JP2008053140A - Semiconductor particulate paste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an oxide semiconductor particulate paste which can form a porous oxide semiconductor layer. <P>SOLUTION: The semiconductor particulate paste contains a titanium group binder composed of oxide titanium particles and titanium isopropoxide, a denaturing agent made from ethylene glycol and/or β-diketone, a porosity promotion agent made from higher alcohol of a carbon number 5 or more and an organic solvent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an oxide semiconductor fine particle paste used for forming an oxide semiconductor layer provided on a negative electrode of a dye-sensitized solar cell.

  Currently, there is great expectation for photovoltaic power generation from the viewpoint of global environmental problems and fossil energy resource depletion problems, and single crystal and polycrystalline silicon photoelectric conversion elements are put into practical use as solar cells. However, this type of solar cell is expensive and has a problem of supply of silicon raw materials, and the practical application of solar cells using materials other than silicon is desired.

  From the above viewpoint, recently, a dye-sensitized solar cell has attracted attention as a solar cell using a material other than silicon. As shown in FIG. 1, this dye-sensitized solar cell uses a transparent conductive film 1b (for example, ITO film) as an electrode substrate 1 on a transparent substrate 1a such as transparent glass or a transparent resin film. A negative electrode structure in which a porous layer 3 of a metal oxide semiconductor such as titanium dioxide is provided on the transparent conductive film 1b and a sensitizing dye (for example, Ru dye) 5 is adsorbed on the surface of the porous layer 3 7 and has such a structure that the negative electrode structure 7 is opposed to the positive electrode 10 with the electrolyte 8 interposed therebetween.

  In the dye-sensitized solar cell having such a structure, when visible light is irradiated from the negative electrode structure 7 side, the dye 5 is excited and transitions from the ground state to the excited state. Then, it is injected into the conduction band of the porous layer 3 of the semiconductor and moves to the positive electrode 10 through the external circuit 12. The electrons that have moved to the positive electrode 10 are carried by the ions in the electrolyte and return to the dye 5. Electric energy is extracted by repeating such a process. The power generation mechanism of such a dye-sensitized solar cell differs from that of a pn junction photoelectric conversion element in that light capture and electron conduction are performed at different locations, which is very similar to a plant photoelectric conversion process. ing.

  By the way, when light irradiation from the negative electrode structure 7 side is performed as described above, the resistance in the transparent conductive film 1b is large, and if the cell (minimum power generation unit functioning as a battery) is enlarged, the internal resistance There is a problem that the conversion efficiency is greatly lowered (Fill factor; FF).

In order to solve such a problem, Patent Document 1 discloses a dye-sensitized solar cell that generates power by irradiating light from the counter electrode side (positive electrode side) of the negative electrode. In the solar cell of this structure, since the light is not irradiated from the negative electrode side, the semiconductor porous layer carrying the dye can be directly provided on the low-resistance metal plate, and the size of the cell is increased. A decrease in FF and conversion efficiency can be effectively avoided.
JP 2001-273937 A

  By the way, the dye-sensitized solar cell as described above is a type that irradiates light from either the negative electrode side or the counter electrode side, and the oxide semiconductor layer carrying the dye formed on the negative electrode side Is generally formed by a sol-gel method. In this method, an oxide semiconductor layer is formed by applying a paste-form sol liquid in which oxide semiconductor fine particles and a binder are dispersed in an organic solvent to the surface of an electrode substrate and baking it. In other words, the alkoxide of the metal forming the oxide semiconductor is used as the binder, and the alkoxide is condensed with the oxide semiconductor fine particles during firing to form a gel in which the oxide semiconductor fine particles are bonded to each other. A physical semiconductor layer will be formed.

  However, the oxide semiconductor layer formed by the sol-gel method using the semiconductor fine particle paste as described above has a problem that it is relatively dense and it is difficult to form a porous layer. In general, an oxide semiconductor layer is more desirable as a solar cell because it is denser and does not scatter light and has better light transmittance. However, according to research by the present inventors, an oxide semiconductor layer is preferable. On the other hand, when the layer is dense, there is a problem in that it is difficult to ensure high conversion efficiency because the amount of adsorption of the dye as the sensitizer decreases. In particular, when irradiating light from the counter electrode side, the oxide semiconductor layer has been considered to require high light transmittance, so the oxide semiconductor layer tends to be a dense layer, and high conversion is required. There was a tendency that it was difficult to obtain efficiency.

  However, the present inventors have found that the oxide semiconductor layer is formed to be appropriately porous, which increases the amount of dye adsorption and is advantageous in obtaining high conversion efficiency, and completes the present invention. It came to do.

