JP2015088416A - Dye for dye-sensitized solar cell, semiconductor electrode, and dye-sensitized solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dye for a dye-sensitized solar cell which has excellent photoelectric conversion efficiency.SOLUTION: There are provided the dye represented by formula I and a dye-sensitized solar cell using the dye. (Rand Rare each a ≥13C alkyl group; R-Rare each an H atom or an alkyl group: Ris a 1-2C alkyl group having an acidic group with a pKa of less than 6; Ris a ≥4C alkyl group or a ≥7C aralkyl group; L is a divalent linking group; and n is 0 or 1)

Description

  The present invention relates to a dye for a dye-sensitized solar cell, a semiconductor electrode, and a dye-sensitized solar cell.

  Global warming due to the increase in carbon dioxide concentration caused by the use of large amounts of fossil fuels, and the increase in energy demand accompanying population growth are recognized as problems related to the survival of humankind. Therefore, in recent years, the use of sunlight that does not generate infinite and harmful substances has been energetically studied. Examples of solar energy that is a clean energy source that is currently in practical use include residential single crystal silicon, polycrystalline silicon, amorphous silicon, and inorganic solar cells such as cadmium telluride and indium copper selenide.

  However, these inorganic solar cells also have drawbacks. For example, a silicon system is required to have a very high purity. Naturally, the purification process is complicated, the number of processes is large, and the manufacturing cost is high. In addition, there is a demand for weight reduction and the like, and in particular, it is disadvantageous in terms of long payback to the user, and there has been a problem in the spread.

  On the other hand, many solar cells using organic materials have been proposed. As an organic solar cell, a Schottky photoelectric conversion element that joins a p-type organic semiconductor and a metal having a low work function, a p-type organic semiconductor and an n-type inorganic semiconductor, or a p-type organic semiconductor and an electron-accepting organic compound are joined. There are heterojunction photoelectric conversion elements, and organic semiconductors used are synthetic dyes and pigments such as chlorophyll and perylene, conductive polymer materials such as polyacetylene, or composite materials thereof. These are thinned by a vacuum deposition method, a casting method, a dipping method, or the like to form a battery material. Although organic materials have advantages such as low cost and easy area enlargement, the photoelectric conversion efficiency is often as low as 1% or less.

  Under such circumstances, a solar cell exhibiting good characteristics has been reported by Dr. Gretzell of Switzerland (see, for example, Non-Patent Document 1). This document also discloses materials and manufacturing techniques necessary for battery fabrication. This solar cell is called a dye-sensitized solar cell or a Gretzel solar cell, and is a wet solar cell using a titanium oxide porous thin film spectrally sensitized with a ruthenium (Ru) complex as a working electrode. The advantage of this method is that it is not necessary to purify inexpensive semiconductors such as titanium oxide to high purity, so that the manufacturing cost can be reduced compared to the inorganic solar cells described above, and the available light is in the visible light region. Because it is widespread, it is possible to effectively convert sunlight, which has a high energy intensity in the visible light region, into electricity.

  However, since noble metal Ru, which has resource limitations, is used, there is a possibility that a problem may occur in the stable supply of the Ru complex when a dye-sensitized solar cell is put into practical use. In addition, due to this resource limitation, the Ru complex itself is expensive, and there may be a problem in terms of cost during mass production. In order to solve such a problem, various proposals have been made for the purpose of changing at least part of the Ru complex to a cheaper organic dye. As examples thereof, various merocyanine dyes, cyanine dyes, 9-phenylxanthene dyes, coumarin dyes and the like are disclosed, but these are considerably inferior to Ru complexes in photoelectric conversion efficiency. (For example, see Patent Documents 1 to 4).

  Recently, organic dyes having photoelectric conversion efficiency comparable to Ru complexes have been disclosed as dyes for color-sensitized solar cells (see, for example, Patent Documents 5, 6 and 7). However, its performance is insufficient and further photoelectric conversion efficiency improvement is demanded.

  Recently, organic dyes having good photoelectric conversion efficiency have also been found, but they are still slightly inferior to the photoelectric conversion efficiency of Ru complexes, and further improvement in photoelectric conversion efficiency is required (for example, And Patent Documents 8 and 9).

