Hole transport material, intermediate of hole transport material, method for producing hole transport material using same, and organic solar cell and photoelectric conversion element using hole transport material

Abstract

Provided is an intermediate of a hole transport material, the intermediate being represented by general formula (1). In formula (1), X1 represents a halogen atom and X2 represents a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, a dialkylamino group having 4 or fewer carbon atoms, or a diphenylamino group which may have a substituent. R1 to R4 may be the same or different and each represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.

Description

Hole Transport Material, Intermediate of Hole Transport Material, Method for Producing Hole Transport Material Using the Same, and Organic Solar Cell and Photoelectric Conversion Element Using Hole Transport Material

[0001] The present invention relates to a hole transport material used as a material for a hole transport layer, an intermediate of the hole transport material, a method for producing a hole transport material using the same, and an organic solar cell and a photoelectric conversion element using the same.

[0002] In recent years, the driving power in electronic circuits has become extremely small, and various electronic components such as sensors can be driven even with weak power. Furthermore, when utilizing sensors, application to self-powered power sources (environmental power generation elements) that can generate and consume power on-site is expected. Among them, solar cells have attracted attention as elements that can generate electricity anywhere there is light.

[0003] As solar cells, inorganic solar cells and organic solar cells are known. However, inorganic solar cells have a problem that their range of use is limited from the viewpoints of high manufacturing costs and difficulty in large-scale production because inorganic semiconductor materials such as silicon are used as p-type semiconductors and n-type semiconductors. Therefore, currently, the development of organic solar cells manufactured using organic semiconductors instead of inorganic semiconductors is underway. Organic solar cells are classified, for example, into dye-sensitized solar cells, organic thin-film solar cells, organic-inorganic hybrid solar cells, and the like.

[0004] An organic solar cell contains a p-type semiconductor and an n-type semiconductor, and a hole transport layer (hole transport layer) is often provided between a photoelectric conversion layer that absorbs light and generates positive and negative charges and an anode. The hole transport layer plays a role of improving the photoelectric conversion efficiency of the solar cell by enabling the positive charges (holes) generated by photoexcitation and the negative charges (electrons) to move efficiently without recombination.

[0005] Among organic solar cells, solar cells equipped with a photoelectric conversion layer containing a perovskite compound, as described in Patent Document 1 and Non-Patent Documents 1 and 2 (hereinafter also referred to as perovskite solar cells), have been reported to exhibit higher photoelectric conversion efficiency than amorphous silicon solar cells in weak indoor light environments, and reports on further improvements in photoelectric conversion efficiency have been successively published. The basic structure of a perovskite solar cell is generally a laminate in which a transparent electrode (cathode), electron transport layer, photoelectric conversion layer (perovskite layer), hole transport layer, and metal electrode (anode) are stacked in this order. In some cases, a mesoporous titania layer is included between the electron transport layer and the perovskite layer, and the photoelectric conversion layer is composed of the perovskite layer and the mesoporous titania layer. Of these layers, the hole transport layer is generally composed of a material containing an organic semiconductor.

[0006] Among the organic semiconductors included in hole transport layer materials reported to date, one example is 2,2′,7,7′-tetrakis-(N,N-dimethoxyphenylamine)-9,9′-spirobifluorene (hereinafter also referred to as Spiro-OMeTAD), which was developed as a hole transport layer material for dye-sensitized solar cells and is described in Non-Patent Document 3. It is also commonly used in the aforementioned perovskite solar cells.

[0007] Furthermore, Patent Documents 2 and 3 disclose a hole transport material having a donor-acceptor-donor type structure, wherein the acceptor portion is composed of an electron-accepting group such as a fluorene ring consisting of carbon atoms and hydrogen atoms, a donor portion containing an electron-donating group such as a 4-(bis(4-methoxyphenyl)amino)phenyl group is introduced at positions 2 and 7 on the fluorene ring, and the same group as the donor portion is introduced at position 9 on the fluorene ring via an intercarbon double bond.

[0008] Japanese Patent Publication No. 2016-539914, Japanese Patent Publication No. 2023-46046, Japanese Patent Publication No. 2024-64714

[0009] Michael M. Lee et al., "Efficient Hybrid Solar Cells Based on Meso-Super structured Organometal Halide Perovskites", Science (2012) 338, P643-647Nam Joong Jeon et al., "Solvent engineering for high-performance in organic-organic hybrid perovskite solar cells", Nature Materials (2014) 13, P897-903Nature volume (1998) 395, P583-585

[0010] However, when Spiro-OMeTAD is used as the material for the hole transport layer, it cannot be said that sufficiently good photoelectric conversion performance is achieved. Therefore, when using this material, it is generally necessary to add a large amount of dopant such as lithium bis(trifluoromethanesulfonyl)imide (hereinafter also referred to as LiTFSI salt) to improve photoelectric conversion performance, and the doping of large amounts of LiTFSI salt has the problem that solar cells have poor durability at high temperatures and high humidity. In addition, the hole transport materials described in Patent Documents 2 and 3 have low yields during synthesis and their photoelectric conversion performance is not sufficient.

[0011] In view of the above problems, the present invention aims to provide a hole transport material that has excellent high temperature and high humidity durability and excellent photoelectric conversion properties even in weak light such as indoor light, an intermediate for the hole transport material, a method for manufacturing the hole transport material using the same, and an organic solar cell and a photoelectric conversion element using the hole transport material.

[0012] To achieve the above objective, the first configuration of the present invention is an intermediate for hole transport materials represented by the following general formula (1). In formula (1), X1 is a halogen atom, and X2 represents a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, a dialkylamino group having 4 or fewer carbon atoms, or a diphenylamino group which may have a substituent. R1 to R4 may be the same or different, and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.

[0013] According to the first configuration of the present invention, by using a compound represented by formula (1) above as an intermediate for a hole transport material that is a material for the hole transport layer of a photoelectric conversion element and a solar cell, a hole transport material with excellent high temperature and high humidity durability and charge (hole) mobility can be manufactured with high purity and high yield.

