Compound and method for producing same, hole transport material, and solar cell

Abstract

This compound is represented by formula (1). In formula (1), R1, R2, R3, R4, R5, Ra, and Rb each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms. This hole transport material contains the compound represented by formula (1). This solar cell has a hole transport layer including said hole transport material.

Description

Compound and method for producing the same, hole transport material, and solar cell

[0001] The present invention relates to a compound and a method for producing the same, 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] 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 that can improve the photoelectric conversion efficiency of a solar cell when used in the solar cell, a method for producing the same, a hole transport material, and a solar cell using the same.

[0008] The compound according to the present invention is represented by formula (1).

[0009]

[0010] In the formula (1), R １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms.

[0011] The hole transport material according to the present invention contains the compound.

[0012] The solar cell according to the present invention comprises 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.

[0013] The method for producing the compound according to the present invention includes a step of reacting a compound represented by formula (A) with a compound represented by formula (B).

[0014] In the formula (B), R １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb are R in the formula (1). １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb represent the same groups.

[0015] According to the present invention, it is possible to provide a novel compound that can improve the photoelectric conversion efficiency of a solar cell when used in the solar cell, a method for producing the same, a hole transport material, and a solar cell using the same.

[0016] 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 1 H-NMR chart.

[0017] 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.

[0018] Hereinafter, the compound name may be followed by "system" to refer to the compound and its derivatives in a comprehensive manner. When the compound name is followed by "system" to represent 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." In the explanation of the formulas, "independently" means that they 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. Furthermore, in this specification, "at least one of A and B" means "A and / or B." "A and / or B" means "A or B, or A and B."

[0019] [First embodiment: Compound and production method thereof] 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)) and a production method thereof. Compound (1) is a 9,9'-spirobifluorene derivative (spirobifluorene-based organic compound).

[0020]

[0021] In formula (1), R １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms.

[0022] Compounds having a spiro skeleton have high photoelectric conversion efficiency in solar cells. As a result of extensive research, the present inventors have found that compound (1) has hole transport ability and, when used in solar cells, can improve the photoelectric conversion efficiency of solar cells compared to other known compounds having a spiro skeleton. The present inventors have also found that compound (1) has excellent solubility in organic solvents and can be used to form a thin film using a solution of compound (1) dissolved in an organic solvent. Compound (1) can form a thin film that achieves 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, to form a hole transport layer.

[0023] The alkyl chain of the substituent in compound (1) is linear or branched and unsubstituted unless otherwise specified. When the alkyl chain has 8 or less carbon atoms, the use of compound (1) in a solar cell can provide a solar cell with excellent photoelectric conversion efficiency.

[0024] The alkyl group having 1 to 8 carbon atoms in compound (1) (i.e., the alkyl group having 1 to 8 carbon atoms in formula (1)) is preferably an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group.

[0025] The alkoxy group having 1 to 8 carbon atoms in compound (1) (i.e., the alkoxy group having 1 to 8 carbon atoms in formula (1)) is preferably an alkoxy group having 1 to 3 carbon atoms, more preferably a methoxy group.

[0026] In order to improve the solubility in organic solvents and the photoelectric conversion efficiency when used as a material for a hole transport layer of a solar cell, the compound (1) may be a compound represented by the formula (1) below: １ , R ２ , R ３ , R ４ , R ５ A compound in which at least one of R a and R b is an alkoxy group having 1 to 8 carbon atoms is preferred. １ , R ２ , R ３ , R ４ , R５ Among them, compounds in which at least one of R a and R b is a methoxy group are more preferred. ３ At least one of Ra and Rb represents a methoxy group, and R ３ Among them, compounds in which R represents a methoxy group or a methyl group are more preferred. ３ At least one of Ra and Rb represents a methoxy group, and R ３ Even more preferred are compounds in which R a and R b each independently represent a methoxy group or a methyl group.

[0027] Suitable examples of compound (1) for improving the solubility in organic solvents and the photoelectric conversion efficiency when used as a material for a hole transport layer of a solar cell include compounds represented by formulas (H-1), (H-2), (H-3), and (H-4) (hereinafter, these may be referred to as compounds (H-1), (H-2), (H-3), and (H-4), respectively). Among these, compounds represented by formula (1) in which R ３ At least one of Ra and Rb represents a methoxy group, and R ３ More preferred are compounds (H-1), (H-2), and (H-4) in which Ra and Rb are each independently a methoxy group or a methyl group.

