JPH11260427A - Transparent semiconductor electrode and photochemical battery by using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve energy conversion efficiency between a transparent semiconductor layer and its adjoining layer, by forming a contour shape having a specific Hausdorff dimension on the opposite surface to a transparent conductor layer interface on the section of the transparent semiconductor layer formed on the transparent conductor layer. SOLUTION: The contour shape of a transparent semiconductor layer 2 on a transparent electrode 1 has a Hausdorff dimension D shown by the equation, 1.5<=D<=2.0, and is preferably an aggregate having a resin-like structure. Therefore, efficiency of photoelectric conversion, occurred by such an action that a mono-molecular layer of a sensitizing pigment 3 absorbs incident light 7 and successively transfers electrons and holes to the transparent semiconductor layer 2 and a carrier transfer layer 4, is improved, besides, the higher a coating ratio is, the better the efficiency is. The Hausdorff dimension is preferably 1.7-2.0 in case that a size length is 10-100 nm, and 1.0-1.5 in case that the size length is 1 μm which is longer than the wavelength of visible ray, and thereby efficiencies of ion diffusion and dispersion of the incident light are improved. The carrier transfer layer 4 may be formed from a conductive solid of ions or electrons or gel-like material other than an electrolyte.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent semiconductor electrode having a fine surface structure and a photochemical cell using the transparent semiconductor electrode.

[0002]

2. Description of the Related Art In general, a photochemical cell using an electrode having a sensitizing dye supported on the surface of a transparent semiconductor layer is disclosed in, for example, JP-A-1-220380 or JP-A-5-504033. A transparent semiconductor electrode or the like having a fine structure obtained by sintering a fine metal oxide is used.

[0003] As a method of manufacturing this transparent semiconductor electrode,
For example, in the case of a titanium oxide film, a method of immersing the transparent electrode in a solution containing an organic titanium compound such as titanium isopropoxide, pulling it up, sintering the transparent electrode, and attaching titanium oxide particles to the transparent electrode surface The method of sintering etc. is taken. Furthermore, the obtained transparent semiconductor film is immersed in a liquid containing a sensitizing dye, the sensitizing dye is adsorbed on the surface of the transparent semiconductor film, and then sandwiched by a counter electrode through a liquid carrier transfer layer, thereby obtaining a wet photochemical battery. Can be obtained.

[0004] The photochemical cell thus obtained operates through the following steps. First, light incident from the transparent electrode side reaches the sensitizing dye carried on the surface of the transparent semiconductor film through the transparent electrode and the transparent semiconductor film, and excites the sensitizing dye. The excited sensitizing dye quickly transfers electrons to the transparent semiconductor film. The electrons that have reached the transparent semiconductor film reach the transparent electrode. The positively charged sensitizing dye receives electrons from ions arriving by diffusing in the carrier transfer layer and is neutralized. The ions that have passed the electrons diffuse in the carrier transfer layer to the counter electrode and receive the electrons. By using the transparent electrode and the counter electrode as a negative electrode and a positive electrode, respectively, the device operates as a wet photochemical cell.

When an ion-conductive solid electrolyte or gel electrolyte, or an electron-conductive organic solid substance is used in place of the liquid carrier transfer layer, a solid-state photochemical cell can be obtained.

[0006] The fine structure of the transparent semiconductor surface thus obtained is produced by depositing the transparent semiconductor fine particles on the surface of the transparent electrode and sintering the same. Therefore, the fine structure of the transparent semiconductor layer surface is substantially uniform in the layer. Becomes When this transparent semiconductor electrode is used in a photochemical cell, if a liquid electrolyte having an ionic conductivity of about 10 ^-1 S / cm is used as the carrier transfer layer, if the thickness of the transparent semiconductor layer is about 50 μm or less, the photoelectric conversion is performed. There was no significant adverse effect on the conversion efficiency, and a photochemical cell with an energy conversion efficiency of about 10% was obtained.

However, in this wet-type photochemical battery, the liquid electrolyte used as the carrier transfer layer leaks to the outside after a long period of use, causing a short life of the battery. Further, such liquid electrolytes are often harmful to the human body, and are dangerous if leaked.