[0014] A partial cross-sectional view of an organic solar cell 100 according to one embodiment of the present invention, showing an example in which the first electrode 2 is an electron injection electrode and the second electrode 6 is a hole injection electrode.

[0015] [1. Structure of Organic Solar Cell] First, a solar cell using the hole transport material of the present invention will be described. Figure 1 is a partial cross-sectional view of an organic solar cell 100 according to one embodiment of the present invention. The organic solar cell 100 (hereinafter simply referred to as solar cell 100) comprises a substrate 1, a first electrode 2, an electron transport layer 3, a photoelectric conversion layer 4, a hole transport layer 5, and a second electrode 6. The first electrode 2 is provided on the substrate 1. The photoelectric conversion layer 4 is laminated on the first electrode 2 via the electron transport layer 3. The second electrode 6 is laminated on the photoelectric conversion layer 4 via the hole transport layer 5. Note that the photoelectric conversion layer 4 may be directly laminated on the first electrode 2 without an electron transport layer. In this case, the electron transport layer 3 shown in Figure 1 is omitted. When the solar cell 100 is used, for example, light L (for example, sunlight or indoor light) is irradiated onto the substrate 1 side of the solar cell 100. Note that when the solar cell 100 is used, light L may be irradiated onto the second electrode 6 side of the solar cell 100.

[0016] <Substrate> The substrate 1 is not particularly limited as long as it can be used for the solar cell 100. The substrate 1 may be transparent or opaque. However, if the surface of the solar cell 100 that faces the substrate 1 is the light-receiving surface, it is preferable that the substrate 1 be transparent. Examples of transparent substrates include transparent rigid substrates such as glass like quartz glass or synthetic quartz plates, and transparent flexible substrates such as transparent resin films or optical resin plates. Transparent flexible substrates have advantages such as ease of processing, reduced manufacturing costs, lighter weight, resistance to breakage, and applicability to curved surfaces.

[0017] <First Electrode> The first electrode 2 is, for example, an electron injection electrode. The first electrode 2 is not limited to a conductive material. Examples of materials with a high work function that can be used as the first electrode 2 include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), carbon (C), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), and zinc oxide (ZnO).

[0018] Furthermore, the material of the first electrode 2 is appropriately selected considering whether the light-receiving surface of the solar cell 100 is the surface on the substrate 1 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 is preferably a transparent electrode. Examples of materials used when the first electrode 2 is a transparent electrode include indium zinc oxide (IZO), ITO, FTO, ZnO-Al, and Zn-Sn-O.

[0019] The total light transmittance of the first electrode 2 is preferably 85% or more, more preferably 90% or more, and particularly preferably 92% or more. When the total light transmittance of the first electrode 2 is 85% or more, when the light-receiving surface of the solar cell 100 is the surface facing the substrate 1, light can be sufficiently transmitted through the first electrode 2 on the substrate 1, and the photoelectric conversion layer 4 can efficiently absorb the light.

[0020] 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 photoelectric conversion layer 4 is sufficiently transmitted to the external circuit. The sheet resistance can be measured, for example, using a resistivity meter (Loresta AXMCP-T370, manufactured by Nitto Seiko Analytech Co., Ltd., 4-probe type) in accordance with JIS (Japanese Industrial Standards) R1637 (Test method for resistivity of fine ceramic thin films - Measurement method by 4-probe method).

[0021] The film 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 film thickness of the first electrode 2 is 0.1 nm or more, the sheet resistance of the first electrode 2 does not become too large, and the charge (holes) generated in the photoelectric conversion layer 4 can be sufficiently transmitted to the external circuit. On the other hand, when the film thickness of the first electrode 2 is 500 nm or less, the total light transmittance of the first electrode 2 is high.

[0022] The first electrode 2 may be a single layer. Alternatively, the first electrode 2 may be composed of multiple layers having different work functions. When the first electrode 2 consists of multiple layers, the film thickness of the first electrode 2 as described above refers to the total film thickness of the multiple layers.

[0023] The first electrode 2 may be formed in a sheet shape over the entire surface of the substrate 1, or it may be formed in a pattern shape 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, the incident light is scattered by the unevenness of the first electrode 2, so that more light is taken up by the photoelectric conversion layer 4, and the energy conversion efficiency of the solar cell 100 is improved.

[0024] <Electron Transport Layer> The electron transport layer 3 is laminated between the first electrode 2 and the photoelectric conversion layer 4. The electron transport layer 3 is provided to facilitate the injection (movement) of electrons from the photoelectric conversion layer 4 to the first electrode 2 (electron injection electrode). By laminating the electron transport layer 3, the electron injection efficiency from the photoelectric conversion layer 4 to the first electrode 2 is increased, and the energy conversion efficiency of the solar cell 100 is improved.

[0025] The material contained in the electron transport layer 3 (electron transport layer material) is not particularly limited as long as it is a material that can stably inject electrons from the photoelectric conversion layer 4 to the second electrode 6. Examples of electron transport layer materials include conductive organic compounds, charge transfer complexes, alkali metals, alkaline earth metals, and organic compounds and metal oxides doped with alkali metals or alkaline earth metals.

[0026] Examples of alkali metals that can be used as electron transport layer materials include lithium, sodium, potassium, rubidium, and cesium. Examples of alkaline earth metals that can be used as electron transport layer materials include beryllium, magnesium, calcium, strontium, and barium. Examples of alkali metal or alkaline earth metal-doped organic compounds that can be used as electron transport layer materials include bathocuproine (BCP) and batphenanthroline (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, with lithium, cesium, barium, or strontium being more preferred. Examples of metal oxides that can be used as electron transport materials include titanium oxide, zinc oxide, and tin oxide.