  That is, an object of the present invention is to provide an oxide semiconductor fine particle paste capable of forming a porous oxide semiconductor layer.

  According to the present invention, there is provided an oxide semiconductor fine particle paste comprising titanium oxide fine particles, a titanium-based binder, an organic solvent, and a porosification accelerator composed of a higher alcohol having 5 or more carbon atoms. Is done.

In the oxide semiconductor fine particle paste of the present invention,
(1) The titanium oxide fine particles have a particle size of 5 to 500 nm,
(2) The titanium-based binder is titanium isopropoxide,
(3) containing the titanium-based binder in an amount of 5 to 60 parts by weight per 100 parts by weight of the titanium oxide fine particles;
(4) Furthermore, glycol ether and / or β-diketone is contained as a modifying agent, and at least a part of the titanium isopropoxide is modified by the modifying agent,
(5) containing the modifying agent in an amount of 0.01 to 30 parts by weight per 100 parts by weight of the titanium isopropoxide;
(6) The organic solvent is a lower alcohol having 4 or less carbon atoms,
(7) containing the porosification agent in an amount of 0.01 to 50 parts by weight per 100 parts by weight of the titanium oxide fine particles;
(8) having a solid content concentration of 10 to 50% by weight;
Is preferred.

According to the oxide semiconductor fine particle paste of the present invention, a porous oxide semiconductor layer can be formed by coating it on a negative electrode substrate or baking it. That is, when this oxide semiconductor layer is viewed in a horizontal cross section with a size of 1 μm × 1 μm, there are 5 to 80% of pores having an area of 10000 nm ² or more per total number of pores. It becomes possible to make it a porous layer. For example, when a paste that does not contain a porosification accelerator (alcohol having 5 or more carbon atoms) is used, the above-described porosification cannot be realized, and the above-described large fine particles cannot be realized. Only a relatively dense oxide semiconductor layer in which almost no holes are formed is formed.

  Therefore, a large amount of dye can be adsorbed and supported on the porous oxide semiconductor layer formed using the oxide semiconductor fine particle paste of the present invention. As a result, a dye-sensitized solar cell having a high conversion rate can be obtained. Can be obtained.

<Oxide semiconductor fine particle paste>
The oxide semiconductor fine particle paste of the present invention is obtained by dispersing fine particles of titanium oxide, which is an oxide semiconductor, in an organic solvent together with a titanium-based binder and a porosification accelerator. A porous oxide semiconductor (titanium dioxide) layer can be formed by applying to the surface and baking.

  In the present invention, the fine particles of titanium oxide used for forming the paste are preferably in the range of 5 to 500 nm, particularly 5 to 350 nm in terms of porosity.

  The titanium-based binder is condensed with the titanium oxide fine particles to cause gelation, and the titanium oxide fine particles are bonded to each other to make them porous. Such a titanium-based binder is preferably an alkoxide of a lower alcohol having 4 or less carbon atoms because it easily gels, and is particularly preferably isopropoxide, most preferably Titanium isopropoxide (tetratitanium isopropoxide) is used.

  In general, such a titanium-based binder is preferably used in an amount of 5 to 60 parts by weight, particularly 10 to 50 parts by weight, per 100 parts by weight of titanium oxide fine particles, in terms of titanium alkoxide. If this amount is small, gelation will not be performed effectively, it will be difficult to form an effective oxide semiconductor layer, and if used in a larger amount than the above range, it will be difficult to make it porous. There is.

  Further, at least a part of the above-mentioned titanium-based binder may be modified with a modifying agent. For such modification, a modifying agent is added to the paste of the present invention. Good. Examples of such modifying agents include glycol ethers and β-diketones such as acetylacetone, and these may be added singly or in combination.

  That is, glycol ether is modified by substituting a part of the alkoxyl group of the titanium-based binder, and β-diketone is modified by forming a chelate bond with a part of the titanium atom in the titanium-based binder. Thus, the gelation during firing can be promoted by such modification. In addition, these modifying agents have a relatively large molecular size, and therefore contribute to the formation of large pores together with the later-described porosification promoter when volatilized during firing, and the effect of promoting the porosification. Also shown. In the present invention, the modifying agent most preferably used is β-diketone.

  In the present invention, the modifying agent is preferably used in an amount of 0.01 to 30 parts by weight, particularly 0.05 to 10 parts by weight, based on 100 parts by weight of titanium isopropoxide. When a denaturing agent is used, it is possible to achieve the most effective porosity.

