JP2000277180A - Photoelectric transfer element and photoelectrochemical battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart absorptive capability in a red to infrared region and to improve photoelectric transfer efficiency at a low cost by including semiconductor particles increased in sensitivity by a polymethine pigment. SOLUTION: A polymethine pigment is expressed by the formula. In the formula, X is a S, O, Se or Te atom. R1, R2, R3 and R4 each are independently a H atom or a substituted group, and R1 and R2, and R3 and R4 may be formed into a cyclic structure by combining them together, respectively. L is a substituted or unsubstituted methine group, and Q represents a non-metal atom group necessary for completing the polymethine pigment. W represents a couple of ions necessary for neutralizing charge. The polymethine pigment preferably has at least one acid group, for instance, a carboxylic acid group, and is desirably contained in at least any of R1, R3 and Q. Titanium oxide fine particles are suitably used as semiconductor fine particles contained in this photoelectric transfer element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photoelectric conversion element using semiconductor fine particles sensitized by a dye. Further, the present invention relates to a photoelectrochemical cell using the same.

[0002]

2. Description of the Related Art Nature (Vol. 353, pp. 737-740, 1991)
And U.S. Pat. No. 4,492,721 disclose a photoelectric conversion element and a solar cell using semiconductor fine particles sensitized with a dye, and materials and manufacturing techniques for producing the same. The proposed battery is a wet solar battery using a titanium dioxide porous thin film spectrally sensitized by a ruthenium complex as a working electrode. The first advantage of this method is that an inexpensive oxide semiconductor such as titanium dioxide can be used without purification to a high degree of purity, so that an inexpensive photoelectric conversion element can be provided. Due to the broad absorption of the dye, light in a considerable wavelength region of visible light can be converted into electricity.

One of the points that require improvement of the dye-sensitized photoelectric conversion element is to use an expensive ruthenium complex dye as a sensitizing dye, and a photoelectric conversion element sensitized with an inexpensive organic dye is known. The development of was desired. In particular,
Development of a dye having high photoelectric conversion efficiency in red to infrared light has been desired.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a dye-sensitized photoelectric conversion element and a photoelectrochemical cell which have absorption in the red to infrared region, are inexpensive and have high photoelectric conversion efficiency.

[0005]

The object of the present invention has been attained by the following items which specify the present invention and preferred embodiments thereof. (1) A photoelectric conversion element containing semiconductor fine particles sensitized by a polymethine dye represented by the following formula (I).

[0006]

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In the formula, X represents a sulfur atom, an oxygen atom, a selenium atom or a tellurium atom. R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom or a substituent, and R ₁ and R ₂ , and R ₃ and R ₄ may be linked to form a ring structure. L represents a substituted or unsubstituted methine group, and Q represents a group of non-metallic atoms necessary to complete a polymethine dye. W represents a counter ion necessary for neutralizing the charge. (2) The photoelectric conversion device according to (1), wherein the polymethine dye has at least one acidic group. (3) The above (2), wherein the acidic group is a carboxylic acid group.
Photoelectric conversion element. (4) The photoelectric conversion element according to any one of (1) to (3), wherein Q is a methine group as a linking group and a nitrogen-containing heterocycle. (5) The photoelectric conversion device according to (4), wherein the nitrogen-containing hetero ring is a ring selected from benzothiazolium, indolenium, benzoxazolium, 2-quinolinium, 4-quinolinium, and a nucleus derived therefrom. (6) The photoelectric conversion device according to (4), wherein the nitrogen-containing heterocycle is an indolenium ring. (7) The photoelectric conversion device according to any one of (1) to (6), wherein the semiconductor fine particles are titanium oxide fine particles. (8) A photoelectrochemical cell using the photoelectric conversion element according to any one of (1) to (7).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The compound of the following formula (I) used as a sensitizing dye in the present invention will be described in detail below.

[0009]

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In the formula, X represents a sulfur atom, an oxygen atom, a selenium atom or a tellurium atom. Preferably it is a sulfur atom or an oxygen atom.

R _{1 to} R ₄ are each independently a hydrogen atom or a substituent, and R ₁ and R ₂ , and R ₃ and R ₄ may be connected to each other to form a ring structure. Examples of the substituent of R _{1 to} R ₄ include an alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 15 carbon atoms, a carboxylic acid group, a phosphoric acid group, a halogen atom,
Examples thereof include a hydroxyl group, an amino group, and a benzo-fused ring, preferably an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 10 carbon atoms, a carboxylic acid group or a benzo-fused ring. These substituents may further have a substituent, and a carboxylic acid group is particularly preferable as the further substituent.