[0027] When the electron transport layer material is a conductive organic compound, a charge transfer complex, or a metal oxide, the film thickness of the electron transport layer 3 is preferably 10 nm or more and 200 nm or less. When the electron transport layer material is an alkali metal, an alkaline earth metal, or an organic compound doped with an alkali metal or alkaline earth metal, the film thickness of the electron transport layer 3 is preferably 0.1 nm or more and 50 nm or less.

[0028] <Photoelectric Conversion Layer> The photoelectric conversion layer 4 may be a bulk heterojunction type photoelectric conversion layer containing a donor (electron donor) and an acceptor (electron acceptor), or it may be a photoelectric conversion layer having a perovskite layer, which is a so-called perovskite.

[0029] In the case of a bulk heterojunction type photoelectric conversion layer, the donor is not particularly limited as long as it functions as a donor, but it is preferably an electron-donating conductive polymer (electron-donating organic material). An electron-donating organic material refers to the organic compound with the lower electron affinity when two organic compounds are brought into contact. In other words, any organic compound that is electron-donating can be used as a donor. The donor is preferably a compound that can be formed into a thin film using a solution in which the donor is dissolved in an organic solvent (for example, a coating method such as the casting method and the spin coating method). The photoelectric conversion layer 4 may contain only the donor and acceptor, or it may contain other compounds.

[0030] Examples of electron-donating conductive polymers 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 be a copolymer obtained by copolymerizing at least two of these electron-donating conductive polymers. Other examples of electron-donating conductive polymers include phthalocyanine-containing polymers, carbazole-containing polymers, and organometallic polymers.

[0031] As an electron-donating conductive polymer that can be used as a donor, a polymer having at least one of a thiophene structure, a benzothiophene structure, and a benzodithiophene structure (polythiophene polymer) is preferred. The polythiophene polymer is preferably capable of absorbing visible light. Furthermore, the polythiophene polymer is preferably of the donor-acceptor (DA) type.

[0032] The acceptor is not particularly limited as long as it functions as an acceptor, but it is preferably a conductive polymer (electron-accepting organic material) that has electron-accepting properties. Electron-accepting organic materials are mainly represented by electron-transporting organic compounds and refer to organic compounds that have a property of readily accepting electrons. More specifically, it refers to the organic compound with the greater electron affinity when two organic compounds are used in contact. In other words, any organic compound that has electron-accepting properties can be used as an acceptor.

[0033] Examples of electron-accepting organic materials include fullerenes and their derivatives (such as PCBMs), carbon nanotubes and their derivatives, perylenes and their derivatives (such as PTCDAs and PTCDIs), naphthalene derivatives (such as NTCDAs and NTCDIs), oligomers and polymers having pyridines and their derivatives as a backbone, fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and their derivatives, tris(8-hydroxyquinolinate)aluminum complexes, bis(4-methyl-8-quinolinate)aluminum complexes, distylyl arylene derivatives, and silole compounds. Fullerene derivatives (such as PCBMs) are particularly preferred, but the material is not limited thereto.

[0034] In the photoelectric conversion layer 4, the ratio of the acceptor mass (MA) to the donor mass (MD) (MA / 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 donor of the solar cell 100 is good, and the energy conversion efficiency of the solar cell 100 is improved.

[0035] The photoelectric conversion layer having a perovskite layer uses a compound represented by the general formula (ABX3). This compound may be a perovskite crystal or a perovskite complex. A can be an organic amino compound such as methylamine, ethylamine, n-butylamine, di-n-butylamine, trimethylamine, triethylamine, methyl-n-hexylamine, methyldiethylamine, tri-n-hexylamine, imidazole, pyrrole, aziridine, formamidine, guanidine, pyridine, 4-t-butylpyridine, phenethylamine, 5-aminovaleric acid, or a monovalent cation formed from cesium, potassium, rubidium, etc., and may be used alone or as a mixture of two or more. B can be a divalent cation such as lead or tin, and may be used alone or in a mixture. In addition, a small amount of a trivalent cation such as indium or antimony may be mixed in. X can be a halogen atom or anion source such as chlorine, bromine, or iodine, and may be used alone or in a mixture of two or more.

[0036] The film thickness of the photoelectric conversion layer 4 is not particularly limited, as long as the desired energy conversion efficiency can be obtained, whether it is a bulk heterojunction photoelectric conversion layer or a perovskite-type photoelectric conversion layer. The film thickness of the photoelectric conversion 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 film thickness of the photoelectric conversion layer 4 is 3000 nm or less, the sheet resistance of the photoelectric conversion layer 4 is more likely to be the desired value. On the other hand, when the film thickness of the photoelectric conversion layer 4 is 0.2 nm or more, a short circuit between the first electrode 2 and the second electrode 6 is less likely to occur.

[0037] <Hole Transport Layer> The hole transport layer 5 is laminated between the photoelectric conversion layer 4 and the second electrode 6. The hole transport layer 5 is provided to facilitate the injection (movement) of holes from the photoelectric conversion layer 4 to the second electrode 6 (hole injection electrode). By laminating the hole transport layer 5, the hole injection efficiency from the photoelectric conversion layer 4 to the second electrode 6 is increased, and the energy conversion efficiency of the solar cell 100 is improved. The hole transport layer 5 contains a 2,7-bis[(4-diphenylamino)phenyl]fluorene derivative represented by the following general formulas (2) to (5).

[0038]

[0039]

[0040] In Formulas (2) and (3), Ar1 may be the same or different and represents an aryl group (phenyl group, naphthyl group, fluorenyl group) which may have a substituent; X2 represents a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, a dialkylamino group having 4 or fewer carbon atoms, or a diphenylamino group which may have a substituent. R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.

[0041]

[0042] In Formula (4), Ar1 and Ar2 may be the same or different and represent an aryl group (phenyl group, naphthyl group, fluorenyl group) which may have a substituent; X2 represents a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, or a dialkylamino group having 4 or fewer carbon atoms. R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.

