JP4247820B2 - Method for manufacturing photoelectric conversion element and photoelectric conversion element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to titanium oxide fine particles, a method for producing a photoelectric conversion element using the same, a photoelectric conversion element, and a photovoltaic cell, and in particular, a high-purity titanium oxide fine particle used for a photoelectric conversion element and a photoelectric conversion element using semiconductor fine particles sensitized with a dye. The present invention relates to a manufacturing method of the above, a photoelectric conversion element manufactured by the method, and a photovoltaic cell using the photoelectric conversion element.
[0002]
[Prior art]
Photoelectric conversion elements are used in various optical sensors, copiers, photovoltaic power generation devices and the like. Various systems such as those using metals, semiconductors, organic pigments and dyes, and combinations of these have been put to practical use as photoelectric conversion elements.
[0003]
For example, a photoelectric conversion element using semiconductor fine particles sensitized with a dye (hereinafter referred to as “dye-sensitized photoelectric conversion element”), and a material and a manufacturing technique for producing the photoelectric conversion element are disclosed (for example, patents). References 1-9.) The advantage of the dye-sensitized photoelectric conversion element is that an inexpensive oxide semiconductor such as titanium dioxide can be used without being purified with high purity, so that a relatively inexpensive photoelectric conversion element can be provided. However, such a photoelectric conversion element does not necessarily have a sufficiently high conversion efficiency, and further improvement in conversion efficiency has been desired.
[0004]
Titanium dioxide is not limited to the use for photoelectric conversion elements, and many studies have been made for the purpose of decomposing pollutants contained in the atmosphere, soil, rivers, etc. by its photocatalytic action. As a production method of these titanium oxides, a sol-gel method (for example, refer to Non-patent Documents 1 and 2), a gel-sol method (for example, refer to Non-patent Document 3), a chloride developed by Degussa, Inc. Known are a method for producing an oxide by high-temperature hydrolysis in an oxyhydrogen salt, a high-temperature hydrolysis method in an oxyhydrogen salt of a chloride, a sulfuric acid method or a chlorine method (for example, see Non-Patent Document 4), and the like. ing. In addition, a method of producing titanium oxide fine particles by a sol-gel method is well known (for example, see Non-Patent Documents 5 to 6). Furthermore, a simple production method based on alkaline conditions using titanium sulfate or titanium oxysulfate as a raw material and adding excess ammonia is also known (see, for example, Patent Document 10). However, there has been a demand for a method for producing titanium dioxide that is simpler, has a high anatase purity of titanium dioxide, and has high photoelectric conversion element performance and high photocatalytic activity.
[0005]
U.S. Pat.No. 4,927,721
[Patent Document 2]
US Pat. No. 4,684,537
[Patent Document 3]
US Patent No. 5084365
[Patent Document 4]
U.S. Pat.No. 5,350,644
[Patent Document 5]
US Pat. No. 5463057
[Patent Document 6]
U.S. Pat.No. 5,525,440
[Patent Document 7]
WO 98/50393 pamphlet
[Patent Document 8]
Japanese Patent Laid-Open No. 7-249790
[Patent Document 9]
Japanese National Patent Publication No. 10-504521
[Patent Document 10]
JP 2002-47012 A
[Non-Patent Document 1]
Sakuo Sakuo, "Science of Sol-Gel Method", Agne Jofusha, 1998
[Non-Patent Document 2]
"Thin-gel coating technology by sol-gel", Technical Information Association, 1995
[Non-Patent Document 3]
Sugimoto Tadao, "Synthesis and size control of monodisperse particles by new synthetic gel-sol method", Materia, 1996, 35, 9, p.1012-1018
[Non-Patent Document 4]
Manabu Kiyono, "Titanium oxide properties and applied technology", Gihodo Publishing, 1997
[Non-Patent Document 5]
Barbe, "Journal of the American Ceramic Society", 1997, 80, 12, p.3157-3171
[Non-Patent Document 6]
S.D.Burnside et al., “Chemistry of Materials”, 1998, Vol. 10, No. 9, p.2419-2425
[Problems to be solved by the invention]
An object of the present invention is to provide titanium oxide fine particles that can be preferably used for a photoelectric conversion element, a method for producing a dye-sensitized photoelectric conversion element exhibiting excellent conversion efficiency, a photoelectric conversion element produced by the method, and the photoelectric conversion element. It is to provide a used photovoltaic cell.
[0006]
[Means for Solving the Problems]
As a result of intensive studies in view of the above object, the present inventor has found that the object of the present invention can be achieved by the following constitution.
(1) In a method for producing a photoelectric conversion element having a layer of semiconductor fine particles adsorbed with at least one dye and a conductive support, the semiconductor fine particles are subjected to oxidation treatment before adsorbing the dye. A method for manufacturing the element.
(2) The method for manufacturing a photoelectric conversion element according to (1), wherein the oxidation treatment is at least one of hydrogen peroxide treatment, UV-ozone treatment, and oxygen plasma treatment.
(3) Production of the photoelectric conversion element according to (1) or (2), wherein the semiconductor fine particles are subjected to hydrogen peroxide treatment and then subjected to at least one of UV-ozone treatment and oxygen plasma treatment. Method.
(4) The method for producing a photoelectric conversion element according to any one of (1) to (3), wherein titanium oxide is used as the semiconductor fine particles.
(5) Using titanium sulfate or titanium oxysulfate as a raw material, among sulfate radicals contained in the raw material, 0.01-0.99 equivalents of sulfate radicals were neutralized with a base, and then prepared by a sol-gel method under acidic conditions Titanium oxide fine particles characterized by that.
(6) The titanium oxide fine particles according to (5), wherein the base that neutralizes the sulfate radical is ammonia water.
(7) The titanium oxide according to (5) or (6), wherein the content of elemental sulfur is 0.03 or less in terms of the intensity ratio of sulfur to titanium in fluorescent X-rays (S-Kα / Ti-Kα) Fine particles.
(8) The method for producing a photoelectric conversion element according to (4), wherein the titanium oxide fine particles according to any one of (5) to (7) are used as the semiconductor fine particles.
(9) A photoelectric conversion device produced by the method according to any one of (1) to (4) and (8).
(10) A photovoltaic cell using the photoelectric conversion element according to (9).
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The photoelectric conversion element of the present invention has a photosensitive layer on a conductive support, and the photosensitive layer is composed of semiconductor fine particles adsorbed with a dye. Hereinafter, the titanium oxide fine particles used as the semiconductor fine particles, the oxidation treatment of the semiconductor fine particles, the photoelectric conversion element, and the photovoltaic cell using the photoelectric conversion element will be described in detail.
[0008]
[I] Titanium oxide fine particles
The titanium oxide fine particles of the present invention are titanium dioxide fine particles obtained from titanium sulfate or titanium oxysulfate as a raw material by a sol-gel method. Titanium dioxide fine particles produced using titanium sulfate or titanium oxysulfate as a raw material have the advantage that crystal forms (rutile and brookite types) other than anatase are less likely to be produced than fine particles produced using chloride, alkoxide, etc. Have. Moreover, the commercially available chemical | medical agent can be used for the titanium sulfate or titanium oxysulfate which is a raw material, respectively easily. In the case of titanium sulfate, a 30% dilute sulfuric acid solution is particularly preferred.
[0009]
The titanium oxide fine particles of the present invention use titanium sulfate or titanium oxysulfate as a raw material, and 1 to 99% (preferably 50 to 95%, more preferably 80 to 90%) of sulfate radicals contained in the raw material. ) Sulfate radicals are neutralized with a base, and the particles are prepared under conditions of pH = less than 7 (preferably pH = 3 or less). As the base for neutralizing the sulfate radical, hydroxides or alkoxides of alkali metals and alkaline earth metals, ammonia, amines, other organic bases (for example, pyridines, anilines, etc.) and the like can be used. Of these, ammonia water is most preferably used.
[0010]
When the above titanium raw material and base are mixed, titanium hydroxide precipitates instantly with heat generation, but when heated to 70-100 ° C. and stirred for 20 minutes to 3 hours (preferably 40 minutes to 90 minutes), the average particle size A sol of 4 to 6 nm titanium dioxide can be obtained. The obtained sol is filtered while hot, and the filtrate is subjected to autoclaving at 150 to 280 ° C. (preferably 180 to 250 ° C.) for 6 to 50 hours (preferably 8 to 20 hours) to obtain an average particle size of 9 Titanium dioxide fine particles having a pure anatase crystal of ˜15 nm can be obtained. The titanium dioxide fine particles produced by such a method contain a small amount of sulfides and the like, but when subjected to the oxidation treatment described later, anatase-type fine particles having almost no impurities can be produced and used for photoelectric conversion elements. Titanium dioxide that is highly effective not only as a semiconductor but also as a photocatalyst material used for pollutant decomposition and the like can be obtained.