L is a substituted or unsubstituted methine group, preferably unsubstituted. Q represents a group of nonmetallic atoms necessary to complete the polymethine dye. For example, 4-
Examples include aniline, 4-phenol, and a heterocycle having one methine group as a linking group to squarylium, and preferably a heterocycle having one methine group. Examples of such a hetero ring include 4-pyrylium, 4-thiopyrylium, and a nitrogen-containing hetero ring. Among them, a nitrogen-containing hetero ring is preferable, and among them, benzothiazolium, indolenium, and benzoyl are preferable. A ring selected from oxazolium, 2-quinolinium, 4-quinolinium, and a nucleus derived therefrom, most preferably an indolenium ring.

W represents a counter ion when a counter ion is required to neutralize the charge. Whether a dye is a cation, an anion, or has a net ionic charge depends on its auxochrome and substituents. When the substituent has a dissociable group, it may dissociate and have a negative charge, and in this case also, the charge of the entire molecule is neutralized by W. Typical cations are inorganic or organic ammonium ions (eg, tetraalkylammonium ions, pyridinium ions) and alkali metal ions, while
The anion may be specifically an inorganic anion or an organic anion, for example, a halogen anion,
(E.g., fluoride ion, chloride ion, bromide ion, iodide ion), substituted arylsulfonate ion (e.g., p-toluenesulfonate ion, p-chlorobenzenesulfonate ion), aryldisulfonate ion (e.g., 1 , 3-benzenedisulfonic acid ion,
1,5-naphthalenedisulfonic acid ion, 2,6-naphthalenedisulfonic acid ion), alkyl sulfate ion (for example, methyl sulfate ion), sulfate ion, thiocyanate ion, perchlorate ion, tetrafluoroborate ion, picric acid Ions, acetate ions, and trifluoromethanesulfonate ions. Further, an ionic polymer or another dye having a charge opposite to that of the dye may be used as a charge-balancing counter ion, or a metal complex ion (for example, bisbenzene-1,2-dithiolatonic nickel (III))
) Is also possible.

The polymethine dye of the formula (I) preferably has at least one acidic group. Examples of the acidic group include a carboxylic acid group, a phosphoric acid group, a sulfonic acid group, a hydroxyl group, and a boric acid group, preferably a carboxylic acid group and a phosphoric acid group, and most preferably a carboxylic acid group. Also,
The acidic group may be bonded anywhere, but is preferably present in at least one of R ₁ , R ₃ and Q.

Hereinafter, specific examples of the compound represented by the formula (I) of the present invention are shown, but the present invention is not limited thereto.

[0016]

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[0017]

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The compound represented by the formula (I) used in the present invention can be synthesized with reference to the description in US Pat. No. 5,231,190 and the references cited therein.

Next, the structure and materials of the photoelectric conversion element and the photoelectrochemical cell of the present invention will be described in detail. In the present invention, the dye-sensitized photoelectric conversion element includes a conductive support, a semiconductor film (photosensitive layer) sensitized by a dye provided on the conductive support, a charge transfer layer, and a counter electrode. The conductive support on which the semiconductor film is provided functions as a working electrode in the photoelectric conversion element. A photoelectrochemical cell that can use this photoelectric conversion element for a battery that works in an external circuit is used. The photosensitive layer is designed according to the purpose, and may have a single-layer structure or a multilayer structure. Light incident on the photosensitive layer excites the dye. Excited dyes have high energy electrons,
The electrons are transferred from the dye to the conduction band of the semiconductor fine particles, and reach the conductive support by diffusion. At this time, the dye molecule is in an oxidized form. In a photoelectrochemical cell, the electrons on the conductive support return to the oxidized dye via the counter electrode and the charge transfer layer while working in an external circuit, and the dye is regenerated. The semiconductor film functions as a negative electrode of this battery. In the present invention, two or more kinds of adsorbed dyes are contained in the semiconductor film. In the present invention, at the boundaries between the layers (for example, the boundary between the conductive layer and the photosensitive layer of the conductive support, the boundary between the photosensitive layer and the charge transfer layer, the boundary between the charge transfer layer and the counter electrode, etc.) They may be mutually diffused and mixed.