[0043]

[0044] In Formula (5), Ar1 and Ar2 may be the same or different and represent an aryl group (phenyl, naphthyl, fluorenyl group) which may have a substituent; R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.

[0045] The hole transport layer 3 may contain only a 2,7-bis[(4-diphenylamino)phenyl]fluorene derivative represented by General Formulas (2) to (5), or may further contain an additive. As the additive, a conventionally known additive such as an interfacial treatment agent can be used.

[0046] In particular, it is preferable that X2 in formulas (2) and (3) is a methyl group or a diphenylamino group having a methoxy group at the para position, Ar1 is a phenyl group having one methoxy group each at the ortho and para positions, or a phenyl group having two methyl groups at the ortho position and one at the para position, and that R1 to R4 are all hydrogen atoms. Specific examples of such 2,7-bis[(4-diphenylamino)phenyl]fluorene derivatives include the compounds HTM-1, HTM-2, and HTM-3, represented by the following chemical formulas. Hereinafter, HTM-1 to HTM-3 will also be referred to as polymer-based HTMs.

[0047]

[0048]

[0049]

[0050] Furthermore, it is preferable that X2 in formula (4) is a fluorine atom, a methyl group, or a methoxy group, Ar1 is a phenyl group having a methoxy group in the para position, and R1 to R4 are all hydrogen atoms. Also, it is preferable that Ar1 and Ar2 in formula (5) are diphenylamino groups having a methoxy group in the para position, and R1 to R4 are all hydrogen atoms. Specific examples of such 2,7-bis[(4-diphenylamino)phenyl]fluorene derivatives include the compounds HTM-4, HTM-5, HTM-6, and HTM-7, represented by the following chemical formulas. Hereinafter, HTM-4 to HTM-7 will also be referred to as monomer-based HTMs.

[0051]

[0052]

[0053]

[0054]

[0055] Compound HTM-7 is a known compound described in Patent Document 2. However, by synthesizing it using the production method of the present invention, which uses a 2,7-bis(4-halogenophenyl)fluorene derivative represented by general formula (1) as an intermediate, the yield of HTM-7 is improved compared to the conventional synthesis method, as shown in the examples described later. Furthermore, the photoelectric conversion efficiency when HTM-7 is used as a hole transport material in organic solar cells is improved compared to HTM-7 synthesized by the conventional synthesis method (HTM-7' described later).

[0056] Furthermore, the 2,7-bis(4-halogenophenyl)fluorene derivative represented by general formula (1) can also be used as a raw material for the 2,7-bis[(4-diphenylamino)phenyl]fluorene derivatives represented by general formulas (2) to (4). That is, by synthesizing the compounds represented by general formulas (2) to (5) using the manufacturing method of the present invention, with the compound represented by general formula (1) as an intermediate, the yield of the compounds represented by general formulas (2) to (5) is improved. In addition, by using the compounds represented by general formulas (2) to (5) as hole transport materials constituting the hole transport layer 5 of the solar cell 100, the mobility of charge (holes) can be improved, and the energy conversion efficiency of the solar cell 100 is improved.

[0057] <Second Electrode> The second electrode 6 is, for example, a hole injection electrode. The second electrode 6 is provided opposite the first electrode 2. The second electrode 6 is not particularly limited as long as it is conductive. The material of the second electrode 6 is appropriately selected, for example, taking into consideration the work function of the hole transport layer 5. If the material of the hole transport layer 5 is a material with a high work function, it is preferable that the material of the second electrode 6 is a material with a low work function.

[0058] Examples of materials that can be used as the material for the second electrode 6 include gold (Au), silver (Ag), cobalt (Co), nickel (Ni), platinum (Pt), carbon (C), indium tin oxide (ITO), tin oxide (SnO2), fluorine-doped tin oxide (FTO), and zinc oxide (ZnO).

[0059] Furthermore, the material of the second electrode 6 is appropriately selected, for example, by considering whether the light-receiving surface of the solar cell 100 is the surface on the substrate 1 side or the surface on the second electrode 6 side. If 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 have to be a transparent electrode.

[0060] The film thickness of the second electrode 6 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 film thickness of the second electrode 6 is 0.1 nm or more, the sheet resistance of the second electrode 6 does not become too large, and the charge generated in the photoelectric conversion layer 4 can be sufficiently transmitted to the external circuit.

[0061] The second electrode 6 may be a single layer. Alternatively, the second electrode 6 may be composed of multiple layers having different work functions. When the second electrode 6 consists of multiple layers, the film thickness of the second electrode 6 as described above refers to the total film thickness of the multiple layers.

[0062] The second electrode 6 may be formed in a sheet shape over the entire surface of the hole transport layer 5, or it may be formed in a pattern shape on the hole transport layer 5.

[0063] <Other Components> In addition to the substrate 1, first electrode 2, electron transport layer 3, photoelectric conversion layer 4, hole transport layer 5, and second electrode 6 described above, the solar cell 100 may further include other components as needed. Examples of other components include a protective sheet layer, filler layer, barrier layer, protective hard coat layer, strength support layer, anti-fouling layer, high light reflectivity layer, light containment layer, ultraviolet blocking layer, infrared blocking layer, and sealing layer. Furthermore, adhesive layers may be laminated between each layer of the solar cell 100 as needed.

[0064] Furthermore, the solar cell 100 is not limited to the structure shown in Figure 1. For example, the first electrode 2 may be a hole injection electrode and the second electrode 6 may be an electron injection electrode. In that case, the stacking order of the hole transport layer 5 and the electron transport layer 3 will be the reverse of that in Figure 1. Specifically, as shown in Figure 2, the hole transport layer 5 is stacked between the first electrode 2 and the photoelectric conversion element 4, and the electron transport layer 3 is stacked between the photoelectric conversion element 4 and the second electrode 6.

[0065] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, in the embodiments described above, an example was given in which the hole transport material of the present invention was used in the hole transport layer 5 of a solar cell 100, but it is not limited to the solar cell 100, and can also be used, for example, as a hole transport layer of a photoelectric conversion element.

