JP4804050B2 - Photoelectric conversion element - Google Patents

Description

  The present invention relates to a photoelectric conversion element.

  The dye-sensitized solar cell element announced by Gretzell et al. In 1991 is a wet solar cell using a titanium oxide porous thin film spectrally sensitized by a ruthenium complex as a working electrode, and can obtain performance equivalent to that of a silicon solar cell. Has been reported (see Non-Patent Document 1). Since this method can use an inexpensive oxide semiconductor such as titania without purifying it with high purity, it can provide an inexpensive dye-sensitized solar cell element, and since the absorption of the dye is broad, it is visible. It has the advantage of being able to convert light in almost all wavelength regions of light into electricity, and has attracted attention.

  The titania porous thin film is generally obtained by applying a high-viscosity dispersion containing titania fine particles on an electrode and baking it at a high temperature. In this conventional method, since baking is performed at a high temperature of 400 ° C. to 600 ° C., the type of support is limited, and formation on a plastic substrate is difficult. Therefore, titania fine particles are deposited on the conductive layer by electrophoresis. A method has been proposed (Patent Document 1). However, in this method, since the treatment is performed at a low temperature, there is a problem that the adhesion between the titania fine particles becomes insufficient, and carriers (electrons) generated upon photoexcitation are easily deactivated at the interface between the particles. In addition, since titania fine particles have a small specific surface area, if the amount of fine particles is increased in order to increase the specific surface area, there is a problem that the uniformity of the formed film is deteriorated and the film is easily peeled off.

  Thus, a method of forming a semiconductor layer by electrophoresis using titania nanotubes having a specific surface area larger than that of titania fine particles has been proposed (Patent Documents 2 and 3). In this method, since the longitudinal direction of the titania nanotube adheres substantially perpendicularly to the conductive layer, there is an advantage that electrons flow smoothly because the electron conduction path is in the longitudinal direction of the tube. However, since the tube used is a conventional tube having a length of about 100 nm to 500 nm, there are many interfaces between the individual tubes, and there is a problem that the electron movement is hindered by them. Furthermore, a thick film is desired to increase the specific surface area. However, since nanotube particles are laminated, there is a problem that the uniformity of the film is deteriorated and the film is easily peeled off.

JP 2002-100416 A JP 2004-31354 A JP 2004-31355 A B. O'Regan, M. Gratzel, "Nature" (UK), 1991, 353, p. 737

  As described above, in the photoelectric conversion element, it is required to form a semiconductor layer having excellent electron conductivity and a uniform film.

  The present invention has been made in view of such a situation, and a tube-shaped titania with a specific surface area of 1 μm or more is specified as a specific surface area of each particle being large and overwhelmingly longer than the conventional one. The above-mentioned problem can be solved by manufacturing by a method and attaching this onto a conductive layer by electrophoresis.

  That is, the present invention provides a photoelectric conversion element comprising at least a conductive substrate, a semiconductor layer, a charge transport layer, and a counter electrode, wherein the semiconductor layer contains titanium or titanium in an electrolyte solution containing ions containing halogen atoms. Formed by depositing nanotube-shaped titania with a longitudinal length of 1 μm or more produced by electrolytic oxidation of the main component alloy on the conductive layer of the conductive substrate by electrophoresis It is related with the photoelectric conversion element characterized by being.

The present invention also relates to the photoelectric conversion element as described above, wherein the nanotube has a specific surface area of 50 m ² / g or more.
The present invention also relates to the above-described photoelectric conversion element, wherein the nanotube has an outer diameter of 5 to 50 nm and a thickness of 2 to 20 nm.
The present invention also relates to the photoelectric conversion element as described above, wherein the electrophoresis is performed using a titania dispersion containing no electrolyte.
The present invention also relates to the photoelectric conversion element described above, wherein the titania dispersion is a mixed dispersion of titania having a nanotube shape and titania having a nanoparticle shape.
The present invention also relates to the photoelectric conversion element as described above, wherein the electrophoresis is performed in a direct current electric field, and the electric field strength is 50 to 300 V / cm.
Moreover, this invention relates to the said photoelectric conversion element characterized by heat-processing the formed semiconductor layer at 100-600 degreeC.
The present invention also relates to the photoelectric conversion element as described above, wherein the semiconductor layer is sensitized with a dye.
Furthermore, this invention relates to the photovoltaic cell using the said photoelectric conversion element.