In a solid-state photochemical battery using an ion-conductive solid electrolyte or gel electrolyte or an electron-conductive organic solid substance instead of a liquid carrier-transporting layer, for example, an ion-conductive polymer solid When an electrolyte is used, the ionic conductivity is 10 ⁻⁴ S / cm or less, and the conductivity is significantly reduced as compared with the liquid carrier moving layer. This is because the diffusion constant and mobility of the carrier in the solid carrier moving layer are very small compared to the liquid electrolyte,
This is because carriers do not sufficiently reach all surfaces of the microstructure of the transparent semiconductor layer having a thickness of about 10 μm.

For this reason, in the conventional solid-state photochemical cell, the efficiency of diffusion of ions or electrons from the carrier transfer layer to the sensitizing dye is reduced. As a result, the photoelectric conversion efficiency is 1/100 or less of that of the conventional wet photochemical cell. Had fallen.

[0010]

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above circumstances, and it is an object of the present invention to efficiently perform energy conversion between a transparent semiconductor layer provided on a transparent electrode and a transparent semiconductor layer. It is to provide a transparent semiconductor electrode that can be used.

Another object of the present invention is to provide a transparent semiconductor layer provided on a transparent electrode, and a transparent semiconductor electrode capable of efficiently performing energy conversion between the transparent semiconductor layer and the transparent semiconductor layer. An object of the present invention is to obtain a photochemical cell having good efficiency.

[0012]

The present invention firstly comprises a transparent conductor layer and a transparent semiconductor layer formed on the transparent conductor layer, and the transparent conductor layer in a cross section of the transparent semiconductor layer. The surface opposite to the interface provides a transparent semiconductor electrode characterized in that its Hausdorff dimension D has a contour shape represented by 1.5 ≦ D ≦ 2.0.

The present invention secondly provides a transparent conductor layer and a surface formed on the transparent conductor layer, the surface of the cross section of the transparent semiconductor layer opposite to the interface of the transparent conductor layer having a Hausdorff dimension D. A transparent semiconductor electrode having a transparent semiconductor layer having a contour represented by 1.5 ≦ D ≦ 2.0, a sensitizing dye layer provided on a surface having the contour, and the sensitizing dye layer. A photochemical battery comprising: a carrier transfer layer provided between the counter electrode layers.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first invention provides a transparent semiconductor electrode having an improved surface structure, comprising a transparent conductor layer and a transparent semiconductor layer formed on the transparent conductor layer. The surface opposite to the transparent conductor layer in the cross section of the transparent semiconductor layer provides a transparent semiconductor electrode having a contour shape in which the Hausdorff dimension D is represented by 1.5 ≦ D ≦ 2.0.

According to a second aspect of the present invention, there is provided a photochemical cell using the above-mentioned transparent semiconductor electrode.
A configuration in which a transparent semiconductor layer, a sensitizing dye layer, and a carrier transfer layer are sequentially provided between a counter electrode layer provided to face the transparent electrode layer, and a sensitizing dye in a cross section of the transparent semiconductor layer. The layer side surface is Hausdorff dimension D 1.5 ≦ D ≦
It has a contour shape represented by 2.0.

[0016] This contour shape is preferably composed of an aggregate of dendritic structures. When the size L is 10 nm ≦ L ≦ 100 nm, the Hausdorff dimension D of the contour shape is preferably expressed as 1.7 ≦ D ≦ 2.0.

The Hausdorff dimension D is more preferably 1.0 ≦ D ≦ 1.5 at a size length of 1 μm. First, the configurations of the transparent semiconductor electrode and the photochemical cell of the present invention will be described with reference to the drawings.

FIG. 1 is a model diagram showing a cross-sectional shape of an example of the transparent semiconductor electrode according to the present invention. This transparent semiconductor electrode includes a transparent electrode 1 and a transparent electrode 1 as shown in FIG.
It is composed of the transparent semiconductor 2 provided above. As shown in the figure, this transparent semiconductor surface is an aggregate of a dendritic structure, and has a fractal shape having self-similarity.

Here, the dendritic structure has a columnar, string-like or plate-like structure having at least one, preferably two, more preferably three or more branched structures. It is preferable that the diameter of the branch becomes smaller as it branches into a trunk, a large branch, and a small branch.

FIG. 2 is a model diagram showing a cross-sectional shape of an example of a photochemical cell using the transparent semiconductor electrode according to the present invention. As shown in FIG. 2, the photochemical cell includes a transparent electrode 1, a transparent semiconductor layer 2 having a fractal-shaped cross section on the opposite side of the transparent electrode 1, and a surface shape having a fractal-shaped contour. It has a configuration in which the formed sensitizing dye monolayer 3, the carrier transfer layer 4 containing the carrier 5, and the counter electrode 6 are formed in this order.

