JP2005085643A - Photoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element with excellent durability and transparency without photoelectric conversion performance deteriorated. <P>SOLUTION: In the photoelectric conversion element having a conductive layer, semiconductor nano-particle layer sensitized by dyes, charge transport layer and counter electrodes, the dyes are expressed in formula (1). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photoelectric conversion element using semiconductor nanoparticles sensitized with a dye.

  Photovoltaic cells are the targets of practical development of solar cells that apply single-crystal silicon, polycrystal, or amorphous silicon photoelectric conversion elements. However, problems such as long manufacturing costs, securing raw materials, and long investment recovery periods are necessary for widespread use. It is necessary to overcome the point. On the other hand, many solar cells using organic materials aimed at increasing the area and reducing the cost have been proposed so far, but have the problems of low conversion efficiency and poor durability. Under such circumstances, materials and manufacturing techniques for producing a photoelectric conversion element using semiconductor nanoparticles sensitized with a dye have been disclosed (see, for example, Non-Patent Document 1 and Patent Document 1). The proposed device was a wet photoelectric conversion device using a porous titanium dioxide thin film spectrally sensitized with a ruthenium complex as a working electrode. The first advantage of this method is that an oxide semiconductor such as titanium dioxide can be used, so that an inexpensive photoelectric conversion element can be provided. The second advantage is that the absorption of the dye used is relatively wide. In other words, light in almost all wavelength regions of visible light can be converted into electricity. However, since an organic solvent having a low boiling point is used as the charge transport material, there is a concern about its durability.

Therefore, various stabilized charge transport materials have been proposed. For example, in order to prevent volatilization and transpiration of the electrolyte solution over time, a photoelectric conversion element solidified using an inorganic hole transport material such as copper iodide or copper thiocyanide has been proposed. However, the photoelectric conversion elements using these hole transport materials have a problem that they are easily short-circuited and deteriorate with time. In addition, these methods have a problem that the dye adsorbed on the semiconductor is deteriorated in the step of forming the hole transport layer, that is, the photoelectric conversion efficiency is lowered, and further, the photoelectric conversion performance is greatly deteriorated with time. There was a problem. In Patent Document 2 below, a phthalocyanine dye is proposed, but the transmittance is low, and there is a problem that transparency is sacrificed when it is desired to use it attached to a daylighting window.
Nature: 353, 737-740 (1991) US Pat. No. 4,927,721 JP 2003-152208 A (pages 1 to 6)

  The objective of this invention is providing the photoelectric conversion element excellent in durability, without deteriorating photoelectric conversion performance. Furthermore, it is providing the photoelectric conversion element with transparency.

The above object of the present invention can be achieved by the following configuration.
(Claim 1)
A photoelectric conversion element having a conductive layer, a semiconductor nanoparticle layer sensitized with a dye, a charge transport layer, and a counter electrode, wherein the dye is represented by the following general formula (1).

(In the formula, Z ₁ and Z ₂ represent heteroatoms, and R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , Y ₁ , Y ₂ , Y ₃ , Y ₄ , Y ₅ and Y ₆ are each hydrogen. Represents an atom or a substituent, X represents a counter ion necessary for neutralizing the electric charge, n represents 0 or 1, and is 0 in the case of an inner salt.)
(Claim 2)
The photoelectric conversion element according to claim 1, wherein a porous isolation layer is provided in the charge transport layer, and the hole transport material is a non-volatile compound.
(Claim 3)
The photoelectric conversion element according to claim 1, wherein the semiconductor nanoparticle layer is anatase-type titanium oxide.
(Claim 4)
The photoelectric conversion element according to claim 1, wherein the conductive layer is mainly composed of tin oxide doped with a trivalent or pentavalent metal atom.

  According to the present invention, a photoelectric conversion element having excellent durability and transparency can be provided without deteriorating photoelectric conversion performance.

The present invention will be described in more detail. The photoelectric conversion element of the present invention comprises at least a conductive layer, a semiconductor nanoparticle layer sensitized with a dye, a charge transport layer, and a counter electrode.
Each layer will be described in detail below.

  The conductive layer is composed of a single layer of a conductive layer or a multilayer of a conductive layer and a substrate. In the case of a single layer, a material that sufficiently retains strength and hermeticity is used as the conductive layer. For example, a metal material (platinum, gold, silver, copper, zinc, titanium, aluminum, etc. or an alloy containing these materials) ) Can be used. In the case of multiple layers, a substrate having a conductive layer containing a conductive agent on the photosensitive layer side can be used. Preferred conductive agents include metals (eg, platinum, gold, silver, copper, zinc, titanium, aluminum, indium, etc. or alloys containing these), carbon, carbon nanotubes, carbon nanohorns, or conductive metal oxides (indium-tin composite oxidation). And tin oxide doped with a trivalent or pentavalent metal atom such as fluorine or antimony). The thickness of the conductive layer is preferably about 10 nm to 10 μm.

  The conductive layer preferably has a lower surface resistance. The range of the surface resistance is preferably 50Ω / □ or less, more preferably 20Ω / □ or less. When irradiating light from the conductive layer, the conductive layer side is preferably substantially transparent. The term “substantially transparent” means that the transmittance is 10% or more in the entire range of light in the visible to near infrared region (400 to 750 nm), preferably 50% or more, and preferably 80% or more. Is more preferable. In particular, it is preferable that the transmittance in a wavelength region where the photosensitive layer is sensitive is high.

