JP4850338B2 - Semiconductor electrode manufacturing method and photochemical battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor electrode for a photochemical battery, a method for producing the same, and a photochemical battery using the electrode.
[0002]
[Prior art]
Solar cells containing an oxide semiconductor sensitized with a dye are known. For example, Japanese Patent Laid-Open No. 1-220380 discloses an oxide semiconductor electrode in which a photosensitizing dye such as a ruthenium metal complex is adsorbed on a semiconductor made of a metal oxide such as porous and crystalline titanium oxide. A dye-sensitized solar cell using the above has been proposed.
Specifically, the dye-sensitized solar cell has a transparent substrate having a conductive surface and an oxide semiconductor film adsorbing a sensitizing dye formed on the conductive surface as a photoelectrode and conductive as a counter electrode. A transparent substrate having a conductive surface is used and an electrolyte solution is sealed between these electrodes.
[0003]
The oxide semiconductor film formed on the conductive surface is formed from a fired product of an oxide semiconductor fine particle aggregate. Specifically, a metal alkoxide is used as a starting material, and a sol-gel method in which an oxide is obtained through hydrolysis and polycondensation, a method in which fine particles of an oxide semiconductor are applied to a conductive surface, and a chemical reaction in an aqueous solution. The liquid phase deposition method is used to deposit an oxide semiconductor thin film on the conductive surface, and the oxide semiconductor formed on the conductive surface and the precursor thereof are baked by these methods. The
[0004]
As described above, the oxide semiconductor electrode requires a firing step for the purpose of obtaining durability and practical energy conversion efficiency. Therefore, the substrate to be an electrode is required to have high heat resistance, and is actually limited to a transparent conductive glass substrate coated with tin oxide, tin-doped indium oxide, fluorine-doped tin oxide, antimony-doped tin oxide, It has been difficult to use a resin having poor heat resistance as a semiconductor electrode substrate.
[0005]
[Problems to be solved by the invention]
The present invention can be applied not only to glass but also to an optically transparent substrate, particularly a synthetic resin having inferior heat resistance, as a substrate material for a semiconductor electrode for a photochemical battery, and to obtain practical energy conversion efficiency. It is an object of the present invention to provide a method for producing a semiconductor electrode, and a photochemical battery using the semiconductor electrode. Furthermore, it aims at providing the semiconductor electrode and photochemical battery excellent in flexibility, workability, etc.
[0006]
[Means for Solving the Problems]
As a result of examining the above problems, the present inventors have formed a layer comprising an oxide semiconductor and / or a precursor thereof on a heat-resistant substrate, and after heating and firing the layer, the obtained oxide semiconductor film is arbitrarily selected. It was found that the above problem can be solved by forming an oxide semiconductor electrode by transferring it onto a light-transmitting substrate.
[0007]
That is, the present invention includes the following inventions.
(1) An oxide semiconductor film obtained by forming a layer containing an oxide semiconductor and / or a precursor thereof on a heat-resistant substrate surface-treated with a layer of a fluororesin or a thermally decomposable resin , and heating and baking the layer. Is transferred onto the substrate to be transferred.
(2) The manufacturing method according to (1), wherein the transfer substrate is a synthetic resin.
(3) The production method according to (1) or (2), wherein the thermally decomposable resin used for the surface treatment of the heat resistant substrate is selected from a (meth) acrylate resin, a cellulose resin, and polyethylene glycol.
(4) The thermodegradable resin used for the surface treatment of the heat-resistant substrate is described in (1) or (2) above, which is selected from poly (2-ethylhexyl (meth) acrylate), polyethyl (meth) acrylate, ethyl cellulose, and polyethylene glycol. Manufacturing method.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The oxide semiconductor used in the present invention is not particularly limited, and a conventionally known semiconductor can be used. For example, oxides of transition metals such as Ti, Nb, Zn, Sn, Zr, Y, La, Ta, Hf, Sr, In, V, Cr, Mo, W, SrTiO ₃ , CaTiO ₃ , BaTiO ₃ , Examples thereof include perovskite oxides such as MgTiO ₃ and SrNb ₂ O ₆ , composite oxides or oxide mixtures thereof. In particular, TiO ₂ and ZnO are preferable from the viewpoint of semiconductor characteristics, corrosion resistance, stability, and safety. Note that these oxide semiconductors are preferably used as fine particles, and the average particle diameter is usually 1 to 1000 nm, preferably 5 to 200 nm.