In the present invention, the semiconductor is a so-called photoreceptor, which plays a role of absorbing light to separate electric charges to generate electrons and holes. In a dye-sensitized semiconductor, light absorption and the resulting generation of electrons and holes mainly occur in the dye, and the semiconductor is responsible for receiving and transmitting the electrons.

As the semiconductor, besides a simple semiconductor such as silicon or germanium, a so-called compound semiconductor represented by a metal chalcogenide (for example, oxide, sulfide, selenide, etc.) or a compound having a perovskite structure is used. be able to. Preferably as a metal chalcogenide titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium,
Examples include niobium or tantalum oxide, cadmium, zinc, lead, silver, antimony, bismuth sulfide, cadmium, selenide of lead, and telluride of cadmium. Other compound semiconductors include phosphides such as zinc, gallium, indium and cadmium, gallium arsenide, copper-indium-selenide, copper-indium-sulfide and the like.

The compound having a perovskite structure is preferably strontium titanate, calcium titanate, sodium titanate, barium titanate, or potassium niobate.

More preferably, the semiconductor used in the present invention is specifically Si, TiO ₂ , SnO ₂ , Fe ₂ O ₃ , WO ₃ , Zn
O, Nb ₂ O ₅ , CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, CdTe, GaP, I
nP, GaAs, CuInS ₂ , and CuInSe ₂ are mentioned. More preferably _{TiO 2, ZnO, SnO 2,} Fe 2 O 3, WO 3, Nb 2 O 5, CdS, Pb
S, CdSe, InP, GaAs, CuInS ₂ , CuInSe ₂ , particularly preferably TiO ₂ or Nb ₂ O ₅ , most preferably TiO ₂
It is.

The semiconductor used in the present invention may be single crystal or polycrystal. Although a single crystal is preferable as the conversion efficiency, a polycrystal is preferable in terms of manufacturing cost, securing of raw materials, energy payback time, and the like, and a fine particle semiconductor having a nanometer to micrometer size is particularly preferable.

The particle diameter of these semiconductor fine particles is preferably 5 to 200 nm as primary particles, and particularly preferably 8 to 1 nm, as an average particle diameter using a diameter when the projected area is converted into a circle.
Preferably it is 00 nm. The average particle size of the semiconductor fine particles (secondary particles) in the dispersion is 0.01 to 10
It is preferably 0 μm.

Further, two or more kinds of fine particles having different particle size distributions may be mixed and used. In this case, the average size of the small particles is preferably 5 nm or less. Also, in order to improve the light capture rate by scattering incident light,
Semiconductor particles having a large particle size, for example, about 300 nm may be mixed.

The method for producing the semiconductor fine particles is described in Sol-gel described in "Sol-gel method science" by Agaku Shofusha (1988) by Sakuhana Sakuhana, "Thin-film coating technology by sol-gel method" (1995) by Technical Information Association. Tadao Sugimoto, "Synthesis of Monodisperse Particles by New Synthetic Gel-Sol Method and Size Morphology Control" Materia, Vol. 35, No. 9, 1012
The gel-sol method described on pages 10 to 1018 (1996) is preferred.

It is also preferred to use a method developed by Degussa to produce an oxide by high-temperature hydrolysis of a chloride in an oxyhydrogen flame.

In the case of titanium oxide, the above-mentioned sol-gel method, gel-sol method, and high-temperature hydrolysis method of chloride in an oxyhydrogen flame are all preferable, but furthermore, Manabu Kiyono's "Titanium oxide physical properties and applied technology" Gihodo Publishing ( 1997) can also be used.

In the case of titanium oxide, among the sol-gel methods described above, in particular, "Journal of American
Ceramic Society Vol. 80, No. 12, 31
Pages 57 to 3171 (1997) "and Burnside et al.," Chemical Materials Vol. 10, No. 9, pages 2419 to 2425 "
The described method is preferred.

As the conductive support, use is made of a support such as metal, which has conductivity, or a glass or plastic support having a conductive layer (conductive agent layer) containing a conductive agent on the surface. Can be. In the latter case, a preferable conductive agent is a metal (for example, platinum, gold, silver, copper, aluminum, rhodium, indium, etc.), carbon, or a conductive metal oxide (indium-tin composite oxide, tin oxide doped with fluorine). And the like). The conductive agent layer preferably has a thickness of about 0.02 to 10 μm.