As the transparent conductive support that supports the conductive layer, a transparent conductive layer made of a conductive metal oxide is preferably formed on the surface of a transparent substrate such as glass or plastic by coating or vapor deposition. Preferred as the transparent conductive layer is tin dioxide or indium-tin oxide doped with fluorine or antimony. As the transparent substrate, a transparent polymer film can be used in addition to a glass substrate such as soda glass which is advantageous in terms of low cost and strength, alkali-free glass which is not affected by alkali elution. Examples of transparent polymer film materials include triacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), polyarylate ( PAr), polysulfone (PSF), polyester sulfone (PES), polyimide (PI), polyetherimide (PEI), cyclic polyolefin, brominated phenoxy resin, and the like. In order to ensure sufficient transparency, the coating amount of the conductive metal oxide is preferably 0.01 to 100 g per 1 m ² of the glass or plastic support.

  It is preferable to use a metal lead for the purpose of reducing the resistance of the transparent conductive support. The material of the metal lead is preferably a metal such as platinum, gold, nickel, titanium, aluminum, copper, or silver. The metal lead is preferably provided on a transparent substrate by vapor deposition, sputtering, or the like, and a transparent conductive layer such as a conductive tin oxide or zinc oxide film is provided thereon. The decrease in the amount of incident light due to the installation of the metal lead is preferably within 10%, more preferably 1 to 5%.

  In the photosensitive layer, the semiconductor acts as a photoconductor, absorbs light, separates charges, and generates electrons and holes. In dye-sensitized semiconductors, light absorption and thus the generation of electrons and holes occurs mainly in the dye, and the semiconductor nanoparticles are responsible for receiving and transmitting these electrons (or holes). The semiconductor used in the present invention is preferably an n-type semiconductor in which conductor electrons become carriers under photoexcitation and give an anode current.

  Examples of semiconductor semiconductors include single semiconductors such as silicon and germanium, compound semiconductors of group III to V elements of the periodic table, metal chalcogenides (eg, oxides, sulfides, selenides, or composites thereof), or A compound having a perovskite structure (for example, strontium titanate, calcium titanate, sodium titanate, barium titanate, potassium niobate, etc.) can be used.

  Preferred metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium, or tantalum oxide, zinc, silver, antimony or bismuth sulfide. Etc.

Preferred specific examples of the semiconductor used in the present invention are Si, TiO ₂ , SnO ₂ , ZnO, Nb ₂ O ₅ , CdS, ZnS, PbS, Bi ₂ S ₃ , CdSe, CdTe, SrTiO ₃ , GaP, InP, and the like. TiO ₂ , ZnO, SnO ₂ , WO ₃ , Nb ₂ O ₅ , SrTiO ₃ , InP, more preferably TiO ₂ or Nb ₂ O ₅ , most preferably TiO ₂ . The TiO ₂ is preferably TiO ₂ containing 70% or more of anatase type crystals, particularly preferably 100% anatase type TiO ₂ . It is also effective to dope metals for the purpose of increasing the electronic conductivity in these semiconductors. As the metal to be doped, trivalent and pentavalent metals are preferable. In order to prevent a reverse current from flowing from the semiconductor to the charge transport layer, it is also effective to dope the semiconductor with a halogen atom.

  The semiconductor used in the present invention may be single crystal or polycrystalline, but a porous film made of semiconductor nanoparticles is particularly preferable from the viewpoint of production cost, securing raw materials, investment recovery period, and the like.

  The particle size of the semiconductor nanoparticles is generally at a level of 1 nm to 1 μm, but the average particle size of the primary particles obtained from the diameter when the projected area is converted into a circle is preferably 5 to 200 nm, preferably 8 to 100 nm. Is more preferable. The average particle size of the semiconductor nanoparticles (secondary particles) in the dispersion is preferably 0.01 to 30 μm. Two or more kinds of fine particles having different particle size distributions may be mixed. In this case, the average size of the small particles is preferably 25 nm or less, more preferably 10 nm or less.

The semiconductor nanoparticles may be a mixture of two or more different types. When two or more kinds of semiconductor nanoparticles are used in combination, one kind is preferably TiO ₂ , ZnO, Nb ₂ O ₅ or SrTiO ₃ . As another kind, SnO ₂ and WO ₃ are preferable. More preferred combinations include ZnO and SnO ₂ , ZnO and WO ₃ or ZnO, SnO ₂ and WO _{3, and the} like. When mixing and using 2 or more types of semiconductor nanoparticles, each particle size may differ. Particularly preferred is a combination in which the semiconductor nanoparticles mentioned as the first type are large in particle size and the semiconductor nanoparticles mentioned as the second type are small. Preferably, a combination of particles having a large particle size of 100 nm or more, for example, 100 to 500 nm, and a small particle size of 15 nm or less, for example, 2 to 15 nm.

