JP2014086238A - 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 having a color tone of blue violet to blue and having excellent photoelectric conversion characteristics, to provide a semiconductor electrode sensitized by the dye for the dye-sensitized solar cell and having an excellent photoelectric conversion efficiency, and to provide a dye-sensitized solar cell using the semiconductor electrode.SOLUTION: Provided are a dye for a dye-sensitized solar cell represented by a general formula (1), a semiconductor electrode sensitized by this dye, and a dye-sensitized solar cell using the semiconductor electrode.

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 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, photoelectric conversion efficiency is often as low as 1% or less, and there is a problem that durability is poor.

  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 complex (hereinafter referred to as 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. For example, various merocyanine dyes, cyanine dyes, 9-phenylxanthene dyes, coumarin dyes, and the like have been disclosed. However, these are considerably inferior to Ru complexes in photoelectric conversion characteristics, and are practical. Most of them were poor (see, for example, Patent Documents 1 to 4).

  In addition, since organic dyes have clear colors such as yellow, red, and blue, which are not found in ruthenium complexes, many applications have been proposed for design applications that make use of the colors (for example, Non-Patent Document 2). reference). Among them, various styryl dyes, squarylium ring-containing dyes, and the like have been proposed as dyes having a color tone of bluish purple to blue (see, for example, Patent Documents 5 and 6), but have sufficient photoelectric conversion characteristics. There was little pigment.

  On the other hand, Patent Document 7 discloses a hemicyanine dye derived from indoline having a specific structure and benzothiazolium. Although these dyes have high photoelectric conversion characteristics among dyes having a color tone of bluish violet to blue, further improvement has been demanded.

JP 11-238905 A JP 2001-76773 A Japanese Patent Laid-Open No. 10-92477 JP 2002-164089 A JP 2003-234133 A JP 2007-70509 A JP 2010-49990 A

Nature, 353, 737 (1991) Applied Physics, Vol. 73, No. 12, 1549 (2004)

  An object of the present invention is to provide a dye-sensitized solar cell dye having a color tone of bluish purple to blue and having excellent photoelectric conversion characteristics, a semiconductor electrode sensitized by the dye-sensitized solar cell dye, and The object is to provide a dye-sensitized solar cell using the semiconductor electrode.

  As a result of intensive studies to solve the above problems, the present inventor has found that a dye for a dye-sensitized solar cell represented by the following general formula (1) (hereinafter referred to as “dye”), a semiconductor sensitized by the dye These goals could be achieved by a dye-sensitized solar cell using the electrode and its semiconductor electrode.

In the general formula (1), R ₁ represents an electron-withdrawing group in which Hammett's substituent constant σ value is a positive value. R ₂ and R ₃ represent a hydrogen atom or an alkyl group, and R ₂ and R ₃ may be linked to form a cyclopentane ring or a cyclohexane ring. L ₁ and L ₂ represent methine group units. L ₃ represents an alkylene group. R ₄ represents an electron donating group in which Hammett's substituent constant σp value is negative. R ₅ represents an acidic group having a pKa of less than 6. X ⁻ represents a counter anion.

  The dye represented by the general formula (1) has a color tone of bluish purple to blue and has excellent photoelectric conversion characteristics. By sensitizing with this dye, a semiconductor having excellent photoelectric conversion efficiency. A dye-sensitized solar cell using the electrode and the semiconductor electrode can be obtained.

