JP2008016383A - Photoelectric conversion material, semiconductor electrode, and photoelectric conversion element using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element excellent in both photoelectric conversion characteristics and durability. <P>SOLUTION: A dye obtained by linking two molecules of a merocyanine dye composed of a pair of a donor unit/an acceptor unit by a bivalent linking group is used. As a result, this dye has at least two acid groups expediting absorbency of a semiconductor in one molecule, and is efficiently absorbed by the semiconductor. A cell in which re-elution of the dye is mitigated and its conversion efficiency is heightened during preservation with the passage of time can be manufactured by combining the donor unit having a specific structure with the acid groups. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoelectric conversion material, a semiconductor electrode, and a photoelectric conversion element using the same.

Global warming due to the increase in CO ₂ concentration caused by the use of a large amount of fossil fuel, and the increase in energy demand accompanying population increase are recognized as problems related to the existence of human beings. For this reason, in recent years, the use of sunlight that is infinite and does not generate harmful substances has been energetically studied. What is currently put into practical use as sunlight, which is a clean energy source, includes 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 that payback to the user is long, and there is 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 the like, 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, there are many problems that the conversion efficiency is as low as 1% or less and the durability is poor.

  Under such circumstances, a solar cell exhibiting good characteristics has been reported by Dr. Gretzell of Switzerland (see Non-Patent Document 1). This document also discloses materials and manufacturing techniques necessary for battery fabrication. The proposed battery 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 as a working electrode. The advantage of this method is that it is not necessary to purify an inexpensive oxide semiconductor such as titanium oxide to high purity, and therefore, it is inexpensive and more usable light extends over a wide visible light region, and the solar light with many visible light components. It is that light can be effectively converted into electricity.

  On the other hand, ruthenium complexes with limited resources are used, so when this solar cell is put to practical use, the supply of ruthenium complexes is in danger. Moreover, since this ruthenium complex is expensive, this problem can be solved if it can be changed to an inexpensive organic dye. Merocyanine dyes, cyanine dyes, and 9-phenylxanthene dyes have been reported as dyes for this battery (see, for example, Patent Documents 1 to 3). However, these dyes have poor adsorptivity to titanium oxide, and a high sensitization effect cannot be obtained. Further, there is a problem that the dye itself supported on titanium oxide has low stability over time. Although high-performance products are disclosed as spectral sensitizing dyes for titanium oxide, there is still a problem with the temporal stability of the dye itself supported on titanium oxide (see, for example, Patent Documents 4 to 5).

Recently, organic dyes having high performance as spectral sensitizing dyes for oxide semiconductors and having excellent stability over time have been disclosed, but from the viewpoint of producing solar cells with practical durability, The performance was still insufficient in terms of stability over time (for example, see Patent Documents 6 to 7).
JP 11-238905 A JP 2001-76773 A Japanese Patent Laid-Open No. 10-92477 JP 2002-164089 A JP 2004-95450 A JP 2004-200068 A JP 2005-19252 A Nature, 353, 737 (1991)

  An object of the present invention is to provide a photoelectric conversion element having high performance and excellent durability.

  As a result of intensive studies to achieve the above problems, the present inventor can achieve the goal by using at least one of the compounds represented by the following general formulas (1), (2), and (3) as a photoelectric conversion material. It was.

  The photoelectric conversion material means all members constituting an element that converts light into electric energy, such as a material constituting a conductive support, a material constituting a semiconductor electrode, an electrolyte, and a material constituting a counter electrode. To do. By adsorbing and supporting a dye that absorbs light in the visible region on a semiconductor electrode that does not have photoelectric conversion capability in the visible region, the photoelectric conversion capability of the semiconductor electrode can be expanded to the visible region. The dye used in is called a sensitizing dye. The dye described in claim 1 of the present invention acts as this sensitizing dye.

Wherein, R ₁ to R ₁₀ represents an aliphatic group, an aromatic group, a heterocyclic group. R ₁ , R ₂ , R ₆ and R ₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Z _{1 to} Z ₆ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. m represents 0 or 1; L ₁ and L ₂ each represent a conjugated methine group unit. L ₃ represents a divalent linking group. However, the molecule (1) has at least two acidic groups of less than pKa6.