  In order to apply the semiconductor nanoparticles on the conductive support, a sol-gel method or the like can be used in addition to a method of applying a dispersion or colloidal solution of the semiconductor nanoparticles on the conductive support. In consideration of mass production of photoelectric conversion elements, physical properties of a semiconductor nanoparticle liquid, flexibility of a conductive support, and the like, a wet film forming method is relatively advantageous. Typical examples of the wet film forming method include a coating method, a printing method, an electrolytic deposition method, and an electrodeposition method. Also, a method of oxidizing metal, a method of depositing in a liquid phase from a metal solution by exchanging ligands, a method of depositing by sputtering, etc., or spraying a metal oxide precursor that thermally decomposes on a heated substrate A method of forming a metal oxide can also be used.

  In addition to the sol-gel method described above, a method of preparing a dispersion of semiconductor nanoparticles includes a method of grinding with a mortar, a method of dispersing while pulverizing using a mill, or a solvent when synthesizing a semiconductor. The method of depositing as a fine particle and using it as it is is mentioned.

  Examples of the dispersion medium include water or various organic solvents (for example, methanol, ethanol, isopropyl alcohol, citronellol, terpineol, dichloromethane, acetone, acetonitrile, ethyl acetate, and the like). At the time of dispersion, for example, a polymer such as polyethylene glycol, hydroxyethyl cellulose, carboxymethyl cellulose, a surfactant, an acid, a chelating agent, or the like may be used as a dispersion aid. By changing the molecular weight of the polyethylene glycol, the viscosity of the dispersion can be adjusted, and a semiconductor layer that is difficult to peel off can be formed and the porosity of the semiconductor layer can be controlled. Therefore, it is preferable to add polyethylene glycol.

  As an application method, the roller method, dip method, etc. as an application (application liquid application) system, the air knife method, blade method, etc. as a metering (application amount control) system, and a system that performs application and metering in the same part, The wire bar method disclosed in Japanese Patent Publication No. 58-4589, the slide hopper method described in US Pat. Nos. 2,681,294, 2,761,419, 2,761,791, and the like. The extrusion method and the curtain coating method are preferred. In addition, spin coating and spray coating are also preferred as other general-purpose means. Furthermore, a wet printing method is also preferable, and intaglio, rubber plate, screen printing, etc. are preferable, including three major printing methods of letterpress, offset and gravure. From these, a preferred film forming method can be selected according to the liquid viscosity and the wet thickness.

The semiconductor nanoparticle layer is not limited to a single layer, but a multi-layer coating of a dispersion of semiconductor nanoparticles having different particle sizes, or a multi-layer coating layer containing different types of semiconductor nanoparticles (or different binders and additives). It can also be applied. Multi-layer coating is also effective when the film thickness is insufficient with a single coating. In general, as the thickness of the semiconductor nanoparticle layer (same as the photosensitive layer) increases, the amount of supported dye increases per unit projected area, so the light capture rate increases, but the diffusion distance of the generated electrons increases, resulting in a charge. Loss due to recombination also increases. Accordingly, the preferred thickness of the semiconductor nanoparticle layer is 0.05 to 100 μm. When used in an optical element, the thickness of the semiconductor nanoparticle layer is preferably 1 to 30 μm, and more preferably 2 to 25 μm. The coating amount per 1 m ² of the semiconductor nanoparticle support is preferably 0.5 to 100 g, more preferably 3 to 50 g.

  After applying the semiconductor nanoparticles on the conductive support, the semiconductor nanoparticles are brought into electronic contact with each other, and heated or pressurized to improve the coating strength and the adhesion to the support. Is preferred. The range of preferable heating temperature is 40 ° C. or higher and 900 ° C. or lower, more preferably 130 ° C. or higher and 600 ° C. or lower. The heating time is about 10 minutes to 10 hours. When using a support having a low melting point or softening point such as a polymer film, high temperature treatment is not preferable because it causes deterioration of the support. Moreover, it is preferable that it is as low as possible (for example, 60 degreeC-360 degreeC) also from a viewpoint of cost. The heat treatment temperature can be lowered by using small semiconductor nanoparticles of 5 nm or less, heat treatment in the presence of mineral acid, metal oxide precursor, etc., and irradiation with ultraviolet rays, infrared rays, microwaves, etc. Or by applying an electric field or ultrasonic waves. These means can be used in appropriate combination. At the same time, for the purpose of removing unnecessary organic substances and the like, it is preferable to use a combination of irradiation, application, heating, decompression, oxygen plasma treatment, pure water cleaning, solvent cleaning, gas cleaning and the like in combination as appropriate. For the purpose of preventing a reverse current from flowing from the semiconductor nanoparticles to the charge transport layer, it is also effective to adsorb an organic substance having a low electronic conductivity other than the dye on the particle surface. The organic substance to be adsorbed is preferably an organic compound such as a fatty acid having a hydrophobic group.

  The semiconductor nanoparticle layer preferably has a large surface area so that a large amount of dye can be adsorbed. The surface area of the semiconductor nanoparticle layer coated on the support is preferably 10 times or more, more preferably 100 times or more the projected area. This upper limit is not particularly limited, but is usually about 1000 times.

  The sensitizing dye used in the dye-sensitive layer is preferably an infrared dye represented by the general formula (1), and most preferably a dye that has no absorption in the visible region or near infrared region, or can sensitize a semiconductor with little absorption. .

In the general formula (1), Z ₁ and Z ₂ may be the same or different, each represents a hetero atom, and preferably a sulfur atom or a selenium atom.