The dye of the present invention is described in detail below. In the general formula (1), R ₁ represents an electron-withdrawing group in which Hammett's substituent constant σ value (hereinafter referred to as Hammett value) is a positive value. This Hammett value is described in various books. For example, “Structure-activity relationship of drugs—Guidelines for drug design and research on mechanism of action” (Chemistry domain, extra number 122; Nankodo (1979)) Chem. Rev. 91, 165 (1991). This Hammett value is a value unique to a substituent that is governed by a specific electronic effect of each substituent, mainly an induced effect (I effect) and a mesomeric effect (M effect). In the present invention, R ₁ has a Hammett value as a reference substituent on the benzene ring substituted by the substituent (in the general formula (1) of the present invention, a vinylene bond (—CH═CH -) Is a site), the σp value is applied for para-position substitution, and the σm value is applied for meta-position substitution. On the other hand, in the ortho-position substitution, in addition to the electronic effect described above, there are many cases where the adjacent steric effect peculiar to the ortho-position substitution has an influence, and therefore, by comparing detailed numerical values such as the σp value and σm value described above. There is little discussion. However, it is widely known that basically similar electronic effects act on ortho-position substitution and para-position substitution, and when the σp value of para-position substitution is a positive value, However, it is well known in the art to assume that the Hammett value is a positive value. Specific examples of these electron-withdrawing groups include halogen atoms (eg, fluorine, chlorine, bromine, iodine, etc.), cyano groups, nitro groups, formyl groups, acetyl groups, carboxy groups, alkoxycarbonyl groups (eg, methoxycarbonyl). Group, ethoxycarbonyl group, etc.), aryloxycarbonyl group (eg, phenoxycarbonyl group, naphthyloxycarbonyl group, etc.), halogen-substituted alkyl group (eg, fluoromethyl group, difluoromethyl group, trifluoromethyl group, pentafluoroethyl group, Hexafluoropropyl group, chloromethyl group, dichloromethyl group, trichloromethyl group, bromomethyl group, dibromomethyl group, tribromomethyl group, etc.), meta-substituted alkoxy group (for example, methoxy group, ethoxy group, propoxy group, butoxy group, F Siloxy group, octyloxy group, decyloxy group, dodecyloxy group, benzyloxy group, etc., meta-substituted aryloxy groups (eg phenoxy group, naphthyloxy group, etc.), carbamoyl groups (eg carbamoyl group, N-methylcarbamoyl group) N-ethylcarbamoyl group, N-propylcarbamoyl group, N-butylcarbamoyl group, N, N-dimethylcarbamoyl group, N, N-diethylcarbamoyl group, N, N-dipropylcarbamoyl group, N, N-dibutylcarbamoyl Group, N-methyl-N-ethylcarbamoyl group, N-methyl-N-propylcarbamoyl group, N-methyl-N-butylcarbamoyl group, N, N-tetramethylenecarbamoyl group, N, N-pentamethylenecarbamoyl group, N, N-hexamethylenecarbamoyl , N- phenylcarbamoyl group, N- (1-naphthyl) carbamoyl group, N- methyl -N- phenylcarbamoyl group, N- ethyl -N- phenylcarbamoyl group, N, etc. N- diphenylcarbamoyl group) is. If possible, these may further have a substituent well known in the art as long as the properties as an electron-withdrawing group are not lost. Of the electron-withdrawing groups described above, preferred as R ₁ are a halogen atom, an alkoxycarbonyl group, a halogen-substituted alkyl group, a meta-substituted alkoxy group, and a meta-substituted aryloxy group. Further, it is preferable that no substituent other than R ₁ exists on the benzene ring to which R ₁ is bonded.

R ₂ and R ₃ are hydrogen atoms or alkyl groups (for example, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, undecyl group, dodecyl group, tetradecyl group, Pentadecyl group and the like, and R ₂ and R ₃ may be linked to form a cyclopentane ring or a cyclohexane ring. Among them, preferred are those in which R ₂ and R ₃ are linked to form a cyclopentane ring or a cyclohexane ring, and particularly preferred are those in which R ₂ and R ₃ are linked to form a cyclopentane ring. .

L ₁ and L ₂ represent methine group units. The methine group unit is composed of a conjugated methine chain having an odd number of carbon atoms, and the number of carbon atoms is preferably 1 or 3 for both L ₁ and L ₂ , and a monomethine group having 1 carbon atom is particularly preferable.

L ₃ represents an alkylene group (for example, a methylene group, an ethylene group, a propylene group, a tetramethylene group, a hexamethylene group, etc., which may be a linear structure or a branched structure). Of these, those having 1 to 4 carbon atoms are preferred, and those having 1 carbon atom are particularly preferred.

R ₄ represents an electron donating group in which Hammett's substituent constant σp value (see description of Hammett value in R ₁ ) is a negative value. Electronic effects of the _{R 4} has on, the Japanese as described in 2010-49990 JP respect quaternary nitrogen atom of benzothiazolium _{ring R 4} are attached, an electron donor _{which R 4} has This is the effect of injecting electrons effectively due to the sex characteristics. Therefore, unlike R ₁ described above, R ₄ is limited to para-position substitution with respect to the quaternary nitrogen atom, so only the σp value is applied. Specific examples of the electron donating group having a negative σp value include an alkyl group (eg, a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an iso-butyl group), an alkoxy group. (For example, methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group, n-hexyloxy group, n-octyloxy group, benzyloxy group, etc.), amino group (for example, amino group, Methylamino group, ethylamino group, dimethylamino group, diethylamino group, di-n-propylamino group, di-n-butylamino group, phenylamino group, diphenylamino group, acetylamino group), hydrazino group, ureido group , Hydroxy groups and the like, but of course not limited thereto. Of these, preferred are an alkyl group, an alkoxy group, a dialkyl-substituted amino group, a hydroxy group and the like, and among them, a dialkyl-substituted amino group, an alkoxy group, and a hydroxy group are particularly preferred. Note that the substituents described above may be further substituted with various substituents as long as they do not deactivate the electron-donating factor of the substituent. Moreover, it is preferable that substituents other than the above-mentioned R ₄ do not exist on the benzothiazolium ring.