  Further, as the porosification accelerator, there are alcohols having 5 or more carbon atoms, such as pentanol, hexanol, heptanol, octanol, nonanol, decanol, and dodecanol, which are used alone or in combination of two or more. Can do. In the present invention, decanol and dodecanol are particularly preferably used. That is, these porosification promoters have moderate volatility and at the same time have relatively large molecules. For this reason, when volatilized by baking of the paste, large pores are formed in the gelled body, thereby forming a porous oxide semiconductor (titanium oxide) layer having a large number of large pores as described above. It becomes possible to do. For example, when such a porosifying agent is not used, a porous oxide semiconductor layer having large pores cannot be formed.

  In the present invention, the above porosification promoter is preferably used in an amount of 0.01 to 50 parts by weight, particularly 0.5 to 10 parts by weight, per 100 parts by weight of titanium oxide fine particles. When this amount is small, it is difficult to form a large effective amount of pores, and thus it is difficult to form a porous oxide semiconductor layer. On the other hand, if the amount is too large, the porous structure is promoted too much, the oxide semiconductor layer to be formed becomes brittle, and there is a possibility that it will be difficult to put it to practical use.

  As the organic solvent for dispersing the above-described titanium oxide fine particles, titanium-based binder, porosification accelerator, and modifying agent used as necessary, any organic solvent can be used without particular limitation as long as it is easily volatile. For example, various ethers, cellosolves, and lower alcohols having 4 or less carbon atoms such as methanol, ethanol, isopropanol, n-butanol, sec-butanol, and t-butanol are suitable. These organic solvents are used alone. You may use, and it can also use in the form of the mixed solvent which combined 2 or more types. Particularly preferably, an alcohol having 4 or less carbon atoms is used. When a lower alcohol having 4 or less carbon atoms is used as the organic solvent, when the type is different from the alcohol forming the alkoxide in the titanium binder, a part of the alkoxyl group in the titanium binder is It has been found that substitution with lower alcohols used as organic solvents (ie, modification) promotes gelation.

  In the present invention, the amount of the organic solvent may be used in such an amount that the paste exhibits an appropriate coating property. In general, the solid content concentration of the paste is 10 to 50% by weight, particularly 15 to 40% by weight. It is better to use it in an amount that is in the range. If the amount of solvent is too large, the paste will have low viscosity and it will be difficult to form a coating layer with a stable thickness due to dripping, etc., and if the amount of solvent is small, it will become highly viscous and workability will be reduced. is there.

As described above, the oxide semiconductor fine particle paste of the present invention comprising the above-described components is applied on a predetermined negative electrode substrate and baked to form a porous titanium oxide layer (oxide semiconductor layer). be able to. The paste can be applied by a known means such as knife coating or roll coating, and the coating amount is such that a titanium oxide layer having a predetermined thickness (for example, about 1 to 15 μm) is formed after firing. . In addition, the firing and firing time after coating are such that the formed titanium oxide layer has a pore size of an area of 10000 nm ² or more per total number of pores as viewed in a horizontal section of 1 μm × 1 μm area. 5 to 80%, especially 20 to 60%, and should be set so as to be present at a temperature of 600 ° C. or less, particularly 250 to 500 ° C. for 5 minutes. It is set to about 1 hour. If this temperature is higher than necessary or longer than necessary, the formed titanium oxide layer becomes dense, so care must be taken. By such firing, the TiO ₂ gel formed by the gelation (dehydration condensation) of the binder component joins the titanium oxide fine particles to each other, and the porous material is made porous by volatilization of the porosification accelerator (and also the modifier). A titanium oxide layer thus formed is formed.

  The titanium oxide layer formed as described above is a dye-sensitized type by adsorbing a sensitizing dye by bringing it into contact with a dye solution, drying the adsorbed dye and removing the solvent from the dye solution. It is used for use as a negative electrode structure of a solar cell. The contact of the dye solution is usually performed by dipping, and the adsorption treatment time (immersion time) is usually about 30 minutes to 24 hours.

As the sensitizing dye to be used, those known per se having a bonding group such as a carboxylate group, a cyano group, a phosphate group, an oxime group, a dioxime group, a hydroxyquinoline group, a salicylate group, an α-keto-enol group are used. Those described in the above-mentioned patent documents, for example, ruthenium complexes, osmium complexes, iron complexes and the like can be used without any limitation. Ruthenium-tris (2,2′-bispyridyl-4,4′-dicarboxylate), ruthenium-cis-diaqua-bis (2,2′-bispyridyl-4,4) in that it has a particularly broad absorption band. Ruthenium-based complexes such as' -dicarboxylate) are preferred. Such a dye solution of a sensitizing dye is prepared using an alcohol-based organic solvent such as ethanol or butanol as a solvent, and the dye concentration is usually about 3 × 10 −4 to 5 × 10 −4 mol / l. It is good to do. By such dye adsorption, the amount of adsorbed dye of the titanium oxide layer becomes about 1 × 10 −8 to 5 × 10 −7 g / cm ² .

