work function of -4.99 eV (see Figure 5a) compared to the PESA of Spiro-OMe-TAD which shows a work function of -4.96 eV (Figure 5b). Compound 1 was also shown to provide a higher PCE % of 12-15% in perovskite solar cell prepared by slot die printing, in comparison to Spiro-OMeTAD.

PHOTOACTIVE SENSITIZER MATERIALS

It will be appreciated that the photoactive sensitizer material may comprise any material suitable for use in solar cells capable of absorbing electromagnetic radiation. For example, suitable photoactive sensitizer materials may be selected from semiconductor materials, semiconductor nanomaterials, light absorbing dyes, perovskite materials, or combinations thereof.

Examples of suitable semiconductor materials are disclosed in

US2014/0090686 (the contents of which are incorporated herein by reference) and may include an element (e.g. silicon or germanium), a compound, (e.g. metal chalcogenides such as cadmium telluride, cadmium selenide, copper indium gallium selenide (CIGS), gallium arsenide, zinc sulfide or zinc selenide), or an alloy, (e.g. indium gallium phosphide).

Examples of suitable semiconductor nanomaterials are disclosed in US

2010/0193025 and WO2013/095924 (the contents each of which are incorporated herein by reference) and may include quantum dots and silicon nanomaterials.

Examples of suitable light absorbing dyes are disclosed in US2012/0266932 and WO2014/125432 (the contents of each of which are incorporated herein by reference), and may include organic dyes (e.g. acridine- and azo-based dyes), and metal complex dyes (e.g. ruthenium based dyes)

The photoactive sensitizer material may be selected to be suitable for solid state solar cells, for example a perovskite material. Perovskite materials

The light absorbing electroactive layer, or solar cell comprising such a layer, may comprise an organic-inorganic perovskite material. The solar cell may comprise one or more layers, which may each be the same or different.

"Perovskite", "perovskite material", "organic-inorganic perovskite material" or like term, for the purpose of this disclosure, refers to any material comprising a

"perovskite structure" and is not limited to any particular perovskite material as such for example CaTi0 ₃ . For the purpose of this disclosure, "perovskite" relates to any material that has the same type of crystal structure as calcium titanium oxide and of materials in which the bivalent cation is replaced by two separate monovalent cations. The perovskite structure has the general stoichiometry AMX3, where "A" and "M" are cations and "X" is an anion. The "A" and "M" cations can have a variety of charges and in the original Perovskite mineral (CaTi03), the A cation is divalent and the M cation is tetravalent. The perovskite formulae includes structures having three or four anions, which may be the same or different, and/or one or two organic cations, and/or metal atoms carrying two or three positive charges, in accordance with the formulae presented elsewhere in this specification.

Organic-inorganic perovskites are hybrid materials exhibiting combined properties of organic composites and inorganic crystalline. The inorganic component forms a framework bound by covalent and ionic interactions which provide high carrier mobility. The organic component helps in the self-assembly process of those materials, it also enables the hybrid materials to be deposited by low-cost technique as other organic materials. Additional property of the organic component is to tailor the electronic properties of the organic-inorganic material by reducing its dimensionality and the electronic coupling between the inorganic sheets.

The structure of the organic-inorganic perovskites are analogous to multilayer quantum well structures, with semiconducting inorganic sheets alternating with organic layers having a large energy gap to provide the inorganic sheets as essentially quantum wells for both electrons and holes. Another option is the bandgaps for the organic and inorganic layers can be offset leading to a type II heterostructure in which the wells for the electrons and holes are in different layers. Those structures of the organic-inorganic perovskites permit their use as sensitizer, which can inject electrons to a scaffold structure and/or a conductive support and at the same time may function as hole conductor.

The organic-inorganic perovskite material that is used in the present disclosure may have a molecular structure corresponding to any one of the formulae (I), (II), (III), and/or (IV) below:

A ₂ MX ₄ (I)

AMX ₃ (II)

ANX ₄ (I II)

BMX ₄ (IV)

wherein A is an monovalent organic cation and B is a bivalent organic cation. A and B may be selected from hydrocarbons comprising up to 15 carbons, and from 1 to 20 heteroatoms (for A) and 2 to 20 heteroatoms (for B), in particular one or two positively charged nitrogen atoms, respectively, besides possibly further heteroatoms selected from N, O and S. Furthermore, A and B may be partially or totally halogenated, independently of said 1 to 20 heteroatoms.