R ₅ represents an acidic group having a pKa of less than 6. 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, and among them, a carboxy group is particularly preferable. These acidic groups may be free acids, such as salts (for example, ammonium salts such as ammonium salt, trimethylammonium salt, triethylammonium salt, tetra-n-butylammonium salt, lithium salt, sodium salt, potassium salt, etc. Alkali metal salts, etc.).

X ⁻ represents a counter anion. Examples thereof include halogen ions (eg, chloride, bromide, iodide, etc.), alkyl sulfate ions (eg, methyl sulfate ion, ethyl sulfate ion, etc.), organic sulfonate ions (eg, methane sulfonate, p-toluene sulfonate). Etc.) and perchlorate ions. Further, when the dye molecule forms an inner salt, this counter anion does not exist.

In addition, in each vinylene bond (—CH═CH—) site connecting the three benzene rings in the general formula (1) described above, Z-type and E-type geometric isomers may be generated in each site. In the present invention, any combination of these geometric isomerisms may be used. In addition, when L ₁ and L ₂ are linked to a double bond linking site, and L ₁ and L ₂ are conjugated methine group units having 3 or more carbon atoms, isomers of geometric structures of each conjugated carbon double bond (cis) Type, trans type) may occur, but in the present invention, the geometric isomerism may be combined in any combination.

When R ₂ and R ₃ in the general formula (1) are both alkyl groups, the carbon atoms at the 2-position and 3-position of the indoline ring to which R ₂ and R ₃ are respectively bonded are asymmetric carbons, There is a possibility that optical isomers of each site may be generated, but in the present invention, any combination of these optical isomers may be used.

  In the dye represented by the general formula (1) of the present invention, the tertiary nitrogen atom of the indoline ring is an electron donating site (donor), and the quaternary nitrogen atom of the benzothiazolium ring is an electron withdrawing site (acceptor). And has a structure in which both are linked by a conjugated double bond. In general, when molecularly designing a sensitizing dye in a photoelectric conversion material, in order to perform electron injection from the dye to the semiconductor more efficiently, an acid that promotes the adsorptivity to the semiconductor in the vicinity of the acceptor site into which electrons flow. Introduce a group. The dye adsorbs on the semiconductor via an acidic group that promotes adsorptivity. After the electron is injected into the semiconductor, the dye becomes a dye cation, and then regenerates as a dye by receiving electron injection from an electrolyte described later. The dye-sensitized solar cell exhibits a function as a battery by repeating the electron transfer cycle of the dye.

  Although it is unclear why the dye of the present invention has improved photoelectric conversion characteristics compared to the dye of the prior art, the following estimation can be made.

The dye represented by the general formula (1) of the present invention has a substituent (hereinafter referred to as a conjugated substituent) in which three benzene rings are conjugated with two vinylene bonds as a substituent of the tertiary nitrogen atom of the indoline ring which is a donor site. It is known that it acts as a so-called electron-withdrawing group as a substituent on the side of the benzene ring farthest from the benzene ring to which the nitrogen atom is bonded in the conjugated substituent structure. R ₁ having a positive Hammett substituent constant σ value is bonded. As a result, it was found that photoelectric conversion characteristics superior to those of the prior art dyes can be obtained.

Since the electronic effect (electron withdrawing effect) of the substituent R ₁ is not bonded to the benzene ring on the side directly bonded to the tertiary nitrogen atom of the indoline ring in the dye structure, It is considered that the donor property of the tertiary nitrogen atom of the indoline ring is not lowered so much and the electron density of the π electron system as the whole conjugated substituent is reduced to some extent. These electronic effects were applied to the photoexcitation of the dye, and then the electron injection from the dye to the semiconductor via the acceptor site from the donor site without inhibiting it. Later, it is assumed that the electron density of the π-electron system of the entire conjugated substituent structure is reduced, thereby improving the efficiency of electron injection from the electrolyte to the dye cation, resulting in improved photoelectric conversion characteristics.

  Specific examples of the dye of the present invention shown by the general formula (1) are given below, but the present invention is not limited to these examples.