In this photochemical cell, the sensitizing dye monolayer 3
After absorbing the incident light 7, the photoelectric conversion can be performed by passing electrons and holes to the transparent semiconductor 2 and the carrier transfer layer 4.

The sensitizing dye monomolecular layer 3 does not need to completely cover the surface of the transparent semiconductor layer 2, but preferably has a higher coverage, and the higher the coverage, the higher the photoelectric conversion efficiency. As the transparent electrode material, tin oxide, zinc oxide, or the like doped with fluorine, indium, or the like, which has little absorption in the visible light region and is conductive, is preferably used.

The transparent semiconductor preferably has a thin depletion layer. In the case of a fine particle structure, the thickness of the depletion layer is preferably smaller than the particle size. As for the composition, it is preferable that the pentavalent metal ion, for example, tantalum, niobium or the like be doped with many oxygen vacancies.

If the carrier concentration is too low, the conductivity is lowered, and if the carrier concentration is too high, a color is formed and light absorption to the sensitizing dye is hindered, so that the carrier concentration is 10 ¹⁰ to 10 ²⁰ / cm ³ ,
It is preferably 10 ¹⁹ / cm ³ .

The transparent semiconductor is a semiconductor having a low absorption in the visible light region, and a metal oxide semiconductor is an oxide of a transition metal such as titanium, zirconium, hafnium, strontium, zinc, indium, yttrium, lanthanum, vanadium, niobium, or the like. Oxide of tantalum, chromium, molybdenum, tungsten, SrTiO ₃ , CaTiO
₃ , perovskites such as BaTiO ₃ , MgTiO ₃ , and SrNb ₂ O ₆ , or composite oxides or oxide mixtures thereof, GaN, and the like are preferable.

The sensitizing dye is a dye that absorbs light and causes charge separation. Such a sensitizing dye is ruthenium-tris, ruthenium-bis, osmium-tris, osmium-bis type transition metal complex, polynuclear complex, ruthenium-cis-diaqua-bipyridyl complex, or phthalocyanine or porphyrin Is preferred. As the carrier transfer layer, acetonitrile or ethylene carbonate containing an ion carrier such as iodide, bromide or hydroquinone, or a mixture thereof is preferable.

As the carrier transfer layer, a liquid ion transfer layer, a solid ion transfer layer, and a solid hole or electron transfer layer are preferably used. As the liquid ion transfer layer, acetonitrile or ethylene carbonate containing an ion carrier such as iodide, bromide or hydroquinone, or a mixture thereof is preferably used.

As the solid ion transfer layer, a gel prepared by mixing the above liquid ion transfer layer with a host polymer such as polyethylene oxide or polyacrylonitrile, polyvinylidene fluoride, polyvinyl alcohol, polyacrylic acid or polyacrylamide is mixed. An electrolyte or a solid electrolyte having a salt such as a sulfonimide salt, an alkyl imidazolium salt, a tetracyanoquinodimethane salt, a dicyanoquinodiimine salt in a polymer side chain such as polyethylene oxide, polyethylene oxide or polyethylene is preferably used.

As a solid hole or an electron transfer layer,
A crystalline or amorphous organic molecule is used. Examples of crystalline materials include various metal phthalocyanines, perylene tetracarboxylic acids, polycyclic aromatics such as perylene and coronene, charge transfer complexes such as tetrathiafulvalene (TTF), and tetracyanoquinodimethane (TCNQ). Examples thereof include conductive polymers such as Alq ₃ represented by the following formula 1, diamine represented by the following formula 2, various oxadiazoles, polypyrrole, polyaniline, poly N-vinylcarbazole, and polyphenylenevinylene represented by the following formula 3.

[0030]

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[0031]

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[0032]

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As the counter electrode, a metal such as platinum, gold or silver, a carbon material such as graphite, and a transparent conductor similar to the above-mentioned transparent electrode are preferably used. Next, the surface structure of the transparent semiconductor used in the present invention will be described.

In the present invention, the surface structure is defined by using the Hausdorff dimension of the cross-sectional profile. The dimension of Hausdorff is described in, for example, Chapter 1 of “Fractal” by Hideki Takayasu, Asakura Shoten. That is,
There are several methods for describing the fractal dimension of a figure. The Hausdorff dimension is a fractal dimension that can be obtained by subdividing an object by a square.