The present invention is described in detail below.
The photoelectric conversion element of the present invention includes at least a conductive substrate, a semiconductor layer, a charge transport layer, and a counter electrode.
The conductive substrate usually has an electrode layer on the substrate. The substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, metal, colorless or colored glass, meshed glass, glass block, etc. are used. Colorless or colored resin may be used. Examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. In addition, the board | substrate in this invention has a smooth surface at normal temperature, The surface may be a plane or a curved surface, and may deform | transform by stress.

The material of the conductive film that functions as an electrode is not particularly limited, and examples thereof include a metal such as gold, silver, chromium, copper, tungsten, and titanium, a metal thin film, and a conductive film made of a metal oxide. Examples of the metal oxide include Indium Tin Oxide (ITO (In ₂ O ₃ : Sn)) obtained by doping a metal oxide such as tin and zinc with a small amount of other metal elements, Fluorine doped Tin Oxide (FTO (SnO ₂ )). : F)), Aluminum doped Zinc Oxide (AZO (ZnO: Al)) and the like are preferably used.
The film thickness of the conductive film is usually 100 to 10,000 μm, preferably 500 to 3000 μm. The surface resistance (resistivity) is appropriately selected, but is usually 0.5 to 500 Ω / sq, preferably 1 to 50 Ω / sq.

  The method for forming the conductive film is not particularly limited, and a known method can be appropriately employed depending on the type of metal or metal oxide used. Usually, a vacuum deposition method, an ion plating method, a CVD method, a sputtering method, or the like is used. In either case, it is desirable that the substrate temperature be formed within a range of 20 to 700 ° C.

The counter electrode (counter electrode) in the photoelectric conversion element of the present invention may have a single layer structure made of a conductive material, or may be composed of a conductive layer and a substrate. The substrate is not particularly limited, and the material, thickness, dimensions, shape, and the like can be appropriately selected according to the purpose. For example, metal, colorless or colored glass, meshed glass, glass block, etc. are used. Resin may be used. Examples of such resins include polyesters such as polyethylene terephthalate, polyamide, polysulfone, polyether sulfone, polyether ether ketone, polyphenylene sulfide, polycarbonate, polyimide, polymethyl methacrylate, polystyrene, cellulose triacetate, and polymethylpentene. Alternatively, the counter electrode may be formed by applying, plating, or vapor-depositing (PVD, CVD) a conductive material directly on the charge transport layer.
As the conductive material, metals such as platinum, gold, nickel, titanium, aluminum, copper, silver, and tungsten, and materials having a small specific resistance such as carbon materials and conductive organic substances are used.
A metal lead may be used for the purpose of reducing the resistance of the counter electrode. The metal lead is preferably made of a metal such as platinum, gold, nickel, titanium, aluminum, copper, silver or tungsten, and particularly preferably made of aluminum or silver.

  The semiconductor layer is produced by electro-oxidizing titanium or an alloy containing titanium as a main component in an electrolytic solution containing ions containing halogen atoms. It is formed by adhering onto the conductive film of the conductive substrate by electrophoresis.

  As titanium or an alloy containing titanium as a main component (hereinafter referred to as titanium alloy), pure industrial titanium whose material is adjusted with oxygen, iron, nitrogen, hydrogen, or the like, or a titanium alloy having a certain degree of press formability is used. JIS (Japanese Industrial Standards) 1 type, 2 types, 3 types, 4 types of various industrial pure titanium, nickel, ruthenium, tantalum, palladium, etc., alloys with improved corrosion resistance, aluminum, As an example, an alloy added with vanadium, molybdenum, tin, iron, chromium, niobium, or the like can be given. As the crystal type of titanium or titanium alloy, α-type, α + β-type, and β-type can be used regardless of single crystal or polycrystal. Regarding the shape, in addition to various shapes such as plate, rod, and mesh, titanium or titanium alloy itself is grown as a film on the surface of dissimilar conductive materials such as plate, rod, and mesh. Examples include, but are not limited to, a semiconductor having a shape such as a plate, a rod, or a mesh, or a surface in which an insulating material is grown with titanium or a titanium alloy as a film.