M is a metal atom, which may be selected from the group consisting of Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Mn ²⁺ Cr ²⁺ , Pd ²⁺ , Cd ²⁺ , Ge ²⁺ , Sn ²⁺ , Pb ²⁺ , Eu ²⁺ , or Yb ²⁺ . M may be Sn ²⁺ or Pb ²⁺ . N is a trivalent metal, which may be selected from the group of Bi ³⁺ and Sb ³⁺ .

X is an anionic compound, and may be selected independently from CI ^" , Br ^" , I ^" , NCS ^" , CN ^" , NCO ^" , and combinations thereof. As there may be three X in formulae (II), the perovskite material may comprise combinations of different halogens. For example, "X ₃ " may be selected from l ₂ CI ^"3 , IBr ^"3 , CI ₂ I ^"3 , Br ₂ l ^"3 , for example. The four anions in "X ₄ " may also be a combination of different halogens. X may be Br ^" or I ^" . All anions in "X ₃ " and "X ₄ " may be identical.

The organic-inorganic perovskite layer may comprise a perovskite-structure of the formula (I), (II), (III) and/or (IV) below,

A ₂ MX ₄ (I)

AMX ₃ (II)

ANX ₄ (I II)

BMX ₄ (IV)

wherein,

A is an organic, monovalent cation selected from primary, secondary, tertiary or quaternary organic ammonium compounds, including N-containing heterorings and ring systems, A having from 1 to 15 carbons and 1 to 20 heteroatoms;

B is an organic, bivalent cation selected from primary, secondary, tertiary or quaternary organic ammonium compounds having from 1 to 15 carbons and 2-20 heteroatoms and having two positively charged nitrogen atoms;

M is a divalent metal cation selected from the group consisting of Cu ²⁺ , Ni ²⁺ , Co ²⁺ , Fe ²⁺ , Mn ²⁺ , Cr ²⁺ , Pd ²⁺ , Cd ²⁺ , Ge ²⁺ , Sn ²⁺ , Pb ²⁺ , Eu ²⁺ , or Yb ²⁺ ;

N is selected from the group of Bi ³⁺ and Sb ³⁺ ; and,

X ₃ and X ₄ are independently selected from I ^" , Br ^" , I ^" , NCS ^" , CN ^" , and

NCO ^" .

M and N may be metal ions that can adopt an octahedral anion coordination. X may be selected from Br ^" and I ^" , and M is Sn ²⁺ or Pb ²⁺ .

The organic-inorganic perovskite material or layer thereof may comprise a perovskite-structure of any one of the formulae (V), (VI), (VII), (VIII), (IX) and (X);

APbX ₃ (V)

ASnX ₃ (VI)

A ₂ PbX ₄ (VII) A ₂ SnX ₄ (VIII)

BPbX ₄ (IX)

BSnX ₄ (X)

wherein A, B and X are as defined elsewhere in this specification. X may be selected from Br ^" and Γ. X may be Γ.

A, for example in any one of formulae (I) to (III), and (V) to (VIII), may be a monovalent cation selected from any one of the compounds of formulae (1 ) to (8) below:

(i) (2) (3) (4)

,3

R

/

R ₍ ¹ R— N ⁺

J \ .. . ₊ _2

R=NH ₂ NH=R' R' ^R' - (5) (6) (7) (8)

wherein,

any one of R ¹ , R ² , R ³ and R ⁴ is independently selected from C1 to C15 aliphatic and C4 to C15 aromatic substituents, wherein any one, several or all hydrogens in said substituent may be replaced by halogen and wherein, if there are two or more carbons, up to half of said carbons in said substituents may be replaced by a N, S or O heteroatom, and wherein, in any one of the compounds (2) to (8), the two or more of substituents present (R ¹ , R ² , R ³ and R ⁴ , as applicable) may be covalently connected to each other to form an optionally substituted ring or ring system.

B may be a bivalent cation selected from any one of the compounds of formulae (9) and (10) below: wherein,

in the compound of formula (9), L is absent or an aliphatic or aromatic linker structure having 1 to 10 carbons, wherein any one, several or all hydrogens in said L may be replaced by halogen and wherein up to half of the carbons in said L may be replaced, independently, by a N, S or O heteroatom ; wherein any one of Ri and R ₂ is independently selected from any one of the substituents (20) to (25) below:

R ³

--NH2 .--NH^R ² — N-— R ²

-— NH ₃ R R R

(20) (21) (22) (23)