[0066] As an example of a photoelectric conversion element, for instance, a semiconductor electrode (first electrode) is fabricated by laminating a hole-blocking layer and a porous electron transport layer on a glass substrate, and further supporting a photosensitizing material. A hole transport layer is formed on this semiconductor electrode (first electrode) by spin coating using a solution of the hole transport material of the present invention dissolved in an organic solvent, and a second electrode is formed by laminating silver on the formed hole transport layer using a vacuum deposition method. The effects of the present invention will be further explained in detail below with reference to examples.

[0067] [Example of synthesis of 2,7-bis[(4-diphenylamino)phenyl]fluorene derivatives] (1-1. Synthesis of polymer-based HTMs (HTM-1 to HTM-3)) (1-1-1. Synthesis of intermediate-1) A stirring bar was placed in a 3000 mL two-necked flask equipped with a reflux condenser, and 25.00 g (0.065 mol) of 2,7-bis(4-chlorophenyl)-9H-fluorene represented by chemical formula (A), 28.00 g (0.084 mol) of 4-(bis(4-methoxyphenyl)amino)benzaldehyde represented by chemical formula (B), and 72.04 g (0.224 mol) of tetrabutylammonium bromide (hereinafter sometimes referred to as "TBAB") were charged in, and the system was purged with nitrogen. Subsequently, 1459 mL of xylene and 461 mL of 40% sodium hydroxide aqueous solution were added, and the mixture was heated to reflux conditions while stirring with a magnetic stirrer, and the reaction was allowed to proceed for 4 hours.

[0068] After the reaction, the organic layer was recovered and washed 12 times with 800 mL of pure water. The xylene solution after washing was dehydrated with 25 g of anhydrous sodium sulfate, and the filtrate was adsorbed with 25 g of activated clay (SA-1, manufactured by Nippon Activated Clay Co., Ltd.). The xylene solution was concentrated to 125 g, and under heating and stirring, 181 g of acetone, 214 g of isohexane, and 165 g of methanol were added to precipitate a solid. The solution containing the solid was cooled to 5°C and stirred for 1 hour, and the solid was filtered off to obtain intermediate-1 (yellow solid; 41.8 g, yield 91.6%, HPLC purity 97.7%). The synthesis scheme is shown below.

[0069]

[0070] (1-1-2. Synthesis of HTM-1) A stirring bar and 3.87 g (0.0055 mol) of intermediate-5, along with 2.31 g (0.0055 mol) of 2,4,6-trimethyl-N-[4-[4-(2,4,6-trimethylanilino)phenyl]phenyl]aniline, 30.025 g (0.00003 mol) of Pd2 (dba), 0.052 g (0.00011 mol) of Xphos, and 1.97 g (0.0205 mol) of sodium-t-butoxide were charged into a 500 mL two-necked flask equipped with a reflux condenser. The system was then purged with nitrogen. Subsequently, 92 mL of xylene was added, and the mixture was heated to reflux conditions while stirring with a magnetic stirrer and reacted for 2 hours. After 2 hours, 0.25 g (0.0022 mol) of chlorobenzene was added while washing with 2 g of xylene, and the mixture was reacted for 2 hours. After 2 hours, 0.75 g (0.0044 mol) of diphenylamine was added while washing with 10 g of xylene, and the mixture was reacted for 2 hours. After 2 hours, the reaction mixture was slowly poured into a 1000 mL beaker with a prepared poor solvent solution (450 g of acetone, 50 g of pure water) while stirring, and a solid was generated. After stirring for 30 minutes, the solid was filtered and vacuum-dried at 90°C. A stirring bar and 200 g of methanol were placed in a 2000 mL beaker, the crude product was added to this solution, and the mixture was stirred and washed for 30 minutes. The washing solution was filtered, and the resulting solid was vacuum-dried at 90°C for 10 minutes to obtain the primary solid.

[0071] 500 mL of toluene was added to a 2000 mL Erlenmeyer flask, and the primary solid was added to the toluene in small amounts while heating and stirring. The toluene solution of the primary solid was added to a 2000 mL separatory funnel. Subsequently, 300 mL of pure water was added and mixed vigorously for 30 seconds. After standing for 1 minute, the lower layer was drained, and another 300 mL of pure water was added. This washing procedure was performed a total of four times. The organic layer after washing and 30 g of ethyl acetate were added to a 2000 mL Erlenmeyer flask and heated and stirred. 10 g of activated clay (SA-1, manufactured by Nippon Activated Clay Co., Ltd.) was added to this liquid to perform adsorption treatment and obtain the secondary solid. Compound HTM-1 was obtained by repeating this purification procedure a total of two times (yield 62.3%). The synthesis scheme is shown below.

[0072]

[0073] (1-1-3. Synthesis of HTM-2) Compound HTM-2 was synthesized in the same manner as in "1-1-2. Synthesis of HTM-1" above, except that 2.31 g (0.0055 mol) of 2,4,6-trimethyl-N-[4-[4-(2,4,6-trimethylanilino)phenyl]phenyl]aniline was replaced with 0.74 g (0.055 mol) of 2,4,6-trimethylamine (yield 43.0%).

[0074] (1-1-4. Synthesis of HTM-3) Compound HTM-3 was synthesized by the same method as in "1-1-2. Synthesis of HTM-1" above, except that 2,4,6-trimethyl-N-[4-[4-(2,4,6-trimethylanilino)phenyl]phenyl]aniline 2.31 g (0.0055 mol) was replaced with 2,4-dimethoxy-N-[4-[4-(2,4-dimethoxyanilino)phenyl]phenyl]aniline 2.51 g (0.055 mol) (yield 47.3%).