[0011]
Moreover, the titanium oxide fine particles of the present invention and the semiconductor fine particle film using the same contain impurities derived from the raw material sulfuric acid. The amount of sulfur-containing impurities can be evaluated by measuring X-ray fluorescence, and is usually the ratio of the intensity of sulfur Kα rays (S-Kα) to the intensity of titanium Kα rays (Ti-Kα). Can be evaluated. The amount of sulfur-containing impurities contained in the particles of the present invention is preferably 0.1 or less in terms of the intensity ratio of S-Kα / Ti-Kα. In addition, when used in a photoelectric conversion element, it is preferable that the amount of sulfur impurities contained in the titanium oxide fine particles and the titanium oxide fine particle film formed on the conductive support is smaller, with an intensity ratio of S-Kα / Ti-Kα. 1 × 10^-Four~ 0.03 is preferred, 1 × 10^-3More preferably, it is -0.01.
[0012]
[II] Oxidation treatment of semiconductor fine particles
In the method for producing a photoelectric conversion element of the present invention, the semiconductor fine particles are oxidized before adsorbing the dye. Thereby, the conversion efficiency of a photoelectric conversion element can be improved. The semiconductor fine particles used for the photoelectric conversion element are preferably titanium dioxide, and particularly titanium dioxide using the above-mentioned titanium sulfate or titanium oxysulfate as a raw material.
[0013]
(A) Semiconductor fine particles
Various semiconductors can be used as the semiconductor fine particles. In particular, titanium dioxide having a high effect of oxidation treatment described later is preferable. As a method for producing semiconductor fine particles, the gel-sol method described in Non-Patent Documents 1 to 3 and the like can be preferably applied. In addition, a method developed by Degussa in which an oxide is produced by high-temperature hydrolysis of a chloride in an oxyhydrogen salt can be preferably used.
[0014]
When the semiconductor fine particles are titanium oxide, the sol-gel method described in Non-Patent Documents 1 and 2, the gel-sol method described in Non-Patent Document 3, the high-temperature hydrolysis method in an oxyhydrogen salt of chloride, A method such as a sulfuric acid method or a chlorine method described in Patent Document 4 can be preferably used. Furthermore, as a sol-gel method, the method of obtaining the titanium dioxide fine particle of a nonpatent literature 5-6 can also be used preferably. The most suitable semiconductor fine particles for the method of the present invention are titanium dioxide fine particles obtained by the sol-gel method using the titanium sulfate or titanium oxysulfate described in [I] as a raw material.
[0015]
(B) Oxidation treatment of semiconductor fine particles
As the method for oxidizing semiconductor fine particles, wet oxidation treatment in a solution containing an oxidizing agent (for example, hydrogen peroxide treatment), dry oxidation treatment in an oxidizing gas atmosphere (for example, UV-ozone treatment, oxygen plasma) Treatment), electrolytic oxidation treatment and the like, and it is preferable to use at least one of hydrogen peroxide treatment, UV-ozone treatment and oxygen plasma treatment. The oxidation treatment is preferably performed after the semiconductor fine particle layer is formed on the conductive support. However, after the semiconductor fine particles are oxidized in advance, an oxidized semiconductor fine particle layer is formed on the conductive support. Also good. In the present invention, by applying several methods selected from the above-described processing methods successively in a preferable order, a further effect can be obtained. Hereinafter, preferable processing methods and processing procedures will be described.
[0016]
(1) Hydrogen peroxide treatment
The hydrogen peroxide treatment is performed by immersing semiconductor fine particles in hydrogen peroxide water. As treatment conditions, it is preferable that the concentration of the hydrogen peroxide solution is 1 to 50% by mass and the treatment temperature is 20 to 50 ° C. The concentration of the hydrogen peroxide solution is 5 to 35% by mass from the viewpoint of the effect and safety. The treatment temperature is more preferably 25 to 40 ° C. Shaking is preferably performed during immersion, and the treatment time varies depending on the concentration and temperature, but is generally 1 minute to 12 hours, preferably 5 minutes to 1 hour. Further, it is preferable that the semiconductor fine particles immersed in the hydrogen peroxide solution are lightly washed with water and then heated at 80 ° C. or higher to remove moisture as much as possible.
[0017]
(2) UV-ozone treatment
In UV-ozone treatment, semiconductor particles are irradiated with UV and oxidized with ozone at the same time. Usually, a conductive support on which semiconductor fine particles or a semiconductor fine particle layer is formed is placed in a sealed atmosphere having an oxygen concentration of 18 to 50% (preferably an oxygen concentration of 20 to 30%), and UV is applied to the semiconductor fine particle layer. UV irradiation and ozone are simultaneously applied to semiconductor fine particles while converting a part of oxygen into ozone by irradiation. The treatment temperature is preferably room temperature, and the treatment time is 1 minute to 2 hours, preferably 5 minutes to 30 minutes. In addition, it is preferable that the processed semiconductor fine particle layer is not particularly washed or heated, and is subjected to a dye adsorption step as soon as possible to form a photosensitive layer.
[0018]
(3) Oxygen plasma treatment
The oxygen plasma treatment is a low-temperature oxygen plasma treatment method in which semiconductor fine particles are allowed to act in oxygen plasma generated at room temperature and under reduced pressure, and a commercially available high-frequency plasma generator can be used. The degree of vacuum is 1 Torr or less, preferably 0.5 Torr or less. The RF intensity serving as an index of the intensity of the oxygen plasma is preferably 10 to 500 W, more preferably 20 to 100 W, and the treatment time varies depending on the RF intensity, but is generally 30 seconds to 1 hour, preferably 5 ~ 20 minutes. Further, it is preferable to heat at 200 ° C. or higher (preferably 450 ° C. or higher) after the oxygen plasma treatment.
[0019]
(4) Processing procedure
In the present invention, it is preferable to perform the above three processes continuously. First, when performing two processes continuously, a hydrogen peroxide process is performed first, and after washing and drying, a UV-ozone process or an oxygen plasma process is performed. By processing in such a procedure, a preferable effect can be obtained rather than processing each alone. Similarly, when the three treatments are performed, it is preferable to perform the hydrogen peroxide treatment first.
[0020]
[III] Photoelectric conversion element
The photoelectric conversion element of the present invention is produced by the above production method, and preferably comprises a conductive layer 10, a photosensitive layer 20, a charge transport layer 30, and a counter electrode conductive layer 40 laminated in this order as shown in FIG. The layer 20 is composed of semiconductor fine particles 21 sensitized with a dye 22 and a charge transport material 23 that has penetrated into the gaps between the semiconductor fine particles 21. The charge transport material 23 in the photosensitive layer 20 is usually the same material used for the charge transport layer 30. An undercoat layer 60 may be provided between the conductive layer 10 and the photosensitive layer 20. Further, a substrate 50 may be provided as a base for the conductive layer 10 and / or the counter electrode conductive layer 40 in order to impart strength to the photoelectric conversion element. In the present invention, the layer composed of the conductive layer 10 and the optionally provided substrate 50 is referred to as “conductive support”, and the layer composed of the counter electrode conductive layer 40 and the optionally provided substrate 50 is referred to as “counter electrode”. Note that the conductive layer 10, the counter electrode conductive layer 40, and the substrate 50 in FIG. 1 may be the transparent conductive layer 10a, the transparent counter electrode conductive layer 40a, and the transparent substrate 50a, respectively. Among such photoelectric conversion elements, a photoelectric cell is connected to an external load to perform electrical work (power generation), and an optical sensor is formed for the purpose of sensing optical information. Among photovoltaic cells, those in which the charge transport material is mainly composed of an ion transport material are called photoelectrochemical cells, and those whose main purpose is power generation by sunlight are called solar cells.
[0021]
In the photoelectric conversion element shown in FIG. 1, the light incident on the photosensitive layer 20 containing the semiconductor fine particles 21 sensitized by the dye 22 excites the dye 22 and the like, and the high energy electrons in the excited dye 22 and the like are the semiconductor fine particles. It is passed to the conduction band 21 and further diffuses to reach the conductive layer 10. At this time, the dye 22 is an oxidant. In the photovoltaic cell, the electrons in the conductive layer 10 return to the oxidized form of the dye 22 through the counter electrode conductive layer 40 and the charge transport layer 30 while working in the external circuit, and the dye 22 is regenerated. The photosensitive layer 20 functions as a negative electrode, and the counter electrode conductive layer 40 functions as a positive electrode. At each layer boundary (for example, the boundary between the conductive layer 10 and the photosensitive layer 20, the boundary between the photosensitive layer 20 and the charge transport layer 30, the boundary between the charge transport layer 30 and the counter conductive layer 40, etc.) They may be diffusively mixed with each other. Each layer and configuration will be described in detail below.