Wherein, R ₁₁ to R ₂₀ represents an aliphatic group, an aromatic group, a heterocyclic group. R ₁₁ , R ₁₂ , R ₁₆ , and R ₁₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Z _{7 to} Z ₁₂ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. n represents 0 or 1. L ₄ and L ₅ each represent a conjugated methine group unit. L ₆ represents a divalent linking group. However, it is assumed that the molecule (2) has at least two acidic groups of less than pKa6.

Wherein, R ₂₁ to R ₃₀ represents an aliphatic group, an aromatic group, a heterocyclic group. R ₂₁ , R ₂₂ , R ₂₆ , and R ₂₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Z _{13 to} Z ₁₈ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. L ₇ and L ₈ represent a conjugated methine group unit. L ₉ represents a divalent linking group. However, it is assumed that the molecule (3) has at least two acidic groups of less than pKa6.

  By using the compounds represented by the general formulas (1), (2), and (3) used in the present invention as sensitizing dyes, excellent conversion efficiency is exhibited and the dye adsorption stability to the semiconductor electrode is excellent. A photoelectric conversion element can be obtained.

The compounds used in the present invention are described in detail below. In the general formula (1), R _{1 to} R ₁₀ are aliphatic groups (for example, alkyl groups such as a methyl group, an ethyl group, an n-propyl group, and an n-octyl group, an alkenyl group such as an allyl group and a butenyl group, An alkynyl group such as a propargyl group, an aralkyl group such as a benzyl group, an aromatic group (eg, a phenyl group, a tolyl group, a naphthyl group), a heterocyclic group (eg, a pyridyl group, a furyl group, a thienyl group, etc.) To express. These may further have various substituents well known in the art. R ₁ , R ₂ , R ₆ and R ₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Moreover, it may have a structure in which other rings are condensed to those rings. R ₁ , R ₂ , R ₆ , and R ₇ are preferably bonded to any one of R ₁ , R _2, R ₆ , and R ₇ with a benzene ring to which a nitrogen atom is bonded. A 5- or 6-membered ring is formed. Examples of these rings include, for example, those described on pages 6 to 7 of the aforementioned JP-A-2005-19252. Among them, preferred is a structure represented by the following chemical formula 4.

In the chemical formula 4, R ₃₁ represents an aliphatic group (synonymous with R _{1 to} R ₁₀ ), an aromatic group (synonymous with R _{1 to} R ₁₀ ), or a heterocyclic group (synonymous with R _{1 to} R ₁₀ ). . Among them, preferred is an aromatic group, and this aromatic group may be further substituted with various substituents. Preferred examples thereof include a vinyl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a hydroxy group, a carboxy group, and a halogen atom.

Preferable examples of R _{3 to} R ₅ and R _{8 to} R ₁₀ include an aliphatic group having 20 or less carbon atoms and an aromatic group having 10 or less carbon atoms. These may have a substituent, and preferred examples thereof include a carboxy group, a sulfo group, a phosphonic acid group, a hydroxy group, an alkoxy group, and an alkylthio group.

Z _{1 to} Z ₆ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. Specific examples of the nitrogen-containing heterocycle include an oxazolidine ring, a thiazolidine ring, an imidazolidine ring, and a pyrazole ring. Preferred examples of specific examples of Z ₂ and Z ₅ when m = 0, and Z ₃ and Z ₆ when m = 1 include the structures shown in the following chemical formula (5).

R _{3 to} R ₅ and R _{8 to} R ₁₀ described above are substituents in the above Z _{1 to} Z ₆ . Therefore, when a plurality of substitutable sites are present in one ring, a plurality of R _{3 to} R ₅ and R _{8 to} R ₁₀ are present in each of Z _{1 to} Z ₆ (note that they are the same or different. It may be present). On the other hand, there may be no substitutable site in any of Z _{1 to} Z ₆ . In that case, any of corresponding R < ₃ > -R < ₅ > and R < ₈ > -R < ₁₀ > does not exist.

L ₁ and L _{2 each} represent a conjugated methine group unit (consisting of an odd number of conjugated methine chains). Among these, a monomethine structure having 1 carbon is preferable.

