Compound, hole transport material, and solar cell

Abstract

This compound is represented by formula (1). In formula (1), R1, R2, R3, R4, R5, R6, R7, and R8 each independently represent a hydrogen atom, a methyl group, a methoxy group, or a fluoro group, and two or more of R1, R2, R3, R4, R5, R6, R7, and R8 represent fluoro groups. This hole transport material contains a compound represented by formula (1). This solar cell (10) is provided with a positive electrode (6), a negative electrode (2), a light absorption layer (4), and a hole transport layer (5). The hole transport layer (5) contains the hole transport material.

Description

Compound, hole transport material, and solar cell

[0001] The present invention relates to a compound, a hole transport material, and a solar cell.

[0002] In recent years, solar cells have been attracting attention as a clean energy source. Among solar cells, solar cells having a perovskite absorption layer containing a perovskite compound as a light absorption layer (photoelectric conversion layer) (hereinafter also referred to as "perovskite solar cells") exhibit high photoelectric conversion efficiency.

[0003] Solar cells generally have a structure in which a transparent electrode (cathode), an electron transport layer, a light absorption layer, a hole transport layer, and a metal electrode (anode) are stacked in this order. High-quality perovskite compounds and electron transport materials have been obtained by various methods. Therefore, hole transport materials are considered important for further improving the performance of solar cells.

[0004] A known hole transport material for solar cells is 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (hereinafter also referred to as "Spiro-OMeTAD"), which was developed as a material for the hole transport layer of dye-sensitized solar cells. Spiro-OMeTAD is also used as a material for the hole transport layer of perovskite solar cells (see, for example, Patent Document 1).

[0005] JP 2024-23624 A

[0006] However, when Spiro-OMeTAD is used as the material for the hole transport layer, it cannot be said that a sufficiently good photoelectric conversion performance is exhibited.

[0007] Furthermore, in order to fabricate lightweight and flexible solar cells, it is desirable to form each layer by coating the material in order to reduce the thickness. However, depending on the structure, 9,9'-spirobifluorene organic compounds are difficult to dissolve in organic solvents, and when used as a material for the hole transport layer of solar cells, it may not be possible to form a thin film that achieves excellent photoelectric conversion efficiency.

[0008] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a novel compound and hole transport material that have excellent solubility in organic solvents and that can improve the photoelectric conversion efficiency of solar cells when used in solar cells, and a solar cell using the same.

[0009] A compound according to one aspect of the present invention is represented by formula (1).

[0010]

[0011] In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 each independently represents a hydrogen atom, a methyl group, a methoxy group, or a fluoro group; R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 At least two of these represent fluoro groups.

[0012] A hole transport material according to another aspect of the present invention includes the above compound.

[0013] A solar cell according to another aspect of the present invention includes an anode, a cathode, a light absorbing layer provided between the anode and the cathode, and a hole transport layer provided between the anode and the light absorbing layer, wherein the hole transport layer contains the hole transport material.

[0014] The compound and hole transport material of the present invention have excellent solubility in organic solvents, and when used in solar cells, can improve the photoelectric conversion efficiency of the solar cells. Furthermore, the solar cells of the present invention can be produced using organic solvents and have excellent photoelectric conversion efficiency.

[0015] 1 is a cross-sectional view showing an example of a schematic configuration of a main part of a solar cell according to a third embodiment of the present invention. 1 1H-NMR chart.

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. The present invention can be modified in various ways within the scope of the object of the present invention, and embodiments obtained by appropriately combining the technical means described in different embodiments are also included in the technical scope of the present invention.

[0017] Hereinafter, the compound name may be followed by "system" to collectively refer to the compound and its derivatives. When the compound name is followed by "system" to refer to the name of a polymer, it means that the repeating unit of the polymer is derived from the compound or its derivative. Furthermore, general formulas and chemical formulas will be collectively referred to as "formulas." Furthermore, "each independently" in the description of a formula means that it may represent the same group or different groups. Furthermore, each component described below may be used alone or in combination of two or more types.

[0018] [First embodiment: Compound] The first embodiment of the present invention relates to a compound represented by the following formula (1) (hereinafter, may be referred to as compound (1)). Compound (1) is a 9,9'-spirobifluorene derivative (spirobifluorene-based organic compound).

[0019]

[0020] In formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 Each of R independently represents a hydrogen atom, a methyl group, a methoxy group, or a fluoro group. 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 Two or more of the groups represent fluoro groups. As used herein, substituents are unsubstituted unless otherwise specified.

[0021] To fabricate lightweight, flexible solar cells, it is desirable to form each layer by coating the material to achieve a thin film. However, depending on the structure, 9,9'-spirobifluorene-based organic compounds may be poorly soluble in organic solvents, and when used as a material for the hole transport layer of a solar cell, it may not be possible to form a thin film that achieves excellent photoelectric conversion efficiency. Compound (1) has a methoxy group and a fluoro group bonded to at least one of the aryl groups of the amino group bonded to the 9,9'-spirobifluorene, so that the aryl group of the amino group bonded to the 9,9'-spirobifluorene is twisted and raised relative to the plane of the 9,9'-spirobifluorene. As a result, the molecules of compound (1) do not adhere too closely to each other, making it difficult for the molecules of compound (1) to aggregate. As a result, the solubility of compound (1) in organic solvents is improved. Therefore, compound (1) has excellent solubility in organic solvents, and it is possible to form a thin film using a solution of compound (1) dissolved in an organic solvent.

[0022] Furthermore, as a result of intensive studies by the present inventors, it has been found that compound (1) has hole transport ability and, when used in a solar cell, can improve the photoelectric conversion efficiency of the solar cell. Compound (1) can form a thin film that can achieve excellent photoelectric conversion efficiency when used as a material for a hole transport layer in a solar cell. Therefore, compound (1) can be suitably used as a hole transport material, for example, in forming a hole transport layer.

[0023] Furthermore, the hole transport material is required to have an appropriate ionization potential so that injected holes can be efficiently transferred to the light absorption layer. The ionization potential (hereinafter, sometimes referred to as "I.P.") of compound (1) is close to the I.P. of perovskite and is slightly shallower (smaller) than the I.P. of perovskite. The I.P. of perovskite is, for example, 5.3 to 5.7 eV. Therefore, when compound (1) is used as a hole transport material in a perovskite solar cell, it can efficiently extract charges generated in the light absorption layer to the outside.

[0024] As described above, compound (1) is a compound represented by the formula (1),1 ~R 8 are fluoro groups, the fluoro group is attached to only one of the two aryl groups of the amino group bonded to the 9,9'-spirobifluorene (i.e., R 1 ~R 4 or R 5 ~R 8 The fluoro group may be bonded to either the ortho position or the meta position relative to the methoxy group in formula (1).