Y ₁ and Y ₄ each represent a hydrogen atom, Y ₁ when Y ₂ is not a hydrogen atom, and Y ₄ when Y ₅ is not a hydrogen atom also represent a methyl group, an ethyl group, a hydroxy group, or a methoxy group. Y ₂ and Y ₅ are a hydrogen atom, an optionally substituted alkyl group having 3 or less carbon atoms (more preferably, for example, a methyl group, an ethyl group, a propyl group, a methoxymethyl group, a hydroxyethyl group, etc.), hydroxy Group, methoxy group, ethoxy group, monocyclic aryl group (more preferably, for example, phenyl group, tolyl group, anisyl group, 2-pyridyl group, 4-pyridyl group, 2-thienyl group, 2-furyl group, etc.) In addition to acetylamino group and propionylamino group, Y ₂ is connected to Y ₁ and Y ₅ is connected to Y ₄ to represent a methylenedioxy group, trimethylene group or tetramethylene group. Y ₃ and Y ₆ each represent a hydrogen atom, and Y ₃ is linked with Y ₂ , Y ₆ and Y ₅ , respectively, to form a methylenedioxy group, ethylenedioxy group, trimethylene group, tetramethylene group, or tetra Also represents a dehydrotetramethylene group.

R ₁ and R ₂ may be the same or different and each represents an optionally substituted alkyl group or alkenyl group having a total carbon number of 12 or less. More preferable substituents for the alkyl group and alkenyl group include, for example, a sulfo group, a carboxy group, a halogen atom, a hydroxy group, an alkoxy group having 6 or less carbon atoms, and an optionally substituted aryl group having 12 or less carbon atoms (for example, Phenyl group, tolyl group, sulfophenyl group, carboxyphenyl group, naphthyl group, 5-methylnaphthyl group, 4-sulfonaphthyl group, etc.), heterocyclic group (for example, furyl group, thienyl group, etc.), carbon number 12 or less Optionally substituted aryloxy groups (for example, chlorophenoxy group, phenoxy group, sulfophenoxy group, hydroxyphenoxy group, naphthyloxy group, etc.), acyl groups having 8 or less carbon atoms (for example, benzenesulfonyl group, methanesulfonyl group) Group, acetyl group, propionyl group, etc.), alkoxycarbon having 6 or less carbon atoms Group (for example, ethoxycarbonyl group, butoxycarbonyl group, etc.), cyano group, alkylthio group having 6 or less carbon atoms (for example, methylthio group, ethylthio group, etc.), optionally substituted arylthio group having 8 or less carbon atoms (for example, , Phenylthio group, tolylthio group, etc.), an optionally substituted carbamoyl group having 12 or less carbon atoms (for example, carbamoyl group, N-ethylcarbamoyl group, etc.), an acylamino group having 12 or less carbon atoms (for example, acetylamino group, Methanesulfonamino group and the like), acylaminocarbonyl group having 8 or less carbon atoms (for example, acetylaminocarbonyl group and methanesulfonylaminocarbonyl group), ureido group having 7 or less carbon atoms (for example, 3-ethylureido group, 3, 3-dimethylureido group etc.). One or more substituents may be present.

R ₄ represents a hydrogen atom, and R ₄ can be linked to R ₃ or R ₅ to form a 5- or 6-membered ring. When R ₄ does not form a ring, it represents an optionally substituted lower alkyl group.

  X represents a counter ion necessary for neutralizing the electric charge. n represents 0 or 1, and is 0 in the case of an inner salt.

Specific examples of the aforementioned nitrogen-containing heterocyclic nucleus in which Z ₁ and Z ₂ are represented as one of the constituent atomic groups include, for example, benzothiazole, 5-methylbenzothiazole, 5-ethylbenzothiazole, 5 -Propylbenzothiazole, 5,6-dimethylbenzothiazole, 5-methoxybenzothiazole, 5-ethoxybenzothiazole, 5,6-dimethoxybenzothiazole, 5-methoxy-6-methylbenzothiazole, 5-phenylbenzothiazole, 5 -P-tolylbenzothiazole, 5-acetylaminobenzothiazole, 5-propionylaminobenzothiazole, 5-hydroxybenzothiazole, 5-hydroxy-6-methylbenzothiazole, 5,6-dioxymethylenebenzothiazole, 4,5 -Dioxymethylene benzothiazo 5,6-trimethylenebenzothiazole, naphth [1,2-d] thiazole, -methylnaphth [1,2-d] thiazole, 8-methoxynaphth [1,2-d] thiazole, 8,9-dihydro Naphthothiazole, benzoselenazole, 5-methylbenzoselenazole, 5-ethylbenzoselenazole, 5-methoxybenzoselenazole, 5-ethoxybenzoselenazole, 5,6-dimethylbenzoselenazole, 5-hydroxybenzoselenazole , 5-hydroxy-6-methylbenzoselenazole, naphtho [1,2-d] selenazole and the like.