More specifically, the length of one side of the space (plane) is r
Is divided into cubic (square) cells, and the number N (r) of cells that include a part of the target shape is considered. The target Hausdorff dimension D is derived from r and N (r) by the relational expression of N (r) to r ^−D . The value of D is a straight line, ie 1
In the case of a uniform structure such as a dimension or a plane, that is, a two-dimensional structure, each has a value of 1 and an integer value reflecting the number of dimensions. For example, a complicated curve has a non-integer value between 1 and 2. , An index indicating the complexity of the target structure. This Hausdorff dimension is specific to the size length of the cube (square) that divides the space (plane). Therefore, by evaluating the Hausdorff dimension of the actual solid surface structure at various size lengths, it is possible to evaluate the surface shape at each size length.

An actual method of measuring the Hausdorff dimension is described below. For example, cross-sectional images of the element at various magnifications are obtained on a transparent semiconductor surface by a technique such as a transmission electron microscope or a confocal laser microscope in which a cross-sectional shape is obtained as a real image. This image is read by a computer to extract the cross-sectional contour shape of the surface. This cross-sectional contour shape,
Subdivide with a square having a certain length of sides, and count the number of squares including the cross-sectional contour part. The number of squares and the length of the side are plotted on a logarithmic axis, and the slope of the obtained curve is defined as the Hausdorff dimension in the length of the side, that is, the size length. This operation is performed on one interface with images of various magnifications, and the Hausdorf dimension of the contour shape is obtained.

A surface in which the Hausdorff dimension of the cross-sectional profile takes a value close to 2 at a certain size length indicates that the surface has large irregularities near the size length.

On the other hand, in a device having a uniform fine particle structure such as a transparent semiconductor electrode according to the prior art, when an object is measured in a narrow size length region near the fine particle size, a non-integer value reflecting a complicated structure is obtained. Shows the Hausdorff dimension,
When an object is measured with a size length equal to or larger than the narrow size region, a uniform structure, that is, an integer dimension is shown.
That is, in a narrow size length region near the particle size,
Carriers on and off the electrode surface can be moved in and out efficiently.
When the carrier moves over a distance longer than the size length, other fine particles hinder diffusion.

A surface having a constant value of the Hausdorff dimension in a region of a larger size length always has a self-similar concavo-convex structure in the size and length region. That is, even if the surface structure is observed at any size length within the size region, a uniform or similar uneven structure is always shown, and the Hausdorff dimension shows a constant non-integer. For this reason, when a transparent semiconductor electrode having a self-similar structure is used as a photoelectrochemical cell, it is possible to capture and diffuse the carrier very near the surface and the carrier relatively far from the surface in the same manner.

A transparent semiconductor electrode having a self-similar structure, that is, a fractal structure exhibiting an appropriate Hausdorff dimension in an appropriate size region, can be used, for example, in a photochemical cell to form a liquid carrier transfer layer having a relatively high conductivity. When a carrier transport layer having a lower conductivity is used in combination, the effect of showing a higher photoelectric conversion efficiency is remarkable when compared with a conventional transparent semiconductor electrode microstructure having a uniform microstructure in the layer when used together. It is.

In the present invention, formation of a thin film under supersaturated conditions is effective as a method for producing a surface having a predetermined Hausdorff dimension. Under non-equilibrium development such as thin film growth and etching, as shown in Chapter 2 of “Fractal Science” edited by Hideki Takayasu, Asakura Shoten, unevenness of a certain size or more is formed due to the balance between surface instability and surface tension. grow up. In order to control the Hausdorf dimension at a desired size length of the surface, it is necessary to maintain a certain supersaturated condition during surface formation. As a surface forming method capable of controlling the degree of non-equilibrium, for example, as shown in JP-A-8-81222, a liquid obtained by suspending titanium oxide fine particles having a particle size of 15 nm in water is coated on conductive glass. After that, the titanium oxide film obtained by baking at a temperature of 450 ° C. is immersed in a 0.5N hydrofluoric acid aqueous solution for 15 minutes to perform an etching treatment, and then an etching method including a step of removing from the aqueous solution and washing. Can be

However, this etching method is a method of shaving off the surface of the once-formed transparent semiconductor electrode by etching, and requires two steps of a surface preparation step and a fine hole cutting step. In the present invention, a fine structure can be produced in a one-step operation by producing a thin film under the above-described non-equilibrium conditions. As a method of preparing a thin film under non-equilibrium conditions,
It is effective to control the electric field gradient perpendicular to the surface of the thin film to be formed. The method using this electric field gradient is to apply an electric voltage to the surface of the transparent electrode immersed together with the counter electrode in the adjusted electrolytic solution to generate an electric double layer, which is a potential gradient in the direction perpendicular to the surface, generated near the surface of the transparent electrode. It is used.