[0022]
(A) Conductive support
The conductive support is composed of (1) a single layer of a conductive layer or (2) two layers of a conductive layer and a substrate. In the case of (1), as the material of the conductive layer, the conductive layer can have sufficient strength and hermeticity and has conductivity (for example, platinum, gold, silver, copper, zinc, titanium, aluminum, A metal material such as an alloy containing these can be used. In the case of (2), a substrate having a conductive layer made of a conductive agent on the photosensitive layer side can be used as the conductive support. Examples of preferable conductive agents include metals (platinum, gold, silver, copper, aluminum, rhodium, indium, etc.), carbon and conductive metal oxides (indium-tin composite oxide, tin oxide doped with fluorine, etc.) Is mentioned. The thickness of the conductive layer is preferably about 0.02 to 10 μm.
[0023]
The lower the surface resistance of the conductive support, the better. This surface resistance is preferably 100Ω / □ or less, more preferably 40Ω / □ or less. The lower limit of the surface resistance is not particularly limited, but is usually about 0.1Ω / □.
[0024]
When irradiating light from the conductive support side, the conductive support is preferably substantially transparent. Substantially transparent means that the light transmittance is 10% or more. The light transmittance of the conductive support is preferably 50% or more, particularly preferably 70% or more.
[0025]
As the transparent conductive support, one formed by applying a transparent conductive layer made of a conductive metal oxide on the surface of a transparent substrate made of glass, plastic, or the like by vapor deposition or the like can be preferably used. Examples of a preferable material for forming the transparent conductive layer include fluorine-doped tin dioxide. As the transparent substrate, a glass substrate made of soda lime float glass advantageous in terms of cost and strength, a transparent polymer film useful for obtaining a flexible photoelectric conversion element at low cost, and the like can be used. Examples of the material forming the transparent polymer film include tetraacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), syndiotactic polystyrene (SPS), polyphenylene sulfide (PPS), polycarbonate (PC), Examples include polyarylate (PAr), polysulfone (PSF), polyester sulfone (PES), polyetherimide (PEI), cyclic polyolefin, and brominated phenoxy resin. In order to ensure sufficient transparency, the amount of the conductive metal oxide applied is 1 m of glass or plastic substrate.²It is preferably 0.01 to 100 g per unit.
[0026]
For the purpose of reducing the resistance of the transparent conductive support, a metal lead can be used as a current collector. The metal lead is preferably made of a metal such as platinum, gold, nickel, titanium, aluminum, copper, or silver, and particularly preferably made of aluminum or silver. It is preferable that a metal lead is disposed on the transparent substrate by vapor deposition, sputtering, or the like, and a transparent conductive layer made of tin oxide doped with fluorine, ITO film, or the like is disposed thereon. It is also preferable that a metal lead is provided on the transparent conductive layer after the transparent conductive layer is provided on the transparent substrate. 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%.
[0027]
(B) Photosensitive layer
In the photosensitive layer, the semiconductor fine particles act as a photoconductor, absorb light and separate charges to generate electrons and holes. In the dye-sensitized semiconductor fine particles, light absorption and generation of electrons and holes thereby occur mainly in the dye, and the semiconductor fine particles play a role of receiving and transmitting these electrons or holes. The semiconductor used in the present invention is preferably an n-type semiconductor which gives an anode current by conducting electrons as carriers under photoexcitation.
[0028]
(1) Semiconductor
The semiconductors used in the present invention are simple semiconductors (silicon, germanium, etc.), III-V group compound semiconductors, metal chalcogenides (oxides, sulfides, selenides, etc.), compounds having a perovskite structure (strontium titanate, titanate) Calcium, sodium titanate, barium titanate, potassium niobate, etc.).
[0029]
Examples of metal chalcogenides include titanium, tin, zinc, iron, tungsten, zirconium, hafnium, strontium, indium, cerium, yttrium, lanthanum, vanadium, niobium or tantalum oxide, cadmium, zinc, lead, silver, antimony or Examples thereof include bismuth sulfide, cadmium or lead selenide, and cadmium telluride. Examples of other compound semiconductors include phosphides such as zinc, gallium, indium, and cadmium, gallium-arsenic or copper-indium selenides, and copper-indium sulfides.
[0030]
The semiconductor used in the present invention is preferably Si, TiO₂, SnO₂, Fe₂O_Three, WO_Three, ZnO, Nb₂O_Five, CdS, ZnS, PbS, Bi₂S_Three, CdSe, CdTe, GaP, InP, GaAs, CuInS₂Or CuInSe₂And more preferably TiO₂, ZnO, SnO₂, Fe₂O_Three, WO_Three, Nb₂O_Five, CdS, PbS, CdSe, InP, GaAs, CuInS₂Or CuInSe₂And combinations thereof, particularly preferably ZnO, SnO₂, WO_Three, TiO₂Or Nb₂O_FiveAnd most preferably TiO₂It is. TiO₂As the crystal form system, anatase type, rutile type, brookite type and the like are known. TiO used in the present invention₂May have any of these crystal forms.
[0031]
The semiconductor used in the present invention may be single crystal or polycrystal, but polycrystal is preferred and advantageous from the viewpoint of production cost, securing raw materials, energy payback time, etc. A porous membrane is particularly preferred. In addition, the semiconductor of the present invention may partially include an amorphous part.
[0032]
The particle size of the semiconductor fine particles is generally on the order of nm to μm, but the average particle size of the primary particles obtained from the diameter when the projected area is approximated to a circle is preferably 5 to 200 nm, more preferably 8 to 100 nm. It is. Moreover, the average particle diameter of the semiconductor fine particles (secondary particles) in the dispersion is preferably 0.01 to 100 μm.
[0033]
Two or more kinds of semiconductor fine particles having different particle size distributions may be mixed and used. In this case, the average particle size of small particles is preferably 5 to 50 nm, and the average size of large particles is preferably 100 to 600. nm. Small particles have the effect of increasing the surface area on which the dye is adsorbed, and large particles have the effect of improving the light capture rate by scattering incident light. The mixing ratio (mass ratio) is preferably 50 to 99% for small particles and 1 to 50% for large particles, more preferably 70 to 95% for small particles and 5 to 30% for large particles.
[0034]
(2) Semiconductor fine particle layer
When forming a semiconductor fine particle layer composed of the above-mentioned semiconductor fine particles on a conductive support, it is common to use a method in which a dispersion or colloid solution containing semiconductor fine particles is applied on the conductive support. Considering mass production of photoelectric conversion elements, physical properties of a dispersion or colloidal solution containing semiconductor fine particles, flexibility of a conductive support, etc., it is relatively desirable to use a wet film forming method. As a wet film forming method, a coating method and a printing method are typical.
[0035]
Examples of methods for preparing a dispersion of semiconductor fine particles include a method of using the dispersion or colloidal solution prepared by the sol-gel method as described above, a method of grinding with a mortar, and a method of dispersing while grinding using a mill. Etc.
[0036]
The dispersion medium used for the dispersion of semiconductor fine particles may be water or various organic solvents (methanol, ethanol, isopropyl alcohol, dichloromethane, acetone, acetonitrile, ethyl acetate, etc.). When dispersing, if necessary, a polymer such as polyethylene glycol, a surfactant, an acid, a chelating agent, or the like may be used as a dispersion aid. By changing the molecular weight of polyethylene glycol, the viscosity of the dispersion can be adjusted and a semiconductor fine particle layer that is difficult to peel off can be formed. Therefore, it is preferable to add polyethylene glycol.
[0037]
Examples of preferable coating methods include the roller method and dip method as application systems, the air knife method and blade method as metering systems, and Japanese Patent Publication No. 58-4589 as the application and metering can be made the same part. Examples thereof include the disclosed wire bar method, the slide hopper method, the extrusion method, the curtain method and the like described in US Pat. Nos. 2,681,294, 2,714,419, 2,767,911, and the like. Moreover, a spin method and a spray method are also preferable as a general purpose machine. As the wet printing method, intaglio, rubber plate, screen printing and the like are preferred, including the three major printing methods of letterpress, offset and gravure. A film forming method may be selected from these according to the liquid viscosity and the wet thickness.