The electrolytic oxidation in the present invention is a technique in which titanium or a titanium alloy is used as an anode in an electrolyte solution, an arbitrary conductive material is used as a cathode, and a titanium oxide is formed on the anode surface by applying a voltage. The state in which titanium or a titanium alloy is an anode is only required once, and includes the case where the anode and the cathode are alternately performed.
In the electrolytic oxidation, the applied voltage is usually 5 to 200 V, preferably 10 to 150 V, more preferably 14 to 110 V, and the current density is 0.2 to 500 mA / cm ² , preferably 0.5 to 100 mA / cm ^2. In the range of 1 minute to 24 hours, preferably 5 minutes to 10 hours. During the electrolysis, it is also possible to change the applied voltage and current density. In this case, electrolysis is performed by applying a pulse having a frequency of 1 × 10 ⁻⁶ Hz to 1 × 10 ⁵ Hz.
Moreover, 0-50 degreeC is preferable and, as for the temperature of the electrolyte solution at the time of anodizing, More preferably, it is 0-40 degreeC.

The electrolyte solution used for the electrolytic oxidation needs a dissolving power capable of dissolving titanium or titanium alloy when anodic polarization of titanium or titanium alloy. It is essential that the electrolyte solution used in the present invention contains an ion containing a halogen atom. The ion containing a halogen atom here is an ion containing any one atom of fluorine, chlorine, bromine and iodine, specifically, fluoride ion, chloride ion, bromide ion, iodide ion. Perchlorate ion, chlorate ion, bromate ion, iodate ion, chlorite ion, bromite ion, hypochlorite ion, hypobromite ion, hypoiodite ion and the like. These ions may be used alone or as a mixture of two or more.
In the present invention, the halogen atom is particularly preferably a chlorine atom.

  The electrolyte solution containing these ions can be either aqueous or non-aqueous, but is preferably aqueous. Specifically, an aqueous solution of an acid or salt that forms ions containing a halogen atom is used. The concentration of the acid or salt is preferably 0.0001 to 10% by volume, more preferably 0.0005 to 5% by volume, and still more preferably 0.0005 to 1% by volume.

The electrolyte solution may contain an acidic compound or basic compound that is different from the acid or salt that forms ions containing halogen atoms. By containing such different kinds of acidic compounds and basic compounds, the reaction rate such as promoting or suppressing the anodic oxidation rate can be controlled.
Examples of such acidic compounds include sulfuric acid, nitric acid, acetic acid, hydrogen peroxide, oxalic acid, phosphoric acid, chromic acid, glycerophosphoric acid and the like in addition to the above-mentioned halide or acid of its oxidant ion. Is not to be done.
Such basic compounds include, but are not limited to, sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia and the like.
The concentration is preferably in the range of 0.001 to 1000, more preferably 0.01 to 50, and still more preferably 0.04 to 5 in terms of molar ratio to the halogen atom-containing ions.

The electrolyte solution may contain a water-soluble titanium compound. Water-soluble titanium compounds are generally hydrolyzed in an aqueous solution to produce titania. By containing this, titania is further produced by hydrolysis on the surface of titanium oxide produced by electrolytic oxidation. Thus, re-dissolution of the titanium oxide into the electrolyte solution can be prevented, and the structure can be strengthened.
Examples of such water-soluble titanium compounds include titanium alkoxides such as titanium isopropoxide, titanium trichloride, titanium tetrachloride, titanium fluoride, ammonium tetrafluorotitanate, titanium sulfate, and titanyl sulfate. Is not to be done. The concentration is preferably in the range of 0.001 to 1000, more preferably 0.01 to 50, and still more preferably 0.04 to 5 in terms of molar ratio to the halogen atom-containing ions.

The electrolyte solution may contain titania fine particles. By containing titania fine particles, the generated titanium oxide can be prevented from redissolving in the electrolyte solution, and the titanium oxide can be strengthened.
Such titania fine particles preferably have a particle size of 0.5 to 100 nm, more preferably 2 to 30 nm. Specific examples include those prepared from titanium ore by a liquid phase method and those synthesized by a vapor phase method, a sol-gel method, and a liquid phase growth method. Here, the gas phase method is a method for producing titania by baking hydrous titanium oxide obtained by heating and hydrolyzing titanium ore with a strong acid such as sulfuric acid at 800 ° C. to 850 ° C. The liquid phase method is a method for producing titania by bringing oxygen and hydrogen into contact with titanium chloride. In the sol-gel method, titanium alkoxide is hydrolyzed in an alcohol aqueous solution to form a sol, and further, a hydrolysis catalyst is added to the sol, left to gel, and the gelled product is baked to titania. It is a method of manufacturing. The liquid phase growth method is a method for obtaining titania by hydrolysis of titanium fluoride, ammonium tetrafluorotitanate, titanyl sulfate or the like.