  The semiconductor fine particle paste of the present invention is applied to a transparent conductive layer such as ITO, for example, as a porous titanium oxide layer, and is a dye sensitized type that generates power by irradiating light from the negative electrode side having the structure shown in FIG. Although it can be used for a solar cell, it is preferably used for a back-irradiated dye-sensitized solar cell that generates power by irradiating light from the counter electrode side. The structure of such a back-illuminated solar cell is shown in FIG.

  In FIG. 2, such a solar cell includes a negative electrode structure 20 as a whole and a counter electrode (positive electrode) structure 21 as a whole, and an electrolyte 23 is interposed between these electrode structures 20, 21. Power is generated by irradiating visible light from the counter electrode structure 21 side and making it incident on the negative electrode structure 20.

  As the electrolyte 23, various electrolyte solutions containing cations such as lithium ions and anions such as chlorine ions can be used as in the case of known solar cells. In addition, it is preferable that an oxidation-reduction pair capable of reversibly taking an oxidized structure and a reduced structure exists in the electrolyte 23. Examples of such an oxidized-reduced pair include iodine-iodine compounds, bromine- Examples thereof include bromine compounds and quinone-hydroquinone. Such an electrolyte 23 is generally sealed with an electrically insulating resin or the like, and is configured not to leak between the electrode structures 20 and 21.

In addition to a liquid electrolyte, a gel electrolyte or a solid electrolyte can be used. Gel electrolytes are, for example, physical gels such as polyacrylonitrile and polymethacrylate that are gelled near room temperature due to physical interaction, and gels that are chemically bonded by acrylate-based and methacrylate-based crosslinking reactions. The chemical gel which forms is mentioned.
Examples of the solid electrolyte include polypyrrole and CuI. When using a gel electrolyte or solid electrolyte, impregnating a low-viscosity precursor into an oxide semiconductor film and causing a two-dimensional or three-dimensional crosslinking reaction by means of heating, ultraviolet irradiation, electron beam irradiation, etc. It can be gelled or solidified. However, in view of power generation efficiency, it is preferable to use an electrolytic solution.

  The negative electrode structure 20 includes a metal substrate 25 that functions as a negative electrode, and an oxide semiconductor layer 29 is usually formed on the metal substrate 25 with a corrosion-resistant conductive layer 27 interposed therebetween. The physical semiconductor layer 29 carries a dye 30 as a sensitizer. As shown in FIG. 1, the oxide semiconductor layer 29 carrying the dye 30 faces the counter electrode structure 21 and is in contact with the electrolyte 23. That is, the oxide semiconductor layer 29 is a porous titanium oxide layer formed by the semiconductor fine particle paste of the present invention described above.

  On the other hand, the counter electrode structure 21 has a structure in which a transparent conductive film 39 is formed on a transparent substrate 37, and an electron reducing conductive layer 40 is formed on the transparent conductive film 39. The layer 40 is in contact with the electrolyte 23.

  That is, in the solar cell of the present invention having the structure shown in FIG. 2, the dye 30 is excited by irradiation with visible light from the counter electrode structure 21 side, and the electrons of the excited dye 30 are converted into the oxide semiconductor layer 29. Is transferred from the metal substrate 25 through the external load 31 to the counter electrode (positive electrode) structure 21, carried from the transparent conductive film 39 through the conductive layer 40 by ions in the electrolyte 23, Return to dye 30. By repeating this, electric energy is taken out by the external load 31, and such a power generation mechanism irradiates light from the negative electrode structure 20 side except that light is irradiated from the counter electrode structure 21 side. It is basically the same as the thing.

  As described above, when light irradiation is performed from the counter electrode structure 21 side, it is not necessary to provide transparency to the negative electrode structure 20 side. For this reason, a low resistance metal substrate is provided on the negative electrode structure 20 side. 25 is provided, and it is not necessary to form a transparent conductive film, which brings a great advantage.