[0038]
The viscosity of the dispersion of semiconductor fine particles greatly depends on the type and dispersibility of the semiconductor fine particles, the type of solvent used, and additives such as surfactants and binders. When the dispersion has a high viscosity (for example, 0.01 to 500 Poise), it is preferable to use an extrusion method, a casting method, or a screen printing method. When the viscosity is low (for example, 0.1 Poise or less), it is preferable to use a slide hopper method, a wire bar method, or a spin method in order to form a uniform film. When the coating amount is large to some extent, it is possible to apply the extrusion method even if the viscosity is low. Thus, a film forming method may be appropriately selected according to the viscosity of the dispersion, the coating amount, the support, the coating speed, and the like.
[0039]
The semiconductor fine particle layer is not limited to a single layer, and a multilayer coating of semiconductor fine particle dispersions having different particle diameters or a multilayer coating containing different types of semiconductor fine particles (or different binders, additives, etc.) You can also Multi-layer coating is also effective when the film thickness is insufficient with a single coating. The extrusion method and slide hopper method are suitable for multilayer coating. In the case of applying multiple layers, the multiple layers may be applied at the same time, or may be successively applied several times to several dozen times. A screen printing method can also be preferably used for successive overcoating.
[0040]
In general, as the semiconductor fine particle layer thickness (same as the photosensitive layer thickness) increases, the amount of supported dye increases per unit projected area and thus the light capture rate increases. Loss due to coupling also increases. Therefore, the preferred thickness of the semiconductor fine particle layer is 0.1 to 100 μm. When using the photoelectric conversion element of this invention for a solar cell, the thickness of a semiconductor fine particle layer becomes like this. Preferably it is 1-30 micrometers, More preferably, it is 2-25 micrometers. Conductive support 1m²The coating amount of the semiconductor fine particles is preferably 0.5 to 400 g, more preferably 5 to 100 g.
[0041]
After coating the semiconductor fine particles on the conductive support, it is preferable to heat-treat the semiconductor fine particles to bring them into electronic contact and improve the coating strength and the adhesion to the conductive support. The heating temperature in the heat treatment is preferably 40 to 700 ° C, more preferably 100 to 600 ° C. The heating time is about 10 minutes to 10 hours. When using a substrate 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 substrate. Also from the viewpoint of cost, it is preferable to perform the heat treatment at the lowest possible temperature. When the heat treatment is performed in the presence of small semiconductor fine particles of 5 nm or less, mineral acid, or the like, the heating temperature can be lowered.
[0042]
A pressure treatment may be performed instead of the heat treatment. The pressure treatment method is written by Lindstrom et al., “Journal of photochemistry and photobiology”, 2001 (Elsevier), 145, p.107-112. Are described in detail. When the pressure treatment is performed, a binder such as a polymer is not used in the semiconductor fine particle coating solution.
[0043]
After the heat treatment or pressure treatment, for example, a chemical plating treatment using a titanium tetrachloride aqueous solution or an electrochemical plating treatment using a titanium trichloride aqueous solution as described in US Pat. No. 5,844,365 is performed. May be.
[0044]
The semiconductor fine particle layer preferably has a large surface area so that a large amount of dye can be adsorbed. The surface area of the semiconductor fine particle layer applied on the conductive support is preferably 10 times or more, more preferably 100 times or more the projected area. The upper limit is not particularly limited, but is usually about 1000 times.
[0045]
(3) Processing
In the present invention, the semiconductor fine particles used for the photosensitive layer may be treated with a solution of a metal compound. As the metal compound, for example, a metal alkoxide or halide selected from the group consisting of scandium, yttrium, lanthanoid, zirconium, hafnium, niobium, tantalum, gallium, indium, germanium, and tin can be used. The metal compound solution (treatment liquid) is usually an aqueous solution or an alcohol solution. Note that “treatment” means an operation of bringing the semiconductor fine particles into contact with the treatment liquid for a certain period of time before adsorbing the pigment to the semiconductor fine particles. The metal compound may or may not be adsorbed on the semiconductor fine particles after contact. The treatment is preferably performed after the semiconductor fine particle layer is formed.
[0046]
As a specific method for the treatment, a method of immersing semiconductor fine particles in the treatment liquid (immersion method) is a preferred example. Moreover, the method (spray method) which sprays a process liquid in a spray form for a fixed time is also applicable. The temperature of the treatment liquid (immersion temperature) when performing the immersion method is not particularly limited, but is typically -10 to 70 ° C, preferably 0 to 40 ° C. The treatment time is also not particularly limited, and is typically 1 minute to 24 hours, preferably 30 minutes to 15 hours. After the immersion, the semiconductor fine particles may be washed with a solvent such as distilled water. Moreover, you may bake in order to strengthen the coupling | bonding of the substance adhering to semiconductor fine particle by the immersion process. The firing conditions may be set similarly to the above-described heat treatment conditions.
[0047]
(4) Dye
The sensitizing dye used in the photosensitive layer is not particularly limited as long as it has absorption characteristics in the visible range and near-infrared range and can sensitize a semiconductor. However, a metal complex dye, a methine dye, a porphyrin dye, and a phthalocyanine dye Can be preferably used, and among them, metal complex dyes are particularly preferable. Phthalocyanines, naphthalocyanines, metal phthalocyanines, metal naphthalocyanines, porphyrins such as tetraphenylporphyrin and tetraazaporphyrin, metal porphyrins, derivatives thereof, and the like can also be used. Dyes used for dye lasers can also be used in the present invention. Moreover, in order to make the wavelength range of photoelectric conversion as wide as possible and increase the conversion efficiency, two or more kinds of dyes can be used in combination. In this case, it is possible to select the dye to be used in combination and its ratio so as to match the wavelength range and intensity distribution of the target light source.
[0048]
The dye preferably has a suitable interlocking group having an adsorption ability to the surface of the semiconductor fine particles. Examples of preferred linking groups include -COOH group, -OH group, -SO₂H group, -P (O) (OH)₂Group and -OP (O) (OH)₂And chelating groups having π conductivity such as oximes, dioximes, hydroxyquinolines, salicylates and α-ketoenolates. -COOH group, -P (O) (OH)₂Group and -OP (O) (OH)₂The group is particularly preferred. These bonding groups may form a salt with an alkali metal or the like, or may form an internal salt. In the case of a polymethine dye, if the methine chain contains an acidic group as in the case where the methine chain forms a squarylium ring or a croconium ring, this part may be used as a linking group. Hereinafter, preferred sensitizing dyes used in the photosensitive layer will be specifically described.
[0049]
(a) Metal complex dye
The metal atom of the metal complex dye used in the present invention is preferably ruthenium Ru. Examples of ruthenium complex dyes include U.S. Pat.Nos. 4,927,721, 4,684,537, 5,844,365, 5,350,644, 5,630,57, 5,525,440. JP-A-7-249790, JP-T-10-504512, WO98 / 50393 pamphlet, JP-A-2000-26487, and the like. Specific examples of preferable metal complex dyes include those described in paragraph numbers 0051 to 0057 of JP-A-2001-320068. The most typical metal complex dyes include D-1 and D-2 below.
[0050]
[Chemical 1]
[0051]
(b) Methine dye
Preferred methine dyes are polymethine dyes such as cyanine dyes, merocyanine dyes and squarylium dyes. Examples of preferred polymethine dyes include JP-A Nos. 11-35836, 11-158395, 11-163378, 11-214730, 11-214731, and European Patent No. 892411. And dyes described in U.S. Pat. No. 911841. For the synthesis of these polymethine dyes, see FM Hamer “Heterocyclic Compounds-Cyanine Dyes and Related Compounds”, John Willie. John Wiley & Sons, New York, London, 1964, DM Sturmer, "Heterocyclic Compounds-Special Topics in Heterocyclic Chemistry" -Specialtopics in Heterocyclic Chemistry ”, John Wiley & Sons, New York, London, 1977, Chapter 18, Section 14, pp.82-515,“ Rods Chemistry of・ Rodd's Chemistry of Carbon Compounds ”, 2nd edition, D Elsevier Science Publishing Company Inc., New York, 1977, Volume IV, Part B, Chapter 15, p.369-422, British Patent 1,077,611, “ Ukrainskii Khimicheskii Zhurnal ”, Vol. 40, No. 3, p.253-258,“ Dyes and Pigments ”, Vol. 21, p.227-234, these references, etc. ing.