[0028]

[0029] [Method for Producing Compound (1)] Next, a method for producing compound (1) will be described. The method for producing compound (1) includes a step (hereinafter sometimes referred to as a reaction step) of reacting a compound represented by formula (A) (2,2',7,7'-tetrabromo-9,9'-spirobi[9H-fluorene]) (hereinafter sometimes referred to as compound (A)) with a secondary amine compound represented by formula (B) (hereinafter sometimes referred to as compound (B)).

[0030]

[0031] In addition, in formula (B), R １ , R ２ , R ３ , R ４ , R５ , Ra, and Rb are R in formula (1). １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb represent the same groups.

[0032] Compound (1) can be obtained by the above-mentioned reaction steps. That is, compound (1) is produced (synthesized) according to the reaction represented by the following reaction formula (r-1) (hereinafter, sometimes referred to as reaction (r-1)) or a method equivalent thereto.

[0033]

[0034] In the reaction (r-1), 1 molar equivalent of the compound (A) is reacted with 4 molar equivalents of the compound (B) to obtain 1 molar equivalent of the target compound (1).

[0035] Reaction (r-1) is carried out by mixing compound (A) and compound (B) with a stirrer. The amount of compound (B) relative to compound (A) is preferably 4 molar equivalents or more and 10 molar equivalents or less per molar equivalent of compound (A).

[0036] The reaction step (i.e., reaction (r-1)) is preferably carried out in the presence of a catalyst. For example, a palladium catalyst is used as the catalyst.

[0037] Examples of the palladium catalyst include palladium(II) chloride, palladium(II) acetate, palladium(II) trifluoroacetate, tris(dibenzylideneacetone)dipalladium(0), di-μ-chlorobis[(η-allyl)palladium(II)], and bis(acetylacetonato)palladium(II).

[0038] Among these palladium catalysts, palladium(II) acetate and tris(dibenzylideneacetone)dipalladium(0) are preferred, with palladium(II) acetate being more preferred.

[0039] The palladium catalyst is more preferably used in combination with an organophosphorus ligand. The palladium catalyst may be used in combination with an organophosphorus ligand, or a palladium catalyst coordinated with an organophosphorus ligand may be used as the palladium catalyst.

[0040] Examples of organic phosphorus ligands include triarylphosphines, trialkylphosphines, trialkylphosphonium borate salts, bidentate phosphines, [4-(N,N-dimethylamino)phenyl]di-tert-butylphosphine (hereinafter sometimes referred to as Amphos), and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (hereinafter sometimes referred to as Xphos). Examples of triarylphosphines include triphenylphosphine and tri-o-tolylphosphine. Examples of trialkylphosphines include tri-tert-butylphosphine and tricyclohexylphosphine. Examples of trialkylphosphonium borate salts include tri-tert-butylphosphonium borate salts. Examples of tri-tert-butylphosphonium borate salts include tri-tert-butylphosphonium tetraphenylborate and tri-tert-butylphosphonium tetrafluoroborate. Bidentate phosphines include 2,2'-bis(diphenylphosphino)diphenyl ether, 9,9-dimethyl-4,5-bis(diphenylphosphino)-9H-xanthene, and 1,1'-bis(diphenylphosphino)ferrocene.

[0041] Among these organic phosphorus ligands, borate salts of tri-tert-butylphosphonium, Amphos, and Xphos are preferred, and borate salts of tri-tert-butylphosphonium are more preferred.

[0042] Examples of palladium catalysts having an organic phosphorus ligand coordinated thereto include tetrakis(triphenylphosphine)palladium(0), bis(triphenylphosphine)palladium(II) dichloride, bis(di-tert-butyl(4-dimethylaminophenyl)phosphine)dichloropalladium(II), and 9-{dicyclohexyl[2',4',6'-tris(propan-2-yl)-[1,1'-biphenyl]-2-yl}-λ-phosphanyl}-O-methanesulfonyl-8-ylmethyl-8-λ-aza-9-para.