JP 11-238905 A JP 2001-76773 A Japanese Patent Laid-Open No. 10-92477 International Publication No. 2002/045199 Pamphlet Japanese Patent No. 4610160 Japanese Patent No. 4326272 JP 2007-115673 A International Publication No. 2010/016612 Pamphlet JP 2013-35936 A

Brian O'Regan & Michael Gratzel, “A low-cost, high-efficiency solar cell based on dyed-sensitive TiO2 films”, Nature, 1991, 53. 737-740

  An object of the present invention is to provide a dye for a dye-sensitized solar cell having excellent photoelectric conversion efficiency, a semiconductor electrode sensitized by the dye for dye-sensitized solar cell, and a dye sensitization using the semiconductor electrode. Type solar cell.

  As a result of intensive studies to achieve the above-mentioned problems, a dye for a dye-sensitized solar cell represented by the general formula [I] (hereinafter sometimes abbreviated as “dye”), a semiconductor electrode sensitized with the dye, The target could be achieved by a dye-sensitized solar cell using a semiconductor electrode.

In the general formula [I], R ₁ and R ₂ represent an alkyl group having 9 or more carbon atoms. R ₃ and R _{4 each} represent a hydrogen atom or an alkyl group, and both may be linked to form a cyclopentane ring or a cyclohexane ring. R ₅ represents a hydrogen atom or an alkyl group. R ₆ represents an alkyl group having 1 to 2 carbon atoms having an acidic group having a pKa of less than 6 as a substituent, and R ₇ represents an alkyl group having 4 or more carbon atoms or an aralkyl group having 7 or more carbon atoms. L represents a divalent linking group, and n represents 0 or 1. The configuration of two hetero five-membered rings containing a sulfur atom may be either Z-type or E-type.

The dye represented by the general formula [I] is a compound classified as a merocyanine dye, and usually has a structure in which an electron donor unit and an electron acceptor unit are connected by a conjugated double bond. The dye of the present invention has a rigid fluorene unit in the molecule, and has a property that a plurality of dyes are easily arranged regularly when adsorbed on a semiconductor. Furthermore, the steric effect of _two alkyl groups having 9 or more carbon atoms (R ₁ and R ₂ ) bonded to the 9-position of fluorene has a barrier effect that reduces direct contact between the semiconductor and the electrolyte. The reverse electron transfer reaction between the semiconductor and the electrolyte during battery operation can be suppressed. In addition, the hydrophobic effect of the _two alkyl groups having 9 or more carbon atoms (R ₁ and R ₂ ) makes it possible to make the electrode surface adsorbed with the dye hydrophobic, and a small amount of moisture contained in the electrolytic solution. It is possible to prevent electrode deterioration due to For the above reasons, the dye of the present invention forms a stable dye aggregate when adsorbed on a semiconductor and has excellent photoelectric conversion efficiency.

  The dye represented by the general formula [I] will be described.

In the general formula [I], R ₁ and R ₂ each represent an alkyl group having 9 or more carbon atoms. Specific examples thereof include nonyl group, decyl group, dodecyl group, tridecyl group, tetradecyl group, eicosyl group, heneicosyl group, docosyl group. And an alkyl group such as a group. When the number of carbon atoms in the alkyl group is 10 or more, the barrier effect for reducing direct contact between the semiconductor and the electrolyte is high, which is particularly effective.

R ₃ and R ₄ each represent an alkyl group such as a methyl group, an ethyl group, an n-butyl group, an n-hexyl group, and an n-octyl group in addition to a hydrogen atom, It may be. R ₃ and R ₄ may be bonded together to form a cyclopentane ring or a cyclohexane ring. Particularly preferred are those in which they are combined to form a cyclopentane ring or a cyclohexane ring.

  Specific examples of L include divalent linking groups as shown below, and these may further have a substituent.

R ₅ represents an alkyl group such as a methyl group or an ethyl group in addition to a hydrogen atom.