[0052]
(5) Dye adsorption on semiconductor fine particles
When adsorbing the dye to the semiconductor fine particles, a method of immersing a conductive support having a well-dried semiconductor fine particle layer in a dye solution or a method of applying a dye solution to the semiconductor fine particle layer can be used. . In the case of the former method, a dipping method, a dip method, a roller method, an air knife method, etc. can be used. When the immersion method is used, 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. In the case of the latter method, a wire bar method, a slide hopper method, an extrusion method, a curtain method, a spin method, a spray method, or the like can be used. In addition, a dye can be applied in an image form by an inkjet method or the like, and the image itself can be used as a photoelectric conversion element.
[0053]
Solvents used in the dye solution (adsorption solution) are preferably alcohols (methanol, ethanol, t-butyl alcohol, benzyl alcohol, etc.), nitriles (acetonitrile, propionitrile, 3-methoxypropionitrile, etc.), nitromethane , Halogenated hydrocarbons (dichloromethane, dichloroethane, chloroform, chlorobenzene, etc.), ethers (diethyl ether, tetrahydrofuran, etc.), dimethyl sulfoxide, amides (N, N-dimethylformamide, N, N-dimethylacetamide, etc.), N-methylpyrrolidone, 1,3-dimethylimidazolidinone, 3-methyloxazolidinone, esters (ethyl acetate, butyl acetate, etc.), carbonates (diethyl carbonate, ethylene carbonate, propylene carbonate, etc.), ketones (acetone, 2-butanone, cyclohexanone Etc.), hydrocarbons (hexane, petroleum ether, benzene, toluene, etc.) or a mixed solvent thereof.
[0054]
The amount of dye adsorbed is the unit area of the semiconductor fine particle layer (1 m²) Is preferably 0.01 to 100 mmol. 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. By using such an amount of adsorbed dye, the effect of sensitizing the semiconductor fine particles can be sufficiently obtained. If the amount of dye adsorbed is too small, the sensitizing effect will be insufficient, and if the amount of dye adsorbed is too large, the dye not attached to the semiconductor will float and the sensitizing effect will be reduced. In order to increase the adsorption amount of the dye, it is preferable to heat-treat the semiconductor fine particles before the adsorption. In order to avoid water adsorbing on the surface of the semiconductor fine particles, it is preferable to quickly adsorb the dye when the temperature of the semiconductor fine particle layer is between 60 to 150 ° C. without returning to room temperature after the heat treatment.
[0055]
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 adsorbing liquid and co-adsorbed on the semiconductor fine particles. Examples of such colorless compounds include steroid compounds having a carboxyl group or a sulfo group (cholic acid, deoxycholic acid, chenodeoxycholic acid, taurodeoxycholic acid, etc.), sulfonates as described below, and the like. .
[0056]
[Chemical formula 2]
[0057]
It is preferable to remove the unadsorbed dye by washing immediately after the adsorption step. Cleaning is preferably performed in a wet cleaning tank using an organic solvent such as acetonitrile or an alcohol solvent.
[0058]
After adsorbing the dye, the fine particles of the semiconductor particles are formed using amines, quaternary ammonium salts, ureido compounds having at least one ureido group, silyl compounds having at least one silyl group, alkali metal salts, alkaline earth metal salts, etc. The surface may be treated. Examples of preferred amines include pyridine, 4-t-butylpyridine, polyvinylpyridine and the like. Examples of preferable quaternary ammonium salts include tetrabutylammonium iodide and tetrahexylammonium iodide. These may be used by dissolving in an organic solvent, or may be used as they are in the case of a liquid.
[0059]
(C) Charge transport layer
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 (i) a charge transport material related to ions, or (ii) a charge transport material related to carrier movement in a solid. (i) Charge transport materials involving ions include molten salt electrolyte compositions containing redox counter ions, solutions in which redox pair ions are dissolved (electrolytic solutions), and redox couple solutions in polymer matrix gels. Examples of so-called gel electrolyte compositions and solid electrolyte compositions impregnated include (ii) charge transport materials that involve carrier movement in solids, such as electron transport materials and hole transport materials. A plurality of these charge transport materials may be used in combination. In the present invention, it is preferable to use a molten salt electrolyte composition or a gel electrolyte composition for the charge transport layer.
[0060]
(1) Molten salt electrolyte composition
The molten salt electrolyte composition includes a molten salt. The molten salt electrolyte composition is preferably liquid at room temperature. The molten salt as the main component is a liquid at room temperature or is an electrolyte having a low melting point, and general examples thereof include WO 95/18456, JP-A-8-259543, “Electrochemistry”. , 1997, Vol. 65, No. 11, p. 923, and the like, and pyridinium salts, imidazolium salts, triazolium salts, and the like. The melting point of the molten salt is preferably 50 ° C. or less, and particularly preferably 25 ° C. or less. Specific examples of the molten salt are described in detail in paragraph numbers 0066 to 0082 of JP-A-2001-320068.
[0061]
The molten salt may be used alone or in combination of two or more. Also, LiI, NaI, KI, LiBF_Four, CF_ThreeCOOLi, CF_ThreeAlkali metal salts such as COONa, LiSCN and NaSCN can also be used in combination. The addition amount of the alkali metal salt is preferably 2% by mass or less, more preferably 1% by mass or less, based on the entire composition. Moreover, it is preferable that 50 mol% or more of the anions contained in the molten salt electrolyte composition are iodide ions.
[0062]
Usually, the molten salt electrolyte composition contains iodine. The iodine content is preferably 0.1 to 20% by mass and more preferably 0.5 to 5% by mass with respect to the entire molten salt electrolyte composition.
[0063]
The molten salt electrolyte composition preferably has low volatility and preferably does not contain a solvent. Even when a solvent is added, the amount of the solvent added is preferably 30% by mass or less based on the entire molten salt electrolyte composition. The molten salt electrolyte composition may be used after gelation as described below.
[0064]
(2) Electrolyte
The electrolytic solution is preferably composed of an electrolyte, a solvent, and an additive. Examples of electrolytes used in the electrolyte include I₂And iodide (LiI, NaI, KI, CsI, CaI₂A combination of metal iodides such as tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide and other quaternary ammonium compound iodine salts), Br₂And bromide (LiBr, NaBr, KBr, CsBr, CaBr₂A combination of metal bromides such as tetraalkylammonium bromide, pyridinium bromide, etc., metal complexes such as ferrocyanate-ferricyanate and ferrocene-ferricinium ions, sodium polysulfide, alkyl Examples thereof include sulfur compounds such as thiol-alkyl disulfides, viologen dyes, hydroquinone-quinones, and the like. Above all, I₂An electrolyte in which LiI or a quaternary ammonium compound iodine salt such as pyridinium iodide or imidazolium iodide is combined is preferable. The electrolyte may be used as a mixture.
[0065]
The electrolyte concentration in the electrolytic solution is preferably 0.1 to 10M, more preferably 0.2 to 4M. Moreover, the preferable addition density | concentration of iodine when adding iodine to electrolyte solution is 0.01-0.5M.
[0066]
The solvent used in the electrolytic solution is preferably a compound that has low viscosity and improved ion mobility, or has a high dielectric constant and improved effective carrier concentration, and can exhibit 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 , Chain ethers such as polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether, alcohols such as methanol, ethanol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether and polypropylene glycol monoalkyl ether, ethylene Glycol, propylene glycol, polyethylene glycol, polypropylene glycol Lumpur, polyhydric alcohols such as glycerin, acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile, dimethyl sulfoxide, aprotic polar substances such as sulfolane, water and the like. These solvents can also be used as a mixture.
[0067]
Also, tert-butyl as described in “Journal of the American Ceramic Society”, 1997, Vol. 80, No. 12, p.3157-3171. It is preferable to add a basic compound such as pyridine, 2-picoline, or 2,6-lutidine to the aforementioned molten salt electrolyte composition or electrolytic solution. A preferable concentration range when adding the basic compound to the electrolytic solution is 0.05 to 2M. When added to the molten salt electrolyte composition, the basic compound preferably has an ionic group. The mass ratio of the basic compound to the entire molten salt electrolyte composition is preferably 1 to 40% by mass, more preferably 5 to 30% by mass.