— NH ~N

R R

(24) (25)

wherein the dotted line in the substituents (20) to (25) represents the bond by which said substituent is connected to the linker structure L;

wherein R ¹ , R ² , and R ³ are independently as defined above with respect to the compounds of formulae (1 ) to (8);

wherein and R ₂ , if they are both different from substituent (20), may be covalently connected to each other by way of their substituents R ¹ , R ² , and R ³ , as applicable, and wherein any one of R ¹ , R ² , and R ³ , if present, may be covalently connected to L or the ring structure of compound (10), independently from whether said substituent is present on or R ₂ ;

and wherein, in the compound of formula (10), the circle containing said two positively charged nitrogen atoms represents an aromatic ring or ring system comprising 4 to 15 carbon atoms and 2 to 7 heteroatoms, wherein said nitrogen atoms are ring heteroatoms of said ring or ring system, and wherein the remaining of said heteroatoms may be selected independently from N, O and S and wherein R ⁵ and R ⁶ are independently selected from H and from substituents as R ¹ to R ⁴ . Halogens substituting hydrogens totally or partially may also be present in addition to said 2 to 7 heteroatoms.

If L is absent, said substituents and R ₂ are directly connected, forming an N- N bond, as illustrated by compound (34) below. If the number of carbons is in L is impair, the number of heteroatoms is smaller than the number of carbons. In the ring structure of formula (10), the number of ring heteroatoms is smaller than the number of carbon atoms.

In the compound of formula (9), L may be an aliphatic or aromatic linker structure having 1 to 8 carbons, wherein any one, several or all hydrogens in said L may be replaced by halogen and wherein 0 to 4 carbons in said L may be replaced, independently, by a N, S or O heteroatom. L may be an aliphatic or aromatic linker structure having 1 to 6 carbons, wherein any one, several or all hydrogens in said L may be replaced by halogen and wherein 0 to 3 carbons in said L may be replaced, independently, by a N, S or O heteroatom.

In the compound of formula (9), said linker L may be free of any O or S heteroatoms. L may be free of N, O and/or S heteroatoms.

In the compound of formula (10), the circle containing said two positively charged nitrogen atoms may represent an aromatic ring or ring system comprising 4 to 10 carbon atoms and 2 to 5 heteroatoms (including said two ring N-atoms).

The ring or ring system in the compound of formula (10) may be free of any O or S heteroatoms. The ring or ring system in the compound of formula (10) may be free of any further N, O and/or S heteroatoms, besides said two N-ring atoms. This does not preclude the possibility of hydrogens being substituted by halogens.

It will be appreciated that if an aromatic linker, compound, substituent or ring comprises 4 carbons, it can comprise at least 1 ring heteroatom.

Any one of R ¹ , R ² , R ³ and R ⁴ is independently selected from C1 to C8 aliphatic and C4 to C8 aromatic substituents wherein any one, several or all hydrogens in said substituent may be replaced by halogen and wherein, if there are two or more carbons, up to half of said carbons in said substituents may be replaced by a N, S or O heteroatom, and wherein two or more of substituents present on the same cation may be covalently connected to each other to form a substituted or unsubstituted ring or ring system. Any one of R ¹ , R ² , R ³ and R ⁴ may be independently selected from Ci- ₁₀ alkyl, C ₂ -i ₀ alkenyl and C ₂ -i ₀ alkynyl, wherein said alkyl, alkenyl and alkynyl, if they comprise 3 or more carbons, may be linear, branched or cyclic, and wherein several or all hydrogens in said substituent may be replaced by halogen.

A and B may be a monovalent or bivalent cation, respectively, selected from optionally substituted C ₅ to C ₆ rings comprising one, two or more nitrogen heteroatoms, wherein one (for A) or two (for B) of said nitrogen atoms is/are positively charged. Substituents of such rings may be selected from halogen and from C^alkyls, C ₂ .

4alkenyls and C ₂ - ₄ alkynyls as defined above. Said ring may comprise further heteroatoms, which may replace one or more carbons in said ring, in particular, heteroatoms may be selected from O, N and S. Bivalent organic cations B comprising two positively charged ring N-atoms are exemplified, for example, by the compound of formula (10) above. Such rings may be aromatic or aliphatic.

A and B may also comprise a ring system comprising two or more rings, at least one of which being from an optionally substituted C ₅ to C ₆ ring as defined as above. The elliptically drawn circle in the compound of formulae (10) may also represent a ring system comprising, for example, two or more rings, but preferably two rings. Also if A comprises two rings, further ring heteroatoms may be present, which are preferably not charged, for example.

The organic cations A and B may comprise one (for A), two (for B) or more nitrogen atom(s) but is free of any O or S or any other heteroatom, with the exception of halogens, which may substitute one or more hydrogen atoms in cation A and/or B. A may comprise one positively charged nitrogen atom. B may comprise two positively charged nitrogen atoms.