R ₆ represents a C 1-2 alkyl group having an acidic group having a pKa of less than 6 as a substituent. Specific examples of the acidic group having a pKa of less than 6 include a carboxy group, a sulfo group, a sulfino group, a sulfeno group, a phosphono group, and a phosphinico group, among which a carboxy group is particularly preferable.

Specific examples of R ₇ include alkyl groups such as butyl group, octyl group, dodecyl group, n-hexadecyl group and octadecyl group, and aralkyl groups such as benzyl group and phenethyl group. The structure of the alkyl group may be either a linear structure or a branched structure, and among them, a linear alkyl group having 4 or more carbon atoms is particularly preferable.

  Next, specific examples of the compound of the general formula [I] according to the present invention will be given, but the present invention is not limited thereto.

  These compounds can be synthesized with reference to the synthesis methods described in, for example, JP-A-8-269345 and WO 2004/01155 pamphlet.

  The dye-sensitized solar cell includes a conductive support, a semiconductor layer (semiconductor electrode) sensitized with a dye provided on the surface of the conductive support, a charge transfer layer, and a counter electrode. The semiconductor layer may be a single layer structure or a stacked structure, and is designed according to the purpose. In addition, at the boundary of this element such as the boundary between the conductive layer and the semiconductor layer of the conductive support, the boundary between the semiconductor layer and the moving layer, the constituent components of each layer may diffuse or mix with each other.

  As the conductive support, there can be used a support made of glass or plastic having a conductive layer containing a conductive agent on its surface, such as a metal having a conductive property in itself. In the latter case, the conductive agent is a metal oxide such as platinum, gold, silver, copper, aluminum or the like, carbon or indium-tin composite oxide (hereinafter abbreviated as “ITO”), fluorine-doped tin oxide or the like. And the like (hereinafter abbreviated as “FTO”). The conductive support preferably has a transparency that transmits light of 10% or more, and more preferably transmits 50% or more. Among these, conductive glass in which a conductive layer made of ITO or FTO is deposited on glass is particularly preferable.

  A metal lead wire may be used for the purpose of reducing the resistance of the transparent conductive substrate. Examples of the material of the metal lead wire include metals such as aluminum, copper, silver, gold, platinum, and nickel. A metal lead wire is installed on a transparent conductive support by vapor deposition, sputtering, pressure bonding, etc., and a method of providing ITO or FTO thereon, or a method of installing a metal lead wire on a transparent substrate having conductivity on the surface. is there.

  Examples of the semiconductor include a single semiconductor such as silicon and germanium, a compound semiconductor typified by a metal chalcogenide, and a compound having a perovskite structure. Metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum oxides; cadmium, zinc, lead, silver, antimony or bismuth Preferable examples include sulfides of cadmium or selenides of lead or cadmium tellurides. Other compound semiconductors are preferably phosphides such as zinc, gallium, indium, and cadmium; gallium arsenide, copper-indium-selenide, copper-indium-sulfide, and the like. As the compound having a perovskite structure, strontium titanate, calcium titanate, sodium titanate, barium titanate, potassium niobate and the like are preferable.

  The semiconductor used in the present invention may be single crystal or polycrystalline. From the viewpoint of photoelectric conversion efficiency, a single crystal is preferable, but from the viewpoint of manufacturing costs, securing raw materials, etc., a polycrystal is preferable. The particle size of the semiconductor is preferably 2 nm or more and 1 μm or less. Regarding the measurement of the particle size, a method by observation with a transmission electron microscope is preferable.

  As a method of forming a semiconductor layer on a conductive support, there are a method of applying a dispersion or colloidal solution of semiconductor fine particles on a conductive support, a sol-gel method, and the like. As a method for producing a dispersion, a sol-gel method, a method of mechanically pulverizing with a mortar, a method of dispersing while pulverizing using a mill, or a fine particle in a solvent when synthesizing a semiconductor, The method of using it as it is is mentioned.