[0075] (1-2. Synthesis of monomer-based HTMs (HTM-4 to HTM-7)) (1-2-1. Synthesis of intermediate-2) Intermediate-2 was obtained by the same method as in "1-1-1. Synthesis of intermediate-1" above, except that 4-(bis(4-methoxyphenyl)amino)benzaldehyde (28.00 g, 0.084 mol) was replaced with 4-fluorobenzaldehyde (10.418 g, 0.084 mol) (yield 38.36 g, yield 92.8%, HPLC purity 98.5%). The synthesis scheme is shown below.

[0076]

[0077] (1-2-2. Synthesis of HTM-4) A stirring bar and 19.56 g (0.039 mol) of intermediate-2, along with 28.33 g (0.124 mol) of 4,4'-dimethoxydiphenylamine, 30.54 g (0.0006 mol) of Pd2 (dba), 1.12 g (0.0024 mol) of 2-dicyclohexylphosphino-2',4',6'-triisopropylphenyl (hereinafter sometimes referred to as "Xphos"), and 14.70 g (0.153 mol) of sodium-t-butoxide were charged into a 3000 mL two-necked flask equipped with a reflux condenser, and the system was purged with nitrogen. Then, 57 mL of xylene was added, and the mixture was heated to reflux conditions and reacted for 3 hours while stirring with a magnetic stirrer. After 3 hours, the reaction solution was filtered, and the filtrate was subjected to two adsorption treatments with 66.6 g of activated clay (SA-1, manufactured by Nippon Activated Clay Co., Ltd.). The xylene solution was concentrated to 163 g, and then 200 g of acetone, 200 g of isohexane, and 200 g of methanol were added under heating and stirring to precipitate a solid. The solution containing the solid was cooled to 5°C and stirred for 1 hour, after which the solid was filtered off to obtain the primary solid (yield 30 g, yield 86.4%, HPLC purity 98.1%).

[0078] The primary solid was dissolved in toluene and subjected to two adsorption treatments with 66.6 g of activated clay (SA-1, manufactured by Nippon Activated Clay Co., Ltd.). After concentrating the filtrate to 140 g, 203 g of acetone and 222 g of isohexane were added under heating and stirring to precipitate the solid. The solution containing the solid was cooled to 5°C and stirred for 1 hour, then the solid was filtered off and dried at 70°C for 8 hours to obtain HTM-4 (orange solid; yield 26 g, yield 76.2%, HPLC purity 99.0%). The synthesis scheme is shown below.

[0079]

[0080] (1-2-3. Synthesis of HTM-5) Intermediate-3 was synthesized in the same manner as in "1-2-1. Synthesis of Intermediate-2" above, except that 4-fluorobenzaldehyde (10.418 g, 0.084 mol) was replaced with 4-methylbenzaldehyde (10.09 g, 0.084 mol) (yield 37.93 g, yield 92.5%, HPLC purity 98.9%).

[0081]

[0082] Compound HTM-5 was synthesized by the same method as described in "1-2-2. Synthesis of HTM-4" above, except that intermediate-2 (19.56 g, 0.039 mol) was replaced with intermediate-3 (19.25 g, 0.039 mol) (yield 25.9 g, yield 75.8%, HPLC purity 98.8%). 1 H-NMR (400MHz, CDCl3); 7.40-6.71 (m, 37H), 3.79 (s, 6H), 3.61 (s, 6H)).

[0083] (1-2-4. Synthesis of HTM-6) Intermediate-4 was synthesized in the same manner as in "1-1-1. Synthesis of Intermediate-1" above, except that 4-fluorobenzaldehyde (10.418 g, 0.084 mol) was replaced with 4-methoxybenzaldehyde (11.44 g, 0.084 mol) (yield 39.3 g, yield 92.5%, HPLC purity 98.8%).

[0084]

[0085] Compound HTM-6 was synthesized by the same method as described in "1-2-2. Synthesis of HTM-4" above, except that intermediate-2 (19.56 g, 0.039 mol) was replaced with intermediate-4 (19.95 g, 0.039 mol) (yield 26.6 g, yield 76.5%, HPLC purity 99.2%).

[0086] (1-2-5. Synthesis of HTM-7) Intermediate-5 was synthesized in the same manner as in "1-2-1. Synthesis of Intermediate-2" above, except that 4-fluorobenzaldehyde (10.418 g, 0.084 mol) was replaced with 4-chlorobenzaldehyde (11.81 g, 0.084 mol) (yield 39.3 g, yield 92.5%, HPLC purity 98.8%).

[0087]

[0088] Compound HTM-7 was synthesized by the same method as described in "1-2-2. Synthesis of HTM-4" above, except that intermediate-2 (19.56 g, 0.039 mol) was replaced with intermediate-5 (19.81 g, 0.039 mol) (yield 32.7 g, yield 77%, HPLC purity 99.8%).

[0089] Table 1 shows the yields and HPLC purity of HTM-1 to 7, intermediates 1 to 5 used in the synthesis of HTM-1 to 7, and intermediate a used in the synthesis of HTM-7' (synthesized differently from HTM-7) and HTM-7'. Note that HPLC purity was not measured for HTM-1 to 3 as they are polymers.

[0090]

[0091]

[0092] As is clear from Table 1, the total yield when HTM-7' (HTM-7) was synthesized via intermediate a was 67.8%, while the total yield when HTM-7 was synthesized via intermediate 5 was 72.1%. Furthermore, the HPLC purity of HTM-7 and HTM-7' was equivalent. From these results, it was confirmed that HTM-1 to 7 can be synthesized in high yield and high purity using intermediates 1 to 5.

[0093] [Manufacturing of Perovskite Organic Solar Cells] A 1.6 mm thick conductive glass substrate (FTN1.6, manufactured by Nippon Sheet Glass Co., Ltd., hereinafter referred to as FTO substrate) with a fluorine-doped tin oxide layer (first electrode) formed on it was used as the substrate. The FTO substrate was cut into 20 mm x 20 mm squares.