[0068]
(3) Gel electrolyte composition
In the present invention, the molten salt electrolyte composition or the electrolytic solution is gelated (solidified) by a method such as addition of a polymer, addition of an oil gelling agent, polymerization including polyfunctional monomers, or a crosslinking reaction of the polymer. You can also. When gelation occurs due to polymer addition, the compounds described in “Polymer Electrolyte Reviews-1 and 2” (JR MacCallum and CA Vincent, ELSEVIER APPLIED SCIENCE) may be used. In particular, polyacrylonitrile and polyvinylidene fluoride can be preferably used. In the case of gelation by adding oil gelling agent, “Journal of the Chemical Society of Japan, Industrial Chemistry Sections”, 1943, 46, p.779, “Journal of the American Chemical”・ Journal of the American Chemical Society ”, 1989, Vol. 111, p.5542,“ Journal of the Chemical Society, Chemical Communications ”, 1993 Year, p. 390, “Angewandte Chemie International Edition in English”, 1996, Volume 35, p. 1949, “Chemistry Letters”, 1996, p. 885, and “Journal of the The compounds described in “Chemical Society, Chemical Communications”, 1997, p.545 can be used. It preferred to use a compound having a de structure. An example of gelling the electrolyte is described in JP-A-11-185863, and an example of gelling the molten salt electrolyte is also described in JP-A 2000-58140, which can also be applied to the present invention.
[0069]
Moreover, when making it gelatinize by the crosslinking reaction of a polymer, it is desirable to use together the polymer and crosslinking agent containing the reactive group which can be bridge | crosslinked. In this case, preferred crosslinkable reactive groups are amino groups and nitrogen-containing heterocycles (pyridine ring, imidazole ring, thiazole ring, oxazole ring, triazole ring, morpholine ring, piperidine ring, piperazine ring, etc.), and preferred bridges. The agent is a bifunctional or higher functional reagent capable of electrophilic reaction with nitrogen atom (halogenated alkyls, halogenated aralkyls, sulfonic acid esters, acid anhydrides, acid chlorides, isocyanate compounds, α, β Saturated sulfonyl compounds, α, β-unsaturated carbonyl compounds, α, β-unsaturated nitrile compounds, etc.). The crosslinking techniques described in JP-A-2000-17076 and 2000-86724 can also be applied.
[0070]
(4) Hole transport material
In the present invention, instead of an ion conductive electrolyte such as a molten salt, an organic solid hole transport material, an inorganic solid hole transport material, or a material in which both are combined can be used.
[0071]
(a) Organic hole transport material
Examples of organic hole transport materials that can be preferably used in the present invention include J. Hagen et al., “Synthetic Metal”, 1997, Vol. 89, p.215-220. “Nature”, 1998, Vol. 395, No. 8, Oct., p583-585, pamphlet of International Publication No. 97/10617, JP-A-59-194393, JP-A-5-234681, U.S. Pat.No. 4,923,774, JP-A-4-308688, U.S. Pat.No. 4,764,625, JP-A-3-269084, 4-129271, 4-175395, 4-264189 Gazette, 4-90851 gazette, 4-364153 gazette, 5-5-2473 gazette, 5-239455 gazette, 5-320634 gazette, 6-1972 gazette, 7-138562 gazette. Aromatic amines described in JP-A-11-252474, JP-A-11-144773, etc., triphenylene described in JP-A Nos. 11-149821, 11-148067, 11-176489, etc. Derivatives etc. It is. Also, “Advanced Materials”, 1997, Vol. 9, No. 7, p.557, “Angewandte Chemie International Edition in English”, 1995, Vol. 34, No. 3, p. 303-307, “Journal of the American Chemical Society”, 1998, Vol. 120, No. 4, p. 664-672, etc., Polypyrrole described in K. Murakoshi, et al., “Chemistry Letters”, 1997, p.471, “Handbook of Organic Conductive Moleculees and Polymers” by NALWA. Molecules and Polymers), 1,2,3,4, published by WILEY, polyacetylene and its derivatives, poly (p-phenylene) and its derivatives, poly (p-phenylenevinylene) and its derivatives, polythienylene Bini Emissions and its derivatives, polythiophene and its derivatives, polyaniline and derivatives thereof, conductive polymers such as poly-toluidine and derivatives thereof can also be preferably used.
[0072]
Tris (4-bromophenyl) aminium hexachloro to control dopant levels as described in “Nature”, 1998, Vol. 395, No. 8, Oct., p.583-585 A compound containing a cation radical such as antimonate may be added to the hole transport material. Li [(CF is also used to control the potential of the oxide semiconductor surface (space charge layer compensation)._ThreeSO₂)₂A salt such as N] may be added.
[0073]
(b) Inorganic hole transport material
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. In addition, 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 preferred range of the ionization potential of the p-type inorganic compound semiconductor varies depending on the dye used, it is generally preferably 4.5 to 5.5 eV, more preferably 4.7 to 5.3 eV. A preferred p-type inorganic compound semiconductor is a compound semiconductor containing monovalent copper, and examples thereof include CuI, CuSCN, and CuInSe.₂, Cu (In, Ga) Se₂, CuGaSe₂, Cu₂O, CuS, CuGaS₂, CuInS₂, CuAlSe₂Etc. 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, Bi₂O_Three, MoO₂, Cr₂O_ThreeEtc.
[0074]
(5) Formation of charge transport layer
The charge transport layer can be formed by one of two methods. 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 directly provided on the photosensitive layer, and the counter electrode is subsequently provided.
[0075]
In the case of the former method, when the charge transport layer is sandwiched, a normal pressure process using capillary action due to immersion 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.
[0076]
In the latter method, when a wet charge transport layer is used, 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 process. Solidification may be performed before or after applying the counter electrode. In the case of forming a charge transport layer made of an electrolytic solution, a wet organic hole transport material, a gel electrolyte composition, or the like, the same method as the method for forming a semiconductor fine particle layer described above can be used.
[0077]
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.
[0078]
(D) Counter electrode
Similar to the conductive support described above, the counter electrode may have a single-layer structure of a counter electrode conductive layer made of a conductive material, or may be composed of a counter electrode conductive layer and a support substrate. Examples of the conductive agent used for the counter electrode conductive layer include metal (platinum, gold, silver, copper, aluminum, magnesium, indium, etc.), carbon, conductive metal oxide (indium-tin composite oxide, fluorine-doped tin oxide, etc.) ) And the like. Among these, platinum, gold, silver, copper, aluminum and magnesium are preferable. The substrate used for the counter electrode is preferably a glass substrate or a plastic substrate, and can be used by applying or vapor-depositing the above-mentioned conductive agent. The thickness of the counter electrode conductive layer is not particularly limited, but is preferably 3 nm to 10 μm. The surface resistance of the counter electrode conductive layer is preferably as low as possible, preferably 50Ω / □ or less, more preferably 20Ω / □ or less.
[0079]
Since light may be irradiated from either 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 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. In order to obtain such properties, glass or plastic on which a metal or a conductive oxide is deposited or a metal thin film may be used as a counter electrode.
[0080]
The counter electrode may be installed by directly applying, plating or vapor-depositing (PVD, CVD) a conductive agent 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 preferred embodiment of the metal lead is the same as that of the conductive support.
[0081]
(E) Other layers
In order to prevent a short circuit between the counter electrode and the conductive support, it is preferable that a dense semiconductor thin film layer is preliminarily applied as an undercoat layer between the conductive support and the photosensitive layer. This method of preventing a short circuit by the undercoat layer is particularly effective when an electron transport material or a hole transport material is used for the charge transport layer. The undercoat layer is preferably TiO₂, SnO₂, Fe₂O_Three, WO_Three, ZnO or Nb₂O_FiveMore preferably TiO₂Consists of. The undercoat layer can be applied by, for example, a spray pyrolysis method described in “Electrochim. Acta”, 1995, Vol. 40, p.643-652, a sputtering method, or the like. The thickness of the undercoat layer is preferably 5 to 1000 nm, more preferably 10 to 500 nm.
[0082]
In addition, 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, between the conductive layer and the substrate, or in the middle of the substrate. The method for forming these functional layers can be appropriately selected from a coating method, a vapor deposition method, a pasting method, and the like according to the material.
[0083]
(F) Specific example of internal structure of photoelectric conversion element
As described above, the internal structure of the photoelectric conversion element can take various forms depending on the purpose. If roughly divided into two, a structure that allows light to enter from both sides and a structure that allows only one side are possible. Examples of a preferable internal structure of the photoelectric conversion element of the present invention are shown in FIG. 1 and FIGS.
