JP2004172110A - Multilayered oxide semiconductor thin film, photoelectric conversion element, and solar battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric conversion element having high photoelectric conversion efficiency by using an easy and low cost procedure for producing a semiconductor fine particle thin film and for using the thin film, and to provide a photochemical cell having the photoelectric conversion element. <P>SOLUTION: The multilayered oxide semiconductor thin film comprises multiply-layered porous oxides each having a different light transmittance. Each layer of the porous oxides has a different hole size. The photoelectric conversion element and the solar battery uses the multilayered oxide semiconductor thin film, which allows a highly dispersed oxide semiconductor paste and a porous oxide semiconductor thin film to be manufactured through a speedy, easy, and low cost procedure, and a photochemical cell showing high efficient photoelectric conversion efficiency to be obtained. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a porous oxide semiconductor thin film, a photoelectric conversion element using the same, and a photochemical battery using the same.

Solar cells are greatly expected as a clean renewable energy source, and practical use of single crystal silicon-based, polycrystalline silicon-based, amorphous silicon-based solar cells, and solar cells composed of compounds such as cadmium telluride and indium copper selenide. Research has been conducted for the realization of power sources, but in order to spread them as household power sources, all batteries have high manufacturing costs, difficulties in securing raw materials, problems with recycling, and difficulties in increasing the area. There are many problems that need to be overcome. Solar cells using organic materials have been proposed with the aim of increasing the area and reducing the cost, but all have a conversion efficiency of about 1%, which is far from practical use. (For example, Non-Patent Document 1 Nature Vol. 261, p. 402, 1976).

In such a situation, in 1991, Gretzel et al. Disclosed a photoelectric conversion element and a solar cell using semiconductor fine particles sensitized with a dye, and materials and manufacturing techniques necessary for manufacturing the solar cell. (Non-Patent Document 2 (Nature Volume 353, 737, 1991), Patent Document 1 (Japanese Patent Laid-Open No. 1-220380))
This battery is a wet solar battery using a porous titania thin film sensitized by a ruthenium dye as a working electrode. The advantage of this solar cell is that it is used without the need to purify inexpensive materials to high purity, so it can be provided as an inexpensive photoelectric conversion element, and the absorption of the dye used is broad, and it can be used over a wide visible light wavelength range. The ability to convert sunlight into electricity. However, for practical use, it is necessary to further improve the conversion efficiency, and there is a need for a semiconductor fine particle thin film capable of preventing aggregation of fine particles and adsorbing a larger amount of a sensitizing dye.

  Japanese Patent Application Laid-Open No. 2002-222971 (Patent Document 2) discloses a dye sensitization method in which a conductive support, a porous photoelectric conversion layer on which a dye is adsorbed, a conductive layer, and a counter electrode are sequentially laminated. In the type photoelectric conversion element, a photoelectric conversion element characterized in that the porous photoelectric conversion layer has a multilayer structure is disclosed. However, there was a need for improvement.

JP-A-1-220380 JP 2002-222971 A Nature Vol.261, p.402, 1976 Nature 353, 737, 1991

    An object of the present invention is to provide a semiconductor fine particle dispersion paste and a semiconductor fine particle thin film by a simple and inexpensive method, and to provide a photoelectric conversion element having high photoelectric conversion efficiency by using such a thin film and a photochemical cell comprising the photoelectric conversion element. That is.

  The present invention relates to a multilayered oxide semiconductor thin film formed by laminating a plurality of porous oxides having different light transmission performances.

  Further, the present invention relates to a multilayered oxide semiconductor thin film formed by laminating a plurality of porous oxides in which each layer has a different pore size or pore size distribution.

  The present invention also relates to the multilayered oxide semiconductor thin film, wherein each layer of the multilayered oxide semiconductor thin film is a different oxide semiconductor.

  The present invention also relates to the above-mentioned multilayered oxide semiconductor thin film, wherein at least one of the multilayered oxide semiconductor thin films is titania.

  Further, the present invention relates to a photoelectric conversion element using the multilayer oxide semiconductor thin film described above.

  The present invention also relates to a solar cell using the above-mentioned photoelectric conversion element.

ADVANTAGE OF THE INVENTION According to this invention, it is possible to produce a highly-dispersed oxide semiconductor paste and a porous oxide semiconductor thin film by an easy and inexpensive method in a short time, and to provide a photochemical battery showing high efficiency photoelectric conversion efficiency May be possible.