[0094] The FTO substrate was protected with masking tape except for the edges (5 mm), and the FTO portion was etched and removed using a cotton swab soaked in 6N hydrochloric acid and zinc powder. After removal, it was washed with deionized water, and the masking tape was removed. Then, the FTO substrate was ultrasonically cleaned for 15 minutes each in the following order: 10% neutral detergent solution (Clean Ace S, manufactured by AS ONE), deionized water, isopropyl alcohol, and acetone. After cleaning, the surface of the FTO substrate was treated with UV-ozone for 30 minutes.

[0095] Next, 200 μL of a 4% aqueous solution of tin(IV) nanoparticles (a mixture of Thermo Fisher's SnO2 aqueous dispersion (15% concentration) and deionized water in a 4:11 ratio) was dropped onto the FTO substrate, and spin coating was performed with acceleration for 3 seconds, rotation for 20 seconds (4000 rpm), and deceleration for 3 seconds until stopping. After that, the substrate was annealed (heat treated) on a hot plate at 150°C for 30 minutes to form an electron transport layer on the FTO substrate.

[0096] 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 under conditions of 21°C ± 1°C and a dew point of -50 ± 5°C.

[0097] Separately, under the glove box, 1.179 g (2.6 mmol) of lead iodide (L0279, manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.0031 g (0.03 mmol) of rubidium chloride (215260, manufactured by Aldrich) were weighed with 1.5 mL of a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) (volume ratio 9.5:0.5), and the mixture was stirred at 70°C for 1 hour to dissolve (Solution (1)).

[0098] Next, 0.017 g (0.11 mmol) of methylammonium iodide (M2556, manufactured by Tokyo Chemical Industries, Ltd.), 0.14 g (0.82 mmol) of formamidinium iodide (F1263, manufactured by Tokyo Chemical Industries, Ltd.), 0.008 g (0.13 mmol) of methylammonium chloride (22007-92, manufactured by Nacalai Tesque Corporation), and 0.014 g (0.12 mmol) of methylammonium bromide (132-18321, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were weighed with 1.5 mL of 2-propanol (IPA), and the mixture was stirred at room temperature for 30 minutes to dissolve (Solution (2)).

[0099] After the dissolved coating solution was cooled to room temperature, 150 μL of solution (1) was dropped onto the substrate coated with the electron transport layer. After 30 seconds, spin coating was performed with acceleration for 0.8 seconds, rotation for 30 seconds (1500 rpm), and deceleration for 0.8 seconds until stopping. After the rotation stopped, the substrate was annealed (heat treated) on a hot plate at 70°C for 5 minutes to form a PbI2 layer on the electron transport layer. After the heat-treated substrate was cooled to room temperature, 150 μL of solution (2) was dropped onto the substrate coated with PbI2, and spin coating was performed with acceleration for 0.8 seconds, rotation for 30 seconds (1500 rpm), and deceleration for 0.8 seconds until stopping. After the rotation stopped, the substrate was annealed (heat treated) on a hot plate at 70°C for 5 minutes, followed by 120°C for 15 minutes, to form a perovskite power generation layer (photoelectric conversion layer).

[0100] Next, the compound HTM-1 synthesized in Example 1 was weighed to a final concentration of 30 mM. In this solar cell configuration, 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl) borate (hereinafter sometimes referred to as "TPFB") was added instead of LiTFSI. TPFB equivalent to 10% by weight of HTM-1 was weighed and dissolved in chlorobenzene to prepare a hole transport layer forming composition. 150 μL of the prepared hole transport layer forming composition solution was dropped, and after 10 seconds, spin coating was performed with acceleration for 5.0 seconds, rotation for 30 seconds (4000 rpm), and deceleration for 1.0 second until stopping, forming a 100 nm hole transport layer on the perovskite power generation layer. The prepared device was left in an environment with 5% humidity for 12 hours. Subsequently, a gold electrode (second electrode) was formed on the hole transport layer by vacuum deposition at a depth of 80 nm, thereby manufacturing the perovskite-type organic solar cell of the present invention 1.

[0101] Perovskite-type organic solar cells according to Invention 2 to 7 were manufactured by the same method as described above, except that compounds HTM-2 to HTM-7 were used instead of compound HTM-1.

[0102] Perovskite-type organic solar cells of Comparative Examples 1 and 2 were manufactured using the same method as described above, except that compound HTM-7' and Spiro-OMeTAD were used instead of compound HTM-7.

[0103] [Evaluation of Photoelectric Conversion Characteristics of Perovskite-Type Organic Solar Cells] The photoelectric conversion efficiency of organic solar cells of Invention 1 to 7 and Comparative Examples 1 and 2, manufactured in Example 2, was evaluated. A solar simulator (HAL-320, manufactured by Asahi Spectrometer Co., Ltd.) was used as the measurement device, and the light intensity of the measurement light source was adjusted to 100 mW / cm2 using a reference solar cell. In the actual measurement, the measurement area was 0.1 cm². 2 The J-V curve characteristics were measured using a source meter (Model 6242, manufactured by ADC) while irradiating a masked solar cell element with light. The measurement was performed once each (total of two measurements) under Forward (forward scan, scanning in the direction of voltage increase) and Reverse (reverse scan, scanning in the direction of voltage decrease) conditions, and the conversion efficiency was determined.

[0104] From the measurement results, the short-circuit current of Reverse (Jsc [mA / cm²]) 2 ]), open-circuit voltage (Voc [V]), curve factor (FF [mW / cm 2 The following was derived: Furthermore, the photoelectric conversion efficiency (PCE [%]) was calculated using the following formula: PCE = (Jsc × Voc × FF / 100) × 100 The PCE of the organic solar cells of Invention 1 to 7 and Comparative Examples 1 and 2 are shown in Table 2 along with Jsc, Voc, and FF.