Examples of the method for producing a transparent semiconductor electrode using a potential gradient include plating, molten salt plating, anodizing, and electrophoretic electrodeposition. In the method of manufacturing a transparent semiconductor electrode using a potential gradient, it is preferable to change the applied voltage by 10% or more or the solvent temperature by 10 degrees or more during energization.

The photochemical cell of the present invention will be described in more detail. In the photochemical cell according to the present invention, the Hausdorff dimension D of the cross-sectional contour shape of the surface of the transparent semiconductor layer has a size length of 10 nm to 100 nm, preferably 3 nm to 100 nm.
100 nm size length, more preferably 3 nm to 30
At a size length of 0 nm, 1.7 ≦ D ≦ 2.0.
Due to this surface structure, in the photochemical cell of the present invention, electrons in the transparent semiconductor from the sensitizing dye and carriers in the carrier transfer layer are both efficiently diffused, and thus have a lower baion conductivity than the liquid electrolyte, for example. Even in the case of a solid-state photochemical cell using a solid electrolyte or the like, high photoelectric conversion efficiency can be obtained.

It is considered that the value of the Hausdorff dimension at a certain size length and the value of the Hausdorff dimension at another significantly different size length are substantially independent. Therefore,
When diffusion of two or more types of particles such as light, electrons, and ions is involved as in the photoelectric conversion process, multiple Hausdorff dimensions can be applied to one surface in consideration of the diffusion constant of each particle. Each can be realized with different size length.

For example, in a photochemical cell, the Hausdorff dimension D of the cross-sectional profile of the surface of the transparent semiconductor layer is 10n.
size length of m-100 nm, preferably 3-100 nm
nm size length, more preferably 3 nm to 300 nm
1.7 ≦ D ≦ 2.0, and a size length of 1 μm longer than the wavelength of visible light, preferably 1 μm.
1.0 ≦ D ≦ 1.5 in a size length of μm to 10 μm
As a result, the scattering of the incident light is efficiently performed on the unevenness having a size of about 1 μm, and the diffusion of the ions is 10 nm.
It is performed efficiently with unevenness having a size of about 100 nm.

As a method for producing a transparent semiconductor used in the photochemical cell of the present invention, an oxide film is grown by an anodic oxidation method in which a metal thin film provided on a transparent electrode is immersed in an electrolytic solution together with a cathode electrode to perform anodic electrolysis. Is preferably used to obtain a transparent semiconductor layer.

In the anodic oxidation method, for example, an aqueous solution of about 0.1 to 1 mol / l of borate, phosphate, tungstate, chromate, oxalate or the like is used as an electrolytic solution. A transparent electrode such as fluorine-doped tin oxide provided with a metal film is immersed in this electrolytic solution together with a counter electrode such as platinum, and a voltage of about 100 V to 300 V is applied to the transparent electrode for about 1 minute to about 10 minutes. This produces oxides. The transparent semiconductor layer is obtained by baking this metal oxide layer at about 400 degrees for about 5 hours. As the metal used for the metal oxide layer, for example, titanium is preferably used.

As another method of forming a transparent semiconductor layer,
An electrophoretic electrodeposition method in which a transparent electrode is immersed together with a cathode electrode in a dispersion medium containing transparent semiconductor fine particles and a current is applied to obtain a transparent semiconductor layer on the transparent electrode surface can be preferably used.

For example, TiO having a diameter of about 5 nm to 20 nm
A transparent electrode, such as tin oxide doped with fluorine, is immersed in a dispersion medium such as water, alcohol, or ketone, in which fine particles such as ₂ are dispersed, together with a counter electrode such as platinum.
By applying a voltage of about 0 V to 1000 V for 1 minute to 10 minutes, fine particles in the dispersion medium precipitate on the surface of the transparent electrode.
The transparent semiconductor layer is obtained by baking this fine particle layer at about 400 degrees for about 5 hours.