The lower the surface resistance of the conductive support, the better. The preferred range of the surface resistance is 100 Ω / cm ² or less, and more preferably 40 Ω / cm ² or less. The lower limit is not particularly limited, but is usually about 0.1 Ω / cm ² .

Preferably, the conductive support is substantially transparent. Substantially transparent means that light transmittance is 10%
The above means that it is preferably at least 50%, particularly preferably at least 70%. As the transparent conductive support, glass or plastic coated with a conductive metal oxide is preferable. Among them, conductive glass in which a conductive layer made of tin dioxide doped with fluorine is deposited on a transparent substrate made of low-cost soda-lime float glass is particularly preferable. In addition, for a low-cost and flexible photoelectric conversion element or solar cell, a transparent polymer film provided with the above conductive layer is preferably used.
Transparent polymer films include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET),
Polyethylene naphthalate (PEN), syndioctatic polysterene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate (PAr), polysulfone (PSF), polyester sulfone (PES), polyetherimide (PE
I), cyclic polyolefins, brominated phenoxy and the like. When a transparent conductive support is used, it is preferable that light be incident from the support side. In this case, the coating amount of the conductive metal oxide is preferably 0.01 to 100 g per 1 m ² of a glass or plastic support.

It is preferable to use a metal lead for the purpose of lowering the resistance of the transparent conductive substrate. The material of the metal lead is preferably a metal such as aluminum, copper, silver, gold, platinum and nickel, and particularly preferably aluminum and silver. It is preferable that the metal lead is provided on a transparent substrate by vapor deposition, sputtering, or the like, and a transparent conductive layer made of tin oxide doped with fluorine or an ITO film is provided thereon. It is also preferable to provide a metal lead on the transparent conductive layer after providing the transparent conductive layer on a transparent substrate. The decrease in the amount of incident light due to the installation of metal leads is 1 to 10%, more preferably 1 to 5%.
It is.

Examples of the method of applying semiconductor fine particles on a conductive support include a method of applying a dispersion or colloid solution of semiconductor fine particles on a conductive support, and the above-mentioned sol-gel method. In consideration of mass production of photoelectric conversion elements, liquid physical properties, and flexibility of a support, a wet film forming method is relatively advantageous. As a wet type film applying method, a coating method and a printing method are typical.

As a method for preparing a dispersion of semiconductor fine particles, in addition to the above-described sol-gel method, a method of grinding with a mortar, a method of dispersing while grinding with a mill, or a method of synthesizing a semiconductor in a solvent when synthesizing a semiconductor. A method of precipitating it as fine particles and using it as it is may be mentioned. Examples of the dispersion medium include water and various organic solvents (eg, methanol, ethanol, isopropyl alcohol, dichloromethane, acetone, acetonitrile, ethyl acetate, etc.). When dispersing,
If necessary, a polymer, a surfactant, an acid, a chelating agent or the like may be used as a dispersing aid.

The application method includes a roller method and a dip method as an application system, an air knife method and a blade method as a metering system, and a method in which application and metering can be performed in the same part.
No. 4,589,294, U.S. Pat. No. 2,761,419, and U.S. Pat.
A slide hopper method, an extrusion method, a curtain method and the like described in US Pat. As a general-purpose machine, a spin method or a spray method is also preferably used.

As the wet printing method, three types of printing methods such as relief printing, offset printing and gravure printing, intaglio printing, rubber printing and screen printing have been conventionally preferred.

From the above methods, a preferable film forming method is selected according to the liquid viscosity and the wet thickness.

The liquid viscosity is greatly affected by the type and dispersibility of the semiconductor fine particles, the type of solvent used, and additives such as a surfactant and a binder. High viscosity liquid (for example, 0.01 to 500 Po
In ise), an extrusion method or a casting method is preferable, and in a low-viscosity liquid (for example, 0.1 Poise or less), a slide hopper method, a wire bar method, or a spin method is preferable, and a uniform film can be formed.

Incidentally, even in the case of applying a low-viscosity liquid by the extrusion method, the application is possible if the applied amount is a certain amount.

Screen printing is often used for applying a high-viscosity paste of semiconductor fine particles, and this technique can also be used.

As described above, the method of applying the wet film may be appropriately selected according to the parameters such as the liquid viscosity of the coating liquid, the coating amount, the support, and the coating speed.