Specific examples of the group represented by R ₁ and R ₂ include, for example, methyl group, ethyl group, propyl group, allyl group, pentyl group, hexyl group, methoxyethyl group, ethoxyethyl group, phenethyl group, tolylethyl group, phenoxyethyl group. Phenoxypropyl group, naphthoxyethyl group, sulfophenethyl group, 2,2,2-trifluoroethyl group, 2,2,3,3-tetrafluoropropyl group, carbamoylethyl group, hydroxyethyl group, 2- (2-hydroxy Ethoxy) ethyl group, carboxymethyl group, carboxyethyl group, ethoxycarbonylmethyl group, sulfoethyl group, 2-chloro-3-sulfopropyl group, 3-sulfopropyl group, 2-hydroxy-3-sulfopropyl group, 3-sulfobutyl Group, 4-sulfobutyl group, 2- (2,3-dihydroxypropyl) Examples include oxy) ethyl group, 2- [2- (3-sulfopropyloxy) ethoxy] ethyl group, acetylaminoethyl group, methylsulfonylaminoethyl group, methylsulfonylaminocarbonylethyl group, acetylaninocarbonylethyl group and the like.

Preferred examples of a lower alkyl group which may be substituted R ₄ represents a methyl group, an ethyl group, a propyl group or a benzyl group, a lower alkyl group or substituted optionally substituted R ₄ represents Preferable specific examples represented by the optionally substituted phenyl group include methyl group, ethyl group, propyl group, butyl group, benzyl group, phenyl group, p-methoxyphenyl group, p-tolyl group and the like.

  Specific examples of the counter ion represented by X include alkali metal ions such as potassium and sodium, ammonium ions such as triethylammonium and N, N-dimethylbenzylammonium, and immonium ions such as pyridinium in the case of a cation. In the case of anions, halide ions such as chlorine ions, bromine ions and iodine ions, sulfonate ions such as p-toluenesulfonate and benzenesulfonate, carboxylate ions such as acetate and the like can be mentioned.

In the sensitizing dye represented by the general formula (1), a more preferable sensitizing dye is at least one of Z ₁ and Z ₂ among the sensitizing dyes represented by the general formula (1). One represents a sulfur atom, Y ₁ and Y ₄ represent a hydrogen atom, Y ₂ and Y ₅ each independently represent a hydrogen atom, a methyl group, an ethyl group, a propyl group, a methoxymethyl group, a hydroxyethyl group, Hydroxy group, methoxy group, ethoxy group, phenyl group, acetylamino group, alkylthio group (for example, methylthio group, ethylthio group, etc.), acyl group having 12 or less carbon atoms (for example, benzoyl group, benzenesulfonyl group, methanesulfonyl group, methanesulfonyl fill group, an acetyl group, in addition to representing a propionyl group, etc.), with a Y ₂ is Y _3, and Y ₅ and Y _6, respectively, methylenedioxy group, a tetramethylene group, or Represents a tetra-dehydroepiandrosterone tetramethylene group.

  Specific examples of preferable sensitizing dyes used in the photosensitive layer are shown below.

  In order to adsorb the dye to the semiconductor nanoparticles, it is necessary to immerse a conductive support having a well-dried semiconductor nanoparticle layer in the dye solution or to apply the dye solution to the semiconductor nanoparticle layer. it can. In the former case, an immersion method, a dip method, a roller method, an air knife method or the like can be used. In the case of the immersion method, the adsorption of the dye may be performed at room temperature or may be performed by heating and refluxing as described in JP-A-7-249790. Examples of the latter application method include a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, and a spray method. Preferred solvents for dissolving the dye include, for example, alcohols (methanol, ethanol, t-butanol, benzyl alcohol, etc.), nitriles (acetonitrile, propionitrile, 3-methoxypropionitrile, etc.), nitromethane, halogenated compounds, etc. Hydrocarbon (dichloromethane, dichloroethane, chloroform, chlorobenzene, etc.), ethers (diethyl ether, tetrahydrofuran, etc.), dimethyl sulfoxide, amides (N, N-dimethylformamide, N, N-dimethylacetamide, etc.), N-methyl Pyrrolidone, 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, esters (ethyl acetate, butyl acetate, etc.), carbonates (diethyl carbonate, ethylene carbonate, propylene carbonate, etc.), ketones (acetone, 2 Butanone, cyclohexanone), hydrocarbons (hexane, petroleum ether, benzene, toluene, etc.) or mixed solvents thereof.

The total adsorption amount of the dye is preferably 0.01 to 100 mmol per 1 m ² of the unit surface area of the porous semiconductor electrode substrate. The amount of the dye adsorbed on the semiconductor nanoparticles is preferably in the range of 0.01 to 1 mmol per gram of semiconductor nanoparticles. By using such an amount of dye adsorbed, a sensitizing effect in a semiconductor can be sufficiently obtained. On the other hand, when the amount of the dye is too small, the sensitizing effect is insufficient, and when the amount of the dye is too large, the dye not attached to the semiconductor floats, which causes a reduction in the sensitizing effect. In order to increase the adsorption amount of the dye, it is preferable to perform a heat treatment before the adsorption. In order to avoid water adsorbing on the surface of the semiconductor nanoparticles after the heat treatment, it is preferable to perform the dye adsorption operation quickly when the temperature of the semiconductor electrode substrate is between 60 ° C. and 150 ° C. without returning to room temperature. Further, for the purpose of reducing the interaction such as aggregation between the dyes, a colorless compound may be added to the dye and co-adsorbed on the semiconductor nanoparticles.