Further, as a method for producing a transparent semiconductor layer used in the photochemical cell of the present invention, a metal thin film grown on a transparent electrode is formed by immersing a transparent electrode in a molten salt containing a metal salt together with a cathode electrode and energizing the same. Further, a method of obtaining a transparent semiconductor layer by oxidizing by an anodizing method is more preferably used.

In the hot-dip plating method, a metal salt such as TiCl ₄ is mixed with LiCl-KCl, NaCl-KCl, LiCl-
Heating with a mixed salt such as NaCl, LiF-KF, and LiF-NaF, immersing a transparent electrode such as tin oxide doped with fluorine in a molten salt together with a counter electrode such as platinum, and 3 A / m ^2- By applying a current of about 30 A / m ² , a Ti metal film is obtained. After the metal film is oxidized by an anodic oxidation method or the like, it is dried at about 200 ° C. for about 3 hours to obtain a transparent semiconductor layer.

[0053] immersed in a solvent containing a sensitizing dye transparent semiconductor layer obtained as described above, by heating, to adsorb the sensitizing dye to the transparent semiconductor layer surface, (C ₃ H
₇ ) A photochemical battery is obtained by sandwiching the electrode with a counter electrode via an electrolytic solution in which acetonitrile containing ₄ NI / I _{2 and the} like and ethylene carbonate are mixed.

As the carrier transfer layer, in addition to the above-mentioned electrolytes, ionic conductors such as gel electrolytes, solid electrolytes, and polymer molten salts, low-molecular organic materials, conjugated polymers, and non-conjugated polymers can be used. An electron or hole conductor can be used, and a solid photochemical battery can be obtained by using these instead of a liquid carrier transfer layer.

Hereinafter, the present invention will be specifically described with reference to examples. Example 1 TiCl ₄ , NaCl, and KCl were added in a weight ratio of 1:
A 1: 1 mixed salt is heated at 400 ° C., and a fluorine-doped tin oxide transparent electrode is immersed together with a platinum electrode in a molten salt melted, and a current of 10 A / m ² is applied using the transparent electrode side as a cathode to obtain a transparent electrode. Mass converted film thickness 1 on electrode surface
A titanium metal thin film of 00 nm was obtained.

When the surface of the obtained titanium metal thin film was observed with a scanning electron microscope, an aggregate having a dendritic structure with a height of about 1 μm was observed. This titanium metal thin film is immersed in a 0.5 mol / l aqueous solution of boric acid chloride together with a platinum electrode, and a voltage of 200 V is applied to the transparent electrode for 5 minutes to oxidize the titanium metal thin film, thereby growing a titanium oxide thin film. I let it.

The obtained titanium oxide thin film was heated at 400 ° C. for 5 hours.
After firing for a time, a transparent semiconductor layer (1) was obtained. When the surface of the transparent semiconductor layer (1) was observed with a scanning electron microscope, an aggregate having a dendritic structure with a height of about 5 μm was observed.

The cross section of the transparent semiconductor layer (1) was observed with a transmission electron microscope to obtain a cross-sectional profile of the surface. As a result of analyzing the outline shape by a computer, the Hausdorff dimension D of the surface of the transparent semiconductor layer (1) showed a value of 1.90 ± 0.05 at a size length of 10 nm to 1 μm.

Example 2 A transparent electrode, such as fluorine-doped tin oxide, was immersed in a dispersion medium in which titanium oxide fine particles having a diameter of 10 nm were dispersed in 1% water at a weight ratio together with a counter electrode, such as platinum, to form a transparent electrode. By applying a voltage of 300 V for 5 minutes, titanium oxide fine particles in the dispersion medium were deposited on the surface of the transparent electrode. The transparent semiconductor layer (2) was obtained by baking this fine particle layer at about 400 degrees for about 5 hours.

When the surface of the transparent semiconductor layer (2) was observed with a scanning electron microscope, an aggregate having a dendritic structure with a height of about 5 μm was observed. The cross section of the transparent semiconductor layer (2) was observed with a transmission electron microscope to obtain a cross-sectional profile of the surface. As a result of analyzing this contour shape using a computer, the Hausdorff dimension D of the surface of the transparent semiconductor layer (2) showed a value of 1.90 ± 0.05 at a size length of 10 nm to 1 μm.