By the above method, titanium metal or an alloy containing titanium as a main component can be anodized to obtain a nanotube-shaped titania having a longitudinal length of 1 μm or more, preferably 2 to 100 μm. The outer diameter of the nanotube-shaped titania is usually 5 to 50 nm, preferably 10 to 30 nm, and the wall thickness is usually 2 to 20 nm, preferably 3 to 10 nm. The specific surface area of the nanotube is 50 m ² / g or more, preferably 70 m ² / g or more.

  The nanotube-shaped titania obtained as described above can be crystallized into an arbitrary crystal type by performing post-treatment such as heat treatment, pressure treatment, electron beam irradiation, and light irradiation, if necessary. For example, in the case of heat treatment, crystallization is performed by performing treatment at a temperature of 100 ° C. to 1200 ° C., preferably 150 ° C. to 800 ° C., for 10 to 500 minutes, preferably 10 to 300 minutes.

In the present invention, the semiconductor layer is formed by depositing the nanotube-shaped titania on the conductive film of the conductive substrate by electrophoresis.
In the electrophoresis method, the conductive film of the conductive substrate and the electrodeposition counter electrode are opposed in parallel at regular intervals, and a dispersion liquid in which nanotube-shaped titania is dispersed in a solvent is injected into this gap, and direct current is applied between both electrodes. This is done by applying a voltage. The strength of the electric field is preferably 50 to 300 V / cm, more preferably 100 to 250 V / cm. Although the space | interval between both electrodes is not specifically limited, 0.1-2 mm is preferable, More preferably, it is 0.2-0.5 mm. The application time is usually about 1 to 10 minutes. The temperature is not particularly limited, and is usually 0 to 50 ° C, preferably 0 to 40 ° C.

  Examples of the solvent used to disperse titania include pure water, alcohol, acetonitrile, THF, hexane, chloroform, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butanol. Alcohol, acetic anhydride, tetrahydrofuran, propylene carbonate, nitromethane, acetonitrile, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, ethylene carbonate, dimethoxyethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxyethane, propiononitrile, glu Talonitrile, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide, dioxolane, sulfora , Trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyl dimethyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, Tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), triphenyl polyethylene glycol phosphate, polyethylene glycol, propylene carbonate, ethylene carbonate, dimethyl sulfoxide, dimethoxyethane, acetonitrile, γ-butyrolactone, sulfolane, dioxolane , Dimethylformamide, dimethoxyethane, tetrahydrofuran, adiponitrile, methoxyacetonitrile, methoxypropionitrile, dimethylacetamide, methylpyrrole Possible, dimethyl sulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, etc., or be used a mixed solvent thereof. The titania content in the dispersion is appropriately determined depending on the voltage condition and the like, but can be usually in the range of 0.01 to 0.1 g / mL. In addition, it is preferable that the titania dispersion does not contain an electrolyte because it becomes an obstacle to the formation of the semiconductor layer.

In the present invention, it is also preferable to use a dispersion obtained by mixing nanoparticle-shaped titania (titania fine particles having a particle diameter of 0.5 to 100 nm) with nanotube-shaped titania. By using in combination with the titania fine particles, the titania in the shape of nanotubes attached to the conductive film of the conductive substrate is reinforced by the titania fine particles, and the titania nanotube semiconductor layer is formed more firmly. The mixing ratio of the titania fine particles is preferably 1 to 50% by mass, more preferably 5 to 20% by mass based on the total amount of titania.
The thickness of the semiconductor layer formed by the electrophoresis method of the present invention is preferably 1 to 30 μm, more preferably 2 to 25 μm.

  The formed semiconductor layer is preferably subjected to heat treatment for the purpose of enhancing electronic contact between titanias and improving adhesion with the conductive substrate. As heat processing temperature, 100 to 600 degreeC is preferable, More preferably, it is 250 to 550 degreeC. Moreover, heat processing time can be normally performed in 10 minutes-10 hours.