[0025] In order to achieve excellent solubility in organic solvents and excellent photoelectric conversion efficiency when used in solar cells, the number of fluoro groups bonded to the aryl group of the amino group bonded to the 9,9'-spirobifluorene in formula (1) is particularly important. 1 ~R 8 When three or more of the groups are fluoro groups, the photoelectric conversion efficiency of a solar cell can be further improved when compound (1) is used in the solar cell.

[0026] In formula (1), as the number of fluoro groups, which are electron-withdrawing groups, increases, the I.P. deepens, and as the number of methoxy groups, which are electron-donating groups, increases, the I.P. shallows. Therefore, when compound (1) is used in the hole transport layer of a perovskite solar cell, it is preferable to adjust the numbers of fluoro groups and methoxy groups so that the I.P. of compound (1) is slightly shallower than the I.P. of the perovskite.

[0027] Furthermore, the ratio of methoxy groups to fluoro groups in the aryl groups of the amino groups bonded to the 9,9'-spirobifluorene is preferably 1:1, and more preferably 2:3. When the ratio of methoxy groups to fluoro groups in the aryl groups of the amino groups bonded to the 9,9'-spirobifluorene is 1:1, the compound has excellent solubility in organic solvents, can achieve a moderate I.P. that is slightly shallower than the I.P. of perovskite, and can further improve the photoelectric conversion efficiency of the solar cell when used in a solar cell. When the ratio of methoxy groups to fluoro groups in the aryl groups of the amino groups bonded to the 9,9'-spirobifluorene is 2:3, the compound has excellent solubility in organic solvents, can achieve a moderate I.P. that is slightly shallower than the I.P. of perovskite, and can further improve the photoelectric conversion efficiency of the solar cell when used in a solar cell.

[0028] Suitable examples of compound (1) include compounds represented by formulas (H-1), (H-2), (H-3), (H-4), (H-5), and (H-6) (hereinafter, these may be referred to as compounds (H-1), (H-2), (H-3), (H-4), (H-5), and (H-6), respectively).

[0029]

[0030] Among these compounds (H-1) to (H-6), compounds (H-2) to (H-6) are preferred because they have particularly excellent solubility in organic solvents and can be completely dissolved in organic solvents at room temperature. Furthermore, among these compounds (H-1) to (H-6), compounds (H-1), (H-2), and (H-4) to (H-6) are preferred because they can provide solar cells with superior photoelectric conversion efficiency. Furthermore, compounds (H-2) and (H-6) are compounds represented by the formula (1), R 1 ~R 8 It is more preferable that three or more of the groups be fluoro groups, since this allows for obtaining a solar cell with even better photoelectric conversion efficiency.

[0031] [Method for Producing Compound (1)] Next, a method for producing compound (1) will be described. Compound (1) can be produced, for example, according to the reaction formula (r-1) below (hereinafter, sometimes referred to as reaction (r-1)) or by a method equivalent thereto.

[0032]

[0033] In reaction (r-1), R 1 ~R 8 are R in formula (1), respectively. 1 ~R 8 is synonymous with.

[0034] In reaction (r-1), 1 molar equivalent of a compound represented by formula (S) (2,2',7,7'-tetrabromo-9,9'-spirobi[9H-fluorene]) (hereinafter, may be referred to as compound (S)) is reacted with 4 molar equivalents of a secondary amine compound represented by formula (A) (hereinafter, may be referred to as secondary amine (A)) to obtain 1 molar equivalent of the target compound (1).

[0035] The reaction (r-1) is preferably carried out in an inert gas atmosphere, such as nitrogen gas or argon gas.

[0036] Reaction (r-1) can be carried out in a solvent, such as a benzene derivative such as xylene or toluene, a hydrophilic solvent such as tetrahydrofuran, 1,4-dioxane, or dimethylformamide, or a hydrophobic solvent such as 2-methyltetrahydrofuran or cyclohexyl methyl ether.

[0037] Reaction (r-1) may be carried out in the presence of a palladium catalyst, such as [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride (PEPPSI (registered trademark)-IPr catalyst), palladium(II) chloride, palladium(II) acetate, palladium(II) trifluoroacetate, tris(dibenzylideneacetone)dipalladium(0), di-μ-chlorobis[(η-allyl)palladium(II)], or bis(acetylacetonato)palladium(II).

[0038] The reaction (r-1) may be carried out in the presence of a base, such as lithium bis(trimethylsilyl)amide, sodium tert-butoxide, potassium tert-butoxide, sodium methylate, tripotassium phosphate, or cesium fluoride.

[0039] The palladium catalyst may also be used in combination with an organophosphorus ligand. Examples of the organophosphorus ligand include triarylphosphines such as triphenylphosphine or tri-o-tolylphosphine; trialkylphosphines such as tri-tert-butylphosphine or tricyclohexylphosphine; trialkylphosphonium borate salts such as tri-tert-butylphosphonium tetraphenylborate or tri-tert-butylphosphonium tetrafluoroborate; bidentate phosphines such as 2,2'-bis(diphenylphosphino)diphenyl ether, 9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene, or 1,1'-bis(diphenylphosphino)ferrocene; and [4-(N,N-dimethylamino)phenyl]di-tert-butylphosphine. The palladium catalyst may be a palladium catalyst coordinated with an organophosphorus ligand.

[0040] The reaction temperature of the reaction (r-1) is preferably the reflux temperature, and the reaction time of the reaction (r-1) is preferably 1 hour or more and 10 hours or less.

[0041] The target compound (1) can be isolated by purifying the resulting reaction product. Examples of purification methods include purification by column chromatography, adsorption purification using silica gel or activated clay, or recrystallization or crystallization using a solvent. Nuclear magnetic resonance analysis (NMR) or the like can be used to identify the resulting compound.

[0042] [Second embodiment: hole transport material] The second embodiment of the present invention relates to a hole transport material. Compound (1) according to the first embodiment of the present invention can be used as a hole transport material. The hole transport material according to this embodiment contains compound (1).

[0043] As described in the first embodiment, compound (1) has excellent solubility in organic solvents and can improve the photoelectric conversion efficiency of solar cells when used in solar cells. Therefore, a hole transport material containing compound (1) has excellent solubility in organic solvents and can be used to form a thin film by dissolving compound (1) in an organic solvent, and can form a thin film that can improve the photoelectric conversion efficiency of solar cells when used in solar cells.