[0043] As described above, reaction (r-1) in the reaction step is preferably carried out in the presence of an organophosphorus ligand and a palladium catalyst, or a palladium catalyst coordinated with an organophosphorus ligand, and even more preferably in the presence of an organophosphorus ligand and a palladium catalyst. When a mixture of an organophosphorus ligand and a palladium catalyst is used, weighing in air is possible, and high reactivity and low cost can be achieved. Furthermore, when a mixture of an organophosphorus ligand and a palladium catalyst is used in this manner, the organophosphorus ligand preferably comprises at least one selected from the group consisting of tri-tert-butylphosphonium borate, Amphos, and Xphos. Furthermore, the palladium catalyst preferably comprises at least one selected from the group consisting of palladium(II) acetate and tris(dibenzylideneacetone)dipalladium(0).

[0044] When reaction (r-1) is carried out in the presence of an organophosphorus ligand and a palladium catalyst, the amount of the organophosphorus ligand relative to the palladium catalyst is preferably 1 molar equivalent to 6 molar equivalents relative to 1 molar equivalent of the palladium catalyst, and the amount of the palladium catalyst relative to compound (A) is preferably 0.0005 molar equivalents to 0.1 molar equivalents relative to 1 molar equivalent of compound (A).

[0045] Furthermore, when the reaction (r-1) is carried out in the presence of a palladium catalyst having an organophosphorus ligand coordinated thereto, the amount of the palladium catalyst having an organophosphorus ligand coordinated thereto relative to compound (A) is preferably 0.0005 molar equivalents or more and 0.1 molar equivalents or less per molar equivalent of compound (A).

[0046] The reaction (r-1) may be carried out in the presence of a base, such as sodium tert-butoxide, potassium tert-butoxide, sodium methylate, tripotassium phosphate, or cesium fluoride.

[0047] When reaction (r-1) is carried out in the presence of a base, the amount of base added relative to compound (A) is preferably 4 molar equivalents or more and 10 molar equivalents or less per molar equivalent of compound (A).

[0048] Reaction (r-1) can be carried out in a solvent. Examples of the solvent include benzene derivatives such as xylene and toluene; hydrophilic solvents such as tetrahydrofuran, 1,4-dioxane, and dimethylformamide; and hydrophobic solvents such as 2-methyltetrahydrofuran and cyclohexyl methyl ether. From the viewpoints of cost and yield, toluene and / or xylene are particularly preferred as the solvent.

[0049] The reaction temperature of the reaction (r-1) is preferably 80° C. or higher and 140° C. or lower. The reaction time of the reaction (r-1) is preferably 1 hour or higher and 10 hours or lower.

[0050] The reaction (r-1) is preferably carried out in an inert gas atmosphere, such as nitrogen gas or argon gas.

[0051] 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, activated clay, etc., recrystallization or crystallization using a solvent, etc. Nuclear magnetic resonance analysis (NMR) or the like can be used to identify the resulting compound.

[0052] [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).

[0053] As described in the first embodiment, compound (1) can improve the photoelectric conversion efficiency of a solar cell when used in the solar cell. Furthermore, compound (1) has excellent solubility in organic solvents, and a thin film can be formed using a solution of compound (1) dissolved in an organic solvent. Therefore, a hole transport material containing compound (1) has excellent solubility in organic solvents, and can form a thin film that can improve the photoelectric conversion efficiency of the solar cell when used in the solar cell.

[0054] 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).

[0055] The hole transport material according to this embodiment may further contain an additive, if necessary. As the additive, a conventionally known additive such as an interface treatment agent can be used.

[0056] [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 light absorbing layer. The hole transport layer contains the compound (1) according to the first embodiment.

[0057] 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.

[0058] 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 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.

[0059] 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.

[0060] (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.

[0061] 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.

[0062] (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.

[0063] 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).

[0064] 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 6 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.

[0065] 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.

[0066] 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.

[0067] 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).

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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 uneven shapes include a textured structure, a pyramidal structure, a wave-shaped structure, a comb-shaped structure, and a nanopillow structure. When the first electrode 2 is uneven, incident light is scattered by the unevenness of the first electrode 2, so that more light is taken in by the light absorbing layer 4, and the photoelectric conversion efficiency of the solar cell 10 is improved.