[0084]
In the structure shown in FIG. 2, the photosensitive layer 20 and the charge transport layer 30 are interposed between the transparent conductive layer 10a and the transparent counter electrode conductive layer 40a, and light is incident from both sides. . In the structure shown in FIG. 3, a metal lead 11 is partially provided on a transparent substrate 50a, a transparent conductive layer 10a is provided thereon, and an undercoat layer 60, a photosensitive layer 20, a charge transport layer 30, and a counter electrode conductive layer 40 are arranged in this order. In addition, a support substrate 50 is arranged, and light is incident from the conductive layer side. The structure shown in FIG. 4 has a conductive layer 10 on a support substrate 50, a photosensitive layer 20 provided through an undercoat layer 60, a charge transport layer 30 and a transparent counter electrode conductive layer 40a, and a metal in part. The transparent substrate 50a provided with the leads 11 is disposed with the metal lead 11 side inward, and has a structure in which light enters from the counter electrode side. In the structure shown in FIG. 5, the subbing layer 60, the photosensitive layer 20 and the charge transport layer 30 are provided between a pair of metal leads 11 provided on a transparent substrate 50a and further provided with a transparent conductive layer 10a (or 40a). In this structure, light enters from both sides. In the structure shown in FIG. 6, a transparent conductive layer 10a, an undercoat layer 60, a photosensitive layer 20, a charge transport layer 30 and a counter electrode conductive layer 40 are provided on a transparent substrate 50a, and a support substrate 50 is disposed thereon. In this structure, light enters from the conductive layer side. The structure shown in FIG. 7 has a conductive layer 10 on a support substrate 50, a photosensitive layer 20 provided through an undercoat layer 60, a charge transport layer 30 and a transparent counter electrode conductive layer 40a, and a transparent substrate thereon. 50a is arranged, and light is incident from the counter electrode side. In the structure shown in FIG. 8, a transparent conductive layer 10a is provided on a transparent substrate 50a, a photosensitive layer 20 is provided via an undercoat layer 60, a charge transport layer 30 and a transparent counter electrode conductive layer 40a are provided, and a transparent layer is provided thereon. The substrate 50a is disposed, and light is incident from both sides. In the structure shown in FIG. 9, the conductive layer 10 is provided on the support substrate 50, the photosensitive layer 20 is provided via the undercoat layer 60, and the solid charge transport layer 30 is further provided. It has a metal lead 11 and has a structure in which light is incident from the counter electrode side.
[0085]
[IV] Photocell
The photovoltaic cell of the present invention is one in which the photoelectric conversion element of the present invention is caused to work with an external load. Among photocells, the case where the charge transport material is mainly composed of an ion transport material is particularly called a photoelectrochemical cell, and the case where the main purpose is power generation by sunlight is called a solar cell.
[0086]
The side surface of the photovoltaic cell is preferably sealed with a polymer, an adhesive or the like in order to prevent deterioration of the constituents and volatilization of the contents. The external circuit itself connected to the conductive support and the counter electrode via a lead may be a known one.
[0087]
Even when the photoelectric conversion element of the present invention is applied to a solar cell, the structure inside the cell is basically the same as the structure of the photoelectric conversion element described above. Moreover, the dye-sensitized solar cell using the photoelectric conversion element of the present invention can basically have the same module structure as a conventional solar cell module. The solar cell module generally has a structure in which cells are formed on a support substrate such as metal or ceramic, and the cell is covered with a filling resin or protective glass, and light is taken in from the opposite side of the support substrate. It is also possible to use a transparent material such as tempered glass for the support substrate, configure a cell thereon, and take in light from the transparent support substrate side. Specifically, a module structure called a super straight type, a substrate type, a potting type, a substrate integrated module structure used in amorphous silicon solar cells, and the like are known, and dye sensitization using the photoelectric conversion element of the present invention is known. As for the type solar cell, the module structure can be appropriately selected according to the purpose of use, the place of use and the environment. Specifically, the structures and embodiments described in Japanese Patent Application Nos. 11-8457 and 2000-268892 are preferable.
[0088]
【Example】
EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
[0089]
Example 1
Preparation of titanium dioxide fine particles
When 16 ml of 25% ammonia water (Wako Pure Chemical Industries, Ltd.) is added to a mixed solution of 32 g of 30% titanium sulfate solution (Wako Pure Chemical Industries, Ltd.) and 20 ml of water, the temperature is approximately 50 ° C. Heat was generated and white titanium hydroxide precipitated instantly. When the temperature was raised to 70 ° C. and the mixture was stirred for 1 hour, the reaction solution turned light blue and white, and a sol dispersion of titanium dioxide was obtained. This sol dispersion was filtered while hot, and the filtrate was transferred to an autoclave container and autoclaved at 225 ° C. for 12 hours. After cooling the container, the obtained titanium dioxide fine particles were separated by a centrifuge. For the purpose of removing impurities such as ammonium sulfate, the operation of adding water again and centrifuging was repeated four times to obtain a dispersion (T-1) of fine titanium dioxide particles. The obtained titanium dioxide particles were pure anatase crystals having an average particle diameter of about 11 nm as measured by fluorescent X-ray (XRD), and the concentration of titanium dioxide was 25% by mass. Further, in the method described in Non-Patent Document 5, a titanium dioxide dispersion (T-2) having a titanium dioxide concentration of 17% by mass was obtained by the same method as Non-Patent Document 5 except that the autoclave temperature was 225 ° C. From the measurement of fluorescent X-ray (XRD) of the obtained particles, the average particle size was about 11 nm as in the case of T-1, but the presence of brookite type and rutile type in addition to anatase was recognized as the crystal type. .
[0090]
Example 2
1． Preparation of coating solution containing titanium dioxide particles
40% by mass of polyethylene glycol (molecular weight 20000, Wako Pure Chemical Industries, Ltd.) with respect to titanium dioxide was added to the titanium dioxide dispersion (T-1) obtained in Example 1 and mixed to obtain a coating solution. (B-1) was obtained. A coating solution (B-2) was similarly obtained for T-2 titanium dioxide.
[0091]
2. Production of titanium dioxide electrode
Transparent conductive glass coated with tin oxide doped with fluorine (Nippon Sheet Glass Co., Ltd., surface resistance: approx. 10Ω / cm²) Apply the above coating liquid (B-1) to the conductive surface side with a doctor blade at a thickness of 120μm and dry it at 25 ° C for 30 minutes, then use an electric furnace (Yamato Scientific muffle furnace FP-32 type). Used and calcined at 450 ° C. for 30 minutes. The coating amount of titanium dioxide after cooling is 18 g / m²The coating layer thickness was 12 μm. This titanium dioxide electrode was designated as an electrode (E-1). Similarly, the coating amount of titanium dioxide using the coating solution of B-2 is 18 g / m²A titanium dioxide electrode (E-2) having a coating layer thickness of 12 μm was prepared.
[0092]
3. Oxidation method and production of oxidation electrode
The following two kinds of semiconductor fine particle electrodes were subjected to the following oxidation treatment according to the procedure shown in Table 1 to obtain oxidation treatment electrodes (S-1) to (S-18).
[0093]
(1) Hydrogen peroxide treatment
The electrode was completely immersed in 30% aqueous hydrogen peroxide (for precision analysis, manufactured by Wako Pure Chemical Industries, Ltd.) and shaken at 25 ° C. for 20 minutes. The electrode was carefully taken out, washed with pure water, and baked at 450 ° C. for 15 minutes.
[0094]
(2) UV-ozone treatment
A semiconductor electrode was placed in a UV-ozone cleaning device (Tokyo Sanyo Vacuum Co., Ltd.), and UV irradiation was performed for 20 minutes at room temperature and atmospheric pressure in an atmosphere with an oxygen concentration of 25% while supplying oxygen gas. After the electrode was taken out from the apparatus, it was immediately advanced to the next dye adsorption step without performing a treatment such as baking.
[0095]
(3) Oxygen plasma treatment
An electrode to be treated is placed on a plate in a high-frequency (RF) plasma generator (BP-1, manufactured by SAMCO), the pressure is reduced to 0.5 Torr while flowing oxygen gas at a flow rate of 20 ml / min, and then the RF power is 50 W The electrode was treated with oxygen plasma for 15 minutes. After stopping the apparatus in sequence, the electrode was taken out and further baked at 450 ° C. for 15 minutes.
[0096]
[Table 1]
[0097]
4). Dye adsorption
The prepared electrodes E-1, E-2 and oxidation-treated electrodes S-1 to S-18 were respectively converted to ruthenium complex dye cis- (dithiocyanate) -N, N′-bis (2,2′-bipyridyl-4 , 4'-Dicarboxylic acid) ruthenium (II) complex (D-1) was immersed for 16 hours. The adsorption temperature is 25 ° C, the solvent of the adsorbent is a mixed solvent of ethanol: t-butanol: acetonitrile = 1: 1: 2 (volume ratio), and the dye concentration is 3 × 10.^-FourMole / liter. The dyed titanium dioxide electrode was washed with acetonitrile.