  In the case of a dispersion prepared by mechanical pulverization or pulverization using a mill, the dispersion is prepared by dispersing at least semiconductor fine particles alone or a mixture of semiconductor fine particles and a resin in water or an organic solvent. Resins used include polymers and copolymers of vinyl compounds such as styrene, vinyl acetate, acrylic acid esters, methacrylic acid esters, silicone resins, phenoxy resins, polysulfone resins, polyvinyl butyral resins, polyvinyl formal resins, polyester resins. , Cellulose ester resin, cellulose ether resin, urethane resin, phenol resin, epoxy resin, polycarbonate resin, polyarylate resin, polyamide resin, polyimide resin and the like.

  As a medium for dispersing the semiconductor fine particles, alcohol-based media such as water, methanol, ethanol, isopropyl alcohol; ketone-based media such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ester-based media such as ethyl formate, ethyl acetate, and n-butyl acetate Medium: Ether-based medium such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, dioxane; Amide-based medium such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone; Dichloromethane, chloroform, Bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene, 1-chloronaphtha Halogenated hydrocarbon media such as n; pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, m-xylene, p- Examples thereof include hydrocarbon-based media such as xylene, ethylbenzene, cumene. These can be used alone or as a mixed medium of two or more.

  Examples of the method for applying the dispersion include a roller method, a dip method, an air knife method, a blade method, a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, and a spray method.

  The semiconductor layer may be a single layer or multiple layers. In the case of multiple layers, a dispersion of semiconductor fine particles having different particle diameters can be applied in multiple layers. Also, different types of semiconductors, and coating layers having different compositions of resins and additives can be applied in multiple layers. Multi-layer coating is an effective means when the film thickness is insufficient with a single coating.

  In general, as the semiconductor layer thickness increases, the amount of supported dye increases per unit projected area, which increases the light capture rate, but also increases the diffusion distance of the generated electrons, resulting in more charge recombination. turn into. Therefore, the film thickness of the semiconductor layer is preferably 0.1 to 100 μm, and more preferably 1 to 30 μm.

The semiconductor fine particles may or may not be heat-treated after being coated on the conductive support. However, heat treatment is preferred from the viewpoints of electronic contact between fine particles, improvement in coating film strength, and improvement in adhesion to the support. Further, microwave irradiation, press treatment, or electron beam irradiation may be performed. These treatments may be performed alone or in combination of two or more. In the heat treatment, the heating temperature is preferably 40 to 700 ° C, more preferably 80 to 600 ° C. The heating time is preferably 5 minutes to 50 hours, and more preferably 10 minutes to 20 hours. Microwave irradiation may be performed from the semiconductor layer forming side of the semiconductor electrode or from the back side. Although there is no restriction | limiting in particular in irradiation time, It is preferable to carry out within 1 hour. The press treatment is preferably performed at 9.8 × 10 ⁶ N / m ² or more, and more preferably at 9.8 × 10 ⁷ N / m ² or more. The pressing time is not particularly limited, but is preferably within 1 hour.

  The semiconductor fine particles preferably have a large surface area so that many dyes can be adsorbed. For this reason, it is preferable that the surface area in the state which coated the semiconductor layer on the support body is 10 times or more with respect to a projection area, and it is more preferable that it is 100 times or more.

  The dye-sensitized solar cell dye represented by the general formula [I] of the present invention may be used alone or in combination of two or more. In addition, for the purpose of reducing the amount of Ru used in a dye-sensitized solar cell that also uses a ruthenium (Ru) complex, the dye of the present invention and a Ru complex may be used in combination. Other merocyanine dyes, cyanine dyes, 9-phenylxanthene dyes, coumarin dyes, phthalocyanine dyes, naphthalocyanine dyes and the like may be used in combination.

  As a method for adsorbing the dye to the semiconductor layer, a method in which the semiconductor layer is immersed in a dye solution or a dye dispersion, or a method in which a dye solution or a dispersion is applied to the semiconductor layer and adsorbed can be used. In the former case, dipping method, dipping method, roller method, air knife method, etc. can be used, and in the latter case, wire bar method, slide hopper method, extrusion method, curtain method, spin method, spray method, etc. Can be used.