  As the oxide semiconductor fine particles in the present invention, for example, oxides such as titanium, niobium, zinc, tin, indium, zirconium, yttrium, lanthanum, tantalum, and semiconductors of perovskite-based oxides such as SrTiO3 and CaTiO3 are preferably used. . Specifically, titanium oxide (TiO2), zinc oxide (ZnO), niobium oxide (Nb2O5), tin oxide (SnO2) or strontium titanate (SrTiO3), zirconium oxide (ZrO2), tungsten oxide (WO3), indium oxide (In2O3), tantalum oxide (Ta2O5), yttrium oxide (Y2O3), or the like can be used. Among them, titanium oxide (titania) is preferable.

  The particle diameter of the oxide semiconductor fine particles is preferably from 5 to 200 nm. Preferably 10 to 100 nm, more preferably 10 to 100 nm is used.

  A paste (dispersion liquid) in which oxide semiconductor fine particles are dispersed is prepared. Water, an organic solvent, or the like can be used as a solvent for the paste.

  The organic solvent is not particularly limited as long as it can disperse the oxide semiconductor fine particles. For example, alcohols such as ethanol and methanol, acetonitrile, acetylacetone, acetone, and the like can be used. Among them, ethanol can be preferably used.

  As a component of the dispersion, an acid, a surfactant, a thickener, a deflocculant, a chelating agent and the like may be contained in addition to the above-mentioned solvent.

    As the acid, nitric acid, hydrochloric acid, acetic acid, phosphoric acid, formic acid, sulfuric acid and the like can be used. Among them, nitric acid is preferred.

    As the surfactant, polyoxyethylene octyl phenyl ether, sodium stearate, oleamidoethyl methyl diethyl ammonium iodide, polyglyceryl ester, and the like can be used. Among them, polyoxyethylene octyl phenyl ether is preferable. As the ratio of the surfactant in the paste, 0.001 to 10% by weight is used. Preferably 0.005 to 0.1 wt%, more preferably 0.01 to 0.05 wt% is used.

  As the thickener, polyalkylene glycol, polyoxyethylene, polyvinyl alcohol, polyvinyl pyridine, polyacrylic acid, or the like can be used. Among them, polyalkylene glycol is preferred. The molecular weight of the polyalkylene glycol is usually from 200 to 4,000,000. Further, the molecular weight is preferably from 20,000 to 500,000. The amount of the thickener is 1 to 50 wt%, preferably 10 to 40 wt%, more preferably 20 to 40 wt% based on the oxide semiconductor.

  Further, the paste component may contain a cellulosic thickener. As the cellulosic thickener, alkyl cellulose, hydroxyalkyl cellulose, carboxymethyl cellulose and the like are preferable.

  Examples of the alkyl cellulose include methyl cellulose, ethyl cellulose, propyl cellulose and the like.

  Examples of the hydroxyalkyl cellulose include hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxymethylpropyl cellulose, ethyl hydroxyethyl cellulose, and the like.

  Among them, methyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose are preferably used. More preferably, hydroxyethyl cellulose and hydroxypropyl cellulose are used.

  As the ratio of the cellulose-based thickener in the paste, 0.001 to 50 wt% is used. Preferably 0.01 to 20 wt%, more preferably 0.1 to 0.5 wt% is used.

As the chelating agent, acetylacetone, benzylacetone, acetic acid and the like are used. Preferably, acetylacetone is used.

  The ratio of the oxide semiconductor fine particles in the paste is 5 to 50% by weight, preferably 20 to 30% by weight.

  In the present invention, a high-dispersion paste of oxide semiconductor fine particles can be produced by applying ultrasonic waves while stirring the above paste. The time for applying the stirring and the ultrasonic wave is 5 minutes to 5 hours. Preferably, one to two hours are used.

  In the present invention, by using pastes having different components as described above, a multi-layer oxide semiconductor thin film can be manufactured in a coating step of casting the paste in multiple stages.

  Examples of the method of casting the paste include a doctor blade method, a squeegee method, a screen printing method, and a spin coating method.

  The obtained film is fired to produce a porous oxide semiconductor thin film.

The sintering temperature of the casting film is 250 to 600 ° C.
Preferably 400-500 ° C is used.
If the sintering temperature is lower than the above range, a favorable sintering state cannot be obtained, and thus the formed film is a high-resistance film, which is not preferable.
If the firing temperature is higher than the above range, the growth of crystallites is remarkable and the specific surface area is undesirably reduced.

The thickness of the thin film is 1 to 50 μm. Preferably, 5 to 30 μm is used.
When the film thickness is smaller than the above range, the amount of dye adsorbed is small and the photoelectric conversion efficiency is not low.
If the film thickness is larger than the above range, incident sunlight cannot be effectively used, which is not preferable.