  The unadsorbed dye is preferably removed by washing immediately after adsorption. The cleaning is preferably performed using a wet cleaning tank and a polar solvent such as acetonitrile or an organic solvent such as an alcohol solvent. Alternatively, the surface of the semiconductor nanoparticles may be treated with an amine or a quaternary salt after adsorbing the dye. Preferable amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like, and preferable quaternary salts include tetrobutylammonium iodide, tetrahexylammonium iodide and the like. When these are liquids, they may be used as they are, or may be used after being dissolved in an organic solvent.

  The charge transport layer is a layer containing a charge transport material having a function of replenishing electrons to the oxidant of the dye. Examples of typical charge transport materials that can be used in the present invention include a solution in which redox pair ions are dissolved, a so-called gel electrolyte in which a polymer matrix gel is impregnated with a redox pair solution, and a redox counter ion. Examples thereof include molten salt electrolytes and solid electrolytes, and compositions containing these electrolytes can be used for the charge transport layer. In addition to a charge transport material that involves ions, an electron transport material or a hole transport material can also be used as a charge transport material that involves carrier movement in a solid. These charge transport materials can be used in combination. In the present invention, it is preferable to use an inorganic or organic hole transport material.

  Molten salt electrolyte Molten salt electrolyte is preferable from the viewpoint of achieving both photoelectric conversion efficiency and durability. The molten salt electrolyte is a liquid electrolyte at room temperature or a solid electrolyte having a low melting point. For example, WO95 / 18456, JP-A-8-259543, etc., Electrochemistry, Vol. 65, No. 11 , P. 923 (1997), etc., and known electrolytes such as pyridinium salts, imidazolium salts, and triazolium salts. A molten salt that becomes liquid at 100 ° C. or lower, particularly near room temperature, is preferred. Alkyl imidazolium salts are particularly preferred. Specific examples of preferred imidazolium salts are shown below.

  It is preferable to add iodine to the electrolyte composition. In this case, the content of iodine is preferably 0.1 to 20% by mass, and 0.5 to 5% by mass with respect to the entire electrolyte composition. It is more preferable that

When an electrolytic solution is used for the electrolytic solution charge transport layer, the electrolytic solution is preferably composed of an electrolyte, a solvent, and an additive. The electrolyte of the present invention is a combination of I ₂ and iodide (as iodide, metal iodide such as LiI, NaI, KI, CsI, CaI ₂ , tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide, etc. 4 Iodine salt of a quaternary ammonium compound), a combination of Br ₂ and bromide (as bromide, bromide of a quaternary ammonium compound such as a metal bromide such as LiBr, NaBr, KBr, CsBr, CaBr ₂ , tetraalkylammonium bromide, pyridinium bromide) In addition, metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides, viologen dyes, hydroquinone-quinones, etc. are used. Door can be. Among these, an electrolyte in which an iodine salt of a quaternary ammonium compound such as I ₂ and LiI, pyridinium iodide, or imidazolium iodide is combined is preferable. The electrolytes described above may be used in combination.

  The preferable electrolyte concentration is 0.1 mol or more and 10 mol or less, more preferably 0.2 mol or more and 4 mol or less. Further, when iodine is added to the electrolytic solution, a preferable concentration of iodine is 0.01 mol or more and 0.5 mol or less.

  The solvent used for the electrolyte is desirably a compound having a low viscosity and improving ion mobility, or having a high dielectric constant and an effective carrier concentration, thereby exhibiting excellent ion conductivity. Examples of such solvents include carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, ether compounds such as dioxane and diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl ether, and polyethylene. Chain ethers such as glycol dialkyl ether and polypropylene glycol dialkyl ether, methanol, ethanol, ethylene glycol monoalkyl ether, alcohols such as propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, ethylene glycol, Propylene glycol, polyethylene glycol, polypropylene Examples include polyhydric alcohols such as coal and glycerol, nitrile compounds such as acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile, aprotic polar substances such as dimethyl sulfoxide and sulfolane, and water. It can also be used as a mixture.

  When the electrolyte is gelled by a polymer crosslinking reaction, it is desirable to use a polymer containing a crosslinkable reactive group and a crosslinking agent in combination. In this case, preferred crosslinkable reactive groups are amino groups and nitrogen-containing heterocycles (for example, pyridine ring, imidazole ring, thiazole ring, oxazole ring, triazole ring, morpholine ring, piperidine ring, piperazine ring, etc.) Preferred cross-linking agents are bifunctional or higher functional reagents capable of electrophilic reaction with a nitrogen atom, for example, alkyl halides, halogenated aralkyls, sulfonic acid esters, acid anhydrides, acid chlorides, and isocyanate compounds.

  In the present invention, it is preferable to use a solid hole transport material that is organic or inorganic or a combination of both, instead of an ion conductive electrolyte such as a molten salt. A charge transport layer containing an inorganic hole transport material is more preferable, and a charge transport layer containing a monovalent copper compound as an inorganic hole transport material is still more preferable.

  There are two possible methods for forming the charge transport layer. One is a method in which a counter electrode is first bonded onto the photosensitive layer, and a liquid charge transport layer is sandwiched between the gaps. The other is a method in which a charge transport layer is provided directly on the photosensitive layer, and a counter electrode is subsequently provided. In the present invention, the charge transport layer is preferably provided by the latter method.

  In the former case, as a method for sandwiching the charge transport layer, a normal pressure process using a capillary phenomenon due to immersion or the like, or a low pressure process in which the gas phase in the gap is replaced with a liquid phase at a pressure lower than normal pressure can be used.