Further, the semiconductor fine particle-containing layer need not be limited to a single layer. It is also possible to apply a multi-layered dispersion liquid having different particle diameters, and different types of semiconductors.
Alternatively, multi-layer coating of coating layers having different compositions of binders and additives can be performed, and multi-layer coating is effective even when the film thickness is insufficient by one-time coating. The extrusion method or slide hopper method is suitable for multi-layer coating. In the case of multi-layer coating, multi-layer coating may be performed at the same time, or several to dozens of times may be sequentially applied. Furthermore, a screen printing method can also be preferably used in the case of successive coating.

Generally, as the thickness of the layer containing semiconductor fine particles increases, the amount of dye carried per unit projected area increases, so that the light capture rate increases. However, the diffusion distance of generated electrons increases, so that the loss due to charge recombination also increases. growing. Therefore, the semiconductor fine particle-containing layer has a preferable thickness, but typically has a thickness of 0.1 to 100 μm. When used as a photoelectrochemical cell, the thickness is preferably 1 to 30 μm, and more preferably 2 to 25 μm. The coating amount of the semiconductor fine particles per 1 m ² of the support is 0.5 to 400.
g, more preferably 5 to 100 g.

The semiconductor fine particles are preferably subjected to a heat treatment in order to bring the particles into electronic contact after being applied to the conductive support and to improve the strength of the coating film and the adhesion to the support. A preferred range of the heat treatment temperature is 40 ° C. or more and less than 700 ° C.,
It is not less than 00 ° C and not more than 600 ° C. The heat treatment time is 1
It is about 0 minutes to 10 hours. When a support having a low melting point or softening point, such as a polymer film, is used, high-temperature treatment is not preferable because the support is deteriorated. Further, it is preferable that the temperature is as low as possible from the viewpoint of cost. The lowering of the temperature can be achieved by the above-mentioned combination of small semiconductor particles having a size of 5 nm or less, heat treatment in the presence of a mineral acid, and the like.

After the heat treatment, chemical plating using, for example, an aqueous solution of titanium tetrachloride for the purpose of increasing the surface area of the semiconductor particles, increasing the purity in the vicinity of the semiconductor particles, and increasing the efficiency of electron injection from the dye into the semiconductor particles. Alternatively, electrochemical plating using an aqueous solution of titanium trichloride may be performed.

It is preferable that the semiconductor fine particles have a large surface area so that many dyes can be adsorbed. For this reason, the surface area in the state where the semiconductor fine particle layer is coated on the support is preferably at least 10 times, more preferably at least 100 times the projected area. The upper limit is not particularly limited, but is usually about 1000 times.

In the present invention, a dye other than formula (I) can be used in combination in order to widen the wavelength range of photoelectric conversion as much as possible and to increase the conversion efficiency. Then, a dye to be used in combination can be selected so as to match the intended wavelength range of the light source and its intensity distribution. Dyes used in combination are metal complex dyes,
Phthalocyanine dyes or methine dyes are preferred.

As a method of adsorbing the dye on the semiconductor fine particles, a method of immersing a working electrode containing well-dried semiconductor fine particles in a dye solution or applying a dye solution to the semiconductor fine particle layer and adsorbing the dye solution can be used. . In the former case, a dipping method, a dipping method, a roller method, an air knife method, or the like can be used. The latter coating method includes a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, and a spray method, and the printing method includes letterpress, offset, gravure, screen printing, and the like.

As in the case of the formation of the semiconductor fine particle layer, the liquid viscosity is not limited to the extrusion method for a high-viscosity liquid (for example, 0.01 to 500 Poise), and various printing methods for the low-viscosity liquid (for example, 0.1 Poise or less). A slide hopper method, a wire bar method, or a spin method is suitable, and a uniform film can be obtained.

As described above, the viscosity of the dye coating solution, the coating amount,
An application method may be appropriately selected according to parameters such as a support and a coating speed. The time required for dye adsorption after coating should be as short as possible in consideration of mass production.

Since the presence of unadsorbed dye causes disturbance of device performance, it is preferable to remove the dye by washing immediately after adsorption. It is preferable to perform cleaning with a polar solvent such as acetonitrile and an organic solvent such as an alcohol solvent using a wet cleaning tank. In order to increase the amount of the adsorbed dye, it is preferable to perform the heat treatment before the adsorption. After the heat treatment, in order to avoid adsorption of water on the surface of the semiconductor fine particles, it is also preferable to quickly adsorb the dye at 40 to 80 ° C. without returning to normal temperature.