The haze of the first layer of the thin film is usually 80 or less. Preferably, the haze value is 30 or less, more preferably 10 or less. Although the haze of the second layer is not particularly defined, usually, a film having a haze value larger than that of the first layer is suitably used.

Further, as the pore size of the thin film of the first layer, a pore having a radius of 30 nm is used, preferably a thin film having a pore of 20 nm, more preferably 10 nm.
The size of the pores in the second layer is not particularly limited, but a membrane having pores larger than the first layer is usually preferably used.

  In the present invention, a photoelectric conversion element can be manufactured by adsorbing a dye on the porous oxide semiconductor thin film.

  As the dye, a metal complex, an organic dye and the like are preferably used. Specific examples include organic dyes such as rose bengal, and metal complex dyes such as ruthenium, osmium, iron, and zinc complexes, and particularly, ruthenium complex dyes are preferable. Further, (N3dye) can be suitably used.

  As a method of adsorbing a dye, there is a method of immersing a porous oxide semiconductor thin film in a dye solution.

  In the present invention, a photochemical battery can be manufactured using the above-mentioned photoelectric conversion element.

The photochemical cell described above can be manufactured by a usual method.
For example, it can be manufactured by combining a photoelectric conversion element and a transparent electrode on which platinum or carbon is deposited as a counter electrode, and putting an electrolyte solution between them.

  As the transparent electrode, metal oxides such as tin oxide and indium tin oxide (ITO) are preferable.

  Examples of the electrolyte include, for example, 3-methoxypropionitrile, acetonitrile, propylene carbonate, and an electrochemically inert solvent such as ethylene carbonate, for example, lithium iodide, iodine, t-butylpyridine, What dissolved 2-dimethyl-3-propyl imidazolium iodide etc. can be used.

  To 5.004 g of a 30 wt% titania fine particle dispersion slurry (20 nm fine particles manufactured by Titanium Industry Co., Ltd.), 0.2 ml of acetylacetone, 1 ml of 2 wt% hydroxyethyl cellulose and 1 ml of a 10 wt% aqueous solution of polyoxyethylene octyl phenyl ether were added, and the mixture was stirred for 1 hour. A sound wave was applied to produce a titania paste. This paste is referred to as paste A. Furthermore, 2.9997 g of titania fine particles were mixed with 7 ml of nitric acid having a pH of 0.7, 0.2 ml of acetylacetone, 0.2 ml of a surfactant, and polyethylene glycol having a molecular weight of 20,000 were further added to the mixture, and stirring and ultrasonic waves were added for 1 hour to prepare a titania paste did. This titania paste is referred to as paste B. Paste A was cast on a transparent electrode using a 50 μm spacer to form a film. This film was dried at room temperature, then paste B was applied in the same manner, dried and baked at 450 ° C. for 30 minutes to form a porous titania thin film. Was prepared.

(Comparative Example 1)
2.9997 g of titania fine particles were mixed with 7 ml of nitric acid having a pH of 0.7, 0.2 ml of acetylacetone and 0.2 ml of a 10 wt% aqueous solution of polyoxyethylene octyl phenyl ether, and polyethylene glycol having a molecular weight of 20,000 were further added, followed by stirring and ultrasonic waves for 1 hour. , To prepare a titania paste. This paste was cast using a 50 μm spacer to prepare a film, and this film was baked at 450 ° C. for 30 minutes to prepare a porous titania thin film. The haze (cloudiness) of this thin film was measured.

  The titania film prepared in Example 1 was immersed in a 0.3 mmol solution of N3dye at 25 ° C. for 24 hours to adsorb the dye to obtain a photoelectric conversion element. Using platinum for the counter electrode, lithium iodide, iodine, t-butylpyridine, and 1.2-dimethyl-3-propylimidazolium iodide in 3-methoxypropionitrile as the electrolyte were 0.1, 0.05, 0.5, and 0.6 mol / l, respectively. A cell was prepared using what was dissolved and adjusted so as to be as follows. Evaluation of the solar cell was performed by irradiating simulated sunlight of AM 1.5, 100 mA / cm 2.

(Comparative Example 2)
Evaluation as a solar cell was performed in the same manner as in Example 2 except that the titania film prepared in Comparative Example 1 was used.