PRINTING COMPOSITIONS

The present disclosure provides a printing composition comprising a solvent and a compound of Formula 1 as described herein. The present disclosure also provides a composition formulated for printing or coating in a roll-to-roll fabrication process, wherein the composition comprises a solvent and a compound of Formula 1 as described herein. The compositions described herein may be referred to as "hole transport compositions", "hole transport formulations" or like term.

The composition may be a printing ink formulation, for example a formulation suitable for application from a slot-die apparatus. It will be appreciated that the slot-die apparatus is typically configured for use in cooperation with a roll-to-roll fabrication process. The composition may be formulated into a solid, paste or gel. The composition may be a thixotropic liquid. The composition may be formulated to achieve a predetermined thickness as a printed thin film, for example having a printed thin film thickness of between 0.1 μιη and 1000 μιτι, 1 μιη and 500 μιη, or between 10 μιη and 200 μιη.

The solvent may be provided by one or more solvents (e.g. co-solvents). The solvent may be an organic solvent. The solvent may comprise one or more organic solvents. The solvents may be removed during or after the printing process.

Alternatively, they may be retained in the printed composition, and may provide properties such as acting as plasticizers. Suitable organic solvents include, but are not limited to, hydrocarbon solvents such as benzene, o-xylene and toluene; ether type solvents such as diethyl ether, tetrahydrofuran, diphenyl ether, anisole and dimethoxybenzene; halogenated hydrocarbon solvents such as methylene chloride, chloroform and chlorobenzene; ketone type solvents such as acetone, methyl ethyl ketone and methyl isobutyl ketone; alcohol type solvents such as methanol, ethanol, propanol, isopropanol, n-butyl alcohol and tert-butyl alcohol; nitrile type solvents such as acetonitrile, propionitrile and benzonitrile; ester type solvents such as ethyl acetate and butyl acetate; carbonate type solvents such as ethylene carbonate and propylene carbonate; and the like. These may be used singly or two or more of them may be used in admixture. The solvents may be provided in the compositions (prior to printing) in an amount based on a total weight of the composition of up to 90 wt%, up to 70 wt%, up to 50 wt%.

The compositions may comprise one or more additives, such as a dopant, electrolyte, binder, polymer, rheological modifier, surfactant, or mixtures thereof.

The one or more additives may be additional film components, which may include additives beneficial to film formation or film morphology. These additives may be removed from the printed composition by evaporation or they may be permanently incorporated into the printed composition or layer. Examples of some additives are hexadecane,1 ,8-diiodooctane (DIO), 1 ,8-octanedithiol (ODT), 1 -chloronaphthalene, N- methyl-2-pyrrolidone, diethylene glycol dibutyl ether, polystyrene, or polysiloxanes, or mixtures of the aforesaid additives.

An additive may be a polymer such as poly(thiophenes) and poly(phenylene vinylenes), which may have semiconductive properties including charge transport properties (see for example Peet et al, Acc. Chem. Res. 2009, 42/1 1 , 1700-1708; R. Po et al, J. Phys. Chem. C 2010, 1 14, 695-706).

The printable composition may be formulated for a range of printing methods, including flexography, gravure, screen, inkjet printing, offset and lithographic printing. The printable composition is printed onto a suitable layered substrate (e.g. substrate "sheet"). Such substrates may be semiconductor substrates, paper, metal, metal- laminated paper, glass, quartz, textiles, polymers, metal-laminated polymers and the like. For roll-to-roll processes it will be appreciated that the substrates (in the form of continuous roll-to-roll "sheets") are flexible. While inkjet and screen printing typically imprint rigid substrates like glass and silicon, mass-printing methods nearly exclusively use flexible foil and paper. Poly(ethylene terephthalate)-foil (PET) is a common choice, due to its low cost and higher temperature stability. Poly(ethylene naphthalate)- (PEN) and poly(imide)-foil (PI) are alternatives. The functional solar cell may be formed from this printed substrate, for example, by the application of electronic connections and other components thereto. Alternatively, the functional solar cell may be pre-formed (i.e., including, for example, electronic connections and other components) from an unprinted substrate, and subsequently printed with the printable composition to form the functional electronic device.

An additive may be an electrolyte such as bis(trifluoromethanesulfonyl)imide and 4-tert-butylpyridine.