The total amount of the dye used is preferably 0.01 to 100 mmol per 1 m ² of the support. The amount of the dye adsorbed on the semiconductor fine particles is preferably 0.01 to 1 mmol per 1 g of the semiconductor fine particles. With such an amount of the dye, a sensitizing effect in the semiconductor can be sufficiently obtained. On the other hand, if the amount of the dye is small, the sensitizing effect becomes insufficient, and if the amount of the dye is too large, the dye not adhering to the semiconductor floats and causes a reduction in the sensitizing effect.

A colorless compound may be co-adsorbed for the purpose of reducing the interaction between dyes such as association. Examples of the hydrophobic compound to be co-adsorbed include steroid compounds having a carboxyl group (for example, cholic acid).

For the purpose of accelerating the removal of excess dye, the surface of the semiconductor fine particles may be treated with an amine after adsorbing the dye. Preferred amines include pyridine, 4-tert-butylpyridine, polyvinylpyridine and the like. When these are liquids, they may be used as they are or may be used by dissolving them in an organic solvent.

Hereinafter, the charge transfer layer and the counter electrode will be described in detail. The charge transfer layer is a layer having a function of replenishing the oxidized dye with electrons. Examples of typical charge transfer layers that can be used in the present invention include a liquid (electrolytic solution) in which a redox couple is dissolved in an organic solvent, and a so-called gel in which a liquid in which a redox couple is dissolved in an organic solvent is impregnated in a polymer matrix. Examples include an electrolyte and a molten salt containing a redox couple.
Further, a solid electrolyte or a hole (hole) transport material can be used.

The electrolyte used in the present invention comprises an electrolyte, a solvent,
And additives. The electrolyte of the present invention is LiI as a combination (iodides I ₂ and an iodide, NaI, KI, CsI, metal iodide such as CaI ₂ or tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide, etc. 4 Iodine salts of quaternary ammonium compounds), Br
Combination of ₂ and bromide (bromide is LiBr, N
ABR, KBr, CsBr, metal bromide such as CaBr ₂ or tetraalkylammonium bromide,
Bromide salts of quaternary ammonium compounds such as pyridinium bromide), metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfide, and viologen Dyes, hydroquinone-quinone and the like can be used. I ₂ and LiI or pyridinium iodide Among these, an electrolyte that combines iodine salt of imidazolium iodide and quaternary ammonium compounds are preferred in the present invention. The above-mentioned electrolytes may be used as a mixture. The electrolyte is EP-718
No.288, WO95 / 18456, J. Electrochem.Soc., Vol.14
3, No. 10, 3099 (1996), Inorg. Chem. 1996, 35, 1168-1178
The salt in a molten state at room temperature (molten salt) described in (1) can also be used. When a molten salt is used as an electrolyte, a solvent need not be used.

The preferred electrolyte concentration is 0.1M or more and 15M or less, more preferably 0.2M or more and 10M or less. When iodine is added to the electrolyte, a preferable concentration of iodine is 0.01 M or more and 0.5 M or less.

As long as the organic solvent used for the electrolytic solution has a high boiling point, deterioration due to volatilization of the electrolytic solution can be prevented. In addition, from the viewpoint of the short-circuit current density and the conversion efficiency of the photoelectric conversion element,
Preferably, the viscosity of the organic solvent is low and the dielectric constant is high. That is, if the viscosity is low, an effect of improving the ion mobility can be obtained, and if the dielectric constant is large, an effect of improving the effective carrier concentration can be obtained. Specific examples of the organic solvent include aprotic polar solvents (for example, nitriles such as acetonitrile, carbonates such as propylene carbonate and ethylene carbonate, dimethylformamide, dimethyl sulfoxide, sulfolane, 1,3-dimethylimidazolinone and 3-methyl). Heterocyclic compounds such as oxazolidinone, etc.).

In the present invention, the electrolyte may be gelled (solidified) by a method such as addition of a polymer, addition of an oil gelling agent, polymerization containing a polyfunctional monomer, or crosslinking reaction of the polymer. Examples of the polymer used for the matrix of the gel electrolyte include polyacrylonitrile and polyvinylidene fluoride.

Examples of the molten salt include lithium iodide and at least one other lithium salt (eg, lithium acetate,
Lithium perchlorate and the like may be mentioned, and the fluidity at room temperature may be increased by mixing a polymer such as polyethylene oxide. In this case, the amount of the polymer added is 1 to 50% by weight.