[0009]
The term “oxide semiconductor precursor” as used in this specification refers to a state in which the oxide semiconductor is finally obtained and can be converted into an oxide semiconductor by heating and baking. As such, for example, metal alkoxide and its hydrolyzate or condensate, metal complex, metal organic acid salt, metal halide, etc. that can form the above-mentioned oxide semiconductor, and further semiconductor by change of crystal structure The thing which shows the physical property as is mentioned. For example, precursors of TiO ₂ semiconductors include metal alkoxides such as titanium ethoxide and titanium propoxide, condensates obtained by hydrolysis and polycondensation of such metal alkoxides, or metals such as titanium acetylacetonate. Examples include a complex, a metal organic acid salt such as titanium octylate, and a metal halide such as titanium tetrachloride as raw materials, and hydrolyzing these solutions.
[0010]
The material of the heat-resistant substrate used in the present invention is not particularly limited as long as it can withstand normal firing conditions. However, a material that does not cause deformation, chemical change or the like even under firing conditions of 300 to 1000 ° C. is preferable. Examples of such a substrate material include metals such as stainless steel, nickel, platinum, gold, and titanium, glass, and heat resistant resins such as polyimide. A plate or sheet made of the above material can be used as the heat resistant substrate. These heat resistant substrates may be used alone, but surface treatment may be applied to the heat resistant substrate for the purpose of imparting transferability (easy to peel) of the oxide semiconductor film. Such treatments include providing a release layer made of fluororesin such as ethylene-tetrafluoroethylene copolymer, polyvinyl fluoride, polychlorotrifluoroethylene, etc., or combusting and decomposing by heat during firing. A method of providing a layer of a resin, for example, a (meth) acrylate resin such as poly (2-ethylhexyl (meth) acrylate) or polyethyl (meth) acrylate, a cellulose resin such as ethyl cellulose, or a thermally decomposable resin such as polyethylene glycol There is.
[0011]
As a method for forming an oxide semiconductor and / or precursor layer thereof on the heat resistant substrate, for example, the following method can be used. Coating liquid by preparing a liquid in which oxide semiconductor fine particles are dispersed in water or an organic solvent or a mixed solvent thereof, a solution or suspension of an oxide semiconductor precursor, or a liquid or slurry in which these are mixed. And The concentration of the oxide semiconductor and / or its precursor in the coating solution is preferably 1 to 70% by weight. Next, the coating liquid is applied onto a heat-resistant substrate by spin coating, dip coating, screen printing, blade coating, or the like, and dried as necessary to form an oxide semiconductor and / or precursor layer. Can be formed. In addition, you may add additives, such as surfactant, a viscosity modifier, and a dispersing agent, to a coating liquid as needed.
[0012]
Next, the heat-resistant substrate on which the layer containing an oxide semiconductor and / or a precursor is formed is heated and fired. It is preferable that the heating and baking conditions are 300 to 1000 ° C. for 1 to 120 minutes. If the temperature is lower than 300 ° C., the sintering does not proceed sufficiently, and sufficient film strength cannot be obtained, or the energy conversion efficiency may decrease because the mobility of electrons in the film decreases. On the other hand, if the temperature is higher than 1000 ° C., the sintering is too advanced to be porous, and the amount of dye adsorbed, which will be described later, decreases, resulting in a decrease in energy conversion efficiency. An oxide semiconductor film is formed over the heat resistant substrate by heating and baking the heat resistant substrate on which the layer including the oxide semiconductor and / or the precursor is formed.
[0013]
The oxide semiconductor film obtained by heating and baking is a porous structure film, and its thickness is usually about 1 to 50 μm, preferably about 5 to 20 μm. The ratio of the actual surface area to the apparent area is 10 or more, preferably 100 or more. The actual surface area is the total surface area of the porous membrane determined by the BET method.