Another additive may include a polymer binder. The polymer binder may be selected to be soluble in the formulation and to bind the hole transport material to the surface of the photoactive sensitiser layer of the sheet. It will be appreciated that the polymer binder may react (e.g. polymerise, cross-link, condense) during printing. Alternatively, a process may be carried out after printing (such as heating, exposure to UV radiation, etc.) which causes the polymer binder to further polymerise, cross-link, condense, or a mixture thereof. The polymer binder may be selected from the group consisting of poly-acrylic, poly-urethane, poly-styrene/poly-acrylic, poly-urethane/poly- acrylic or polyamide polymers, cellulosic binders or commercially formulated binders. The polymer binders may be used in the form of a blend of two or more members, for example blends of low molecular weight and high molecular weight fractions of the same polymer. The polymer binder may be substantially transparent to visible light and/or infra-red light. The polymer binder which remains in the solar cell sheet may provide desirable properties such as flexibility, conformity and mechanical robustness, in addition to promoting good adhesion. For example, the polymer binder may be a polyacrylic, polyurethane, polystyrene/polyacrylic, polystyrene/polyurethene or polyamide polymer, which for example is present in an amount of 5-15% by weight.

METHODS OF MANUFACTURING SOLAR CELLS

The present disclosure also provides a method of manufacturing a hole transport layer on a layered solar cell sheet comprising a step of printing a hole transport composition comprising a solvent and a compound of Formula 1 as described herein onto a photoactive sensitizer layer of the layered solar cell sheet to form a hole transport layer thereon.

There is also provided a method of manufacturing a solar cell comprising the steps of:

providing a layered solar cell sheet comprising a substrate sheet, a first electrode layer, optionally an electron transport layer, and a photoactive sensitizer layer;

printing a hole transport composition comprising a solvent and a compound of Formula 1 as described herein onto the photoactive sensitizer layer of the layered solar cell sheet to form a hole transport layer; and providing a second electrode on the hole transport layer to form the solar cell.

The present disclosure also provides a method of manufacturing a hole transport layer on a layered solar cell sheet by roll-to-roll processing comprising a step of printing a hole transport composition comprising a solvent and a compound of Formula 1 as described herein onto a photoactive sensitizer layer of the layered solar cell sheet to form a hole transport layer thereon.

The present disclosure also provides a method of manufacturing one or more layers of a solar cell comprising the steps of:

providing a layered solar cell sheet comprising a substrate sheet, a first electrode layer, optionally an electron transport layer, and a photoactive sensitizer layer;

delivering the layered solar cell sheet through a roll-to-roll fabrication process that comprises applying to the photoactive sensitizer layer of the layered solar cell sheet, a hole transport layer composition comprising a solvent and a compound of Formula 1 as described herein to form a hole transport layer on the layered solar cell sheet; and

providing a second electrode on the hole transport layer to form the solar cell. The solar cell may be a solid state sensitized solar cell. The photoactive sensitizer layer may comprise or consist of a perovskite material to provide a solid state perovskite sensitized solar cell (PSSC).

The layered solar cell sheet may comprise an electrode, for example indium tin oxide (ITO), and a transparent film, for example glass or polyethylene terephthalate (PET). The layered solar cell sheet may be provided by a substrate sheet (e.g. flexible PET sheet) comprising a first electrode layer, an electron transport layer (e.g. ZnO) and photoactive sensitiser layer (e.g. perovskite).

Applying the hole transport composition to the layered solar cell sheet may comprise a printing or coating technique, for example a slot-die printer configured for cooperation with the roll-to-roll fabrication process. The roll-to-roll fabrication process may comprise a slot-die printer for applying the composition to the sheet.

One or more of the other layers of the solar cell may be applied to the substrate in the printing or roll-to-roll fabrication process. For example, the layered solar cell sheet may comprise a substrate sheet and a first electrode layer, and prior to formation of the hole transport layer, an optional electron transport layer and a photoactive sensitizer layer may be sequentially applied onto the layered solar cell sheet in the printing or roll-to-roll fabrication process. The printing or roll-to-roll fabrication process may comprise further steps, for example heating, annealing or sintering steps. The photoactive sensitizer layer may be formed in situ on the solar cell sheet during the fabrication process. One or more layers may be thermally annealed. Solvents for the compositions may for example include chlorobenzene or o-xylene.

The roll-to-roll (R2R) manufacturing process is a large scale industrial technique used for manufacturing organic solar cells. R2R is particularly suitable for flexible solar cell sheets. The flexible solar cell sheets may be a continuous roll-to-roll sheet.