L ₃ represents a divalent linking group (for example, an alkylene group, an arylene group, an alkyleneoxy group, etc., which may be further substituted with various substituents). Preferable examples of the divalent linking group include an alkylene group having 6 to 12 carbon atoms and an alkyleneoxy group having 6 to 18 carbon atoms.

It is assumed that the molecule of the general formula (1) described above has at least two acidic groups (for example, carboxy group, sulfo group, phosphonic acid group, etc.) of less than pKa6. Among them, preferred is a carboxy group, and this carboxy group is particularly preferably present in the aforementioned R _{3 to} R ₅ and R _{8 to} R ₁₀ .

In the general formulas (2) and (3), R _{11 to} R ₂₀ and R _{21 to} R ₃₀ are synonymous with R _{1 to} R ₁₀ in the general formula (1), and Z _{7 to} Z ₁₂ and Z _13. to Z ₁₈ has the same meaning in Z ₁ to Z ₆ as well. L ₄ , L ₅ and L ₇ and L ₈ are synonymous with L ₁ and L ₂ , and L ₆ and L ₉ are synonymous with L ₃ . Similarly to the general formula (1), the molecules of the general formulas (2) and (3) have at least two pKa6 acidic groups (for example, carboxy group, sulfo group, phosphonic acid group, etc.). Yes. Among them, preferred is a carboxy group, and this carboxy group is represented by R _{13 to} R ₁₅ and R _{18 to} R ₂₀ in the general formula (2), and R _{23 to} R ₂₅ in the general formula (3). It is particularly preferable that R _{28 to} R ₃₀ are present.

  Although the specific example of the compound used for this invention below is given, these do not limit this invention at all.

  These compounds can be easily synthesized by a known synthesis method. A typical synthesis example is described below.

(Synthesis of Exemplary Compound B-2)
Synthesis of intermediate A 4.8 g of 1,2-bis (2-aminoethoxy) ethane, 6.6 g of triethylamine, and 100 ml of ethanol were mixed, and 4.9 g of carbon disulfide was added over 15 minutes while cooling in an ice-water bath and stirring. It was dripped. The mixture was stirred at the same temperature for 1 hour, then 6.1 g of monochloroacetic acid was added, the bath temperature was further raised, and the mixture was heated to reflux for 5 hours. After returning the reaction solution to room temperature, the supernatant was removed by decantation, and the remaining brown oil was dissolved in 75 ml of ethyl acetate. And this ethyl acetate solution was wash | cleaned in order of water and a saturated salt solution (each 100ml x 1 time), and after drying with anhydrous magnesium sulfate, the solvent was depressurizingly distilled and 8.1g of intermediate body A was obtained.

Synthesis of Intermediate B Intermediate A (8.0 g), ethyl isothiocyanatoacetate (6.1 g) and N, N-dimethylformamide (50 ml) were mixed, cooled in an ice-water bath and stirred, and 1,8-diazabicyclo-7-undecene 4 g was added dropwise over 10 minutes. The mixture was stirred at the same temperature for 1 hour, then 7.0 g of ethyl bromoacetate was added, the bath temperature was further raised, and the mixture was heated and stirred at a bath temperature of 120 ° C. for 2 hours. Subsequently, the solvent was distilled off under reduced pressure, and the residual oil was purified by silica gel column chromatography (developing solvent chloroform / methanol = 40/1) to obtain 2.5 g of Intermediate B.

Synthesis of Intermediate C 1.2 g of Intermediate B, 30 ml of acetic acid and 15 ml of concentrated hydrochloric acid were mixed and stirred with heating at a bath temperature of 120 ° C. for 3 hours. Subsequently, the solvent was distilled off under reduced pressure, 20 ml of 2-propanol was added to the residue, and the mixture was stirred at room temperature. After 1 hour, the crystallized solid was collected by filtration, washed with 2-propanol, water, and acetone in this order and dried to obtain 0.6 g of Intermediate C.