[0014]
In the oxide semiconductor film thus formed, a collecting electrode for taking out current is arranged. The collector electrode may be formed either before or after the heat-firing treatment, and as a method thereof, a layer of metal or oxide conductor is deposited on the oxide semiconductor or its precursor by vapor deposition or sputtering. A method, a method in which metal fine particles or oxide conductor fine particles are mixed with a resin or a solvent and applied onto an oxide semiconductor or a precursor thereof, a light-transmitting metal mesh is disposed on a heat-resistant substrate, and the above-described coating is applied on the mesh. Examples thereof include a method of forming an oxide semiconductor film integrated with a metal mesh by applying a liquid.
[0015]
A dye may be adsorbed (chemical adsorption, physical adsorption, deposition, etc.) as a sensitizer on the oxide semiconductor film formed as described above. The adsorption of the dye may be performed either before or after the transfer to the transfer substrate. As a method for adsorbing the dye, for example, the substrate on which the oxide semiconductor film is formed may be immersed in a solution in which the dye is dissolved in an organic solvent. If necessary, the solution may be heated for the purpose of performing pressure reduction treatment or promoting adsorption so that the solution quickly enters the inside of the semiconductor film.
[0016]
The dye that can be used in the present invention is not particularly limited as long as it has absorption in the visible light region and / or the infrared light region, and examples thereof include metal complexes and organic dyes.
Examples of metal complexes include metal complexes such as ruthenium, osmium, iron, zinc and platinum, metal phthalocyanines such as copper phthalocyanine and titanyl phthalocyanine, chlorophyll or derivatives thereof. Among these, a ruthenium complex is preferable from the viewpoint of sensitization effect and durability. Examples of the ruthenium complex include RuL ₂ (CN) ₂ , RuL ₂ (SCN) ₂ , RuL ₃ (CN) and the like. Here, L is a ligand such as 2,2′-bipyridyl-4,4′-dicarboxylate, which has a functional group such as a carboxyl group, a hydroxyl group, a sulfone group, or the like to the oxide semiconductor film. It is preferable from the point of adsorptivity.
[0017]
Examples of organic dyes include phthalocyanine, cyanine dyes, merocyanine dyes, xanthene dyes, triphenylmethane dyes, rose bengal, rhodamine B, and the like. For the same reason, carboxyl groups, hydroxyl groups, sulfone groups, etc. It is preferable to introduce a functional group of
[0018]
Next, a method for transferring the oxide semiconductor film formed over the heat-resistant substrate to the substrate to be transferred will be described.
The substrate to be transferred is not particularly limited as long as it is light-transmitting, and a substrate made of a synthetic resin can be used in addition to a conventionally used glass substrate.
[0019]
Examples of the synthetic resin include, for example, polyolefins such as polyethylene, polypropylene, polyisobutylene, polystyrene, and ethylene-propylene rubber, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer. Polymers, cellulose derivatives such as ethyl cellulose and cellulose triacetate, poly (meth) acrylic acid and its ester compounds, polyvinyl acetals such as polyvinyl acetate, polyvinyl alcohol and polyvinyl butyral, polyacetal, polyamide, polyimide, nylon, urethane resin, epoxy Resin, silicone resin, fluororesin, polycarbonate, urea resin, melamine resin, phenol resin, resorcinol resin, furan resin, etc. . Among these synthetic resins, polyolefins or polyester resins are preferable because they have good light transmittance, resistance to an electrolytic solution, and little gas permeation.
[0020]
When a synthetic resin is used, a film having a thickness of 10 to 1000 μm can be used as a substrate to be transferred.
As a method for transferring the oxide semiconductor film to the substrate to be transferred, a method in which the oxide semiconductor film and the substrate to be transferred are bonded together using an adhesive, and then peeled off from the heat-resistant substrate, or the adhesive itself is used. For example, a method in which the oxide semiconductor film is attached to the substrate to be transferred and then peeled off from the heat resistant substrate can be used.