  When adsorbing the dye, a condensing agent may be used in combination. The condensing agent may be either one that acts as a catalyst that physically or chemically binds the dye to the inorganic surface, or one that acts stoichiometrically to favorably shift the chemical equilibrium. . Further, a thiol or hydroxy compound may be added as a condensation aid.

  The medium for dissolving or dispersing the dye is an alcoholic medium such as water, methanol, ethanol or isopropyl alcohol; a ketone medium such as acetone, methyl ethyl ketone or methyl isobutyl ketone; an ester type such as ethyl formate, ethyl acetate or n-butyl acetate. Medium: Ether-based medium such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, dioxane; Nitrile-based medium such as acetonitrile and propionitrile; N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2- Amide-based media such as pyrrolidone; dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenze Halogenated hydrocarbon media such as bromobenzene, iodobenzene, 1-chloronaphthalene; n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, Examples thereof include hydrocarbon media such as o-xylene, m-xylene, p-xylene, ethylbenzene and cumene. These can be used alone or in admixture of two or more.

  The temperature for adsorbing the dye is preferably -50 ° C or higher and 200 ° C or lower. Further, the adsorption may be performed while stirring. Examples of the stirring method include, but are not limited to, a stirrer, a ball mill, a paint conditioner, a sand mill, an attritor, a disperser, and ultrasonic dispersion. The time required for adsorption is preferably from 5 seconds to 1000 hours, more preferably from 10 seconds to 500 hours, and even more preferably from 1 minute to 150 hours.

  In the present invention, when the dye is adsorbed on the semiconductor layer, a steroidal compound may be used in combination and co-adsorbed.

  0.01-1000 mass parts is preferable with respect to 1 mass part of pigment | dyes, and, as for the quantity of a steroid type compound, 0.1-100 mass parts is more preferable.

  After adsorbing the dye or co-adsorbing the dye and the steroidal compound, a basic compound such as t-butylpyridine, 2-picoline, 2,6-lutidine, or phosphoric acid, phosphate ester, alkyl phosphorus You may immerse in the organic solvent containing acidic compounds, such as an acid, an acetic acid, and propionic acid.

  As the charge transfer layer, an electrolytic solution in which a redox couple is dissolved in an organic solvent, a gel electrolyte in which a polymer matrix is impregnated with a liquid in which the redox couple is dissolved in an organic solvent, a molten salt containing a redox couple, a solid electrolyte, an inorganic A hole transport material, an organic hole transport material, or the like can be used.

  The electrolytic solution is preferably composed of an electrolyte, a solvent, and an additive. Preferred electrolytes are metal iodide-iodine combinations such as lithium iodide, sodium iodide, potassium iodide, cesium iodide, calcium iodide; quaternary grades such as tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide, etc. Iodine salt of ammonium compound-iodine combination; metal bromide-bromine combination such as lithium bromide, sodium bromide, potassium bromide, cesium bromide, calcium bromide; quaternary ammonium such as tetraalkylammonium bromide, pyridinium bromide Bromine-bromine combinations of compounds; metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions; sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides ; Viologen dyes, hydroquinone - such as quinones and the like. The above-mentioned electrolytes may be a single combination or a mixture. Further, a molten salt in a molten state at room temperature can also be used as the electrolyte. When this molten salt is used, it is not necessary to use a solvent.

  The electrolyte concentration in the electrolytic solution is preferably 0.05 to 20M, and more preferably 0.1 to 15M. Solvents used for the electrolyte include carbonate solvents such as ethylene carbonate and propylene carbonate; heterocyclic compounds such as 3-methyl-2-oxazolidinone; ether solvents such as dioxane, diethyl ether and ethylene glycol dialkyl ether; methanol and ethanol Alcohol solvents such as polypropylene glycol monoalkyl ether; nitrile solvents such as acetonitrile and benzonitrile; aprotic polar solvents such as dimethyl sulfoxide and sulfolane are preferred. Moreover, you may use together basic compounds, such as t-butyl pyridine, 2-picoline, and 2, 6- lutidine.