[0072] 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 .

[0073] Various known methods may be appropriately used 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.

[0074] (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.

[0075] 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 conductive organic compounds, charge transfer complexes, alkali metals, alkaline earth metals, organic compounds doped with alkali metals or alkaline earth metals, and metal oxides.

[0076] 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) and bathophenanthroline (Bphen) doped with alkali metals or alkaline earth metals. Preferred alkali metals and alkaline earth metals used for doping are lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, or barium, and more preferred are lithium, cesium, barium, or strontium. Examples of metal oxides that can be used as electron transport materials include titanium oxide, zinc oxide, and tin oxide.

[0077] 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.

[0078] The electron transport layer 3 can be formed by a known method such as vacuum deposition.

[0079] (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 passed through the substrate 1, the first electrode 2, and the electron transport layer 3.

[0080] The light absorbing layer 4 may be a bulk heterojunction type light absorbing layer (photoelectric conversion layer) containing a donor (electron donor) and an acceptor (electron acceptor), or may be a perovskite absorbing layer containing a perovskite compound.

[0081] 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. An 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 also contain other compounds.

[0082] 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, and 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.

[0083] 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.

[0084] 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.

[0085] Examples of electron-accepting organic materials include fullerene and its derivatives (PCBM, etc.), carbon nanotubes and their derivatives, perylene and its derivatives (PTCDA, PTCDI, etc.), naphthalene derivatives (NTCDA, NTCDI, etc.), oligomers or polymers having pyridine and its derivatives in their skeletons, fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and their derivatives, tris(8-hydroxyquinolinato)aluminum complexes, bis(4-methyl-8-quinolinato)aluminum complexes, distyrylarylene derivatives, silole compounds, etc. Among these, fullerene derivatives (PCBM, etc.) are particularly suitable as the electron-accepting organic material, but the present invention is not limited to this.

[0086] 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.

[0087] In a perovskite solar cell, a light absorbing layer 4 containing a perovskite compound represented by formula (2) is used. ３ (2)

[0088] 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.

[0089] In formula (2), examples of A include monovalent cations such as alkali metal cations and organic cations. Examples of monovalent alkali metal cations include potassium cations (K ＋ ), rubidium cation (Rb ＋ ), cesium cation (Cs ＋ Examples of monovalent organic cations include methylammonium cation (CH ３ NH ３ ＋ ), formamidinium cation (NH ２ CHNH ２ ＋ These monovalent cations may be used alone or in combination of two or more.

[0090] In formula (2), examples of B include lead cations (Pb ２＋ ), tin cations (Sn ２＋ ) and other divalent cations. Indium cations (In ３＋ ), antimony cation (Sb ３＋ These cations may be used alone or in combination of two or more.

[0091] In formula (2), examples of X include fluoride anion (F － ), chloride anion (Cl － ), bromide anion (Br － ), 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.

[0092] The thickness of the light absorbing layer 4 is not particularly limited, regardless of whether it is a bulk heterojunction light absorbing layer or a perovskite-type light absorbing layer, as long as the desired photoelectric conversion efficiency is obtained. 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 attain 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.

[0093] The light absorbing layer 4 is formed by applying a coating liquid for a light absorbing layer onto an underlying layer (electron transport layer 3 in the example shown in FIG. 1 ) that serves as the underlying layer, 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.

[0094] (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 5 contains the compound (1) according to the first embodiment of the present invention. The hole transport layer 5 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.

[0095] 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 charges generated in the light absorption layer 4 can be efficiently extracted to the outside, thereby improving the photoelectric conversion efficiency of the solar cell 10.

[0096] 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.

[0097] (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.

[0098] 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 stacked on the first electrode 2, for example.

[0099] 1 illustrates an example in which the first electrode 2 is a cathode, the second electrode 6 is an anode, and a cathode, an electron transport layer, a light absorbing layer, a hole transport layer, 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 an anode, and the second electrode 6 may be a cathode. In this case, the stacking order of the hole transport layer 5 and the electron transport layer 3 is reversed from that 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, a light absorbing layer, an electron transport layer, and a cathode are provided on the substrate 1 in this order from the substrate 1 side.