In the photoelectric conversion element of the present invention, a semiconductor layer that is modified (adsorbed, contained, etc.) with a dye is used for the purpose of improving the light absorption efficiency of the semiconductor layer.
The dye is not particularly limited as long as it has absorption characteristics in the visible region and the near infrared region and improves (sensitizes) the light absorption efficiency of the semiconductor layer, but metal complex dyes, organic dyes, natural dyes, and semiconductors are not limited. preferable. In addition, in order to impart adsorptivity to the semiconductor layer, a functional group such as a carboxyl group, a hydroxyl group, a sulfonyl group, a phosphonyl group, a carboxylalkyl group, a hydroxyalkyl group, a sulfonylalkyl group, or a phosphonylalkyl group is included in the dye molecule. Those having a group are preferably used.

  As the metal complex dye, a complex of ruthenium, osmium, iron, cobalt, zinc, mercury (for example, mellicle chrome), metal phthalocyanine, chlorophyll, or the like can be used. Examples of organic dyes include, but are not limited to, cyanine dyes, hemicyanine dyes, merocyanine dyes, xanthene dyes, triphenylmethane dyes, metal-free phthalocyanine dyes, and the like. As a semiconductor that can be used as a dye, an amorphous semiconductor having a large i-type light absorption coefficient, a direct transition semiconductor, or a fine particle semiconductor that exhibits a quantum size effect and efficiently absorbs visible light is preferable. Usually, one of various semiconductors, metal complex dyes and organic dyes, or two or more kinds of dyes can be mixed in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency. Further, the dye to be mixed and its ratio can be selected so as to match the wavelength range and intensity distribution of the target light source.

  As a method for adsorbing the dye to the semiconductor layer, for example, a solution in which the dye is dissolved in a solvent is applied on the semiconductor layer by spray coating or spin coating and then dried. In this case, the substrate may be heated to an appropriate temperature. Alternatively, a method in which a semiconductor layer is immersed in a solution and adsorbed can be used. The immersion time is not particularly limited as long as the dye is sufficiently adsorbed, but is preferably 10 minutes to 30 hours, more preferably 1 to 20 hours. Moreover, you may heat a solvent and a board | substrate when immersing as needed. The concentration of the dye in the case of forming a solution is about 1 to 1000 mmol / L, preferably about 10 to 500 mmol / L.

  The solvent to be used is not particularly limited, but water and an organic solvent are preferably used. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and t-butanol, acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, and the like. Nitriles, aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene and p-xylene, aliphatic hydrocarbons such as pentane, hexane and heptane, alicyclic hydrocarbons such as cyclohexane, acetone and methyl ethyl ketone , Ketones such as diethyl ketone and 2-butanone, ethers such as diethyl ether and tetrahydrofuran, ethylene carbonate, propylene carbonate, nitromethane, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoa , Dimethoxyethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxyethane, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethyl sulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, Ethyldimethyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, tridecyl phosphate, tris phosphate (trifluoromethyl), tris phosphate (pentafluoro) Ethyl), triphenyl polyethylene glycol phosphate, polyethylene glycol and the like.

  In order to reduce the interaction such as aggregation between the dyes, a colorless compound having properties as a surfactant may be added to the dye adsorption liquid and co-adsorbed to the semiconductor layer. Examples of such colorless compounds include steroid compounds such as cholic acid having a carboxyl group or sulfo group, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, sulfonates, and the like.

  It is preferable to remove the unadsorbed dye by washing immediately after the adsorption step. Washing is preferably performed using acetonitrile, an alcohol solvent or the like in a wet washing tank.

  After adsorbing the dye, a semiconductor using an amine, a quaternary ammonium salt, a ureido compound having at least one ureido group, a silyl compound having at least one silyl group, an alkali metal salt, an alkaline earth metal salt, etc. The surface of the layer may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferred quaternary ammonium salts include tetrabutylammonium iodide, tetrahexylammonium iodide and the like. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.

  The charge transport layer contains a charge transport material having a function of replenishing electrons to the oxidant of the dye. The charge transport material used in the present invention may be a charge transport material related to ions or a charge transport material related to carrier movement in a solid. Examples of the charge transport material in which ions are involved include a solution in which a redox counter ion is dissolved, a gel electrolyte composition in which a polymer matrix gel is impregnated with a solution of a redox pair, a solid electrolyte composition, and the like. Examples of the charge transport material involved in the electron transport material include an electron transport material and a hole transport material. A plurality of these charge transport materials may be used in combination.