  The electrolyte can be gelled by techniques such as polymer addition, oil gelling agent addition, polymerization including polyfunctional monomers, and polymer crosslinking reaction. Preferable polymers for gelation by addition of polymer include polyacrylonitrile, polyvinylidene fluoride, and the like. Preferred gelling agents for gelation by adding an oil gelling agent include dibenzylidene-D-sorbitol, cholesterol derivatives, amino acid derivatives, trans- (1R, 2R) -1,2-cyclohexanediamine alkylamide derivatives, alkyl Examples include urea derivatives, N-octyl-D-gluconamidobenzoate, double-headed amino acid derivatives, quaternary ammonium derivatives, and the like.

  Preferred monomers for polymerization with polyfunctional monomers include divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, and the like. Can do. Furthermore, esters and amides derived from acrylic acid such as acrylamide and methyl acrylate and α-alkyl acrylic acid, esters derived from maleic acid and fumaric acid such as dimethyl maleate and diethyl fumarate, butadiene, cyclohexane Dienes such as pentadiene, aromatic vinyl compounds such as styrene, p-chlorostyrene, sodium styrenesulfonate, vinyl esters, acrylonitrile, methacrylonitrile, vinyl compounds having a nitrogen-containing heterocyclic ring, vinyls having a quaternary ammonium salt A monofunctional monomer such as a compound, N-vinylformamide, vinyl sulfonic acid, vinylidene fluoride, vinyl alkyl ethers, and N-phenylmaleimide may be contained. 0.5-70 mass% is preferable and the polyfunctional monomer which occupies for the monomer whole quantity has more preferable 1.0-50 mass%.

  The above-mentioned monomers can be polymerized by radical polymerization. The monomer for gel electrolyte that can be used in the present invention can be radically polymerized by heating, light, electron beam or electrochemical. The polymerization initiator used when the crosslinked polymer is formed by heating is 2,2'-azobisisobutyronitrile, 2,2'-azobis (2,4-dimethylvaleronitrile), dimethyl-2 Azo initiators such as 2,2'-azobis (2-methylpropionate), peroxide initiators such as benzoyl peroxide, and the like are preferable. The addition amount of these polymerization initiators is preferably 0.01 to 20% by mass and more preferably 0.1 to 10% by mass with respect to the total amount of monomers.

  When the electrolyte is gelled by a polymer crosslinking reaction, it is desirable to use a polymer containing a reactive group necessary for the crosslinking reaction and a crosslinking agent in combination. Preferable examples of the reactive group necessary for the crosslinking reaction include nitrogen-containing heterocycles such as pyridine, imidazole, thiazole, oxazole, triazole, morpholine, piperidine and piperazine. Preferred cross-linking agents include bifunctional or higher functional reagents capable of electrophilic reaction with nitrogen atoms such as alkyl halides, halogenated aralkyls, sulfonic acid esters, acid anhydrides, acid chlorides, and isocyanates.

  When an inorganic hole transport material is used instead of the electrolyte, copper iodide, copper thiocyanide, or the like can be introduced into the electrode by a casting method, a coating method, a spin coating method, a dipping method, or electrolytic plating.

  It is also possible to use an organic charge transport material instead of the electrolyte. Charge transport materials include hole transport materials and electron transport materials. Examples of the former include, for example, oxadiazoles shown in Japanese Patent Publication No. 34-5466, triphenylmethanes shown in Japanese Patent Publication No. 45-555, and Japanese Patent Publication No. 52-4188. Pyrazolines shown in JP-A-55-42380, hydrazones shown in JP-B-56-123544, oxadiazoles shown in JP-A-56-123544, etc., JP-A-54-58445 And tetrasylbenzidines disclosed in JP-A-58-65440, and stilbenes disclosed in JP-A-60-98437. Among them, examples of the charge transport material used in the present invention are shown in JP-A-60-24553, JP-A-2-96767, JP-A-2-183260, and JP-A-2-226160. Particularly preferred are the hydrazones described, and the stilbenes shown in JP-A-2-51162 and JP-A-3-75660. Moreover, these can be used individually or in mixture of 2 or more types.

  On the other hand, examples of the electron transport material include chloranil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 1,3,7-trinitrodibenzothiophene, or 1,3,7-trinitrodibenzothiophene-5,5-dioxide . These electron transport materials can be used alone or as a mixture of two or more.