  These compounds can be easily synthesized with reference to a synthesis method described in, for example, JP 2010-49990 A.

  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 is preferably a transparent conductive support having a transparency that transmits light of 10% or more, and more preferably a support that 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.

  For the purpose of reducing the resistance of the transparent conductive support, a metal lead wire may be used. 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 placed on a transparent conductive support by vapor deposition, sputtering, pressure bonding, etc., and ITO or FTO is provided thereon, or a metal lead wire is placed on a transparent support having conductivity on the surface. There is.

  Examples of the semiconductor contained in the semiconductor layer include a single semiconductor such as silicon and germanium, a compound semiconductor typified by a metal chalcogenide, or 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, bismuth. And sulfides, cadmium, selenide of lead, telluride of cadmium, and the like. Other compound semiconductors are preferably phosphides such as zinc, gallium, indium, 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.

  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 media such as water, methanol, ethanol, or isopropyl alcohol, ketone media such as acetone, methyl ethyl ketone, or methyl isobutyl ketone, ethyl formate, ethyl acetate, or n-butyl acetate, etc. Ester media such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, and amide media such as N, N-dimethylformamide, N, N-dimethylacetamide, or N-methyl-2-pyrrolidone , Dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene Zen, iodobenzene, or halogenated hydrocarbon media such as 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o -A hydrocarbon medium such as xylene, m-xylene, p-xylene, ethylbenzene, or cumene. These can be used alone or as a mixed medium of two or more.

  Examples of the dispersion application method 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, or different types of semiconductors, and application layers having different compositions of resins and additives can be applied in multiple layers. In addition, when the film thickness is insufficient with a single coating, the multilayer coating is an effective means.

  In general, as the thickness of the semiconductor layer increases, the amount of supported dye increases per unit projected area and the light capture rate increases. However, the diffusion distance of the generated electrons also increases, and the recombination of charges also increases. End up. 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 (1) 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 of adsorbing the dye to the semiconductor layer, a method of immersing a working electrode containing semiconductor fine particles in a dye solution or a dye dispersion, or a method of applying a dye solution or a dispersion to the semiconductor layer and adsorbing it is used. Can do. 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 catalytically acting that physically or chemically binds the dye to the inorganic surface, or one that acts stoichiometrically to favorably shift the chemical equilibrium. . Furthermore, you may add a thiol or a hydroxy compound as a condensation adjuvant.

  The medium for dissolving or dispersing the dye is water, methanol, ethanol, isopropyl alcohol, alcohol-based media such as t-butyl alcohol, ketone-based media such as acetone, methyl ethyl ketone, or methyl isobutyl ketone, ethyl formate, ethyl acetate, or Ester media such as n-butyl acetate, ether media such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane or dioxane, nitrile media such as acetonitrile and propionitrile, N, N-dimethylformamide, N, N- Amide media such as dimethylacetamide or N-methyl-2-pyrrolidone, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloro Halogenated hydrocarbon media such as tylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodobenzene, or 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, Examples of the hydrocarbon medium include cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, 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 5 seconds to 1000 hours, more preferably 10 seconds to 500 hours, and even more preferably 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.

  Specific examples of the steroidal compound include those shown in E-1 to E-10 below. 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 after 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 You may immerse in the organic solvent containing acidic compounds, such as phosphoric 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, and calcium iodide, and quaternary compounds such as tetraalkylammonium iodide, pyridinium iodide, and imidazolium iodide. 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 Compound bromine salt-bromine combination, ferrocyanate-ferricyanate, metal complex such as ferrocene-ferricinium ion, sulfur compound such as sodium polysulfide, alkylthiol-alkyl disulfide , Viologen dye, hydroquinone - such as quinone, 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, ethanol Alcohol solvents such as polypropylene glycol monoalkyl ether, nitrile solvents such as acetonitrile and benzonitrile, and 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 a polyfunctional monomer include divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, and the like. be able to. 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.

  Further, for the purpose of improving the charge transfer efficiency in the charge transfer layer, a certain 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, phenanthrenequinone, and 4-nitro. Aldehydes such as benzaldehyde, ketones such as 9-benzoylanthracene, indandione, 3,5-dinitrobenzophenone, or 3,3 ', 5,5'-tetranitrobenzophenone, phthalic anhydride, 4-chloronaphthalic anhydride Acid anhydrides such as terephthalalmalononitrile, 9-anthrylmethylidenemalononitrile, 4-nitrobenzalmalononitrile, or cyano compounds such as 4- (p-nitrobenzoyloxy) benzalmalononitrile, 3-benzalphthalide , 3- (α Cyano -p- Nitorobenzaru) phthalide, or 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 the present invention, a method in which the conductive substrate is transparent on the surface holding the semiconductor fine particle layer and sunlight is incident from the conductive 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.