Synthesis of B-2 Intermediate C 0.20 g, the following intermediate D 0.28 g, ammonium acetate 0.05 g, and acetic acid 50 ml were mixed and heated to reflux for 10 hours. After cooling to room temperature, the precipitated solid was collected by filtration, washed with acetic acid and methanol in this order and then dried to obtain 0.35 g of a crude product. This was purified by silica gel column chromatography (developing solvent chloroform / methanol = 10/1) to obtain 0.15 g of exemplified compound B-2.
Absorption maximum (DMF): 534 nm, melting point: 247 ° C. to (decomposition)

  The compound used for the photoelectric conversion material of the present invention is a compound classified as a merocyanine dye. The merocyanine dye has a structure in which a unit having a donor substituent in a molecule and a unit having an acceptor substituent are connected by a conjugated double bond. When a merocyanine dye is used as a sensitizing dye for a semiconductor, it is common to introduce an acidic group that promotes the adsorptivity with the semiconductor onto the acceptor unit of the dye. The dye is adsorbed onto the semiconductor via an acidic group that promotes adsorptivity. However, the adsorptivity is insufficient from a practical viewpoint, and there is a problem that the dye is re-dissolved in the electrolytic solution when the photoelectric conversion element is stored over time. As shown in the present invention, by using a dye obtained by connecting two molecules of a merocyanine dye composed of a pair of donor unit / acceptor unit with a divalent linking group, the dye to the electrolyte during storage with time It has been found that re-elution of can be effectively prevented. The dye of the present invention has at least two acidic groups that promote the adsorptivity to a semiconductor in one molecule, and is efficiently adsorbed on the semiconductor. By combining a donor unit having a specific structure and an acidic group, it is possible to produce a cell having both reduced re-elution of dye during storage with time and high conversion efficiency.

  For the purpose of improving battery performance, it is widely known to add a basic substance (for example, 4-t-butylpyridine) to the electrolytic solution. In the case of a dye having low adsorption stability to a semiconductor, re-dissolution of the dye in the electrolyte cannot be ignored if a basic substance coexists in the electrolyte. Since the dye of the present invention has excellent adsorption stability to a semiconductor, it is possible to effectively improve battery performance by adding a basic substance to the electrolytic solution.

  The photoelectric conversion element of the present invention comprises a substrate having conductivity on the surface, a semiconductor layer sensitized by a dye placed on the conductive surface, 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 be diffused or mixed with each other.

  As the substrate having conductivity on the surface, a substrate having conductivity on the support itself such as metal, or a glass or plastic support having a conductive layer containing a conductive agent on the surface can be used. 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. (Hereinafter abbreviated as “FTO”) and the like. The substrate having conductivity on the surface preferably has a transparency that transmits 10% or more of light, 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.

  For the purpose of lowering the resistance of the surface conductive layer in the transparent substrate having conductivity on the surface, 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. The metal lead wire is installed on the transparent conductive support by vapor deposition, sputtering, pressure bonding, or the like, and a method of providing ITO or FTO thereon or a metal lead wire on a transparent substrate having conductivity on the surface.

  As the semiconductor, a single semiconductor such as silicon or germanium, a compound semiconductor typified by a metal chalcogenide, a compound having a perovskite structure, or the like can be used. Metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, or tantalum oxide, cadmium, zinc, lead, silver, antimony, bismuth. Sulfide, cadmium, lead selenide, cadmium telluride 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. As the conversion efficiency, a single crystal is preferable, but a polycrystal is preferable in terms of manufacturing cost, securing raw materials, and the like, and the particle size of the semiconductor is preferably 2 nm or more and 1 μm or less.

  As a method for forming a semiconductor layer on a substrate having conductivity on the surface, 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. The dispersion can be prepared by the above-mentioned sol-gel method, a method of mechanically pulverizing with a mortar, etc., a method of dispersing while pulverizing using a mill, or a fine particle in a solvent when synthesizing a semiconductor. And a method of using it as it is.

  In the case of a dispersion prepared by mechanical pulverization or pulverization using a mill, it is formed 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.