  That is, in order to excite the dye 30 by irradiating light from the negative electrode structure 20 side, it is necessary to form the oxide semiconductor layer 29 on a transparent conductive film such as ITO. It cannot be provided on the substrate 25. However, since transparent conductive films such as ITO have high electrical resistance, high conversion efficiency and high internal resistance (FF) can be secured when the cell is small, but conversion is possible when the cell is enlarged. This results in a significant reduction in efficiency and FF. However, in the case of adopting a structure in which light is irradiated from the counter electrode structure 21 side, the oxide semiconductor layer 29 does not go through a transparent conductive film such as ITO, and a metal substrate through a corrosion-resistant conductive layer 27 if necessary. Therefore, even when the cell area is increased, it is possible to effectively prevent a decrease in FF and conversion efficiency. It is.

The metal substrate 25 provided in the negative electrode structure 20 described above is not particularly limited as long as it is made of a metal material having low electrical resistance, but generally has a specific resistance of 6 × 10 ⁻⁶ Ω · m or less. For example, a metal or an alloy having aluminum, such as aluminum, iron (steel), or copper is used. Further, the thickness of the metal substrate 25 is not particularly limited as long as it has a thickness enough to maintain an appropriate mechanical strength. Moreover, if productivity is not considered, the metal substrate 25 may be formed in the resin film etc. by vapor deposition etc., for example. Of course, the substrate such as the resin film does not need to be transparent.

  In the present invention, a corrosion-resistant conductive layer 27 is formed on the surface of the metal substrate 25 as shown in the figure, and the oxide semiconductor layer 29 is formed through the corrosion-resistant conductive layer 27. It is preferable to be provided. Providing such a corrosion-resistant conductive layer 27 has a remarkable effect in terms of the rectifying barrier and durability. That is, the corrosion-resistant conductive layer 27 is formed of a metal having corrosion resistance with respect to the electrolyte 23 such as nickel or titanium. By providing the layer 27, the electrolyte 23 of the metal substrate 25 is provided. Corrosion due to corrosion can be prevented, performance deterioration due to such corrosion can be avoided, and durability can be improved. In addition, such a metal having corrosion resistance has a higher resistance than the metal substrate 25, and thus prevents reverse current (reverse electron transfer) and becomes an effective rectification barrier. As a result, conversion efficiency is improved. It is possible to increase, avoid variations in conversion efficiency, and secure stable battery performance. Such a corrosion-resistant conductive layer 27 can be easily formed by a plating method, but can also be formed by rolling and integration with the metal substrate 25 by a cladding method.

  Moreover, said corrosion-resistant conductive layer 27 can also be formed by chemical conversion treatment. In the chemical conversion treatment, a film is basically deposited on the metal surface from an aqueous solution by a chemical reaction. Recently, a coating liquid having a predetermined composition is applied to such a reaction type, followed by drying by heating. A method called a coating type for forming an insolubilized film has been developed, and the corrosion-resistant conductive layer 27 can be formed by any chemical conversion treatment.

  For example, in both the reaction type and the coating type, the formed film is roughly classified into a chromium type and a non-chromium type, but the chromium type film generally has high corrosion resistance, and the non-chromium type film has corrosion resistance. Although it is inferior, there are advantages that the load to the environment is small and the adhesion to the metal substrate 25 is high.

  Typical examples of the reactive chromium-based film are those based on the alkali-chromate method, the chromate method, the phosphoric acid-chromate method, and the like.

The alkali-chromate method includes an MBV method in which a film is chemically formed by high-temperature treatment with an aqueous solution mainly composed of sodium carbonate, sodium chromate, sodium hydroxide, etc., sodium carbonate, sodium chromate, silicic acid High temperature treatment with aqueous solution containing sodium (water glass), etc. to form a film, EW method, high temperature treatment with aqueous solution containing sodium carbonate, sodium chromate, basic chromium carbonate, potassium permanganate, etc. In any case, the film composition is mainly composed of Al ₂ O ₃ , Cr ₂ O _3, etc., when an aluminum substrate is used as an example.

The chromate method is a method of forming a film chemically by immersing a metal substrate in an aqueous solution containing chromate or dichromate as the main component and, if necessary, fluoride added. In the system, further CN ions are added to the aqueous solution. The composition of such a film is generally Cr (OH) ₂ .HCrO ₄ , Al (OH) ₂ .2H ₂ O when aluminum is taken as an example.
In the acceleration system, CrFe (CN) ₆ is further included in the film.

Furthermore, in the phosphoric acid-chromate method, a film is formed using a chromic acid or dichromic acid aqueous solution containing phosphoric acid, and fluoride is added to the aqueous solution as necessary. The film formed by such a method is mainly composed of CrPO ₄ , AlPO ₄ , and AlO (OH) when aluminum is taken as an example.