In contrast to single device methods involving a single substrate, R2R manufacturing processes allow for the continuous production of solar cell sheets and are not limited to a discrete and finite substrate size. Furthermore, R2R manufacturing processes allow for the continuous manufacture of multilayer films, such as solar cells, without having to stop the process between each layer addition.

The general R2R manufacturing process is shown in Figure 6a. A sheet material is unwound from the cylindrical unwinding portion (12), and is rewound at the cylindrical rewinding portion (13). The processing portion (14) is where the layer or layers are coated onto the sheet (e.g. substrate). A portion of the sheet (14) receives the layer being applied by a printing or coating apparatus that cooperates with the roll- to-roll process. The printing or coating apparatus may be a knife-over-edge, curtain, gravure and slot-die coating or printing apparatus.

One R2R manufacturing process that is particularly suitable for large scale industrial manufacturing of solar cells uses a slot die coating or printing apparatus that cooperates with the roll-to-roll process, which is shown in Figure 6b and is a reliable technique to deliver cost-effective thin films. The sheet is unwound from the cylindrical unwinding portion (12) and a portion of the sheet (14) receives the layer being applied by a slot-die printing or coating apparatus (15). The layer being applied (16) is fed through the slot-die printing or coating apparatus where it interacts with the portion of the sheet (14) receiving the layer, and is smoothed out by the slot-die apparatus.

Suitable viscosities of compositions as described herein used in the slot die apparatus as described above may be in the range of 1 to 10,000 mPas, 10 to 1000 mPas, 20 to 500 mPas, 30 to 300 mPas, 40 to 200 mPas or 50 to 100 mPas. The viscosities may be measured at a shear rate of 100 1/s at a temperature of 20 °C.

Suitable coating speeds of the layers or compositions as described herein used in the slot die apparatus as described above may be in the range of 0.01 to 200 mms ^"1 , 0.1 to 100 mms ^"1 , 0.2 to 75 mms ^"1 , 0.3 to 50 mms ^"1 , 0.4 to 30 mms ^"1 , 0.5 to 20 mms ^"1 or 1 to 10 mms ^"1 . Suitable application rate from the slot die apparatus of the composition being applied to the sheet may be in the range of 0.1 to 100 μΙ_ cm ^"2 , 0.2 to 50 μΙ_ cm ^"2 , 0.4 to 40 μΙ_ cm ^"2 , 0.6 to 30 μΙ_ cm ^"2 , 0.8 to 20 μΙ_ cm ^"2 or 1 to 10 μΙ_ cm ^"2 . Suitable shim size may be in the range of 0.001 to 10 mm, 0.005 to 8 mm, 0.01 to 5 mm, 0.02 to 1 mm or 0.04 to 0.5 mm. For example, the shim size may be 0.05 mm. The meniscus guide width may be in the range of 1 to 1000 μιη, 10 to 750 μιη, 50 to 500 μιη, or 100 to 300. For example, the meniscus guide may be 200 μιη. The gap between the meniscus guide and the sheet (coating layer thickness) may be in the range of 1 to 10,000 μιη, 10 to 1000 μιη, 20 to 500 μιη, or 50 to 250 μιη. The slot die channel width may be in the range of 1 to 5000 mm, 2 to 2000 mm, 4 to 1000 mm, 6 to 500 mm, 8 to 100 mm or 10 to 20 mm.

A number of slot dies may be used in the R2R process to provide sequential layering of compositions onto the sheet. For example, the number of slot dies may be 3 as shown in Figure 6c, where different layers are systematically coated onto the sheet. While not limited to any one configuration or order of layer addition, a suitable configuration may be provided by a first layer (16) being a hole blocking material layer (or electron transport material or n-conductor), the second layer (17) being a photoactive sensitizer layer, such as a perovskite material, and the third layer (18) being a hole transport material layer comprising a compound of Formula 1 as described herein.

The R2R process may be carried out in an inert atmosphere or air. The environment temperature in which the R2R process is carried out may be in the range of 1 to 100 , 5 to 75 °C or 10 to 50°C. The humidity the coating is carried out may be in the range of 1 to 100%, 10 to 75% or 20 to 50%.

Optional steps in the R2R process may include one or more annealing, drying, cleaning, sintering, evaporation or heating steps, which may be applied to one or more of the layers.

EXAMPLES

In order that the present disclosure may be more clearly understood, particular embodiments are described in further detail below by reference to the following non- limiting experimental materials, methodologies and examples. PREPARATION OF COMPOUNDS

Example

A' ² ,A' ² ,A' ^{2 2 7} ,A' ⁷ , _i V ^{7 7,} -octakis(4-methoxyphenyl)-[9,9'- bifluorenylidene]-2,2',7,7'-tetraamine

Scheme 1 : Synthesis of BFD-OMe-TAD (Compound 1 )

Synthesis of 2, 2', 7, 7' -substituted bifluoroenylidene derivative, (BFD-OMe-TAD), Compound 1.