[0100] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0101] The compounds (H-1) to (H-4) described in the first embodiment were synthesized by the following method. In addition, 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.

[0102] [Synthesis of Compound (H-1)] Compound (H-1) was synthesized according to the following reaction scheme.

[0103]

[0104] In the above reaction, a 500 mL two-necked flask equipped with a reflux condenser, a thermometer, and a stirrer was used as a reaction vessel, and the reaction vessel was placed in an oil bath. Into this reaction vessel were placed 0.0633 mol (27.000 g) of a secondary amine compound represented by formula (B-1) (hereinafter, may be referred to as compound (B-1)), 0.01578 mol (10.000 g) of compound (A) (2,2′,7,7′-tetrabromo-9,9′-spirobi[9H-fluorene]), 0.00027 mol (0.060 g) of palladium (II) acetate as a palladium catalyst, 0.00052 mol (0.273 g) of tri-tert-butylphosphonium tetraphenylborate as an organic phosphorus ligand, and 0.09494 mol (9.110 g) of sodium tert-butoxide as a base, and the atmosphere in the reaction vessel was replaced with nitrogen while stirring at room temperature. Thereafter, 150,000 g of xylene as an organic solvent was charged into the reaction vessel, and the reaction liquid in the reaction vessel was stirred with a magnetic stirrer while the oil bath was heated to a temperature of 105° C. or higher and 110° C. or lower (a liquid temperature of the reaction liquid of 100° C. or higher and 105° C. or lower). Thereafter, the reaction liquid in the reaction vessel was reacted for 3 hours while maintaining the temperature of the oil bath and the liquid temperature of the reaction liquid within the above ranges.

[0105] Thereafter, the oil bath was cooled to 60° C., and disappearance of compound (A) was confirmed by TLC (thin layer chromatography).

[0106] Next, 50,000 g of ethyl acetate was added to the reaction vessel. Subsequently, a clay adsorption treatment was carried out. The clay adsorption treatment was carried out in the following manner. First, 19,000 g of activated clay was added to the reaction solution in the reaction vessel. Next, the oil bath was heated to 80°C or higher, and the reaction solution in the reaction vessel was stirred for 10 minutes. After that, hot filtration was carried out, and the filtrate was collected. This clay adsorption treatment was carried out a total of four times.

[0107] Next, the filtrate obtained from the fourth clay adsorption treatment was concentrated in an evaporator until its mass reached 100,000 g. Then, while stirring the filtrate, a poor solvent mixture of 50,000 g of isohexane and 50,000 g of methanol was added in small amounts to precipitate a solid. The solid was collected by filtration and vacuum-dried at 100° C. for 5 hours to obtain a primary solid.

[0108] Next, 40,000 g of tetrahydrofuran (THF) was added to this primary solid and stirred. This dissolved the primary solid in THF. Next, a total of about 80 g of methanol as a poor solvent was added little by little to the TFT in which this primary solid had been dissolved, causing a solid to precipitate. This solid was collected by filtration and vacuum-dried at 100°C for 5 hours to obtain a secondary solid.

[0109] Next, this secondary solid was dissolved in 100,000 g of toluene and washed twice in a separatory funnel with a total of 150 mL of water. The aqueous layer was then removed, and anhydrous sodium sulfate was added to the remaining organic layer. The mixture was stirred at room temperature for 30 minutes, and then filtered to recover the filtrate. Next, 100,000 g of ethyl acetate was added to the recovered filtrate, and the filtrate was heated to 80°C. The filtrate was then subjected to a clay adsorption treatment once. The clay adsorption treatment of the filtrate was carried out according to the following procedure. First, 14,000 g of activated clay was added to the filtrate and stirred for 10 minutes. The filtrate was then filtered.

[0110] Subsequently, the filtrate after the clay adsorption treatment was concentrated in an evaporator until its mass reached 100,000 g. Thereafter, while stirring the filtrate, a mixed solution of 50,000 g of isohexane and 50,000 g of methanol as a poor solvent was added in small amounts to the filtrate to precipitate a solid. The solid was collected by filtration and vacuum-dried at 100°C for 5 hours to obtain a pale yellow compound (H-1) as a product. The yield of compound (H-1) was 14.3 g, a yield of 45.0%.