  When the charge transport layer is provided directly on the photosensitive layer, the wet charge transport layer is provided with a counter electrode without being dried, and measures for preventing liquid leakage at the edge portion are taken. In the case of a gel electrolyte, there is a method in which it is applied in a wet state and solidified by a method such as polymerization. In this case, the counter electrode can be applied 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 same methods as those for the semiconductor nanoparticle layer and the dye can be used. In the case of a solid electrolyte or a solid hole transport material, a charge transport layer can be formed by a dry film forming process such as a vacuum deposition method or a CVD method, and then a counter electrode can be provided. The organic hole transport material can be introduced into the electrode by techniques such as vacuum deposition, casting, coating, spin coating, dipping, electrolytic polymerization, and photoelectrolytic polymerization. Also in the case of an inorganic solid compound, it can be introduced into the electrode by techniques such as casting, coating, spin coating, dipping, electrolytic deposition, and electroless plating. In the present invention, when a monovalent copper compound is contained as the hole transport material, it is preferable to use an electrolytic plating method or an electroless plating method.

  You may be comprised from the counter electrode conductive layer and the support substrate. As the conductive material used for the counter electrode conductive layer, metal (for example, gold, silver, copper, aluminum, etc.), carbon, carbon nanotube, carbon nanohorn, or conductive metal oxide (indium-tin composite oxide, fluorine-doped tin oxide, etc.) ). Among these, aluminum and magnesium can be preferably used as the counter electrode layer. An example of a preferable support substrate for the counter electrode is glass or plastic, and the above-described conductive agent is applied or vapor-deposited on the glass or plastic. The thickness of the counter electrode conductive layer is not particularly limited, but is preferably 2 nm to 10 μm. The lower the surface resistance of the counter electrode layer, the better. The range of the surface resistance is preferably 700Ω / □ or less, more preferably 30Ω / □ or less.

  Since light may be irradiated from one or both of the conductive support and the counter electrode, in order for light to reach the photosensitive layer, at least one of the conductive support and the counter electrode may be substantially transparent. . From the viewpoint of improving the power generation efficiency, it is preferable to make the conductive support transparent so that light is incident from the conductive support side. In this case, the counter electrode preferably has a property of reflecting light. As such a counter electrode, glass or plastic deposited with a metal or conductive oxide, or a metal thin film can be used.

  The counter electrode may be formed by directly applying, plating, or vapor-depositing (PVD, CVD) a conductive material on the charge transport layer, or attaching the conductive layer side of the substrate having the conductive layer. As in the case of the conductive support, it is preferable to use a metal lead for the purpose of reducing the resistance of the counter electrode, particularly when the counter electrode is transparent. The preferable metal lead material and installation method, the reduction in the amount of incident light due to the metal lead installation, and the like are the same as those for the conductive support.

In order to prevent short circuit between the other layer counter electrode and the conductive support, it is preferable to coat a dense semiconductor thin film layer as an undercoat layer between the conductive support and the photosensitive layer in advance. This is particularly effective when an electron transport material or a hole transport material is used. Preferred as the undercoat layer is TiO ₂ , SnO ₂ , ZnO, or Nb ₂ O ₅ , and more preferably TiO ₂ . A functional layer such as a protective layer or an antireflection layer may be provided on the outer surface of one or both of the conductive support and the counter electrode acting as an electrode, between the conductive layer and the substrate, or in the middle of the substrate. For forming these functional layers, a coating method, a vapor deposition method, a bonding method, or the like can be used depending on the material. The internal structure of the photoelectric conversion element can have various forms according to the purpose. However, if divided roughly into two, a structure that allows light to enter from both sides and a structure that allows only one side are possible.

  The external circuit itself connected to the conductive support and the counter electrode via a lead may be a known one. When the photoelectric conversion element of the present invention is applied to a photoelectric conversion element, the structure inside the cell is basically the same as the structure of the photoelectric conversion element described above. The dye-sensitized photoelectric conversion element of the present invention can basically have the same module structure as a conventional photoelectric conversion element module. The photoelectric conversion element module generally has a structure in which a cell is formed on a support substrate such as metal or ceramic, the cell is covered with a filling resin or protective glass, and light is taken in from the opposite side of the support substrate. A transparent material such as tempered glass can be used for the support substrate, and a cell can be formed thereon so that light is taken in from the transparent support substrate side. For example, a substrate-integrated module structure used in an amorphous silicon solar cell or the like is known, and the module structure of the dye-sensitized photoelectric conversion element of the present invention can be appropriately selected depending on the purpose of use, use place, and environment. .

  Hereinafter, the present invention will be specifically described by way of examples.

Example Preparation of titanium dioxide dispersion: Titanium oxide dispersion with 100% anatase type fine particles, pH = 0.9, 0.20 g of PEG (polyethylene glycol) with a molecular weight of 20,000 was added to 10 g, and dissolved sufficiently. Dispersed to obtain a dispersion.