In the present invention, an organic or inorganic material or a combination thereof can be used in place of the electrolyte. Examples of hole transport materials include aromatic amines, polypyrrole, polythiophene, polyacetylene, polyaniline, polyphenylene, and the like.

With respect to the method of forming the charge transfer layer, two methods are conceivable. One is a method in which a counter electrode is first adhered to a semiconductor fine particle-containing layer carrying a sensitizing dye, and a liquid charge transfer layer is sandwiched between the counter electrodes. Another one
The first is a method in which the charge transfer layer is directly provided on the semiconductor fine particle-containing layer, and the counter electrode is subsequently provided.

As the method of sandwiching the charge transfer layer in the former case, a normal pressure process utilizing a capillary phenomenon due to immersion or the like and a vacuum process of replacing the gas phase with a liquid phase at a pressure lower than normal pressure can be used. In the latter case, the wet charge transfer layer is provided with a counter electrode in an undried state, and measures are taken to prevent liquid leakage at the edge. In the case of a gel electrolyte, there is also a method of applying it by a wet method and solidifying it by a method such as polymerization. In this case, a counter electrode can be provided after drying and fixing. As a method for applying a wet organic hole transport material or a gel electrolyte in addition to the electrolytic solution, the immersion method, the roller method, the dipping method, the air knife method, the extrusion method, and the slide method are the same as the method for applying the semiconductor fine particle-containing layer and the dye. Hopper method, wire bar method, spin method, spray method,
A casting method, various printing methods, and the like are conceivable. In the case of a solid electrolyte or a solid hole (hole) transport material, the charge transfer layer can be formed by a dry film forming process such as a vacuum evaporation method or a CVD method, and then a counter electrode can be provided.

The counter electrode functions as a positive electrode of the photoelectrochemical cell when the photoelectric conversion element is a photoelectrochemical cell. The counter electrode is usually synonymous with the conductive support described above, but the support is not necessarily required in a configuration that maintains sufficient strength. However, having a support is advantageous in terms of hermeticity. In order for light to reach the photosensitive layer, at least one of the conductive support and the counter electrode described above must be substantially transparent. In the photoelectrochemical cell of the present invention, it is preferable that the conductive support is transparent and sunlight is incident from the support side. In this case, it is more preferable that the counter electrode has a property of reflecting light.

As a counter electrode of the photoelectrochemical cell, glass or plastic on which a metal or a conductive oxide is deposited can be used, and the metal thin film is formed so as to have a thickness of 5 μm or less, preferably 5 nm to 3 μm. It can also be formed by forming by a method such as vapor deposition or sputtering. In the present invention, it is preferable to use glass on which platinum is deposited or a metal thin film formed by deposition or sputtering as a counter electrode.

As described in the description of the application of the charge transfer layer, there are two types of application of the counter electrode: the application on the charge transfer layer and the application on the semiconductor fine particle-containing layer first. In any case, depending on the type of the counter electrode material and the type of the charge transfer layer, the counter electrode material can be appropriately formed on the charge transfer layer or the semiconductor fine particle-containing layer by a method such as application, lamination, vapor deposition, or bonding. For example, in the case of attaching a counter electrode, a substrate provided as a conductive layer can be attached by a method such as application, evaporation, or CVD of the above conductive material. When the charge transfer layer is solid, the above-mentioned conductive material is directly applied thereon, plated, PVD,
The counter electrode can be formed by a technique such as CVD.

Further, a layer having other necessary functions such as a protective layer and an antireflection film can be provided on the conductive support or the counter electrode of the working electrode. When such layers are separated in function by multiple layers, simultaneous multilayer coating and sequential coating can be performed, but simultaneous multilayer coating is more preferable in terms of productivity. In the simultaneous multi-layer coating, the slide hopper method and the extrusion method are suitable in consideration of productivity and uniformity of film formation. In addition, these functional layers can be provided by a technique such as vapor deposition or pasting depending on the material.

[0070]

The present invention will be specifically described below with reference to examples. 1. Preparation of Coating Solution Containing Titanium Dioxide Particles Dispersion of titanium dioxide having a titanium dioxide concentration of 11% by weight in the same manner as described in Barb's Journal of American Ceramic Society, Vol. 80, p. 3157, except that the autoclave temperature was 230 ° C. I got something. The average size of the resulting titanium dioxide particles was about 10 nm. To this dispersion was added polyethylene glycol (molecular weight: 20,000, manufactured by Wako Pure Chemical Industries) at 30% by weight based on titanium dioxide and mixed to obtain a coating solution.