  Furthermore, for the purpose of improving the charge transfer efficiency in the charge transfer layer, a certain kind of electron withdrawing compound can be added to the charge transfer layer. Examples of the electron-withdrawing compound include quinones such as 2,3-dichloro-1,4-naphthoquinone, 1-nitroanthraquinone, 1-chloro-5-nitroanthraquinone, 2-chloroanthraquinone, and phenanthrenequinone; 4-nitro Aldehydes such as benzaldehyde; ketones such as 9-benzoylanthracene, indandione, 3,5-dinitrobenzophenone, 3,3 ', 5,5'-tetranitrobenzophenone; phthalic anhydride, 4-chloronaphthalic anhydride, etc. Cyano compounds such as terephthalalmalononitrile, 9-anthrylmethylidenemalononitrile, 4-nitrobenzalmalononitrile, 4- (p-nitrobenzoyloxy) benzalmalononitrile; 3-benzalphthalide, 3 -(Α-cyano-p-ni Robenzaru) phthalide, 3- (alpha-cyano -p- Nitorobenzaru) -4,5,6,7 such phthalides such as tetrachloro phthalide can be cited.

  When forming a charge transfer layer using a charge transport material, a resin may be used in combination. When the resin is used in combination, polystyrene resin, polyvinyl acetal resin, polysulfone resin, polycarbonate resin, polyester resin, polyphenylene oxide resin, polyarylate resin, acrylic resin, methacrylic resin, phenoxy resin, and the like can be given. Among these, polystyrene resin, polyvinyl acetal resin, polycarbonate resin, polyester resin, and polyarylate resin are preferable. These resins may be used alone or as a copolymer in combination of two or more.

  There are two main methods for forming the charge transfer layer. One is a method in which a counter electrode is first bonded onto a semiconductor layer that has adsorbed a dye, and a liquid charge transfer layer is sandwiched in the gap. The other is a method in which a charge transfer layer is provided directly on a semiconductor layer adsorbed with a dye. In the latter case, a counter electrode is newly provided on the charge transfer layer.

  In the former case, examples of the method for sandwiching the charge transfer layer include a normal pressure process using capillary action due to immersion and a vacuum process in which the gas phase is replaced with a liquid phase at a pressure lower than normal pressure. In the latter case, in the wet charge transfer layer, it is necessary to provide a counter electrode without being dried to prevent liquid leakage at the edge portion. In the case of a gel electrolyte, there is a method in which it is applied in a wet manner and solidified by a method such as polymerization. In that case, you may provide a counter electrode after drying and fixing. In addition to the electrolytic solution, the organic charge transport material solution and gel electrolyte can be applied in the same manner as the semiconductor layer and pigment application, as well as the immersion method, roller method, dipping method, air knife method, extrusion method, slide Examples include the hopper method, wire bar method, spin method, spray method, casting method, and various printing methods.

  The counter electrode can be used on a support having a conductive layer in the same manner as the substrate having conductivity on the surface, but the support is not necessarily required when the conductive layer itself has sufficient strength and sealing properties. Specific examples of the material used for the counter electrode include metals such as platinum, gold, silver, copper, aluminum, rhodium and indium, carbon compounds, and conductive metal oxides such as ITO and FTO. There is no particular limitation on the thickness of the counter electrode.

  In order for light to reach the semiconductor layer, at least one of the conductive substrate and the counter electrode on the surface holding the semiconductor layer must be substantially transparent. In the photoelectric conversion element of this invention, the board | substrate which has electroconductivity on the surface holding the semiconductor layer is transparent, and the method of making sunlight inject from the electroconductive board | substrate side holding the semiconductor layer is preferable. In this case, a material that reflects light is preferably used for the counter electrode, and a metal, glass, plastic, or metal thin film on which a conductive oxide is deposited is preferable.