  Solvents for dispersing the semiconductor fine particles include alcohol solvents such as water, methanol, ethanol, and isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ethyl formate, ethyl acetate, and n-butyl acetate. Ester solvents, diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or ether solvents such as dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, or amide solvents such as N-methyl-2-pyrrolidone , Dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-dichlorobenzene, fluorobenzene, bromobenzene, iodine Halogenated hydrocarbon solvents such as debenzene or 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene, benzene, toluene, o-xylene, Examples thereof include hydrocarbon solvents such as m-xylene, p-xylene, ethylbenzene, and cumene. These can be used alone or as a mixed solvent of two or more.

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

  Furthermore, 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 need not be heat-treated after being coated on a substrate having conductivity on the surface, but from the viewpoint of improving the electronic contact between the particles and the strength of the coating film and the adhesion to the support, Heat treatment is preferred. Furthermore, microwave irradiation, press treatment, or electron beam irradiation may be performed, and 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. The 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 9.8 × 10 ⁶ Pa or more, and more preferably 9.8 × 10 ⁷ Pa or more. There is no particular limitation on the pressing time, but it is preferably performed within 1 hour.

The semiconductor fine particles preferably have a large surface area so that many dyes can be adsorbed. The specific surface area in a state of coated with a semiconductor layer on a support is preferably 1 to 1,000 m ² / g, and more preferably 10 to 500 m ² / g.

  In the semiconductor electrode and the photoelectric conversion element of the present invention, at least one compound represented by the general formulas (1), (2), and (3) is used as a sensitizing dye. Two or more kinds 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 one that has a catalytic action that is supposed to physically or chemically bind the dye to the inorganic surface, or one that acts stoichiometrically to favorably shift the chemical equilibrium. Furthermore, a thiol or a hydroxy compound may be added as a condensation aid.

  Solvents for dissolving or dispersing the dye are water, methanol, ethanol, alcohol solvents such as isopropyl alcohol, ketone solvents such as acetone, methyl ethyl ketone, or methyl isobutyl ketone, ethyl formate, ethyl acetate, or n-butyl acetate. Ester solvents such as diethyl ether, dimethoxyethane, tetrahydrofuran, dioxolane, or dioxane, nitrile solvents such as acetonitrile, propionitrile, N, N-dimethylformamide, N, N-dimethylacetamide, or Amide solvents such as N-methyl-2-pyrrolidone, dichloromethane, chloroform, bromoform, methyl iodide, dichloroethane, trichloroethane, trichloroethylene, chlorobenzene, o-di Halogenated hydrocarbon solvents such as lolobenzene, fluorobenzene, bromobenzene, iodobenzene, or 1-chloronaphthalene, n-pentane, n-hexane, n-octane, 1,5-hexadiene, cyclohexane, methylcyclohexane, cyclohexadiene , Hydrocarbon solvents such as benzene, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, or cumene, and these can be used alone or as a mixture of two or more.

  The temperature at which these are used and the dye is adsorbed is preferably -50 ° C or higher and 200 ° C or lower. Further, this 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 or more and 1000 hours or less, more preferably 10 seconds or more and 500 hours or less, and further preferably 1 minute or more and 150 hours or less.

  In the present invention, a steroidal compound may be used in combination when the compound represented by the general formulas (1), (2), and (3) is adsorbed on the semiconductor layer as a dye.

  Specific examples of the steroid compound include those shown in (E-1) to (E-10). 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, basic compounds such as t-butylpyridine, 2-picoline, 2,6-lutidine, or phosphoric acid, phosphate ester, alkyl phosphoric acid Further, it may be dipped in an organic solvent containing an acidic compound such as acetic acid or propionic acid.

  As the charge transfer layer according to the present invention, 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 the redox couple, A solid electrolyte, an inorganic hole transport material, an organic hole transport material, or the like can be used.

  The electrolytic solution used in the present invention 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 Bromine-bromine combinations of compounds, metal complexes such as ferrocyanate-ferricyanate, ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide, alkylthiol-alkyldisulfides, viologen Dye, hydroquinone - 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, 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. Further, basic compounds such as t-butylpyridine, 2-picoline, and 2,6-lutidine may be used in combination.