The electrolyte solution as a charge transport material involving ions is preferably composed of an electrolyte, a solvent, and an additive. Examples of the electrolyte used in the electrolytic solution, iodine and iodide (LiI, NaI, KI, CsI, metal iodide such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, quaternary ammonium such as imidazolium iodide A combination of bromine and bromide (metal bromide such as LiBr, NaBr, KBr, CsBr, CaBr, CaBr ₂ , quaternary ammonium compound bromide such as tetraalkylammonium bromide, pyridinium bromide, etc.) Examples thereof include metal complexes such as Russianate-ferricyanate and ferrocene-ferricinium ions, sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides, viologen dyes, and hydroquinone-quinone. Among them, an electrolyte in which I ₂ and a quaternary ammonium compound iodine salt such as LiI or pyridinium iodide, imidazolium iodide or the like are combined is preferable. The electrolyte may be used as a mixture.

  Any solvent can be used as long as it is generally used in electrochemical cells and batteries. Specifically, acetic anhydride, methanol, ethanol, tetrahydrofuran, propylene carbonate, nitromethane, acetonitrile, dimethylformamide, dimethyl sulfoxide, hexamethylphosphoamide, ethylene carbonate, dimethoxyethane, γ-butyrolactone, γ-valerolactone, sulfolane, dimethoxy Ethane, propiononitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, dimethylacetamide, methylpyrrolidinone, dimethyl sulfoxide, dioxolane, sulfolane, trimethyl phosphate, triethyl phosphate, tripropyl phosphate, ethyldimethyl phosphate, tributyl phosphate, phosphorus Tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, trinonyl phosphate, phosphoric acid Tridecyl, tris phosphate (trifluoromethyl), tris phosphate (pentafluoroethyl), triphenyl polyethylene glycol phosphate, polyethylene glycol, and the like can be used. In particular, propylene carbonate, ethylene carbonate, dimethyl sulfoxide, dimethoxyethane, acetonitrile, γ-butyrolactone, sulfolane, dioxolane, dimethylformamide, dimethoxyethane, tetrahydrofuran, adiponitrile, methoxyacetonitrile, methoxypropionitrile, dimethylacetamide, methylpyrrolidinone, dimethylsulfoxide , Dioxolane, sulfolane, trimethyl phosphate and triethyl phosphate are preferred. Also, room temperature molten salts can be used. Here, the room temperature molten salt is a salt composed of an ion pair that is melted at room temperature (that is, in a liquid state) and usually has a melting point of 20 ° C. or lower and is a liquid at a temperature exceeding 20 ° C. Is a salt. The solvent may be used alone or in combination of two or more.

  Further, it is preferable to add a basic compound such as 4-t-butylpyridine, 2-picoline, or 2,6-lutidine to the above-described molten salt electrolyte composition or electrolytic solution. A preferable concentration range when adding the basic compound to the electrolytic solution is 0.05 to 2 mol / L. When added to the molten salt electrolyte composition, the basic compound preferably has an ionic group. The blending ratio of the basic compound with respect to the entire molten salt electrolyte composition is preferably 1 to 40% by mass, more preferably 5 to 30% by mass.

The material that can be used as the polymer matrix is not particularly limited as long as the polymer matrix alone, or the solid state or gel state is formed by the addition of a plasticizer, the addition of a supporting electrolyte, or the addition of a plasticizer and a supporting electrolyte. Generally used so-called polymer compounds can be used.
Examples of the polymer compound exhibiting characteristics as the polymer matrix include hexafluoropropylene, tetrafluoroethylene, trifluoroethylene, ethylene, propylene, acrylonitrile, vinylidene chloride, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, methyl Examples thereof include polymer compounds obtained by polymerizing or copolymerizing monomers such as acrylate, ethyl acrylate, methyl methacrylate, styrene, and vinylidene fluoride. These polymer compounds may be used alone or in combination. Among these, a polyvinylidene fluoride polymer compound is particularly preferable.

  Further, instead of the ion conductive electrolyte, an organic solid hole transport material, an inorganic solid hole transport material, or a material in which both are combined can be used.