[0098]
5). Production of photoelectric conversion element
(Photoelectric conversion element using electrolyte as charge transport material)
The color-sensitized electrode (2 cm × 2 cm) produced as described above was superposed on a platinum-deposited glass of the same size (see FIG. 10). Next, an electrolyte solution (0.65 mol / liter 1,3-dimethylimidazolium iodide and 0.05 mol / liter iodine solution containing acetonitrile) is impregnated into the gap between the two glasses using capillary action.₂By introducing into the electrode, photoelectric conversion elements CT-1 and 2 and CS-1 to CS-18 shown in Table 2 were obtained. As shown in FIG. 10, the obtained photoelectric conversion element is composed of conductive glass 1 (with conductive layer 3 placed on glass 2), TiO adsorbed with dye.₂The layer 4, the charge transport layer (electrolytic solution) 5, the platinum layer 6, and the glass 7 are stacked in this order.
[0099]
6). Measurement of photoelectric conversion efficiency
Simulated sunlight was generated by passing light from a 500 W xenon lamp (USHIO Co., Ltd.) through a spectral filter (AM1.5 manufactured by Oriel). The intensity of this light is 100 mW / cm in the vertical plane²Met. A silver paste was applied to the end of the conductive glass of the photoelectric conversion element to form a negative electrode, and the negative electrode and platinum-deposited glass (positive electrode) were connected to a current-voltage measuring device (Keutley SMU238 type). The current-voltage characteristics were measured while irradiating simulated sunlight vertically, and the conversion efficiency was obtained. Table 2 below shows the conversion efficiency of each photoelectric conversion element.
[0100]
[Table 2]
[0101]
According to Table 2, photoelectric conversion elements (CS-1 to 9) using titanium oxide fine particles made of titanium sulfate as a raw material are more than photoelectric conversion elements (CS-10 to 18) using titanium oxide fine particles by a conventional sol-gel method. It can also be seen that the conversion efficiency is high. When the titanium oxide electrode is oxidized, both photoelectric conversion elements improve the conversion efficiency. From the comparison of differences in conversion efficiency, the electrode made from titanium sulfate (E-1) is more effective. I understand. In addition, it is understood that the oxidation treatment is more effective when the hydrogen peroxide treatment is performed first, followed by the UV-ozone treatment and / or the oxygen plasma treatment (CS-4,5, CS-8,9, CS-13,14 and CS-17,18).
[0102]
Example 3
1. Production of oxidation electrodes with different processing conditions
The titanium dioxide electrode (E-1) produced in the same manner as in Example 2 was subjected to oxidation treatment under the treatment conditions shown in Table 3 to obtain oxidation treatment electrodes (S-19 to S-21).
[0103]
[Table 3]
[0104]
2. Measurement of sulfur element content relative to titanium element
Oxidation electrodes (S-1 to S-3, S-9 and S-19 to S-21) obtained by subjecting titanium dioxide electrode E-1 produced using titanium sulfate as a raw material to oxidation treatment under various different conditions; As comparative examples, a titanium dioxide electrode E-1 not subjected to oxidation treatment and a titanium dioxide electrode E-2 produced using titanium isopropoxide as a raw material were cut into a size of 3 cm × 3 cm, respectively. (Shimadzu Corporation, XRF-1700) was used to measure the contents of titanium and sulfur. Measurement was performed under the conditions of tube Rh, 40 KV, and 95 mA, and both elements were measured with Kα rays. Table 4 shows the strength and strength ratio of each electrode.
[0105]
3. Production of photoelectric conversion element and measurement of conversion efficiency
In the same manner as in Example 2, photoelectric conversion elements were produced using the electrodes shown in Table 4, and the conversion efficiency of each photoelectric conversion element was measured. The results are shown in Table 4.
[0106]
[Table 4]
[0107]
From Table 4, the electrode (E-1) using titanium oxide fine particles made of titanium sulfate as a raw material has a semiconductor fine particle more than the electrode (E-2) using titanium oxide fine particles made of a titanium alkoxide of a comparative example as a raw material. Although the amount of elemental sulfur contained in is large, the amount is reduced by oxidation treatment, and even if the same treatment method is used, the amount of sulfur is further reduced by strengthening the conditions or increasing the number of times. It can be seen that this leads to improvement in conversion efficiency. In addition, the S-9 electrode, which is continuously subjected to different oxidation treatments, can reduce the amount of impurities to the same level as the reference electrode (E-2) that does not contain sulfur, and is a pure anatase-type titanium dioxide electrode. It can be seen that
[0108]
Example 4
A photoelectric conversion element was produced in the same manner as in Example 2 except that a long wave ruthenium dye (D-2), a merocyanine dye, and a squarylium dye were used instead of the ruthenium complex dye (D-1). When the conversion efficiency of each obtained photoelectric conversion element was measured in the same manner as in Example 2, the same excellent conversion efficiency as in the case of using the ruthenium complex dye (D-1) was shown.
[0109]
【The invention's effect】
As described above in detail, a dye-sensitized photoelectric conversion element having a conversion efficiency superior to that of the prior art can be obtained by using, as a semiconductor electrode, semiconductor fine particles that have been subjected to oxidation treatment before dye adsorption. In particular, the conversion efficiency of the photoelectric conversion element is improved by performing at least one oxidation treatment of hydrogen peroxide treatment, UV-ozone treatment, and oxygen plasma treatment, and further conversion is performed by continuously treating them with a suitable procedure. Efficiency can be improved. In titanium dioxide using titanium sulfate, high-purity pure anatase-type titanium dioxide fine particles can be obtained by performing an oxidation treatment.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to a preferred embodiment of the present invention.
FIG. 2 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to another preferred embodiment of the present invention.
FIG. 3 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
FIG. 4 is a partial cross-sectional view showing the structure of a photoelectric conversion element according to still another preferred embodiment of the present invention.
FIG. 5 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
FIG. 6 is a partial cross-sectional view showing the structure of a photoelectric conversion element according to still another preferred embodiment of the present invention.
FIG. 7 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
FIG. 8 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
FIG. 9 is a partial cross-sectional view showing the structure of a photoelectric conversion device according to still another preferred embodiment of the present invention.
10 is a partial cross-sectional view illustrating a structure of a photoelectric conversion element manufactured in Example 2. FIG.
[Explanation of symbols]
10 ... conductive layer
10a ・ ・ ・ Transparent conductive layer
11 ... Metal lead
20 ... Photosensitive layer
21 ... Semiconductor fine particles
22 ... Dye
23 ... Charge transport material
30 ... Charge transport layer
40 ... Counterelectrode conductive layer
40a ・ ・ ・ Transparent counter electrode conductive layer
50 ... Board
50a ・ ・ ・ Transparent substrate
60 ... Undercoat layer
1 ... conductive glass
2 ... Glass
3. Conductive layer
4 ... TiO₂layer
5 ... Electrolyte
6 ... Platinum layer
7 ... Glass

Claims (7)

In a method for manufacturing a photoelectric conversion element having a layer of semiconductor fine particles to which at least one dye is adsorbed and a conductive support, the semiconductor fine particles are treated with hydrogen peroxide before adsorbing the dye , and then UV-ozone treatment and oxygen are performed. A method for manufacturing a photoelectric conversion element, comprising performing at least one of plasma treatments . The method for manufacturing a photoelectric conversion element according to claim 1 , wherein titanium oxide is used as the semiconductor fine particles. The method for manufacturing a photoelectric conversion element according to claim 2, wherein the titanium oxide uses titanium sulfate or titanium oxysulfate as a raw material, and 0.01 to 0.99 equivalents of sulfuric acid among sulfate radicals contained in the raw material. after neutralizing the roots with a base, a sol under acidic conditions - a method for manufacturing a photoelectric conversion element characterized in that which was produced by gel method. In the method for manufacturing a photoelectric conversion device according to claim 3, the method for manufacturing a photoelectric conversion element, wherein the base to neutralize the sulfate radical is ammonia water. 5. The method for producing a photoelectric conversion device according to claim 3, wherein a content of sulfur element in the titanium oxide fine particles is 0.03 in terms of an intensity ratio of sulfur to titanium (S-Kα / Ti-Kα) of fluorescent X-rays. The manufacturing method of the photoelectric conversion element characterized by the following. The photoelectric conversion element produced by the method in any one of Claims 1-5 . A photovoltaic cell using the photoelectric conversion element according to claim 6 .