  In the present invention, the electrolyte can be gelled by a technique such as addition of a polymer, addition of an oil gelling agent, polymerization including polyfunctional monomers, or a crosslinking reaction of the polymer. Preferable polymers in the case of gelation by polymer addition include polyacrylonitrile, polyvinylidene fluoride and the like. Preferred gelling agents for gelation by adding an oil gelling agent include dibenzylden-D-sorbitol, cholesterol derivatives, amino acid derivatives, alkylamide derivatives of trans- (1R, 2R) -1,2-cyclohexanediamine, alkylureas Derivatives, N-octyl-D-gluconamide benzoate, double-headed amino acid derivatives, quaternary ammonium derivatives and the like can be mentioned.

  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 and the like. Dienes such as pentadiene, aromatic vinyl compounds such as styrene, p-chlorostyrene and sodium styrene sulfonate, vinyl esters, acrylonitrile, methacrylonitrile, vinyl compounds having a nitrogen-containing heterocyclic ring, vinyl having a quaternary ammonium salt A monofunctional monomer such as a compound, N-vinylformamide, vinylsulfonic acid, vinylidene fluoride, vinyl alkyl ethers, 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) and peroxide initiators such as benzoyl peroxide 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 crosslinkable reactive group include nitrogen-containing heterocycles such as pyridine, imidazole, thiazole, oxazole, triazole, morpholine, piperidine, piperazine, etc. Preferred crosslinking agents include alkyl halides, halogens Bifunctional or higher functional reagents capable of electrophilic reaction with nitrogen atoms such as aralkyl fluoride, sulfonic acid ester, acid anhydride, acid chloride, and isocyanate can be exemplified.

  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, electrolytic plating, or the like.

  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 disclosed in Japanese Patent Publication No. 34-5466, triphenylmethanes disclosed in Japanese Patent Publication No. 45-555, and Japanese Patent Publication No. 52-4188. Pyrazolines shown in the above, hydrazones shown in JP-B-55-42380, oxadiazoles shown in JP-A-56-123544, etc., JP-A-54-58445 And tetrasylbenzidines disclosed in JP-A No. 58-65440, and stilbenes disclosed in JP-A No. 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, 1,3,7-trinitrodibenzothiophene-5,5-dioxide, etc. . 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, 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- - Nitorobenzaru) phthalide, or 3- (alpha-cyano -p- Nitorobenzaru) -4,5,6,7 can be mentioned phthalides such as tetrachloro phthalide like.

  When forming a charge transfer layer using a charge transport material, a resin may be used in combination. When 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 mentioned. 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 pasted on a semiconductor layer carrying a sensitizing dye, and a liquid charge transfer layer is sandwiched in the gap, and the other is on a semiconductor layer carrying a sensitizing dye. This is a method of directly providing a charge transfer layer. 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 a capillary phenomenon 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 thereof include a hopper method, a wire bar method, a spin method, a spray method, a 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 supporting the sensitizing dye, at least one of the conductive substrate and the counter electrode must be substantially transparent on the surface holding the semiconductor layer. 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 charge transfer layer by a technique such as coating, vapor deposition, or CVD.

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

  6 hours of paint conditioner (manufactured by Red Devil) with 2 g of titanium oxide (P-25 manufactured by Nippon Aerosil Co., Ltd.), 0.2 g of acetylacetone, and 0.3 g of surfactant (Triton X-100 manufactured by Aldrich) together with 6.5 g of water. Dispersion treatment was performed. 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 onto an FTO glass substrate so as to have a film thickness of 12 μm, dried at room temperature, and then fired at 100 ° C. for 1 hour and further at 550 ° C. for 1 hour.

  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) to prepare a dye solution having a concentration of 0.3 mM. The semiconductor electrode prepared previously was immersed in these dye solutions at room temperature for 15 hours to perform an adsorption treatment, thereby preparing a working electrode. As the counter electrode, a titanium plate on which platinum was sputtered was used. Both electrodes were arranged so as to face each other, and an electrolytic solution was injected between them to produce a photoelectric conversion element. As the electrolytic solution, a 3-methoxyacetonitrile solution of lithium iodide 0.1 M, iodine 0.05 M, and 1,2-dimethyl-3-n-propylimidazolium iodide 0.5 M was used.