[0044] Furthermore, as described in the first embodiment, the I.P. of compound (1) is close to the I.P. of perovskite (e.g., 5.3 to 5.7 eV) and is slightly shallower than the I.P. of perovskite. Therefore, when a hole transport material containing compound (1) is used in a perovskite solar cell, it can efficiently extract charges generated in the light absorption layer to the outside. This can improve the energy conversion efficiency of the solar cell. Therefore, the hole transport material according to this embodiment can be particularly suitably used as a hole transport material for perovskite solar cells.

[0045] The hole transport material according to this embodiment may be any one of compounds (1) represented by formula (1) used alone or in combination of two or more thereof. The hole transport material according to this embodiment may further contain a hole transport material other than compound (1).

[0046] The hole transport material according to this embodiment may further contain additives as needed. As the additives, conventionally known additives such as an interface treatment agent can be used.

[0047] [Third embodiment: solar cell] A third embodiment of the present invention relates to a solar cell. The solar cell according to this embodiment includes at least an anode, a cathode, a light absorbing layer provided between the anode and the cathode, and a hole transport layer provided between the anode and the photoelectric conversion layer. The hole transport layer contains the compound (1) according to the first embodiment.

[0048] The solar cell according to this embodiment may be, for example, an organic thin-film solar cell, or an organic-inorganic hybrid solar cell such as a perovskite solar cell.

[0049] The structure of a solar cell 10 according to this embodiment will be described below with reference to FIG. 1 . FIG. 1 is a cross-sectional view showing an example of a schematic configuration of a main part of a solar cell 10 according to this embodiment. The solar cell 10 shown in FIG. 1 includes a first electrode 2, an electron transport layer 3, a light absorption layer 4, a hole transport layer 5, and a second electrode 6. In the example shown in FIG. 1 , the first electrode 2 is a cathode, and the second electrode 6 is an anode. Therefore, the electron transport layer 3, the light absorption layer 4, and the hole transport layer 5 are provided in this order from the first electrode 2 side.

[0050] A solar cell 10 according to this embodiment may include a substrate 1, as shown in Fig. 1. The substrate 1 is used as a support for supporting a stack including the first electrode 2, the electron transport layer 3, the light absorbing layer 4, the hole transport layer 5, and the second electrode 6. The first electrode 2 is provided on the substrate 1.

[0051] (Substrate) The substrate 1 is not particularly limited as long as it can be used in a solar cell. The substrate 1 may be a transparent or semi-transparent light-transmitting substrate, or an opaque, non-light-transmitting substrate. When the substrate 1 and the first electrode 2 are light-transmitting, the surface of the solar cell 10 on the substrate 1 side can be used as a light-receiving surface. Therefore, when the substrate 1 is a light-transmitting substrate, by making the first electrode 2 a light-transmitting electrode, light (e.g., sunlight or indoor light) may be irradiated onto the surface of the solar cell 10 on the substrate 1 side during use of the solar cell 10. Note that when the surface on the substrate 1 side serves as the light-receiving surface, the substrate 1 only needs to be light-transmitting, but is preferably transparent.

[0052] Examples of transparent substrates include transparent rigid substrates (more specifically, glass such as quartz glass, synthetic quartz plates, etc.) and transparent flexible substrates (more specifically, transparent rigid substrates such as transparent resin films and synthetic quartz plates, and transparent flexible substrates such as transparent resin films and optical resin plates). Transparent flexible substrates have advantages such as ease of processing, reduced manufacturing costs, light weight, resistance to cracking, and applicability to curved surfaces. Furthermore, the substrate 1 may be a circuit board or an array substrate provided with a plurality of driving elements such as thin film transistors (TFTs). When the solar cell 10 is part of a device such as a large-scale power supply, a power supply for outdoor equipment, a power supply for indoor electronic equipment, or a portable power supply, the substrate 1 is a support of the device.

[0053] (First electrode and second electrode) As described above, one of the first electrode 2 and the second electrode 6 is an anode (hole injection electrode), and the other is a cathode (electron injection electrode). The first electrode 2 and the second electrode 6 are made of a conductive material. Furthermore, a translucent electrode is used for at least one of the first electrode 2 and the second electrode 6 (specifically, the electrode on the surface that will be the light-receiving surface of the solar cell 10). As described above, the solar cell 10 may be irradiated with light on the surface on the substrate 1 side, or on the surface on the second electrode 6 side. Furthermore, light may be irradiated on both the surface on the substrate 1 side and the surface on the second electrode 6 side of the solar cell 10.

[0054] The materials for the first electrode 2 and the second electrode 6 are not particularly limited as long as they are conductive. Preferably, the anode is made of a material with a relatively high work function, and the cathode is made of a material with a relatively low work function. Examples of materials with a relatively high work function include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), carbon (C), indium tin oxide (ITO), tin oxide (SnO), fluorine-doped tin oxide (FTO), and zinc oxide (ZnO). Examples of materials with a relatively low work function include calcium (Ca), lithium (Li), indium (In), aluminum (Al), magnesium (Mg), samarium (Sm), terbium (Tb), ytterbium (Yb), zirconium (Zr), and lithium fluoride (LiF).

[0055] Furthermore, as described above, the materials for the first electrode 2 and the second electrode 6 are appropriately selected taking into consideration whether the light-receiving surface of the solar cell 10 is the surface on the substrate 1 side (first electrode 2 side) or the surface on the second electrode 6 side. When the light-receiving surface is the surface on the substrate 1 side, the first electrode 2 only needs to be light-transmitting, but is preferably a transparent electrode. Similarly, when the light-receiving surface is the surface on the second electrode 6 side, the second electrode 2 only needs to be light-transmitting, but is more preferably a transparent electrode. Note that when the light-receiving surface is the surface on the substrate 1 side, the first electrode 2 is preferably a transparent electrode, but the second electrode 6 does not need to be a transparent electrode.

[0056] When a translucent electrode is used for the first electrode 2 or the second electrode 6, the translucent electrode may be, for example, a transparent or semi-transparent electrode made of a metal thin film. However, transparent electrodes such as indium zinc oxide (IZO), fluorine-doped tin oxide (FTO), indium tin oxide (ITO), ZnO—Al (aluminum-doped zinc oxide), and Zn—Sn—O (zinc tin oxide (ZTO)) are preferably used.

[0057] The total light transmittance of the translucent electrode is preferably 85% or more, more preferably 90% or more, and particularly preferably 92% or more. In particular, when the first electrode 2 is a translucent electrode, if the total light transmittance of the first electrode 2 is 85% or more, and the light receiving surface of the solar cell 10 is the surface on the substrate 1 side, light can be sufficiently transmitted through the first electrode 2 on the substrate 1, and the light can be efficiently absorbed by the light absorbing layer 4.