[0021]
The adhesive that can be used in the transfer step is not particularly limited, and various synthetic resins and inorganic adhesives can be used. Synthetic resins include, for example, polyethylene, polypropylene, polyisobutylene, polystyrene, polyolefins such as ethylene-propylene rubber, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, cellulose derivatives such as ethyl cellulose, cellulose triacetate, Copolymer of poly (meth) acrylic acid and its ester, polyvinyl acetal such as polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyamide, polyimide, nylon, polyester resin, urethane resin, epoxy resin, silicone resin, fluorine Examples thereof include resins. Examples of the inorganic adhesive include alkali metal silicates such as low melting point glass and sodium silicate. Among these adhesives, polyolefins, ethylene-vinyl acetate copolymers, urethane resins, epoxy resins, and silicone resins are preferable from the viewpoints of adhesiveness, resistance to an electrolytic solution, light transmittance, and transferability. Moreover, an additive can be used for these adhesives as needed. Examples of the additive include a crosslinking agent, a dispersant, a tackifier, a leveling agent, a plasticizer, and an antifoaming agent.
[0022]
More specifically, a method for bonding the oxide semiconductor film and the transfer substrate using such an adhesive is described. For example, an adhesive dissolved or dispersed in an organic solvent or water is formed on the oxide semiconductor film. Alternatively, it is applied to a transfer substrate, and the oxide semiconductor film and the transfer substrate are bonded together and dried, and a heat-melted adhesive is applied to the oxide semiconductor film or the transfer substrate and bonded. And a method in which the resin film made of the synthetic resin as described above is sandwiched between the oxide semiconductor film and the substrate to be transferred, and is heated and bonded. Although the thickness of an adhesive bond layer is not specifically limited, 5-300 micrometers, Preferably it is 10-200 micrometers.
A photochemical battery can be manufactured using the semiconductor electrode manufactured as described above.
[0023]
As the electrolyte layer, an electrolyte solution is usually used. In addition, a gel or solid electrolyte is also used. The electrolyte solution is not particularly limited, and examples thereof include a solution containing a redox pair such as I / I ₃ , Br / Br ₃ , and quinone / hydroquinone. Specifically, in the case of I / I ₃ , a solution in which iodine and an ammonium salt of iodine are dissolved in an organic solvent such as acetonitrile, ethylene carbonate, propylene carbonate or the like is used.
[0024]
In addition, materials that transport electrons and holes can also be applied. Various metal phthalocyanines, perylene tetracarboxylic acids, polycyclic aromatics such as perylene and coronene, charge transport materials such as arylamines, and conductive polymers such as polypyrrole and polyphenylene vinylene. Etc. can be used. The thickness of these electrolyte layers is usually about 1 to 50 μm.
[0025]
As the counter electrode, any conductive material can be used, and examples thereof include metal materials such as gold, platinum, silver, and copper, and the above-described conductive glass and carbon. Those having a catalytic ability to be carried out in (1) are preferred, and platinum, platinum-plated or platinum-deposited conductive material surfaces, carbon, and the like can be mentioned.
When manufacturing a photochemical cell using the semiconductor electrode of the present invention, a photochemical cell such as a dye-sensitized solar cell can be manufactured by bringing the semiconductor electrode of the present invention and the counter electrode into contact with an electrolyte.
[0026]
【Example】
Example 1
<Formation of TiO ₂ film>
In a mixed solution of 3.6 ml of water and 0.4 ml of acetylacetone, 12 g of crystalline titanium oxide particles (trade name P-25, manufactured by Nippon Aerosil Co., Ltd., average particle size 21 nm) were added and well dispersed in a mortar. Further, 16 ml of water was gradually added with stirring, and finally 0.2 ml of a surfactant (Triton X-100 manufactured by Aldrich) was added and stirred well to prepare a titanium oxide slurry containing 38% by weight of titanium oxide.
[0027]
Next, poly (2-ethylhexyl methacrylate) is applied to a stainless steel plate having a thickness of 1.1 mm as a heat resistant substrate to a thickness of about 10 μm and used as a collecting electrode on the poly (2-ethylhexyl methacrylate). What stuck the mesh net | network (made by Niraco) was prepared separately. On this substrate, the above slurry was applied in an area of 1.5 × 1.5 cm and a thickness of 50 μm, and dried at room temperature for 5 hours. Next, it was heated and fired in air at 450 ° C. for 30 minutes, and poly (2-ethylhexyl methacrylate) was thermally decomposed to produce a titanium oxide semiconductor electrode having a current collecting electrode.