Examples of organic hole transport materials that can be preferably used include triphenylene derivatives, oligothiophene compounds, polypyrrole, polyacetylene and / or derivatives thereof, poly (p-phenylene) and / or derivatives thereof, poly (p-phenylene vinylene) and Examples thereof include conductive polymers such as / or derivatives thereof, polythienylene vinylene and / or derivatives thereof, polythiophene and / or derivatives thereof, polyaniline and / or derivatives thereof, polytoluidine and / or derivatives thereof. In order to control the dopant level, a compound containing a cation radical such as tris (4-bromophenyl) aminium hexachloroantimonate may be added to the hole transport material. In addition, a salt such as Li [(CF ₃ SO ₂ ) ₂ N] may be added in order to perform potential control (space charge layer compensation) on the surface of the metal oxide semiconductor.

A p-type inorganic compound semiconductor can be used as the inorganic hole transport material, and the band gap is preferably 2 eV or more, more preferably 2.5 eV or more. Further, the ionization potential of the p-type inorganic compound semiconductor needs to be smaller than the ionization potential of the dye adsorption electrode in order to reduce the holes of the dye. Although the preferable range of the ionization potential of the p-type inorganic compound semiconductor varies depending on the dye used, it is preferably 4.5 to 5.5 eV, more preferably 4.7 to 5.3 eV. Preferred p-type inorganic compound semiconductor is a compound semiconductor containing monovalent copper, _{examples, CuI, CuSCN, CuInSe 2,} Cu (In, Ga) Se 2, CuGaSe 2, Cu 2 O, CuS, CuGaS 2 CuInS ₂ , CuAlSe _{2 and the} like. Among these, CuI and CuSCN are preferable, and CuI is most preferable. Examples of other p-type inorganic compound semiconductors include GaP, NiO, CoO, FeO, Bi ₂ O ₃ , MoO ₂ , Cr ₂ O _{3 and the} like.

  The charge transport layer can be formed by one of two methods. The first method is a method in which a semiconductor layer and a counter electrode are bonded together, and a liquid charge transport layer is sandwiched between the gaps. The second method is a method in which a charge transport layer is provided directly on the semiconductor layer, and a counter electrode is provided thereafter.

In the case of the former method, when sandwiching the charge transport layer, a normal pressure process using capillary action by dipping or the like, or a vacuum 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 a wet charge transport layer is used in the latter method, a counter electrode is usually applied in an undried state to prevent liquid leakage at the edge. Moreover, when using a gel electrolyte composition, you may solidify by methods, such as superposition | polymerization, after apply | coating this with a wet method. Solidification may be performed before or after applying the counter electrode.

  When a solid electrolyte composition or a solid hole transport material is used, 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 a vacuum deposition method, a casting method, a coating method, a spin coating method, a dipping method, an electrolytic polymerization method, a photoelectrolytic polymerization method, or the like. The inorganic solid compound can be introduced into the electrode by a casting method, a coating method, a spin coating method, a dipping method, an electrolytic deposition method, an electroless plating method, or the like.

  As described above, a tube-shaped titania having a large specific surface area and a length of 1 μm or more is manufactured by a specific method, and this is attached to the conductive layer by electrophoresis, so that it has excellent electronic conductivity. A semiconductor layer having a uniform film can be formed.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Example 1]
<< Production of nanotube-shaped titania >>
Titania was obtained by electrolytic oxidation of 19.9 cm x 5 cm purity 99.9% titanium in a 0.3% perchloric acid aqueous solution at a constant voltage of 30V. Using SEM and TEM, it was confirmed that the tube structure was about 20 nm in diameter, about 5 nm in thickness, and about 10 μm in length. The specific surface area by nitrogen adsorption was 220 m ² / g.
<< Production of semiconductor layer (titania electrode) by electrophoresis >>
3 g of the filtered titania nanotube was dispersed in 100 ml of t-butanol using an ultrasonic homogenizer. Using this dispersion, F-SnO ₂ was used as an electrode, and electrophoresis was performed at a distance of 0.3 mm between electrodes and 200 V / cm to obtain a cloudy film on F-SnO ₂ . The film thickness was 11 μm.
<< Evaluation of photoelectric conversion characteristics >>
The obtained film was baked at 450 ° C. for 1 hour and immersed in a ruthenium dye (Rutenium 535-bisTBA: SOLARONIX) / ethanol solution (3.0 × 10 ⁻⁴ mol / L) for 15 hours to form a dye layer. The obtained substrate and the Pt surface of the glass with the Pt thin film are combined, and an acetonitrile solution containing 0.3 mol / L lithium iodide and 0.03 mol / L iodine is infiltrated by capillary action, and the periphery is an epoxy adhesive. Sealed with. A lead wire was connected to the conductive layer portion of the transparent conductive substrate and the counter electrode.
When the cell thus obtained was irradiated with pseudo-sunlight (1 kW / m ² ) and the current-voltage characteristics were measured, good photoelectric conversion characteristics (conversion efficiency 7.1%) were obtained.