Pseudo sunlight (AM1.5G, irradiation intensity 100 mW / cm ² ) generated from a solar simulator (YSS-40S, manufactured by Yamashita Denso Co., Ltd.) as a light source from the working electrode side of the photoelectric conversion element thus manufactured. The photoelectric conversion characteristics were evaluated using an electrochemical measurement device (SI-1280B, manufactured by Solartron). The results are shown in Table 1.

  Furthermore, the adsorption stability of the dye to the semiconductor electrode was evaluated. The dye of the present invention and the dye of the following comparison were dissolved in a mixed solution of t-butyl alcohol / acetonitrile (1/1) to prepare a dye solution having a concentration of 0.3 mM. In this dye solution, the previously produced semiconductor electrode was immersed at room temperature for 15 hours for adsorption treatment. Next, the dye-adsorbing semiconductor electrode was immersed in 3-methoxyacetonitrile, which is an electrolyte solvent, and stored for 10 days under light shielding, sealing, and room temperature. The state of dye support on the semiconductor electrode after storage was visually observed. The results are shown in Table 2.

  The dye (B-1 to B-3) of the present invention and the comparative dye (C-3) are dissolved in a mixed solution of t-butyl alcohol / acetonitrile (1/1) to obtain a dye solution having a concentration of 0.3 mM. Produced. 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 at room temperature for 15 hours to perform an adsorption treatment. The electrolyte is a lithium iodide 0.1M, iodine 0.05M, 1,2-dimethyl-3-n-propylimidazolium iodide 0.5M 3-methoxyacetonitrile solution, and the counter electrode is sputtered with platinum on a titanium plate. We used what we did. Hereinafter, photoelectric conversion characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 3. Similarly, the adsorption stability of the dye to the semiconductor electrode was evaluated in the same manner as in Example 1. The results are shown in Table 4.

  As is apparent from the above results, it can be seen that the compound of the present invention is excellent in both photoelectric conversion efficiency and adsorption stability to a semiconductor.

  Examples of utilization of the present invention include photosensors that are sensitive to light of a specific wavelength, in addition to photoelectric conversion elements such as solar cells.

Claims (4)

A photoelectric conversion material characterized by using at least one of the compounds represented by the following general formulas (1), (2), and (3).

Wherein, R ₁ to R ₁₀ represents an aliphatic group, an aromatic group, a heterocyclic group. R ₁ , R ₂ , R ₆ and R ₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Z _{1 to} Z ₆ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. m represents 0 or 1; L ₁ and L ₂ each represent a conjugated methine group unit. L ₃ represents a divalent linking group. However, the molecule (1) has at least two acidic groups of less than pKa6.

Wherein, R ₁₁ to R ₂₀ represents aliphatic group, an aromatic group or a heterocyclic group. R ₁₁ , R ₁₂ , R ₁₆ , and R ₁₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Z _{7 to} Z ₁₂ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. n represents 0 or 1. L ₄ and L ₅ each represent a conjugated methine group unit. L ₆ represents a divalent linking group. However, it is assumed that the molecule (2) has at least two acidic groups of less than pKa6.

Wherein, R ₂₁ to R ₃₀ represents an aliphatic group, an aromatic group, a heterocyclic group. R ₂₁ , R ₂₂ , R ₂₆ , and R ₂₇ may be connected to a benzene ring to which a nitrogen atom is bonded to form a ring. Z _{13 to} Z ₁₈ each represents an atomic group necessary for forming a 5- or 6-membered nitrogen-containing heterocyclic ring. L ₇ and L ₈ represent a conjugated methine group unit. L ₉ represents a divalent linking group. However, it is assumed that the molecule (3) has at least two acidic groups of less than pKa6.   In the semiconductor electrode comprising a substrate having conductivity on the surface, a semiconductor layer coated on the conductive surface, and a dye adsorbed on the surface of the semiconductor layer, the general formulas (1), (2), A semiconductor electrode comprising at least one compound represented by (3).   The semiconductor layer is titanium, tin, zinc, iron, copper, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, tantalum, cadmium, lead, silver, antimony, bismuth, molybdenum, aluminum 3. The semiconductor electrode according to claim 2, comprising at least one metal chalcogenide selected from gallium, chromium, cobalt, and nickel.   A photoelectric conversion element using the semiconductor electrode according to claim 2.