Typical examples of the reactive non-chromic coating include boehmite method, zinc phosphate method, and non-chromate chemical conversion treatment. The boehmite method is a method used for the treatment of aluminum. It is treated with high-temperature pure water or saturated steam (a small amount of triethanolamine or aqueous ammonia may be added as a film accelerator) to the surface. This is a method for forming a film, and the film composition is mainly Al ₂ O ₃ .3H ₂ O (Bayerite) or Al ₂ O ₃ .H ₂ O (Boehmite) depending on the processing temperature or the like. In addition, the zinc phosphate method is to form a film by treating the surface of the metal substrate 25 with an aqueous solution containing zinc phosphate, nitrate, and fluoride at a low temperature. The main constituent is Zn ₃ (PO ₄ ) ₂ .4H ₂ O or AlPO ₄ . Furthermore, the non-chromate chemical conversion treatment method forms a film by treating the surface of a metal substrate with an aqueous solution containing an organic metal such as a methylated product of Ti or Zr, phosphoric acid, nitric acid or tannic acid. In the case of aluminum, is mainly composed of Me (OH) PO ₄ .Al ₂ O ₃ or Al (Me-chelate).

  On the other hand, the coating type is a coating solution in which a metal oxide such as chromium, zirconia or titanium, colloidal silica or the like is dispersed in an acrylic resin such as polyacrylic acid or a solution of a coupling agent such as a silane coupling agent (coating solution). Is coated with a roller or the like and dried to form an insolubilized film. When the corrosion-resistant conductive layer 27 is formed by such a method, it is preferable to use a coating liquid that does not contain a resin and to form a film that does not contain a resin component. That is, when the corrosion-resistant conductive layer 27 contains a resin component, the resin component is volatilized during firing when forming the oxide semiconductor layer 29 described later, and as a result, the reverse current prevention effect, the electrolyte This is because the resistance to the damage is impaired.

  When the corrosion-resistant conductive layer 27 is formed by chemical conversion treatment as described above, it can be continuously formed by immersion in a treatment liquid, spraying, roller application, or the like. There is no need for expensive equipment, which is particularly advantageous in terms of productivity. In particular, when the corrosion-resistant conductive layer 27 is formed by a coating type chemical conversion treatment, a washing treatment such as water washing after the film formation is unnecessary, which is particularly preferable in terms of productivity.

  The thickness of the above-described corrosion-resistant conductive layer 27 is desirably as thin as possible as long as appropriate corrosion resistance and rectifying barrier property (reverse current prevention property) are ensured. Specifically, it is suitable that it is 1,000 nm or less, particularly 5 to 500 nm, most preferably 5 to 100 nm.

  The oxide semiconductor layer 29 formed on the corrosion-resistant conductive layer 27 is a porous titanium oxide layer formed using the oxide semiconductor fine particle paste of the present invention, as described above. As described above, the sensitizing dye 30 is adsorbed and supported by bringing the dye solution into contact with this layer. That is, the oxide semiconductor (titanium oxide) layer 29 has a porous structure having a large number of large-sized pores as described above, and therefore, the adsorption amount of the sensitizing dye 30 is large, and as a result, a high conversion rate. This is a great advantage of the semiconductor fine particle paste of the present invention.

  In the present invention, the porous oxide semiconductor layer 29 as described above preferably has a thickness in the range of 1 to 15 μm, particularly 3 to 10 μm. That is, if the thickness is too thin, a sufficient amount of the dye 30 cannot be adsorbed, and it may be difficult to obtain high conversion efficiency. In addition, when the thickness is increased more than necessary, the degree of light scattering in the oxide semiconductor layer 29 increases, the light transmittance decreases, and a sufficient amount of light does not enter the oxide semiconductor layer 29. As a result, the conversion efficiency tends to decrease despite the large amount of dye adsorption.

  Further, as described above, in the dye-sensitized solar cell of the present invention, since the dye 30 is excited by irradiating light from the counter electrode (positive electrode) 21 side, the counter electrode 20 must be transparent. And a transparent conductive film 39 is formed on the transparent substrate 37.