[Example 2]
<< Fabrication of semiconductor layer by electrophoresis >>
3 g of the filtered titania nanotubes obtained in Example 1 and 0.5 g of titania nanoparticles (Nippon Aerosil Co., Ltd., P-25) were dispersed in 100 ml of t-butanol with an ultrasonic homogenizer. Using this dispersion, F-SnO ₂ was used as an electrode, and electrophoresis was performed at a distance of 0.3 mm between electrodes and 200 V / cm to obtain a cloudy film on F-SnO ₂ . The film thickness was 12 μm.
<< Evaluation of photoelectric conversion characteristics >>
The obtained film was baked at 450 ° C. for 1 hour and immersed in a ruthenium dye (Rutenium 535-bisTBA: SOLARONIX) / ethanol solution (3.0 × 10 ⁻⁴ mol / L) for 15 hours to form a dye layer. The obtained substrate and the Pt surface of the glass with the Pt thin film are combined, and an acetonitrile solution containing 0.3 mol / L lithium iodide and 0.03 mol / L iodine is infiltrated by capillary action, and the periphery is an epoxy adhesive. Sealed with. A lead wire was connected to the conductive layer portion of the transparent conductive substrate and the counter electrode.
When the cell thus obtained was irradiated with pseudo-sunlight (1 kW / m ² ) and the current-voltage characteristics were measured, good photoelectric conversion characteristics (conversion efficiency 7.3%) were obtained.

[Comparative Example 1]
<< Production of nanotube-shaped titania >>
According to JP-A-2002-241129, titania nanotubes were dissolved in an aqueous ethanol solution by dissolving titanium isopropoxide, and diluted hydrochloric acid was added as a hydrolysis catalyst and allowed to stand, followed by firing at 600 ° C. for 2 hours. The pulverized titania powder was dispersed in a 20 wt% aqueous sodium hydroxide solution, hydrothermally synthesized at 110 ° C. for 20 hours, and neutralized and washed with hydrochloric acid to obtain titania nanotubes. The obtained tube had a diameter of 8 nm and an average length of 150 nm, but many amorphous crystals other than the tube were also observed.
<< Fabrication of semiconductor layer by electrophoresis >>
3 g of the filtered titania nanotube was dispersed in 100 ml of t-butanol using an ultrasonic homogenizer. Electrophoresis was performed using F-SnO ₂ as an electrode and a distance between electrodes of 0.3 mm and 200 V / cm using this dispersion, but the film formed on F-SnO ₂ was brittle and after drying, F-SnO _{2 was used.} The film could not be obtained.

Claims (9)

  In a photoelectric conversion element including at least a conductive substrate, a semiconductor layer, a charge transport layer, and a counter electrode, the semiconductor layer is made of titanium or an alloy containing titanium as a main component in an electrolyte solution containing ions containing halogen atoms. It is formed by depositing a nanotube-shaped titania having a longitudinal length of 1 μm or more produced by electrolytic oxidation onto a conductive layer of the conductive substrate by electrophoresis. A photoelectric conversion element. The photoelectric conversion element according to claim 1, wherein the nanotube has a specific surface area of 50 m ² / g or more.   The photoelectric conversion element according to claim 1 or 2, wherein the nanotube has an outer diameter of 5 to 50 nm and a thickness of 2 to 20 nm.   The photoelectric conversion element according to claim 1, wherein the electrophoresis is performed using a titania dispersion liquid that does not contain an electrolyte.   The photoelectric conversion element according to claim 1, wherein the titania dispersion is a mixed dispersion of titania having a nanotube shape and titania having a nanoparticle shape.   The photoelectric conversion element according to claim 1, wherein the electrophoresis is performed with a direct current electric field, and the strength of the electric field is 50 to 300 V / cm.   The photoelectric conversion element according to any one of claims 1 to 6, wherein the formed semiconductor layer is heat-treated at 100 to 600 ° C.   The photoelectric conversion element according to claim 1, wherein the semiconductor layer is sensitized with a dye. The photovoltaic cell using the photoelectric conversion element in any one of Claims 1-8.