[0105]

[0106] As shown in Table 2, the organic solar cells of Invention 1 to 3, which used compounds HTM-1 to HTM-7 as hole transport materials, all had a PCE of 15.5% or higher, showing photoelectric conversion efficiency equivalent to or higher than that of the organic solar cell of Comparative Example 2, which used Spiro-OMeTAD as the hole transport material. In particular, the organic solar cells of Invention 1 to 4, which used HTM-1 to 4 as hole transport materials, all had a PCE of 16% or higher, showing extremely high photoelectric conversion efficiency.

[0107] Furthermore, the organic solar cell of the present invention 7, which uses compound HTM-7 as the hole transport material, showed a higher photoelectric conversion efficiency compared to the organic solar cell of Comparative Example 1, which uses compound HTM-7' as the hole transport material.

[0108] Based on these results, it was confirmed that using compounds HTM-1 to HTM-7 as hole transport materials can effectively improve the photoelectric conversion efficiency of solar cells.

[0109] The present invention relates to a hole transport material used as a material for a hole transport layer, and can be used in photoelectric conversion elements and organic solar cells using the same. By utilizing the present invention, it is possible to provide a hole transport material that has excellent high temperature and high humidity durability and excellent photoelectric conversion performance even in weak light such as indoor light, as well as a photoelectric conversion element and organic solar cell using the same.

Claims

1. An intermediate for hole transport materials represented by the following general formula (1). (In formula (1), X1 is a halogen atom, and X2 is a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, a dialkylamino group having 4 or fewer carbon atoms, or a diphenylamino group which may have a substituent. R1 to R4 may be the same or different, and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.) 2. In the intermediate of the hole transport material according to claim 1, X1 of the general formula (1) is a chlorine atom or a bromine atom, X2 is a chlorine atom, a bromine atom or a fluorine atom, a methyl group or a methoxy group, and R1 to R4 are all hydrogen atoms.

3. A hole transport material represented by the following general formulas (2) to (4). (In formulas (2) and (3), Ar1 represents an optionally substituted aryl group (phenyl group, naphthyl group, fluorenyl group), and X2 represents a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, a dialkylamino group having 4 or fewer carbon atoms, or an optionally substituted diphenylamino group. R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms. In formula (4), Ar1 and Ar2 may be the same or different and represent an optionally substituted aryl group (phenyl group, naphthyl group, fluorenyl group), and X2 represents a halogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, or a dialkylamino group having 4 or fewer carbon atoms. R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.) 4. In the hole transport material according to claim 3, X2 in the general formulas (2) and (3) is a methyl group or a diphenylamino group having a methoxy group at the para position, Ar1 is a phenyl group having one methoxy group each at the ortho and para positions, or a phenyl group having two methyl groups at the ortho position and one at the para position, and R1 to R4 are all hydrogen atoms.

5. In the hole transport material according to claim 3, X2 in the general formula (4) is a fluorine atom, a methyl group, or a methoxy group, Ar1 and Ar2 are phenyl groups having a methoxy group in the para position, and R1 to R4 are all hydrogen atoms.

6. A hole transport material represented by the following general formula (5), which uses an intermediate of a hole transport material represented by the following general formula (1) as a raw material. (In formula (1), X1 represents a halogen atom, and X2 represents an optionally substituted diphenylamino group. R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms. In formula (5), Ar1 and Ar2 may be the same or different and represent an optionally substituted aryl group (phenyl, naphthyl, or fluorenyl group), and R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.) 7. In the hole transport material according to claim 6, Ar1 and Ar2 of general formula (5) are diphenylamino groups having a methoxy group in the para position, and R1 to R4 are all hydrogen atoms.

8. A method for producing hole transport materials represented by the following general formulas (2) to (5), using an intermediate of a hole transport material represented by the following general formula (1) as a raw material. (In formula (1), X1 is a halogen atom, X2 is a halogen atom, a hydrogen atom, an alkyl group having 4 or less carbon atoms, an alkoxy group having 4 or less carbon atoms, a phenyl group, a dialkylamino group having 4 or less carbon atoms, or a diphenylamino group which may have a substituent. R1 to R4 may be the same or different and represent a hydrogen atom, an alkyl group having 4 or less carbon atoms, or an alkoxy group having 4 or less carbon atoms. In formulas (2) to (4), Ar1 and Ar2 may be the same or different and represent an aryl group which may have a substituent (phenyl group, naphthyl group, fluorenyl group), and X2 is a halogen R1 represents a hydrogen atom, a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, an alkoxy group having 4 or fewer carbon atoms, a phenyl group, or a dialkylamino group having 4 or fewer carbon atoms. R1 to R4 may be the same or different, and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms. In formula (5), Ar1 and Ar2 may be the same or different, and represent an aryl group (phenyl, naphthyl, or fluorenyl group) which may have substituents, and R1 to R4 may be the same or different, and represent a hydrogen atom, an alkyl group having 4 or fewer carbon atoms, or an alkoxy group having 4 or fewer carbon atoms.

9. An organic solar cell comprising: a substrate; a first electrode which is an electron injection electrode laminated on the substrate; an electron transport layer laminated on the first electrode; a photoelectric conversion layer laminated on the electron transport layer; a hole transport layer laminated on the photoelectric conversion layer; and a second electrode which is a hole injection electrode laminated on the hole transport layer, wherein the hole transport layer contains the hole transport material described in claim 3.

10. An organic solar cell comprising: a substrate; a first electrode which is a hole injection electrode laminated on the substrate; a hole transport layer laminated on the first electrode; a photoelectric conversion layer laminated on the hole transport layer; an electron transport layer laminated on the photoelectric conversion layer; and a second electrode which is an electron injection electrode laminated on the electron transport layer, wherein the hole transport layer contains the hole transport material described in claim 3.

11. A photoelectric conversion element comprising: a substrate; a first electrode having a hole blocking layer and a porous electron transport layer laminated on the substrate and further supporting a photosensitizing material; a hole transport layer laminated on the first electrode; and a second electrode laminated on the hole transport layer, wherein the hole transport layer contains the hole transport material described in claim 3.

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