Example 3 A transparent semiconductor layer (3) was obtained in the same manner as in Example 2, except that the applied voltage was set at 200 V for 3 minutes and thereafter at 400 V for 2 minutes. When the surface of the transparent semiconductor layer (3) was observed with a scanning electron microscope, irregularities with an interval of about 1 μm and an aggregate of a dendritic structure with a height of about 100 nm were observed on the surface.

The cross section of the transparent semiconductor layer (3) was observed with a transmission electron microscope to obtain a sectional profile of the surface. As a result of analyzing this contour shape by a computer, the Hausdorff dimension D of the surface of the transparent semiconductor layer (3) was 10 nm in size length.
1.90 ± 0.1 at １００100 nm, 1 μm-5 μm
The value of 1.4 ± 0.1 was shown at a size length of m.

Example 4 A transparent semiconductor (4) was obtained in the same manner as in Example 2 except that SrTiO ₃ fine particles having a diameter of 10 nm were used instead of titanium oxide.

When the surface of the transparent semiconductor (4) was observed with a scanning electron microscope, an aggregate having a dendritic structure with a height of about 5 μm was observed. The cross section of the transparent semiconductor layer (4) was observed with a transmission electron microscope to obtain a cross-sectional profile of the surface. As a result of analyzing this contour shape by a computer, the Hausdorff dimension D of the surface of the transparent semiconductor layer (4) was 1.90 ± 0.1 at a size length of 10 nm to 100 nm.
The value of was shown.

Example 5 A transparent semiconductor layer (5) was obtained in the same manner as in Example 4, except that the applied voltage was set at 200 V for 3 minutes and then at 400 V for 2 minutes. When the surface of the transparent semiconductor layer (5) was observed with a scanning electron microscope, irregularities with a spacing of about 1 μm and an aggregate of a dendritic structure with a height of about 100 nm were observed on the surface.

The cross section of the transparent semiconductor layer (5) was observed with a transmission electron microscope to obtain a sectional profile of the surface. As a result of analyzing this contour shape by a computer, the Hausdorff dimension D of the surface of the transparent semiconductor layer (5) was 10 nm in size length.
1.90 ± 0.1 at １００100 nm, 1 μm-5 μm
The value of 1.4 ± 0.1 was shown at a size length of m.

Comparative Example 1 2 mol / l of TiCl ₄ was dissolved in ethanol and then methanol was added to obtain a titanium alkoxide containing 50 mg / ml titanium. This was hydrolyzed, applied to the surface of the transparent electrode, and baked at 450 ° C. for 15 minutes. This application and baking were repeated 10 times to obtain a transparent semiconductor layer (6).

When the surface of the transparent semiconductor layer (6) was observed with a scanning electron microscope, a structure having fine holes of a uniform size with a hole diameter of about 10 nm was observed. The cross section of the transparent semiconductor layer (6) was observed with a transmission electron microscope to obtain a cross-sectional profile of the surface. As a result of analyzing this contour shape by a computer, the Hausdorff dimension D of the surface of the transparent semiconductor layer (6) shows a value of 1.90 ± 0.05 at a size length of 10 nm to 20 nm.
In the size region of nm or less, a value of about 1.2 ± 0.2 was shown.

Examples 6 to 10 and Comparative Example 2 The transparent semiconductor layers (1) to (6) obtained as described above were replaced with cis-bis (isothiocyanato) bis (2,2 ′). The sensitizing dye represented by bipyridyl 4,4'-dicarboxylate) ruthenium is immersed in an ethanol solution, and heated and refluxed at the boiling point of the solution for 30 minutes to adsorb the sensitizing dye on the surface of the transparent semiconductor layer. Thereby, the sensitizing dye was supported in the state of a monomolecular layer.

Transparent semiconductor layer carrying sensitizing dye (1)
Using the transparent semiconductor layer (6), various photochemical cells were formed as follows. Preparation of Wet Photochemical Cell Transparent semiconductor electrodes (1) to (6) supporting the above sensitizing dye were prepared, and (C ₃ H ₇ ) ₄ NI and by the I ₂ sandwich the electrolyte solution and mixed for 20% and 80% by acetonitrile and ethylene carbonate containing equal portions to volume ratio to obtain the wet photochemical cell.