  As the transparent substrate 37, a transparent glass plate or a transparent resin film or sheet is used. As the transparent resin film or sheet, any film can be used as long as it is transparent. For example, low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, or ethylene, Polyolefin resins such as random or block copolymers of α-olefins such as propylene, 1-butene and 4-methyl-1-pentene; ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol copolymer, ethylene- Ethylene-vinyl compound copolymer resin such as vinyl chloride copolymer; Styrenic resin such as polystyrene, acrylonitrile-styrene copolymer, ABS, α-methylstyrene-styrene copolymer; polyvinyl alcohol, polyvinyl pyrrolidone, polychlorinated Vinyl, polyvinylidene chloride, vinyl chloride Vinylidene chloride copolymers, vinyl resins such as polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate; polyamides such as nylon 6, nylon 6-6, nylon 6-10, nylon 11 and nylon 12 Resin; Polyester resin such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate; Polyphenylene oxide; Cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; Starch such as oxidized starch, etherified starch and dextrin; Can be used. In general, a polyethylene terephthalate film is preferably used from the viewpoint of strength and heat resistance. The thickness and size of the transparent substrate 37 are not particularly limited, and are appropriately determined according to the use of the dye-sensitized solar cell to be finally used.

  Typical examples of the transparent conductive film 39 include a film made of an indium oxide-tin oxide alloy (ITO film), a film in which tin oxide is doped with fluorine (FTO film), and the like. An ITO film is preferred because it has desirable characteristics. These are formed on the transparent substrate 37 by vapor deposition, and the thickness is usually about 5 to 7 μm.

  An electron reducing conductive layer 40 is formed on the transparent conductive film 39. That is, the conductive layer 40 has a high electron reducing property, and the electrons that have flowed into the transparent conductive film 39 are quickly transferred to the electrolyte 23. Such a conductive layer 40 is usually formed of platinum. The conductive layer 40 is preferably as thin as 6 nm or less, thereby ensuring high visible light transmittance. Such a thin conductive layer 40 can be easily formed by vapor deposition of platinum, for example, and the thickness may be 1 nm or more. If this thickness is less than 1 nm, variations in thickness are likely to occur, and it may be difficult to obtain stable electron reducibility.

  As shown in FIG. 2, the dye-sensitized solar cell of the present invention having the negative electrode structure 20 and the counter electrode structure 21 having the structure as described above is disposed between the electrode structures 20 and 21 and the electrolyte 23 therebetween. It is put to use by being opposed to each other and sealing the electrolyte with a resin or the like.

  In the back-irradiated dye-sensitized solar cell described above, the oxide semiconductor layer 29 provided in the negative electrode structure 20 is a porous one having extremely large pores. It contains many layers and has high conversion efficiency.

  In addition, since the dye-sensitized solar cell having the structure shown in FIG. 2 generates power by irradiating light from the counter electrode structure 21 side of the negative electrode structure 20, it has a low resistance as a support substrate for the oxide semiconductor layer 29. The metal substrate 25 can be used. As a result, the cell area can be increased without lowering the conversion efficiency and the efficiency factor (FF), which is extremely practical. Furthermore, since current collection is performed via the low-resistance metal substrate 25, cells can be connected without using a special current collection member such as a grid, which is extremely advantageous in terms of productivity and cost. is there.

The excellent effect of the present invention will be described in the following experimental example.
(Example 1)
A titanium alkoxide solution in which tetratitanium isopropoxide as a binder was diluted with an organic solvent (butanol) was prepared (titanium isopropoxide concentration: 2 mol / L). In addition, it was confirmed by infrared absorption analysis (IR) that a part of isopropoxyl group in titanium isopropoxide was substituted with a butyl group in the titanium alkoxide solution.

  To this titanium alkoxide solution, titanium dioxide fine particles (general-purpose titania particles having a particle size of 15 to 350 nm), acetylacetone (modifying agent), decanol (porosification accelerator) and butanol / ethanol mixed solvent (mixing ratio: 50) / 50) was added, and the mixture was stirred and shaken to prepare an oxide semiconductor fine particle paste. In this paste, it was confirmed by IR that a chelate bond was formed on the titanium atom in titanium isopropoxide. The composition of this paste is as follows.

Paste composition Solid content concentration: 20% by weight
Binder (titanium isopropoxide):
20 parts by weight per 100 parts by weight of titanium dioxide fine particles Modification agent (acetylacetone):
6 parts by weight per 100 parts by weight of titanium dioxide fine particles Porosification accelerator (decanol):
2 parts by weight per 100 parts by weight of titanium dioxide fine particles

Next, an aluminum plate (thickness: 0.3 mm) subjected to a phosphoric acid chromate treatment (treatment layer: about 50 nm) was prepared as a metal substrate, and the paste prepared above was applied onto this aluminum plate, and the aluminum plate was treated at 0.4 ° C. at 450 ° C. Firing was performed for 5 hours to form a titanium oxide layer having a thickness of 8 μm. The surface of the titanium oxide layer is observed with an electron microscope. From the photograph, the formed titanium oxide layer has fine pores with an area of 10,000 nm ² or more per 1 μm × 1 μm area. The porous layer was 30% per number of pores.