[0111] The resulting product: １ H-NMR (proton nuclear magnetic resonance) analysis (magnetic field strength: 600 MHz) 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 Deuterated chloroform was used as a solvent for measuring the H-NMR spectrum. The magnetic field strength was set to 600 MHz. Figure 2 shows the H-NMR spectrum of the obtained compound (H-1). １ The H-NMR chart is shown below.

[0112] [Synthesis of Compound (H-2)] As shown in the following reaction scheme, compound (H-2) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0633 mol (25.000 g) of a secondary amine compound represented by formula (B-2) (hereinafter, may be referred to as secondary amine (B-2)) was used instead of 0.0633 mol (27.000 g) of compound (B-1). The yield of compound (H-2) was 14.2 g, a yield of 47.7%.

[0113]

[0114] [Synthesis of Compound (H-3)] As shown in the following reaction scheme, compound (H-3) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0633 mol (23.200 g) of a secondary amine compound represented by formula (B-3) (hereinafter, may be referred to as secondary amine (B-3)) was used instead of 0.0633 mol (27.000 g) of compound (B-1). The yield of compound (H-3) was 13.7 g, a yield of 49.0%.

[0115]

[0116] [Synthesis of Compound (H-4)] As shown in the following reaction scheme, compound (H-3) was obtained as a product in the same manner as in the synthesis of compound (H-1), except that 0.0633 mol (26.000 g) of a secondary amine compound represented by formula (B-4) (hereinafter, may be referred to as secondary amine (B-4)) was used instead of 0.0633 mol (27.000 g) of compound (B-1). The yield of compound (H-3) was 15.2 g, a yield of 49.6%.

[0117]

[0118] [Synthesis of Compound (h-1)] Compound (h-1) was synthesized according to the following reaction scheme.

[0119]

[0120] A 500 mL two-necked flask equipped with a reflux condenser, a thermometer, and a stirrer was used as a reaction vessel, and this reaction vessel was placed in an oil bath. Into this reaction vessel were placed 0.0633 mol (31.900 g) of a secondary amine compound represented by formula (b-1) (hereinafter, may be referred to as compound (b-1)), 0.01578 mol (10.000 g) of compound (A) (2,2′,7,7′-tetrabromo-9,9′-spirobi[9H-fluorene]), 0.00027 mol (0.060 g) of palladium (II) acetate as a palladium catalyst, 0.00052 mol (0.273 g) of tri-tert-butylphosphonium tetraphenylborate as an organic phosphorus ligand, and 0.09494 mol (9.110 g) of sodium tert-butoxide as a base, and the atmosphere in the reaction vessel was replaced with nitrogen while stirring at room temperature. Thereafter, 150,000 g of xylene as an organic solvent was charged into the reaction vessel, and the reaction liquid in the reaction vessel was stirred with a magnetic stirrer while the oil bath was heated to a temperature of 105° C. or higher and 110° C. or lower (a liquid temperature of the reaction liquid of 100° C. or higher and 105° C. or lower). Thereafter, the reaction liquid in the reaction vessel was reacted for 3 hours while maintaining the temperature of the oil bath and the liquid temperature of the reaction liquid within the above ranges.

[0121] Thereafter, the oil bath was cooled to 60° C., and disappearance of compound (A) was confirmed by TLC.

[0122] Next, 50,000 g of ethyl acetate was added to the reaction solution in the reaction vessel, and the reaction solution in the reaction vessel was washed three times with a total of 200,000 g of ion-exchanged water in a separatory funnel. Next, the aqueous layer was removed, and the remaining organic layer was concentrated and dried in an evaporator to solidify it.

[0123] The resulting solid was then subjected to column chromatography using chloroform as a developing solvent. A spot containing compound (h-1) was isolated by column chromatography, and purified compound (h-1) was obtained from the isolated spot. The yield of compound (h-1) was 24.4 g, a yield of 66.2%.

[0124] The compounds (H-2) to (H-4) and (h-1) were also measured. １ From the chemical shift values ​​of the H-NMR spectrum, it was confirmed that the target compound was obtained.