Synthesis of compound a: 2, 2', 7, 7'-tetrabromo-9, 9'-bifluorenylidene

6.76 (20 mmol) 2,7-Dibromo-9-fluorenone and 4.04g (10 mmol) Lawesson's reagent were conducted in a 10 mL glass microwave reaction vessel sealed with a septum and ring cap. The reactants were irradiated under constant power at 400 W without temperature regulation. Reaction run time was programmed to discontinue and begin cooling upon reaching a preset maximum temperature above the melting point of the 2,7-dibromo-9-fluorenone (ca. 205-207 °C). Upon cooling, the resulting red solid was washed in a Soxhiet extractor by acetone until the eluent going to colourless. The residual red solid (6 g, 93% yield) was used directly for next step without any further purification.

An alternative two-step route to the tetrabromobifluorenylidne compound (a) is

In this case 2,7-Dibromo-9-fluorenone is reacted with 1 ,3-ethanedithiol in chloroform with boron trifluoride acetic acid to give the dithioketal (International PCT publication no. WO2013/098313). This dithioketal is then desulfurized and coupled to give the desired 2, 2', 7, 7'-tetrabromo-9, 9'-bifluorenylidene by the action of tungsten hexacarbonyl in heated chlorobenzene (J. Org. Chem. 1990, 55(6), 1871 -1881 ).

Compound 1: 2, 2',7, - N2,N2,N2',N2',N7,N7,N7',N7'-octakis(4-methoxyphenyl)-[9,9'- bifluorenylidene]-2,2', 7, 7'-tetraamine (BFD-OMe- TAD)

In a 250 ml_ two-necked flask, 4,4'-dimethoxydiphenylamine (10.68 g, 46.4 mmol), 2,2',7,7'-tetrabromo-bifluorenylidene (a) (6 g, 6.32 mmol), caesium carbonate (30 g, 93 mmol), palladium(ll) acetate (0.336 g, 1 .52 mmol) and tri-tert-butylphosphine (12 g of 10%(w/w) solution in hexane, 6.08 mmol) were mixed. Next, 100 ml_ of anhydrous toluene was added into the flask under a nitrogen atmosphere. The reaction mixture was heated to reflux at 1 10 for 12 h under a nitrogen atmosphere. After cooling to room temperature, the reaction mixture was extracted with ethyl acetate and brine water and dried over anhydrous MgS0 ₄ . After the solvent was evaporated, the residue was purified by column chromatography (ethyl acetate/hexane=1 /2). The eluent was concentrated and recrystallised in diethyl ether to afford a brown solid in 85% yield (6.65 g).

Characterisation of Compound 1: BFD-OMe-TAD

¹ H NMR (400 MHz, CDCI ₃ ) δ 7.96 (d, J = 2.0 Hz, 4H, aromatic Ha), 6.86 - 6.80 (m, 16H, aromatic He), 6.80 - 6.78 (m, 8H, aromatic Ho), 6.76 - 6.70 (m, 16H, aromatic Hd), 3.74 (s, 24H, H @OMe) ¹³ C NMR (100MHz, CDCI ₃ ) δ 155.24, 147.05, 142.01 , 141 .59, 139.39, 135.25, 125.51 , 125.12, 121 .58, 1 19.58, 1 14.78, 55.61 . MALDI-TOF (no matrix): m/z = 619.757 (M ²⁺ ); 1238.535 (M ⁺ )

Example 2 - Compound 2

Synthesis of 2, 2 7, 7'-substituted bifluoroenylidene derivative

Compound 1 Compound 2

The above Compound 2 was preparedfrom Compound 1 by catalytic hydrogenation. Example 3 - Compound 3

Synthesis of 3, 3 6, 6'-substituted bifluoroenylidene derivative

The above compound 3 was prepared by the same method as that described above for compound 1 .

Example 4 - Compound 4

Synthesis of 2, 2 7, 7'substituted bifluoroenylidene

The above compound 4 was prepared by an analogous method to compound

1 . In this case the required tetrabromo core 2, 2', 7, 7' -tetrabromo-9, 9'-bicarbazyl can be made by the oxidation of the 2,7-dibromocarbazole as described for the isomer 3,6- dibromocarbazole in J. Chem. Soc. 1927, 1214-1221 by McLintock and Tucker. Once in hand, the 2', 7, 7'-tetrabromo-9, 9'-bicarbazyl can be used in place of 2, 2', 7, T- tetrabromo-9, 9'-bifluorenylidene in method described for the synthesis of compound 1 to give compound 4.