[0058] Furthermore, the sheet resistance of the first electrode 2 is preferably 20 Ω / sq or less, and more preferably 15 Ω / sq or less. When the sheet resistance of the first electrode 2 is 20 Ω / sq or less, the charge generated in the light absorbing layer 4 is sufficiently transmitted to an external circuit. The sheet resistance can be measured, for example, using a resistivity meter ("Loresta AXMCP-T370", four-probe type, manufactured by Nitto Seiko Analytech Co., Ltd.) by a method in accordance with JIS (Japanese Industrial Standards) R1637 (Testing method for resistivity of fine ceramic thin films - Measurement method using the four-probe method).

[0059] The thickness of the first electrode 2 is preferably 0.1 nm or more and 500 nm or less, and more preferably 1 nm or more and 300 nm or less. When the thickness of the first electrode 2 is 0.1 nm or more, the sheet resistance of the first electrode 2 does not become too high, and the charges (holes) generated in the light absorbing layer 4 can be sufficiently transmitted to an external circuit. On the other hand, when the thickness of the first electrode 2 is 500 nm or less, the total light transmittance of the first electrode 2 becomes high.

[0060] The thickness of the second electrode 6 is preferably 0.1 nm to 500 nm, more preferably 1 nm to 300 nm. When the thickness of the second electrode 6 is 0.1 nm or more, the sheet resistance of the second electrode 6 does not become too high, and the charges generated in the light absorbing layer 4 can be sufficiently transmitted to an external circuit.

[0061] The first electrode 2 and the second electrode 6 may each be a single layer or may be composed of multiple layers having different work functions. When the first electrode 2 is composed of multiple layers, the thickness of the first electrode 2 described above means the total thickness of the multiple layers. Similarly, when the second electrode 6 is composed of multiple layers, the thickness of the second electrode 6 described above means the total thickness of the multiple layers.

[0062] The first electrode 2 may be formed in a sheet shape over the entire surface of the substrate 1, or may be formed in a pattern on the substrate 1. The shape of the first electrode 2 may be flat or uneven. Examples of the uneven shape include a textured structure, a pyramidal structure, a wave-shaped structure, a comb-shaped structure, and a nanopillow structure. When the first electrode 2 has an uneven shape, incident light is scattered by the unevenness of the first electrode 2, so that more light is taken in by the photoelectric conversion layer 4, and the photoelectric conversion efficiency of the solar cell 10 is improved.

[0063] The second electrode 6 may be formed in a sheet shape on the entire surface of the hole transport layer 5 , or may be formed in a pattern on the hole transport layer 5 .

[0064] Various known methods may be appropriately employed to form the first electrode 2 and the second electrode 6. Instead of forming the first electrode 2, a commercially available product in which the first electrode 2 is provided on the substrate 1 may be used.

[0065] (Electron Transport Layer) The electron transport layer 3 is provided between the cathode (first electrode 2 in the example shown in FIG. 1 ) and the light absorbing layer 4. The electron transport layer 3 is provided so as to facilitate the transport (injection) of electrons from the light absorbing layer 4 to the cathode. The provision of the electron transport layer 3 increases the efficiency of electron transport from the light absorbing layer 4 to the first electrode 2, thereby improving the photoelectric conversion efficiency of the solar cell 10.

[0066] The electron transport material contained in the electron transport layer 3 is not particularly limited as long as it is a material that can stably transport electrons from the light absorbing layer 4 to the second electrode 6. Examples of the electron transport material include a conductive organic compound, a charge transfer complex, an alkali metal, an alkaline earth metal, an organic compound doped with an alkali metal or alkaline earth metal, and a metal oxide.

[0067] Examples of alkali metals that can be used as electron transport materials include lithium, sodium, potassium, rubidium, and cesium. Examples of alkaline earth metals that can be used as electron transport materials include beryllium, magnesium, calcium, strontium, and barium. Examples of organic compounds doped with alkali metals or alkaline earth metals that can be used as electron transport materials include bathocuproine (BCP) or bathophenanthroline (Bphen) doped with alkali metals or alkaline earth metals. Examples of alkali metals and alkaline earth metals used for doping include lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, and barium, and lithium, cesium, barium, and strontium are more preferred. Examples of metal oxides that can be used as electron transport materials include titanium oxide, zinc oxide, and tin oxide.

[0068] When the electron transport material is a conductive organic compound, a charge transfer complex, or a metal oxide, the thickness of the electron transport layer 3 is preferably 10 nm or more and 200 nm or less. When the electron transport material is an alkali metal, an alkaline earth metal, or an organic compound doped with an alkali metal or an alkaline earth metal, the thickness of the electron transport layer 3 is preferably 0.1 nm or more and 50 nm or less.

[0069] The electron transport layer 3 can be formed by a known method such as vacuum deposition.

[0070] (Light-absorbing layer) The light-absorbing layer 4 absorbs light incident from the light-receiving surface side and performs photoelectric conversion. For example, when the light-receiving surface of the solar cell 10 is the surface on the substrate 1 side, the light-absorbing layer 4 absorbs light that has transmitted through the base material 1, the first electrode 2, and the electron transport layer 3.

[0071] The light absorbing layer 4 may be a bulk heterojunction type photoelectric conversion layer containing a donor (electron donor) and an acceptor (electron acceptor), or may be a perovskite absorbing layer containing a perovskite compound.

[0072] In the case of a bulk heterojunction light-absorbing layer, the donor is not particularly limited as long as it functions as a donor, but is preferably a conductive polymer (electron-donating organic material) with electron-donating properties. The electron-donating organic material refers to the organic compound with the smaller electron affinity when two organic compounds are used in contact. In other words, any organic compound with electron-donating properties can be used as the donor. The donor is preferably a compound that can be formed into a thin film by a method (e.g., a coating method such as a casting method or a spin coating method) using a solution in which the donor is dissolved in an organic solvent. The light-absorbing layer 4 may contain only a donor and an acceptor, or may contain other compounds.

[0073] Examples of conductive polymers having electron-donating properties that can be used as donors include polyphenylene, polyphenylene vinylene, polysilane, polythiophene, polybenzodithiophene, polycarbazole, polyvinylcarbazole, porphyrin, polyacetylene, polypyrrole, polyaniline, polyfluorene, polyvinylpyrene, polyvinylanthracene, or derivatives thereof. The donor may also be a copolymer obtained by copolymerizing at least two of these conductive polymers having electron-donating properties. Other examples of conductive polymers having electron-donating properties include phthalocyanine-containing polymers, carbazole-containing polymers, and organometallic polymers.