To 5.004 g of a 30 wt% titania fine particle dispersion slurry (20 nm fine particles manufactured by Titanium Industry Co., Ltd.), 0.2 ml of acetylacetone, 1 ml of 2 wt% hydroxyethyl cellulose and 1 ml of a 10 wt% aqueous solution of polyoxyethylene octyl phenyl ether were added, and the mixture was stirred for 1 hour. A sound wave was applied to produce a titania paste. This paste was cast on a transparent electrode using a 50 μm spacer, and a film was prepared. After drying, the film was baked at 450 ° C. for 30 minutes to prepare a porous titania thin film. The haze (cloudiness) of this thin film was measured.

To 5.000 g of a 30 wt% titania fine particle dispersion slurry (50 nm fine particles manufactured by Titanium Industry Co., Ltd.), 0.2 ml of acetylacetone, 1 ml of 2 wt% hydroxyethyl cellulose and 1 ml of a 10 wt% aqueous solution of polyoxyethylene octyl phenyl ether were added, and the mixture was stirred for 1 hour. A sound wave was applied to produce a titania paste. This paste was cast on a transparent electrode using a 50 μm spacer, and a film was prepared. After drying, the film was baked at 450 ° C. for 30 minutes to prepare a porous titania thin film. The haze (cloudiness) of this thin film was measured.

2.5 g of a 30% titania fine particle dispersion slurry in which 50 nm fine particles and 20 nm fine particles are dispersed are mixed with 2.5 g each (manufactured by Titanium Industry Co., Ltd.). 1 ml of an aqueous octylphenyl ether solution was added, and the mixture was stirred for 1 hour and ultrasonic waves were applied thereto to prepare a titania paste. This paste was cast on a transparent electrode using a 50 μm spacer, and a film was prepared. After drying, the film was baked at 450 ° C. for 30 minutes to prepare a porous titania thin film. The haze (cloudiness) of this thin film was measured.

To 5.004 g of a 30 wt% titania fine particle dispersion slurry (20 nm fine particles manufactured by Titanium Industry Co., Ltd.), 0.2 ml of acetylacetone, 1 ml of 2 wt% hydroxyethyl cellulose and 1 ml of a 10 wt% aqueous solution of polyoxyethylene octyl phenyl ether were added, and the mixture was stirred for 1 hour. A sound wave was applied to produce a titania paste. This paste was cast on a transparent electrode using a 100 μm doctor blade and dried, and the same operation was performed to form a film. After drying, the film was baked at 450 ° C. for 30 minutes to form a porous titania thin film. The pore size distribution of this thin film was measured.

2.9997 g of titania fine particles were mixed with 7 ml of nitric acid having a pH of 0.7, 0.2 ml of acetylacetone, 0.2 ml of a surfactant, and polyethylene glycol having a molecular weight of 20,000 were further added to the mixture, and stirring and ultrasonic waves were added for 1 hour to prepare a titania paste. This paste was cast on a transparent electrode using a 100 μm doctor blade and dried, and the same operation was performed to form a film. After drying, the film was baked at 450 ° C. for 30 minutes to form a porous titania thin film. The pore size distribution of this thin film was measured.

Table 1 summarizes the evaluations of Example 2 and Comparative Example 2 as solar cells.
In the table, Jsc indicates a short-circuit current. Voc indicates an open circuit voltage. FF indicates a fill factor. η indicates the photoelectric conversion efficiency.

FIG. 1 shows an electron microscope image of a cross section of a film obtained according to Example 4 of the present invention. As is clear from the figure, the film of the present invention is a film having a gradient structure without a discontinuous interface. FIG. 2 shows an enlarged view at the center of an electron microscope image of a cross section of the film obtained according to Example 4 of the present invention. FIG. 3 shows photographs of the films obtained in Examples 3 to 5 of the present invention and Comparative Example 1, and shows the results of haze (cloudiness). FIG. 4 shows the results of measuring the pore size distribution of the membrane obtained according to Example 6 of the present invention. FIG. 5 shows the results of measuring the pore size distribution of the membrane obtained according to Example 7 of the present invention.

Claims (6)

A multilayered oxide semiconductor thin film formed by laminating a plurality of porous oxides having different light transmission performances. A multilayered oxide semiconductor thin film formed by laminating a plurality of porous oxides, each layer having a different pore size. The multilayer oxide semiconductor thin film according to claim 1, wherein each layer of the multilayer oxide semiconductor thin film is a different oxide semiconductor. 4. The multilayered oxide semiconductor thin film according to claim 1, wherein at least one of the multilayered oxide semiconductor thin films is titania. A photoelectric conversion element using the multilayered oxide semiconductor thin film according to claim 1. A solar cell using the photoelectric conversion element according to claim 5.

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