Example 5 - Hole-Transporting Layer Ink Formulation

For the hole transporting layer ink, 15 mg BFD-OMeTAD (Compound ), 0 μΙ_ of Lithium bis(trifluoromethanesulfonyl) imide (Li-TFSI) (170 mg mL ^"1 in acetonitrile), and 5 μΙ_ of 4-tert-butylpyridine were dissolved in 1 ml_ chlorobenzene. The HTL ink was filtrated by 0.45 μιη filter and then coated onto the perovskite film.

Example 6 - Perovskite solar cell device Fabrication (as per Figure 7)

For slot-die coated perovskite solar cell devices, ITO-coated glass (Shenzhen Display, 5 Ω sq ^"1 ) was successively sonicated for 5 min each in Deconex 12PA detergent solution, distilled water, acetone, and 2-propanol. The substrates were then exposed to UV-ozone (Novascan PDS-UVT) cleaning at room temperature for 15 min. For the electron transporting layer, ZnO nanoparticles were prepared following a literature procedure. The solution was coated onto ITO glass using a slot-die head with 50 μιη shim and 200 μιη thick meniscus guide at 3 mm s ^"1 coating speed and 1 μΙ_ cm ^"2 solution feed. The shim with 13 mm channel was used with the same width of meniscus guide, and the gap between the meniscus guide and the substrate was fi xed at 100 μιη. The ZnO films were then annealed at 120 °C for 10 min in air. For the perovskite layer, a Pbl ₂ (99%, Sigma-Aldrich) precursor solution (0.7 M, 322 mg/mL) in Ν,Ν-dimethylformamide was prepared by stirring at 70 °C for 1 h in air. The solution was cooled to room temperature and transferred to the slot-die head without filtration. In this case, 200 μιη gap between the meniscus guide and the substrate was used to maximize the wet film thickness. Coating was carried out at speed of 5 mm s ^"1 with 1 μΙ_ cm ^"2 solution feed. The wet film was then dried by N ₂ gas-quenching (25 L min ^"1 through a 1 mm ^χ 13 mm nozzle from a 25 mm distance), transferred to an enclosed sample carrier and kept in the carrier for 10 min. CH ₃ NH ₃ I (Dyesol Co.) of 10 mg ml_ ^"1 solution in 2-propanol was prepared for perovskite conversion. The Pbl ₂ layers were dipped into the CH ₃ NH ₃ I solution for 3 min, rinsed with 2-propanol before the film dried, and then the solvent was quickly removed by N ₂ gas-blowing. For the fully slot-die coated perovskite layer, the same CH ₃ NH ₃ I solution was transferred to the slot-die head without filtration and coated onto the cloudy Pbl ₂ layer at speed of 1 mm s ^"1 with 7 μΙ_ cm ^"2 solution feed. The Pbl ₂ substrates were pre-heated to various temperatures by using a heated bed in slot-die coater before CH ₃ NH ₃ I coating, and the gap between the meniscus guide and the substrate was fixed at 100 μιη. When a CH ₃ NH ₃ I solution was coated onto the Pbl ₂ at 70 °C, the film color was changed to a dark brown immediately due to the perovskite conversion. Once perovskite layer was formed, the hole transporting layer was coated immediately to minimize exposure to moisture. For the hole transporting layer, 1 ml_ of BFD-OMeTAD solution (15 mg ml_ ^"1 in

chlorobenzene), 10 μΙ_ of Li-bis(trifluoromethanesulfonyl) imide (170 mg ml_ ^"1 in acetonitrile), and 5 μΙ_ of 4-tert-butylpyridine were mixed, filtrated by 0.45 μιη filter, and then transferred to the slot-die head. The solution was coated onto the perovskite film at 7 mm s ^"1 speed with 3 μΙ_ cm ^"2 solution feed without thermal treatment, and the gap between the meniscus guide and the substrate was also fixed at 100 μιη. All slot-die coating processes were carried out in air. Temperature and relative humidity were typically 25-30 °C and 30-40%, respectively. For an evaporated electrode, the samples were carried to a vacuum evaporator and 100 nm of Ag was deposited through a shadow mask to produce a 10 mm ² active area.

The performance of the perovskite solar cell device fabricated as per Example 6 is shown in Figure 8, and summarised in the below table.