[0074] As a conductive polymer having electron-donating properties that can be used as a donor, a polymer having at least one of a thiophene structure, a benzothiophene structure, and a benzodithiophene structure (a polythiophene-based polymer) is preferred. The polythiophene-based polymer is preferably capable of absorbing visible light. Furthermore, the polythiophene-based polymer is preferably a donor-acceptor (DA) type.

[0075] The acceptor is not particularly limited as long as it functions as an acceptor, but is preferably a conductive polymer (electron-accepting organic material) with electron-accepting properties. An electron-accepting organic material is an organic compound that is mainly represented by an electron-transporting organic compound and has the property of readily accepting electrons. More specifically, when two organic compounds are used in contact with each other, the organic compound with the greater electron affinity is the one that is used. In other words, any organic compound with electron-accepting properties can be used as an acceptor.

[0076] Examples of electron-accepting organic materials include fullerene or a derivative thereof (such as PCBM), carbon nanotubes or a derivative thereof, perylene or a derivative thereof (such as PTCDA or PTCDI), naphthalene derivatives (such as NTCDA or NTCDI), oligomers or polymers having pyridine or a derivative thereof in the skeleton, fluorinated metal-free phthalocyanine, fluorinated metal phthalocyanines or derivatives thereof, tris(8-hydroxyquinolinato)aluminum complex, bis(4-methyl-8-quinolinato)aluminum complex, distyrylarylene derivatives, and silole compounds. Among these, fullerene derivatives (such as PCBM) are particularly suitable as the electron-accepting organic material, but the present invention is not limited to this.

[0077] In the light-absorbing layer 4, the ratio (MA / MD) of the mass of the acceptor (MA) to the mass of the donor (MD) is preferably 0.1 or more and 2.0 or less, and more preferably 1.0 or more and 2.0 or less. When the ratio (MA / MD) is within this range, the balance between the acceptor and the donor in the solar cell 10 is good, and the energy conversion efficiency of the solar cell 10 is improved.

[0078] In a perovskite solar cell, a light absorbing layer 4 containing a perovskite compound represented by formula (2) is used. ABX3 (2)

[0079] The perovskite compound is a compound represented by formula (2) in which A is a monovalent cation, B is a divalent cation, and X is a halide anion. The perovskite compound may be a perovskite crystal or a perovskite complex.

[0080] In formula (2), examples of A include monovalent cations such as alkali metal cations and organic cations. Among them, A is preferably a potassium cation (K + ), rubidium cation (Rb + ), cesium cation (Cs + ), methylammonium cation (CH3NH3 + ), or formamidinium cation (NH2CHNH2 + ) (hereinafter referred to as FA + The use of these cations allows the formation of stable three-dimensional crystals, resulting in stable solar cells. These monovalent cations may be used alone or as a mixture of two or more types.

[0081] In formula (2), examples of B include lead cations (Pb 2+ ), or tin cations (Sn 2+ ) and other divalent cations. Indium cations (In 3+ ), antimony cation (Sb 3+ These cations may be used alone or as a mixture of two or more kinds. Among them, B is preferably Pb 2+ is preferred because it can form stable three-dimensional crystals.

[0082] In formula (2), examples of X include fluoride anion (F - ), chloride anion (Cl - ), bromide anion (Br - ), or iodide anion (I -In formula (2), all three X's may be the same halide anion, or may be a mixture of two or more types of halide anions. For example, the spectral sensitivity characteristics can be changed by changing the type and ratio of the halide anions. Among them, I - or Br - or a combination thereof is preferred because it can form a stable three-dimensional crystal, and X is at least Br - It is more preferred that the composition contains:

[0083] Among the above-mentioned combinations, in formula (2), A is K + , Rb + , Cs + , (CH3)4N + , and HC(NH2)2 + B represents any one cation selected from the group consisting of Pb 2+ and X represents (I 1-y Br y ) - Preferably, y is greater than 0 and equal to or less than 1, and more preferably, y is greater than 0.25 and equal to or less than 1.

[0084] The thickness of the light-absorbing layer 4 is not particularly limited, as long as the desired photoelectric conversion efficiency can be obtained, whether the light-absorbing layer 4 is a bulk heterojunction photoelectric conversion layer or a perovskite-type photoelectric conversion layer. The thickness of the light-absorbing layer 4 is preferably 0.2 nm or more and 3000 nm or less, and more preferably 10 nm or more and 600 nm or less. When the thickness of the light-absorbing layer 4 is 3000 nm or less, the sheet resistance of the light-absorbing layer 4 is likely to have a desired value. On the other hand, when the thickness of the light-absorbing layer 4 is 0.2 nm or more, a short circuit between the first electrode 2 and the second electrode 6 is unlikely to occur.

[0085] The light absorbing layer 4 is formed by applying a coating liquid for a light absorbing layer onto a base layer (electron transport layer 3 in the example shown in FIG. 1 ) that serves as the base, and then drying the coating liquid. Examples of methods for applying the coating liquid for a light absorbing layer include a casting method and a spin coating method.

[0086] (Hole Transport Layer) The hole transport layer 5 is provided between the light absorbing layer 4 and the anode (second electrode 6 in the example shown in FIG. 1 ). The hole transport layer 5 is provided so as to facilitate the transport (injection) of holes from the light absorbing layer 4 to the anode. The provision of the hole transport layer 5 increases the efficiency of hole transport from the light absorbing layer 4 to the anode, thereby improving the photoelectric conversion efficiency of the solar cell 10. The hole transport layer 3 contains the compound (1) according to the first embodiment of the present invention. The hole transport layer 3 may contain only the compound (1) according to the first embodiment of the present invention, or may further contain an additive. As the additive, a conventionally known additive such as an interface treatment agent can be used.

[0087] By using the compound (1) according to the first embodiment of the present invention as the hole transport material constituting the hole transport layer 5, the photoelectric conversion efficiency of the solar cell 10 can be improved.

[0088] The hole transport layer 5 is formed by applying a hole transport layer coating liquid containing the compound (1) according to the first embodiment of the present invention onto an underlying underlayer (light absorbing layer 4 in the example shown in FIG. 1 ) and drying the applied liquid. Examples of methods for applying the hole transport layer coating liquid include casting and spin coating. The hole transport layer coating liquid is prepared by dissolving or dispersing a hole transport material containing at least the compound (1) according to the first embodiment of the present invention in a solvent.