Further, the titanium oxide layer was immersed in a dye solution composed of a ruthenium complex dye dispersed in ethanol having a purity of 99.5% for 18 hours, and then dried to obtain a negative electrode structure. The ruthenium complex dye used is represented by the following formula.
[Ru (dcbpy) ₂ (NCS) ₂ ] · 2H ₂ O

On the other hand, a counter electrode (positive electrode) structure composed of an ITO / PET film deposited with platinum was prepared.
A dye-sensitized solar cell having the structure shown in FIG. 2 was produced in which the electrolyte was sandwiched between the counter electrode structure and the negative electrode structure produced above, and the periphery was sealed with resin. As the electrolyte used _was added 4-tert-butylpyridine LiI / I 2 a (0.5 mol / 0.05 mol) to those dissolved in methoxypropionitrile.

When the conversion efficiency of the obtained battery was measured, the measurement area was 1 cm ² and was as follows.
Conversion efficiency: 3.60%
FF (internal resistance): 0.55
J _SC (short circuit current density): 11.0 mA / cm ²
V _OC (open voltage): 0.60V

(Example 2)
Except not using acetylacetone (modifying agent) and decanol (porosification accelerator), a paste for forming an oxide semiconductor layer having a solid content concentration of 20% by weight was prepared in exactly the same manner as in Experimental Example 1, Using the paste, a titanium oxide layer having a thickness of 8 μm was formed on an aluminum plate subjected to phosphoric acid chromate treatment (treated layer: about 50 nm) in the same manner as in Experimental Example 1.

The surface of this titanium oxide layer is observed with an electron microscope. From the photograph, the formed titanium oxide layer has 1 μm × 1 μm area, and pores with an area of 10000 nm ² or more per total number of pores. 20%.

Next, using the aluminum plate having the titanium oxide layer on the surface, a dye-sensitized solar cell having the structure shown in FIG. When the conversion efficiency of the obtained battery was measured, the measurement area was 1 cm ² and was as follows.
Conversion efficiency: 1.84%
FF (internal resistance): 0.56
J _SC (short circuit current density): 4.32 mA / cm ²
V _OC (open voltage): 0.76V

The figure which shows schematic structure of the dye-sensitized solar cell of the type which irradiates light from a negative electrode side and generates electric power. The figure which shows schematic structure of the dye-sensitized solar cell of the type which irradiates light from a counter electrode side and generates electric power.

Explanation of symbols

20: Negative electrode structure 21: Counter electrode (positive electrode) structure 23: Electrolyte 25: Metal substrate 27: Corrosion-resistant conductive layer 29: Oxide semiconductor (titanium oxide) layer 30: Dye 37: Transparent substrate 39: Transparent Conductive film 40: conductive layer

Claims (9)

  An oxide semiconductor fine particle paste comprising titanium oxide fine particles, a titanium-based binder, an organic solvent, and a porosification agent made of a higher alcohol having 5 or more carbon atoms.   The oxide semiconductor fine particle paste according to claim 1, wherein the titanium oxide fine particles have a particle size of 5 to 500 nm.   The oxide semiconductor fine particle paste according to claim 1, wherein the titanium-based binder is titanium isopropoxide.   The oxide semiconductor fine particle paste according to claim 3, wherein the titanium-based binder is contained in an amount of 5 to 60 parts by weight per 100 parts by weight of the titanium oxide fine particles.   The oxidation according to claim 3 or 4, further comprising glycol ether and / or β-diketone as a modifying agent, wherein at least a part of the titanium isopropoxide is modified by the modifying agent. Semiconductor fine particle paste.   The oxide semiconductor fine particle paste according to claim 5, wherein the modifying agent is contained in an amount of 0.01 to 30 parts by weight per 100 parts by weight of the titanium isopropoxide.   The oxide semiconductor fine particle paste according to any one of claims 1 to 4, wherein the organic solvent is a lower alcohol having 4 or less carbon atoms.   The oxide semiconductor fine particle paste according to any one of claims 1 to 5, which contains the porosification accelerator in an amount of 0.01 to 50 parts by weight per 100 parts by weight of the titanium oxide fine particles.   The oxide semiconductor fine particle paste according to any one of claims 1 to 6, having a solid content concentration of 10 to 50 wt%.

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