[0028]
<Transfer>
Heat-meltable EVA (ethylene-vinyl acetate copolymer) sheet (trade name: Takemelt Thickness 150 μm, manufactured by Takeda Pharmaceutical Co., Ltd.) and corona-treated 50 μm biaxially stretched polyethylene terephthalate (PET) film on the obtained semiconductor electrode The layers were sequentially stacked and bonded with a heat roll laminator heated to 110 ° C. Subsequently, the semiconductor electrode was peeled off from the stainless steel plate to obtain a PET substrate semiconductor electrode in which a titanium oxide semiconductor was formed on the PET film via EVA as a transfer substrate.
[0029]
<Dye adsorption>
The obtained PET substrate semiconductor electrode was immersed in an ethanol solution (3 × 10 ⁻⁴ M) of cis-bis (isothiocyanate) bis (2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium for 24 hours. A sensitizing dye was adsorbed on titanium oxide to prepare a dye-sensitized titanium oxide semiconductor electrode.
[0030]
<Production of photochemical battery>
A photochemical battery was constructed by bringing a dye-sensitized titanium oxide semiconductor electrode and its counter electrode into contact with an electrolytic solution. As the counter electrode, an ITO-coated PET film having a surface resistance of 50Ω / □ with platinum deposited on the ITO surface was used. As the electrolytic solution, a mixture of ethylene carbonate and acetonitrile (capacity ratio 80/20) containing 0.5M tetrapropylammonium iodide and 0.05M iodine as the electrolyte was used. A 25 μm PET film was sandwiched between the electrodes as a spacer, and the end was sealed with an epoxy resin.
[0031]
<Characteristic evaluation of photochemical battery>
The characteristic evaluation of the produced photochemical battery was performed by irradiating AM1.5 artificial sunlight (1000 W / m ² ) defined in JIS C8911. As a result, the energy conversion efficiency was 5.5%.
Furthermore, after repeating the operation of applying a 1 cm diameter rod to the front side of this photochemical battery and bending it to the back side and then bending it to the opposite side, the energy conversion efficiency was measured and found to be 5.0%. It was.
[0032]
(Reference Example 1)
A titanium oxide slurry prepared in the same manner as in the example was applied to the ITO surface of an ITO-coated PET film having a surface resistance of 50Ω / □. After drying at room temperature for 5 hours, a heat treatment was performed at 100 ° C. for 30 minutes to produce a titanium oxide semiconductor electrode. The dye adsorption and the production of the photochemical battery were carried out in the same manner as in the examples.
The energy conversion efficiency was measured and found to be 2.7%.
Further, as in the example, the bending operation was performed and the energy conversion efficiency was measured, and it was 0.8%. When the state of the titanium oxide film was visually observed, a part of the titanium oxide film was peeled off from the ITO-coated PET substrate.
[0033]
【The invention's effect】
According to the present invention, a method of manufacturing a semiconductor electrode using a substrate of any material can be provided. In particular, according to the present invention, it is possible to provide a semiconductor electrode having practical energy conversion efficiency using a synthetic resin substrate having poor heat resistance, which cannot be applied under conventional heating and baking conditions. And a highly efficient photochemical battery can be provided. According to the present invention, since a synthetic resin which is superior in flexibility and workability and is lightweight as a substrate can be used as a substrate as compared with the glass conventionally used as a substrate, the degree of freedom of installation place is high, and even on a flat surface It is possible to provide a semiconductor electrode and a photochemical battery that can be installed even on a curved surface and are easy to install.

Claims (4)

An oxide semiconductor film obtained by forming a layer containing an oxide semiconductor and / or a precursor thereof on a heat-resistant substrate surface-treated with a layer of a fluororesin or a thermally decomposable resin and heating and firing the layer is formed. A method for producing a semiconductor electrode, wherein the semiconductor electrode is transferred onto a transfer substrate.   The manufacturing method according to claim 1, wherein the substrate to be transferred is a synthetic resin. The production method according to claim 1 or 2, wherein the thermally decomposable resin used for the surface treatment of the heat resistant substrate is selected from a (meth) acrylate resin, a cellulose resin, and polyethylene glycol. The production method according to claim 1 or 2, wherein the thermally decomposable resin used for the surface treatment of the heat resistant substrate is selected from poly (2-ethylhexyl (meth) acrylate), polyethyl (meth) acrylate, ethyl cellulose and polyethylene glycol.