[0089] (Other Components) The solar cell 10 may further include other components, as needed, in addition to the substrate 1, first electrode 2, electron transport layer 3, light absorption layer 4, hole transport layer 5, and second electrode 6 described above. Examples of other components include one or a combination of two or more selected from the group consisting of a protective sheet layer, a filler layer, a barrier layer, a protective hard coat layer, a strength support layer, an antifouling layer, a highly light-reflecting layer, a light-confining layer, an ultraviolet-blocking layer, an infrared-blocking layer, and an encapsulant layer. Furthermore, the solar cell 10 may include an adhesive layer laminated between each layer, as needed.

[0090] 1 , the solar cell according to this embodiment may also omit the electron transport layer 3. The solar cell according to this embodiment may not have an electron transport layer, and may have the light absorbing layer 4 directly laminated on the first electrode 2, for example.

[0091] 1 illustrates an example in which the first electrode 2 is an anode, the second electrode 6 is a cathode, and a cathode, an electron transport layer 3, a light absorbing layer 4, a hole transport layer 5, and an anode are provided on the substrate 1 in this order from the substrate 1 side. However, the solar cell according to this embodiment is not limited to this, and for example, the first electrode 2 may be the anode and the second electrode 6 may be the cathode. In this case, the stacking order of the hole transport layer 5 and the electron transport layer 3 is reversed from that shown in FIG. 1. When the first electrode 2 is an anode and the second electrode 6 is a cathode, for example, an anode, a hole transport layer 5, a light absorbing layer 4, an electron transport layer 3, and a cathode are provided on the substrate 1 in this order from the substrate 1 side.

[0092] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0093] Compounds (H-1) to (H-6) described in the first embodiment were synthesized by the following method. Also, a comparative compound represented by formula (h-1) (hereinafter, sometimes referred to as compound (h-1)) and a comparative compound represented by formula (h-2) (hereinafter, sometimes referred to as compound (h-2)) were synthesized by the following method.

[0094] (Synthesis of Compound (H-1)) Compound (H-1) was synthesized according to the following reaction scheme.

[0095]

[0096] In the above reaction, a 500 mL two-neck flask equipped with a reflux condenser, a thermometer, and a stirrer was used as a reaction vessel. Into this reaction vessel, 0.0354 mol (9.39 g) of secondary amine (A-1), 0.0074 mol (4.67 g) of compound (S) (2,2',7,7'-tetrabromo-9,9'-spirobi[9H-fluorene], 0.00044 mol (0.060 g) of tris(dibenzylideneacetone)dipalladium(0) as a palladium catalyst, and 0.001 g of [4-(N,N-dimethylamino)phenyl]di-tert-butylphosphine as an organophosphorus ligand were added. 77 mol (0.47 g) of toluene and 0.0384 mol (3.688 g) of sodium tert-butoxide as a base were charged, and the atmosphere inside the reaction vessel was replaced with nitrogen while stirring at room temperature. Thereafter, 150 g of xylene as an organic solvent was charged into the reaction vessel, and the reaction solution in the reaction vessel was heated to the reflux temperature while stirring with a magnetic stirrer, and the reaction was carried out for 4 hours. Then, the disappearance of compound (S) was confirmed by TLC (thin layer chromatography).

[0097] After the reaction, the temperature of the reaction solution in the reaction vessel was cooled to 80°C. Next, 6.1 g of activated clay "SA-1" (manufactured by Japan Activated Clay Co., Ltd.) was added to the reaction solution in the reaction vessel, and the mixture was stirred for an additional 30 minutes. Thereafter, the reaction solution in the reaction vessel was filtered, and a clay adsorption treatment for recovering the filtrate was carried out twice. Next, the obtained filtrate was concentrated using an evaporator to obtain a brown oil.

[0098] The resulting oil was purified by column chromatography (developing solvent: toluene) and then concentrated using an evaporator. The concentrated oil was dissolved in a small amount of THF, and the resulting solution was added dropwise using a dropper to a beaker containing 100 g of isohexane and stirred. The precipitated solid (powder) was collected by filtration.

[0099] The filtered solid was then dried in a vacuum oven at 100°C for 3 hours to obtain a pale yellow compound (H-1) as a product. The yield of compound (H-1) was 5.97g, or 59.0%.

[0100] The resulting product: 1H-NMR (proton nuclear magnetic resonance) analysis was performed. 1 From the chemical shift values ​​of the H-NMR spectrum, the obtained product was confirmed to be the target compound (H-1). 1 DMSO (dimethyl sulfoxide) was used as a heavy solvent for measuring the H-NMR spectrum. 1 The H-NMR chart is shown below.

[0101] (Synthesis of Compound (H-2)) As shown in the following reaction scheme, a pale yellow compound (H-2) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.39 g) of the secondary amine (A-1) was replaced with 0.0354 mol (10.03 g) of the secondary amine compound represented by formula (A-2) (hereinafter, sometimes referred to as secondary amine (A-2)). The yield of compound (H-2) was 5.51 g, a yield of 51.7%.

[0102]

[0103] (Synthesis of Compound (H-3)) As shown in the following reaction scheme, a pale yellow compound (H-3) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.39 g) of the secondary amine (A-1) was replaced with 0.0354 mol (10.45 g) of the secondary amine compound represented by formula (A-3) (hereinafter, sometimes referred to as secondary amine (A-3)). The yield of compound (H-3) was 5.04 g, a yield of 45.7%.

[0104]

[0105] (Synthesis of Compound (H-4)) As shown in the following reaction scheme, a pale yellow compound (H-4) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.89 g) of a secondary amine compound represented by formula (A-4) (hereinafter, sometimes referred to as secondary amine (A-4)) was used instead of 0.0354 mol (9.39 g) of secondary amine (A-1). The yield of compound (H-4) was 6.02 g, a yield of 57.1%.

[0106]

[0107] (Synthesis of Compound (H-5)) As shown in the following reaction scheme, a pale yellow compound (H-5) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.39 g) of a secondary amine compound represented by formula (A-5) (hereinafter, may be referred to as secondary amine (A-5)) was used instead of 0.0354 mol (9.39 g) of secondary amine (A-1). The yield of compound (H-5) was 5.97 g, which was a yield of 59.0%.

[0108]

[0109] (Synthesis of Compound (H-6)) As shown in the following reaction scheme, a pale yellow compound (H-6) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.39 g) of the secondary amine (A-1) was replaced with 0.0354 mol (10.03 g) of the secondary amine compound represented by formula (A-6) (hereinafter, sometimes referred to as secondary amine (A-6)). The yield of compound (H-6) was 5.46 g, a yield of 51.2%.