Preparation of Gel Electrolyte Photochemical Cell The above-mentioned wet photochemical cell was manufactured except that an equal amount of polyvinyl alcohol and polyacrylic acid were mixed into the electrolytic solution, and the electrolytic solution was sandwiched and heat-treated at 100 ° C. for 2 hours. A gel electrolyte photochemical cell was obtained in the same manner as in the production.

Production of Solid Electrolyte Photochemical Cell A DMSO solution in which 30% by weight of tetracyanoquinodimethane was dispersed in polyethylene glycol was applied,
The charge transport layer dried under nitrogen was sandwiched between the sensitizing dye-carrying transparent semiconductor electrode and a counter electrode composed of a glass substrate on which platinum was deposited, thereby obtaining a solid electrolyte photochemical cell.

Dry photochemical cell Diamine is sprayed on the surface of the transparent semiconductor electrode carrying the sensitizing dye, and heated at 280 ° C. for 10 minutes in dry nitrogen to melt the diamine. After heating, a counter electrode obtained by depositing platinum on a glass substrate was placed on the diamine layer, and cooled to room temperature to obtain dry photochemical cells. When a cross section of this battery was observed by SEM, a diamine layer having a thickness of 5 μm was confirmed.

For each of the photochemical cells of Examples 6 to 10 and Comparative Example 2 obtained using the transparent semiconductor layers (1) to (6), a liquid electrolyte and a solid electrolyte using a polymer molten salt were used, respectively. The resultant was irradiated with light at a light amount of 750 mW / cm ² using a pseudo solar light source manufactured by Wacom, and its photoelectric conversion efficiency was measured by a source measure unit 236 of Keithley. The results obtained are shown in 1 below.

[0075]

[Table 1]

As is clear from Table 1, the photochemical cell according to the present invention has a superior photoelectric conversion efficiency as compared with the conventional photochemical cell. Also. In particular, when the electrolyte portion is solidified, the effect is remarkable.

[0077]

Since the transparent semiconductor electrode of the present invention has a surface structure having a desirable Hausdorff dimension in a specific size region, the transparent semiconductor layer provided on the transparent electrode is adjacent to the transparent semiconductor layer. Energy conversion with the layer can be performed efficiently.

In the photochemical cell of the present invention, the photoelectric conversion efficiency can be improved by using a transparent semiconductor electrode having a surface structure having a desirable Hausdorff dimension in a specific size region.

Further, according to the present invention, by using such a transparent semiconductor electrode, even when the electrolyte portion is solidified and the ionic conductivity is lowered, the loss of the photoelectric conversion efficiency can be reduced by one degree. It can be suppressed sufficiently lower than a transparent semiconductor having such a fine particle structure.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a cross-sectional shape of an example of a transparent semiconductor electrode of the present invention.

FIG. 2 is a schematic view illustrating a structure of a main part of a photochemical cell using the transparent semiconductor electrode of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent electrode 2 ... Transparent semiconductor layer 3 ... Dye 4 ... Carrier moving layer 5 ... Carrier in carrier moving layer 6 ... Counter electrode 7 ... Incident light

Claims (6)

[Claims] 1. A transparent conductor layer and a transparent semiconductor layer formed on the transparent conductor layer, and a surface opposite to the transparent conductor layer interface in a cross section of the transparent semiconductor layer has a Hausdorff dimension D. Has a contour represented by 1.5 ≦ D ≦ 2.0. 2. The transparent semiconductor electrode according to claim 1, wherein the contour of the surface is formed of an aggregate of a dendritic structure. 3. The contour shape has a Hausdorff dimension D whose size length L is 10 nm ≦ L ≦ 100 nm.
The transparent semiconductor electrode according to claim 1, wherein 1.7 ≦ D ≦ 2.0. 4. The transparent semiconductor electrode according to claim 3, wherein said Hausdorff dimension D satisfies 1.0 ≦ D ≦ 1.5 at a size length of 1 μm. 5. A transparent conductor layer and a surface formed on the transparent conductor layer and having a Hausdorff dimension D of 1.1 on the surface of the cross section of the transparent semiconductor layer opposite to the transparent conductor layer interface.
A transparent semiconductor electrode having a transparent semiconductor layer having a contour represented by 5 ≦ D ≦ 2.0, a sensitizing dye layer provided on a surface having the contour, the sensitizing dye layer and the counter electrode And a carrier transfer layer provided between the layers. 6. The photochemical cell according to claim 5, wherein the carrier transfer layer is made of a solid or gel material having ionic or electronic conductivity.