[0125] Table 1 shows the molecular weight and amount of each raw material for compounds (H-1) to (H-4) and (h-1), as well as the molecular weight, yield and yield of compounds (H-1) to (H-4) and (h-1). In Table 1, "Mw" indicates molecular weight.

[0126]

[0127] Next, solar cells (S-1) to (S-4) according to Examples 1 to 4 and solar cells (s-1) to (s-2) according to Comparative Examples 1 and 2 were produced by the following method.

[0128] [Production of Solar Cell (S-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.

[0129] 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.

[0130] 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.

[0131] Thereafter, the FTO substrate was annealed (heat treated) at 150° C. for 30 minutes using a hot plate to form an electron transport layer made of tin (IV) oxide nanoparticles with a thickness of about 20 nm.

[0132] 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 at a temperature of 23°C ± 1°C and a dew point temperature of -20 ± 5°C.

[0133] Separately, in a glove box, 0.692 g (1.5 mmol) of lead iodide (product name "L0279" manufactured by Tokyo Chemical Industry Co., Ltd.), 0.059 g (0.225 mmol) of cesium iodide (product name "C2205" manufactured by Tokyo Chemical Industry Co., Ltd.), and 0.219 g (1.275 mmol) of formamidine hydroiodide (product name "F0974" manufactured by Tokyo Chemical Industry Co., Ltd.) were mixed with 1.25 mL of a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (volume ratio 4:6), and the mixture was stirred at 70°C for 1 hour to dissolve the solids. This prepared a solution containing a perovskite compound (hereinafter sometimes referred to as a perovskite solution) as a coating liquid for a light-absorbing layer. The perovskite solution was then cooled to room temperature.

[0134] Next, 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. The spin coating was performed under the following conditions. First, 30 seconds after dropping the perovskite solution, the spin coater was accelerated to a rotation speed of 3000 rpm over 0.8 seconds and maintained at 3000 rpm for 50 seconds. The spin coater was then further accelerated to a rotation speed of 6000 rpm over 0.8 seconds, and the rotation speed was maintained at 6000 rpm for 30 seconds. During this time, 200 μL of ethyl acetate was dropped. The ethyl acetate was dropped 4 seconds after the spin coater rotation speed reached 6000 rpm. Then, 30 seconds after the spin coater rotation speed reached 6000 rpm, the spin coater was decelerated for 1 second and the spin coater rotation was stopped.

[0135] After the spin coater was stopped, the FTO substrate spin-coated with the perovskite solution was annealed (heat treated) at 135° C. for 15 minutes using a hot plate, thereby forming a perovskite layer with a thickness of approximately 500 nm as a light absorption layer on the electron transport layer.

[0136] 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 (hereinafter, this may be referred to as the "hole transport material solution preparation step"). 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.

[0137] 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 (S-1).

[0138] [Production of solar cells (S-2) to (S-4) and (s-1) to (s-2)] Instead of compound (H-1), compounds (H-2) to (H-4), (h-1) or a compound represented by formula (h-2) shown in Table 1 (Spiro-OMeTAD, hereinafter, may be referred to as compound (h-2)) were used to form a hole transport layer. Solar cells (S-2) to (S-4) and (s-1) to (s-2) were produced in the same manner as in the production of solar cell (S-1). For compound (h-2), Sigma-Aldrich's Spiro-MeOTAD product "SHT-263 Solarpur (registered trademark) (product number: 902500)" (molecular weight 1225.4) was used.

[0139]

[0140] [Evaluation] The photoelectric conversion characteristics of each of the solar cells produced in Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated by the following method. The evaluation was carried out in an environment of a temperature of 23°C and a humidity of 30% RH unless otherwise specified.

[0141] (Photoelectric conversion characteristics) First, the measurement area was 0.1 cm per point. ２Each solar cell was masked so that the J (current)-V (voltage) curve characteristics were measured using a source meter (a voltage-current generator with measurement function) while irradiating light onto the masked solar cell using a solar simulator. Measurements were carried out at eight locations per solar cell. The solar simulator used was a spectrometer "HAL-320" manufactured by Asahi Spectrometer 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, once for each position, under the conditions of forward scanning, in which the voltage is scanned in the direction increasing, and reverse scanning, 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. ２ The photoelectric conversion efficiency (PCE, unit: %) was calculated by the following formula (i): PCE = (Jsc × Voc × FF / 100) × 100 (i)

[0142] 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 eight locations measured for each solar cell.