(Synthesis Example: Synthesis of Dye D-13)
Intermediate A: 0.80 g, Intermediate B: 0.50 g, and 50 ml of methanol were mixed and heated under reflux for 6 hours. Subsequently, the mixture was cooled to room temperature, and the precipitated solid was collected by filtration, further washed with 30 ml of methanol and dried to obtain 0.75 g of a crude product. This was purified by silica gel column chromatography (developing solvent: chloroform / methanol = 10/1 (volume ratio)) to obtain 0.60 g of Dye D-13.
Absorption maximum (methanol solution): 561 nm

Example 1
<Preparation of dye-sensitized solar cell>
Paint conditioner (2 g titanium oxide (Nippon Aerosil Co., Ltd., trade name: P-25), 0.2 g acetylacetone, 0.3 g surfactant (trade name: Triton X-100, made by Aldrich Co.) together with 6.5 g water (Red Devil) for 6 hours. Further, 0.2 g of concentrated nitric acid, 0.4 ml of ethanol, and 1.2 g of polyethylene glycol (# 20,000) were added to 4.0 g of this dispersion to prepare a paste. This paste was applied on an FTO glass substrate so as to have a film thickness of 10 μm, dried at room temperature, and then baked at 100 ° C. for 1 hour and further at 550 ° C. for 1 hour to obtain a semiconductor electrode.

  The dye of the present invention shown in Table 1 and the dye of the following comparison were each dissolved in a mixed solution of t-butyl alcohol / acetonitrile (1/1 = volume ratio) to prepare a dye solution having a concentration of 0.3 mM. A semiconductor electrode prepared previously was immersed in these dye solutions 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.

<Evaluation of photoelectric conversion efficiency>
Pseudo sunlight (AM1.5G, irradiation intensity) generated from a solar simulator (manufactured by Yamashita Denso Co., Ltd., device name: YSS-40S) as a light source from the working electrode side of the dye-sensitized solar cell thus produced. 100mW / cm < ² >) was irradiated, and the photoelectric conversion characteristic was measured using the electrochemical measuring device (The solartron company make, apparatus name: SI-1280B). About the photoelectric conversion efficiency of each dye-sensitized solar cell produced using the present invention and the comparative dye obtained as described above, the relative value when the photoelectric conversion efficiency of the comparative dye C-1 is 100 As evaluated. Moreover, the color tone of the working electrode was visually evaluated. The results are shown in Table 1.

(Example 2)
Dyes of the present invention (D-3, D-4, D-6, D-7, D-13, D-16, D-17, D-21) and comparative dyes (C-1, C-3) Was dissolved in a mixed solution of t-butyl alcohol / acetonitrile (1/1 = volume ratio) to prepare a dye solution having a concentration of 0.3 mM. The steroid compound (E-1) was dissolved in this dye solution at a concentration of 0.6 mM. Subsequently, the semiconductor electrode produced in Example 1 was immersed in this dye solution for 3 hours at room temperature to perform an adsorption treatment. Hereinafter, photoelectric conversion characteristics were evaluated in the same manner as in Example 1. About the photoelectric conversion efficiency of each dye-sensitized solar cell produced using the present invention and the comparative dye obtained as described above, the relative value when the photoelectric conversion efficiency of the comparative dye C-1 is 100 As evaluated. Moreover, the color tone of the working electrode was visually evaluated. The results are shown in Table 2.

  As is clear from the results of Tables 1 and 2, the photoelectric conversion material using the compound of the present invention has a color tone of bluish purple to blue, has a higher photoelectric conversion efficiency than the comparative compound, and has excellent photoelectric conversion characteristics. You can see that it has. In addition, the superiority of the particularly preferred embodiment of the present invention is also apparent from the comparison of D-1, D-9, D-12 and other dyes of the present invention.

  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 (1).

(In General Formula (1), R ₁ represents an electron-withdrawing group in which Hammett's substituent constant σ value is a positive value. R ₂ and R ₃ represent a hydrogen atom or an alkyl group, and R ₂ and R ₃ May be linked to form a cyclopentane ring or a cyclohexane ring, L ₁ and L ₂ represent a methine group unit, L ₃ represents an alkylene group, R ₄ represents a Hammett substituent constant σp value is negative The value represents an electron donating group, R ₅ represents an acidic group having a pKa of less than 6. X ⁻ represents a counter anion.)   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.