[0110]

[0111] (Synthesis of Compound (h-1)) As shown in the following reaction scheme, a pale yellow compound (h-1) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.39 g) of the secondary amine (A-1) was replaced with 0.0354 mol (8.75 g) of the secondary amine compound represented by formula (a-1) (hereinafter, sometimes referred to as secondary amine (a-1)). The yield of compound (h-1) was 6.10 g, a yield of 63.6%.

[0112]

[0113] (Synthesis of Compound (h-2)) As shown in the following reaction scheme, a pale yellow compound (h-2) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0354 mol (9.39 g) of the secondary amine (A-1) was replaced with 0.0354 mol (7.26 g) of the secondary amine compound represented by formula (a-2) (hereinafter, sometimes referred to as secondary amine (a-2)). The yield of compound (h-2) was 4.82 g, a yield of 57.8%.

[0114]

[0115] The compounds (H-2) to (H-6), (h-1) and (h-2) were also measured. 1 From the chemical shift values ​​of the H-NMR spectrum, it was confirmed that the target compound was obtained.

[0116] Next, solar cells (B-1) to (B-6) according to Examples 1 to 6 and solar cells (b-1) to (b-3) according to Comparative Examples 1 to 3 were produced by the following method.

[0117] (Production of Solar Cell (B-1)) A 1.6 mm thick conductive glass substrate (product name "FTN1.6" manufactured by Nippon Sheet Glass Co., Ltd., hereinafter sometimes referred to as FTO substrate) on which a fluorine-doped tin oxide (FTO) layer was formed was used as the substrate. This FTO substrate was cut into a 20 mm x 20 mm square.

[0118] Next, the cut FTO substrate was protected with mending tape except for a portion 5 mm from the edge. The FTO layer on the FTO substrate protected with the mending tape was then removed by etching using a cotton swab dipped in 6N hydrochloric acid with dissolved zinc powder. The removed FTO substrate was washed with ion-exchanged water, and the masking tape was removed. The FTO substrate was then ultrasonically cleaned in a neutral detergent solution (AS ONE Corporation's "Clean Ace S" (product name) diluted 10 times) for 15 minutes, followed by ultrasonic cleaning in ion-exchanged water, isopropyl alcohol, and acetone, in that order, for 15 minutes each. The surface of the FTO substrate was then subjected to UV treatment in an ozone atmosphere (hereinafter sometimes referred to as ultraviolet-ozone treatment) for 30 minutes.

[0119] Next, 200 μL of a 4% aqueous solution of tin(IV) oxide nanoparticles was dropped onto the FTO substrate and spin-coated using a spin coater. The spin coating was performed under the following conditions: First, after the 4% aqueous solution of tin(IV) oxide nanoparticles was dropped, the spin coater was accelerated to a rotation speed of 4000 rpm over 3 seconds and maintained at 4000 rpm for 20 seconds. The rotation speed was then decelerated for 3 seconds and the spin coater rotation was stopped. The 4% aqueous solution of tin(IV) oxide nanoparticles was prepared by mixing a 15% aqueous dispersion of SnO (manufactured by Thermo Fisher Scientific) with ion-exchanged water in a ratio of 4:11.

[0120] Thereafter, the FTO substrate was annealed (heat treated) at 150° C. for 30 minutes using a hot plate to form an electron transport layer of tin (IV) oxide nanoparticles having a thickness of 20 nm.

[0121] Next, the FTO substrate on which this electron transport layer was formed was subjected to UV-ozone treatment again for 15 minutes, and then placed in a glove box in an atmosphere having a temperature of 23°C ± 1°C and a dew point temperature of -20 ± 5°C.

[0122] Separately, in a glove box, 0.357 g (0.775 mmol) of lead iodide (product name "L0279" manufactured by Tokyo Chemical Industry Co., Ltd.), 0.174 g (0.475 mmol) of lead bromide (product name "L0346" manufactured by Tokyo Chemical Industry Co., Ltd.), 0.011 g (0.050 mmol) of rubidium iodide (product number "251445" manufactured by Sigma-Aldrich), and 0.039 g (0.105 mmol) of cesium iodide (product name "C2205" manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed. 1.25 mL of a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (volume ratio 4:1) was added to 0.181 g (1.05 mmol) of formamidine hydroiodide (product name "F0974" manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.000306 g (0.00125 mmol) of 5-aminovaleric acid hydroiodide (product name "A2984" manufactured by Tokyo Chemical Industry Co., Ltd.), and the mixture was stirred at room temperature for 2 hours to dissolve the solid content. As a result, FA 0.84 Cs 0.12Rb 0.04 Pb(I 0.75 Br 0.25 A solution containing a perovskite compound having a composition represented by the formula (hereinafter sometimes referred to as a perovskite solution) 3 was prepared.

[0123] 150 μL of this perovskite solution was dropped onto the electron transport layer of the FTO substrate in a glove box and spin-coated using a spin coater. Spin coating was performed under the following conditions. First, after dropping the perovskite solution, the spin coater was accelerated to a rotation speed of 1000 rpm over 1 second and maintained at 1000 rpm for 10 seconds. The spin coater was then accelerated to a rotation speed of 5000 rpm over an additional 2 seconds, and then maintained at 5000 rpm for 40 seconds. During this time, 800 μL of chlorobenzene was dropped. The chlorobenzene was dropped 32 seconds after the spin coater rotation speed reached 5000 rpm. Then, 40 seconds after the spin coater rotation speed reached 5000 rpm, the spin coater was decelerated for 1 second and the spin coater rotation was stopped.

[0124] After the spin coater was stopped, the FTO substrate spin-coated with the perovskite solution was annealed (heat treated) at 60° C. for 1 minute using a hot plate, and then further annealed at 100° C. for 45 minutes. As a result, a perovskite layer with a thickness of approximately 500 nm was formed as a light absorption layer on the electron transport layer.

[0125] Next, 75 mg of compound (H-1) as a hole transport material, 9.1 mg of lithium bis(trifluoromethanesulfonyl)imide as an additive, and 26.5 mg of 4-tert-butylpyridine were dissolved in a mixed solvent of 1 mL of chlorobenzene and 0.017 mL of acetonitrile to prepare a hole transport material solution containing compound (H-1) as a hole transport layer coating liquid. The prepared hole transport material solution was spin-coated using a spin coater at a rotation speed of 4000 rpm for 30 seconds to form a hole transport layer with a thickness of 100 nm on the perovskite layer. The laminate thus formed was left to stand in an environment with a humidity of 5% for 12 hours.

[0126] Thereafter, a gold electrode was deposited on the hole transport layer to a thickness of 80 nm by vacuum deposition to form a solar cell (B-1).