[0143] The terms used in Table 2 are as follows: "Actual" indicates an example, and "Ratio" indicates a comparative example. "F" indicates forward, and "R" indicates reverse. "Solubility" indicates the solubility of the hole transport material in the organic solvent (i.e., a mixed solvent of 1 mL of chlorobenzene and 0.017 mL of acetonitrile) in the above-mentioned preparation step of the hole transport material solution. "A" indicates that the hole transport material was completely dissolved in the organic solvent in the above-mentioned preparation step of the hole transport material solution. "B" indicates that the hole transport material was not completely dissolved in the organic solvent in the above-mentioned preparation step of the hole transport material solution.

[0144]

[0145] Compounds (H-1) to (H-4) shown in Tables 1 and 2 are compounds (1) represented by formula (1). In addition, these compounds (H-1) to (H-4) are compounds (1) represented by formula (1) where R １ , R ２ , R ３ , R ４ , R ５ Furthermore, these compounds (H-1) to (H-4) are compounds in which at least one of R a and R b is a methoxy group. ３ At least one of R, R, and R is a methoxy group; ３ is a methoxy group or a methyl group.

[0146] As shown in Table 2, these compounds (H-1) to (H-4) have excellent solubility in organic solvents and could be completely dissolved in the organic solvent in the above-mentioned hole transport material solution preparation process. On the other hand, compound (h-1) could not be completely dissolved in the organic solvent in the above-mentioned hole transport material solution preparation process. Therefore, the PCE was low.

[0147] Furthermore, as shown in Table 2, the solar cells (S-1) to (S-4) in which the hole transport layer was formed using the compounds (H-1) to (H-4) all exhibited higher PCE than the solar cells (s-1) to (s-2) according to the comparative example.

[0148] From the above results, it was confirmed that the PCE of a solar cell can be effectively improved by using compound (1) (for example, any of compounds (H-1) to (H-4)) as a hole transport material.

[0149] Furthermore, as shown in Examples 1, 2, and 4, in formula (1), R ３ At least one of Ra and Rb is a methoxy group, and R ３ It has been confirmed that when compound (1) (e.g., compound (H-1), (H-2), or (H-4)) in which R a and R b are each independently a methoxy group or a methyl group is used as a hole transport material, the PCE of the solar cell can be further improved.

[0150] The compound and hole transport material according to the present invention can be used, for example, in solar cells. The solar cells according to the present invention can also be used, for example, in large-scale power supplies, power supplies for outdoor equipment, power supplies for indoor electronic devices, and portable power supplies.

Claims

1. A compound represented by formula (1). (In the formula (1), R １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms.

2. In the formula (1), R １ , R ２ , R ３ , R ４ , R ５ 2. The compound of claim 1, wherein at least one of R a and R b represents a methoxy group.

3. In the formula (1), R ３ 3. The compound according to claim 2, wherein at least one of R a and R b represents a methoxy group, and R 3 represents a methoxy group or a methyl group.

4. The compound according to claim 3, wherein in formula (1), Ra and Rb each independently represent a methoxy group or a methyl group.

5. The compound according to claim 1, wherein the formula (1) is represented by formula (H-1), (H-2), (H-3), or (H-4).

6. A hole transport material comprising the compound according to any one of claims 1 to 5.

7. 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 6.

8. A method for producing the compound according to claim 1, comprising the step of reacting a compound represented by formula (A) with a compound represented by formula (B). (In the formula (B), R １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb are R in the formula (1). １ , R ２ , R ３ , R ４ , R ５ , Ra, and Rb represent the same groups.

9. A method for producing a compound according to claim 8, wherein in the step, the compound represented by formula (A) is reacted with the compound represented by formula (B) in the presence of an organophosphorus ligand and a palladium catalyst, or a palladium catalyst coordinated with an organophosphorus ligand.

10. The method for producing the compound according to claim 9, wherein the organophosphorus ligand comprises at least one member selected from the group consisting of tri-tert-butylphosphonium borate, [4-(N,N-dimethylamino)phenyl]di-tert-butylphosphine, and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl.

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