2. Preparation of titanium dioxide electrode adsorbing dye Transparent conductive glass coated with fluorine-doped tin oxide (manufactured by Nippon Sheet Glass, surface resistance is about 10Ω / c
m ² ), apply this coating solution to the conductive surface side with a doctor blade.
After coating at a thickness of 0 μm and drying at 25 ° C. for 30 minutes,
45 with an electric furnace (muffle furnace FP-32 manufactured by Yamato Scientific)
It was baked at 0 ° C. for 30 minutes. The amount of titanium dioxide applied is 1
It was 5 g / m ² and the film thickness was 10 μm. After taking out the glass and cooling, the dye solution shown in Table 1 in ethanol (3
(× 10 ⁻⁴ mol / l) for 3 hours. The glass to which the dye was dyed was immersed in 4-tert-butylpyridine for 15 minutes, washed with ethanol, and air-dried. The coating amount of the dye was appropriately selected from the range of 0.1 to 10 mmol / m ² according to the type of the dye.

3. Preparation of Photoelectrochemical Cell A TiO ₂ electrode substrate (2 cm × 2 cm) color-sensitized with each of the dyes prepared as described above was overlaid with a platinum-deposited glass of the same size (see FIG. 1). . Next, an electrolytic solution (0.05 mol / liter of iodine using a mixture of acetonitrile and N-methyl-2-oxazolidinone in a volume ratio of 90:10 as a solvent, lithium iodide 0 (0.5 mol / liter solution) and introduced into a TiO ₂ electrode to obtain photoelectrochemical cells 1 to 10 shown in Table 1. According to the present embodiment, as shown in FIG. 1, conductive glass 1 (a conductive agent layer 2 is provided on glass), TiO ₂ electrode 3, dye layer 4,
A photoelectrochemical cell in which the electrolyte 5, the platinum layer 6, and the glass 7 were sequentially laminated was produced.

4. Measurement of photoelectric conversion wavelength and photoelectric conversion efficiency The photoelectric conversion ability of the photoelectrochemical cell of the present invention is
IPCE (Incident Photonto Current Conversion Efficie
ncy) Measured by a measuring device. Table 1 summarizes the wavelength at which the photoelectrochemical cell using each dye exhibits the maximum conversion ability and the photoelectric conversion efficiency with monochromatic light.

[0074]

[Table 1]

Photoelectrochemical cells using any of the dyes of the present invention have high photoelectric conversion characteristics in the red to infrared region.

[0076]

According to the present invention, a dye-sensitized photoelectric conversion element and a photoelectrochemical cell having high photoelectric conversion characteristics in the red to infrared region can be provided. The dye used in the present invention is less expensive than conventional ruthenium complexes.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a photoelectrochemical cell prepared in an example.

[Explanation of symbols]

1 conductive glass 2 conductive agent layer 3 TiO ₂ layer 4 dye layer 5 electrolyte 6 platinum layer 7 Glass

Claims (6)

[Claims] 1. A photoelectric conversion element containing semiconductor fine particles sensitized by a polymethine dye represented by the following formula (I). Embedded image In the formula, X represents a sulfur atom, an oxygen atom, a selenium atom or a tellurium atom. R ₁ , R ₂ , R ₃ and R ₄ are each independently a hydrogen atom or a substituent, and R ₁ and R ₂ , and R ₃
And R ₄ may be linked to each other to form a ring structure. L represents a substituted or unsubstituted methine group, and Q represents a group of non-metallic atoms necessary to complete a polymethine dye. W represents a counter ion necessary for neutralizing the charge. 2. The photoelectric conversion device according to claim 1, wherein said polymethine dye has at least one acidic group. 3. The photoelectric conversion device according to claim 1, wherein Q comprises a methine group as a linking group and a nitrogen-containing heterocycle. 4. The photoelectric conversion device according to claim 3, wherein the nitrogen-containing hetero ring is a ring selected from benzothiazolium, indolenium, benzoxazolium, 2-quinolinium, 4-quinolinium and a nucleus derived therefrom. . 5. The photoelectric conversion device according to claim 1, wherein said semiconductor fine particles are titanium oxide fine particles. 6. A photoelectrochemical cell using the photoelectric conversion element according to claim 1.