[0127] (Production of solar cells (B-2) to (B-6) and (b-1) to (b-3)) Instead of compound (H-1), compounds (H-2) to (H-6), (h-1), (h-2) or a compound represented by formula (h-3) (Spiro-OMeTAD, hereinafter sometimes referred to as compound (h-3)) shown in Table 1 were used to form a hole transport layer. Solar cells (B-2) to (B-6) and (b-1) to (b-3) were produced in the same manner as in the production of solar cell (B-1). For compound (h-3), a reagent "Spiro-MeOTAD (product number: 792071)" manufactured by Sigma-Aldrich Japan LLC was used.

[0128]

[0129] <Evaluation> The compounds (H-1) to (H-6) used in Examples 1 to 6 and the compounds (h-1) to (h-3) used in Comparative Examples 1 to 3 were evaluated for I.P. and solubility in organic solvents by the following methods. The evaluation results are shown in Table 1 below, along with the molecular weights of the compounds (H-1) to (H-6) and (h-1) to (h-3). The evaluations were carried out at a temperature of 23°C and a humidity of 50% RH, unless otherwise specified.

[0130] (I.P.) Powders of each of the compounds (H-1) to (H-6) and (h-1) to (h-3) were used as samples, and the samples were directly irradiated with light in an air atmosphere using an air photoelectron spectrometer ("AC-3" (trade name) manufactured by Riken Keiki Co., Ltd.) to measure the threshold energy at which photoelectrons are emitted, thereby measuring the ionization potential of the samples.

[0131] An atmospheric photoelectron spectrometer can measure photoelectrons from a sample surface without placing the sample in a vacuum. Ultraviolet light emitted from a deuterium lamp is monochromatized by a spectrometer and irradiated onto the sample. The wavelength of the ultraviolet light and the energy of one photon are increased in steps within the wavelength range of 412 to 180 nm and the range of 3.0 to 7.0 eV, respectively. When the energy of the irradiated light exceeds the IP of the sample, photoelectrons are emitted from the sample surface into the atmosphere and captured by an open counter.

[0132] (Solubility) Compounds (H-1) to (H-6) and compounds (h-1) to (h-3) were each dissolved in chlorobenzene at a concentration of 9.1% by mass. The evaluation criteria were as follows: A (good): Completely dissolved at room temperature. B (slightly poor): Completely dissolved by heating. C (poor): Not completely dissolved even when heated.

[0133]

[0134] (Photoelectric Conversion Characteristics) The photoelectric conversion characteristics of each of the solar cells manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were evaluated by the following method. First, the measurement area was 0.1 cm2 per point. 2 The J (current)-V (voltage) curve characteristics were measured using a source meter (a voltage-current generator with measurement function) while irradiating light onto each masked solar cell using a solar simulator. Measurements were carried out at three locations per solar cell. The solar simulator used was a spectrometer "HAL-320" manufactured by Asahi Spectroscopy Co., Ltd. The light intensity of the measurement light source was 100 mW / cm using a reference solar cell. 2 The source meter used was a source meter (Model 6242) manufactured by ADC Corporation. The J-V curve characteristics were measured twice per location, once for each condition: forward scan, in which the voltage is scanned in the direction increasing, and reverse scan, in which the voltage is scanned in the direction decreasing. Next, from the measurement results, the short-circuit currents (Jsc, unit: mA / cm) for both forward and reverse were calculated. 2The photoelectric conversion efficiency (PCE, unit: %) was calculated by the following formula (i): PCE = (Jsc × Voc × FF / 100) × 100 (i)

[0135] Table 2 shows the photoelectric conversion characteristic values ​​(PCE, Jsc, Voc, FF) of each solar cell at the location where PCE was maximum among the three locations measured for each solar cell. In Table 1, "R" indicates reverse. In Table 1, the reverse value that gives a higher value than forward is taken as PCE.

[0136]

[0137] Compounds (H-1) to (H-6) shown in Table 1 are compounds (1) represented by formula (1). The evaluation results for solubility in organic solvents for compounds (H-1) to (H-6) were A or B, demonstrating excellent solubility in organic solvents. Furthermore, the I.P. of compounds (H-1) to (H-6) is close to the I.P. of perovskite (e.g., 5.3 to 5.7 eV) and is slightly shallower than the I.P. of perovskite. For this reason, compounds (H-1) to (H-6) can be suitably used as hole transport materials for perovskite solar cells.

[0138] Furthermore, as shown in Table 2, the solar cells (B-1) to (B-6) in which the hole transport layer was formed using the compounds (H-1) to (H-6) all exhibited higher PCE than the solar cells (b-1) to (b-3) according to the comparative example.

[0139] From the above results, it was confirmed that the PCE of solar cells can be effectively improved by using the compounds (H-1) to (H-6) as hole transport materials.

[0140] Furthermore, as shown in Examples 2 and 6, in formula (1), R 1 ~R 8 It has been confirmed that when three or more of the groups are fluoro groups, the PCE of the solar cell can be further improved when compound (1) is used in the solar cell.

[0141] The compound according to the present invention can be used, for example, in a solar cell. The solar cell according to the present invention can also be used, for example, in a large-scale power supply, a power supply for outdoor equipment, a power supply for indoor electronic equipment, and a portable power supply.

Claims

1. A compound represented by formula (1). (In the formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 each independently represents a hydrogen atom, a methyl group, a methoxy group, or a fluoro group; R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 Two or more of these represent fluoro groups.) 2. The compound according to claim 1, wherein the formula (1) is formula (H-1), (H-2), (H-3), (H-4), (H-5), or (H-6).

3. In the formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 The compound according to claim 1 , wherein three or more of 4. (In the formula (1), R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 The compound according to claim 3, wherein the ratio of methoxy groups to fluoro groups in 5. A hole transport material comprising the compound of claim 1.

6. A solar cell comprising: an anode; a cathode; a light absorbing layer provided between the anode and the cathode; and a hole transport layer provided between the anode and the light absorbing layer, wherein the hole transport layer comprises the hole transport material according to claim 5.

7. The solar cell according to claim 6, wherein the light absorbing layer contains a perovskite compound represented by formula (2): ABX3 (2) (in formula (2), A is K + , Rb + , Cs + , CH3NH3 + , and NH2CHNH2 + B represents any one cation selected from the group consisting of Pb 2+ X represents (I 1-y Br y ) - and y is greater than 0 and equal to or less than 1.

8. The solar cell according to claim 7, wherein in formula (2), y is greater than 0.25 and equal to or less than 1.

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