(Preparation of TiO ₂ electrode adsorbed with dye)
Comparative conductive layer a: A titanium dioxide layer (thickness 80 nm) was formed on the conductive surface side of conductive PEN (area resistance 10Ω / □, 25 mm × 25 mm) coated with tin oxide doped with fluorine. Adhesive tape was applied to a part of this substrate (3 mm from the peripheral edge) as a spacer, and the above-mentioned titanium dioxide dispersion was applied thereon using a Teflon (R) rod. After application, the adhesive tape was peeled off and air-dried at room temperature for 30 minutes. Next, this coated PEN was put in a dry box and heated in air at 180 ° C. for 2 minutes. After taking out PEN and cooling to room temperature, it was added to a dehydrated ethanol solution (3 × 10 ⁻⁴ mol / L) of a gallium complex of an unsubstituted phthalocyanine dye of Example 1 of JP-A-2003-152208 as a comparative dye at 60 ° C. It was immersed for 2 hours and adsorbed onto titanium dioxide on PET. The dye-adsorbed electrode is washed with dehydrated acetonitrile, then air-dried, cut into a 25 mm × 25 mm square, the undercoat layer and the semiconductor layer are removed leaving the central portion 10 mm × 10 mm (light receiving portion), and the electrode a is formed. Obtained. The coating amount of the photosensitive layer (titanium dioxide layer adsorbed with the dye) thus obtained was about 5.0 g / m ² .

  Conductive layer of the present invention: Prepared in the same manner as the comparative conductive layer, but here, the dye of the present invention shown in the specific examples was used. The composition of titanium dioxide is shown in Table 1. As shown in Table 1, conductive layers doped with fluorine ions, indium, antimony, and phosphorus were prepared as tin oxide doping materials.

  Formation of hole transport layer: The hole transport layer was prepared by the following coating process.

  Coating process: 1 mm width around the exposed portion of the conductive layer surface and the light receiving portion was protected and placed on a hot plate heated to 100 ° C. for 2 minutes. Dissolve the molten salt in an acetonitrile solution (3.2% by mass of the imidazolium salt described in Table 1), slowly add 0.2 ml to the conductive layer while volatilizing acetonitrile over about 10 minutes, and then add 1 g of iodine. A hole transport layer was formed by leaving on a hot plate for 2 minutes. It was confirmed from the cross-sectional SEM that the hole transport layer substantially penetrated into the porous film formed of the semiconductor nanoparticles of the conductive layer.

  Preparation of hole transport layer having separator layer: The same kind and the same amount of molten salt as above, after laminating a polyethylene film having a thickness of 12 μm with pores of 10 nm on the prepared hole transport layer. Was dissolved in an acetonitrile solution and 0.2 ml was added to the conductive layer while volatilizing acetonitrile for about 10 minutes. After coating, the solution was left on a hot plate for 2 minutes to form a hole transport layer having a separator layer. .

  Production of photoelectric conversion element: Comparative conductive layer a in which the charge transport layer (hole transport layer) is formed as described above, and each of the conductive layers of the present invention, and aluminum deposition PEN of the same size (thickness of the aluminum layer) = 10 nm, PEN film thickness = 200 μm). (A combination of an electrode and a hole transport layer is as shown in Table 1.) A stretched film (25 μm thickness) of polyvinylidene chloride was sandwiched between the overlapping portions other than the light receiving portion, and heated at 125 ° C. for 30 seconds. Furthermore, the overlapping edge portion was sealed using an epoxy resin sealant.

Measurement of photoelectric conversion efficiency: Simulated sunlight was generated by passing light from a 600 W xenon lamp (manufactured by Toshiba) through a spectral filter. The intensity of this light was 100 mW / cm ² . Simulated sunlight was irradiated, and electricity generated between the conductive glass and the counter electrode layer of the optical element was measured with a current-voltage measuring device. The short circuit current is listed in Table 1. Further, the photoelectric conversion element was shielded from light, left at room temperature (25 ± 5 ° C.) and in the atmosphere for 24 hours, and then measured in the same manner. The short-circuit current after aging is shown in Table 1. In the table, “no aging” means a state in which the photoelectric conversion element is not aged after being manufactured.

  Measurement of visible light transmittance: The integral transmittance from 400 nm to 700 nm was measured.

  From Table 1, it can be seen that the photoelectric conversion element of the present invention using the infrared dye of the present invention and the hole transporting material has a great advantage in the short-circuit current after the lapse of time as compared with the comparative example. It can be seen that the insertion of the separator increases the short-circuit current. Further, the visible light transmittance is 80% or more, and the transparency is high.

Claims (4)

A photoelectric conversion element having a conductive layer, a semiconductor nanoparticle layer sensitized with a dye, a charge transport layer, and a counter electrode, wherein the dye is represented by the following general formula (1).

(In the formula, Z ₁ and Z ₂ represent heteroatoms, and R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , Y ₁ , Y ₂ , Y ₃ , Y ₄ , Y ₅ and Y ₆ are each hydrogen. Represents an atom or a substituent, X represents a counter ion necessary for neutralizing the electric charge, n represents 0 or 1, and is 0 in the case of an inner salt.) The photoelectric conversion element according to claim 1, wherein a porous isolation layer is provided in the charge transport layer, and the hole transport material is a non-volatile compound. The photoelectric conversion element according to claim 1, wherein the semiconductor nanoparticle layer is anatase-type titanium oxide. The photoelectric conversion element according to claim 1, wherein the conductive layer is mainly composed of tin oxide doped with a trivalent or pentavalent metal atom.