  As described above, there are two types of coating of the counter electrode: when applied on the charge transfer layer and when applied on the semiconductor layer. In any case, the counter electrode material can be appropriately formed on the charge transfer layer or the semiconductor layer by a technique such as coating, laminating, vapor deposition, or bonding depending on the type of the counter electrode material or the type of the charge transfer layer. When the charge transfer layer is solid, the counter electrode can be formed directly on the conductive material by a method such as coating, vapor deposition, or chemical vapor deposition (CVD).

  EXAMPLES Next, although an Example demonstrates this invention still in detail, this invention is not limited to these at all.

Example 1
<Preparation of dye-sensitized solar cell>
Titanium oxide paste: 1.2 g of PST-18NR (catalyst chemical industry, average particle size 18 nm) and titanium oxide paste: PST-400C (catalyst chemical industry, average particle size 400 nm) 0.3 g in a mortar Were sufficiently kneaded for 10 minutes to prepare an electrode manufacturing paste. This paste was applied onto an FTO glass substrate (manufactured by AGC Fabrytec, product name: VU) so as to have a film thickness of 5 μm, dried at room temperature, baked at 100 ° C. for 30 minutes, and further at 450 ° C. for 1 hour, A semiconductor electrode was obtained.

  Dye A-2 was dissolved in a mixed solution of t-butanol / acetonitrile (volume ratio: 1/1) to prepare a dye solution having a concentration of 0.5 mM. The previously prepared semiconductor electrode was immersed in this dye solution at room temperature for 3 hours to perform an adsorption treatment, thereby preparing a dye-adsorbing semiconductor electrode (working electrode). As the counter electrode, a titanium plate on which platinum was sputtered was used. Both electrodes were placed so as to face each other, and an electrolyte was injected between them to produce a dye-sensitized solar cell. The electrolyte was 3-methoxypropionitrile of lithium iodide 0.1M, iodine 0.05M, 1,2-dimethyl-3-n-propylimidazolium iodide 0.5M, 4-t-butylpyridine 0.05M. The solution was used.

(Examples 2 to 16)
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that the dye A-2 was changed to the dye shown in Table 1.

(Comparative Examples 1-4)
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that the dye A-2 was changed to the comparative dyes C-1 to C-4.

<Evaluation 1: Photoelectric conversion efficiency>
From the working electrode side of the dye-sensitized solar cell, artificial sunlight (AM1.5G, irradiation intensity 100 mW / cm ² ) generated from a solar simulator (manufactured by Yamashita Denso Co., Ltd., device name: YSS-40S) as a light source. The photoelectric conversion efficiency of the dye-sensitized solar cells of Examples 1 to 16 and Comparative Examples 1 to 4 was evaluated using an electrochemical measurement device (manufactured by Solartron, device name: SI-1280B). The results are shown in Table 1. The open circuit voltage, short circuit current density, and photoelectric conversion efficiency of Examples 1 to 16 and Comparative Examples 2 to 4 are shown as relative values based on the evaluation results of Comparative Example 1.

  As is clear from Table 1, it can be seen that the dye of the present invention is superior in photoelectric conversion efficiency as compared with the dye of the comparative example.

  The dye for dye-sensitized solar cells of the present invention can be used for an optical sensor sensitive to light of a specific wavelength in addition to the dye-sensitized solar cell.

Claims (3)

A dye for a dye-sensitized solar cell represented by the following general formula [I].

(In the general formula [I], R ₁ and R ₂ represent an alkyl group having 9 or more carbon atoms, and may be bonded by R ₁ and R ₂ to form a cyclic structure. R ₃ and R ₄ are hydrogen atoms. Or an alkyl group, which may combine to form a cyclopentane ring or a cyclohexane ring, R ₅ represents a hydrogen atom or an alkyl group, and R ₆ has an acidic group having a pKa of less than 6 as a substituent. R ₇ represents an alkyl group having 4 or more carbon atoms or an aralkyl group having 7 or more carbon atoms, L represents a divalent linking group, and n represents 0 or 1 (The configuration of the two hetero five-membered rings containing a sulfur atom may be either Z-type or E-type.)   A semiconductor electrode sensitized with the dye for a dye-sensitized solar cell according to claim 1.   A dye-sensitized solar cell using the semiconductor electrode according to claim 2.