JPH10112337A - Wet solar cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric resistance on the interface between a pigment sensitizing semiconductor electrode and an electromotive force taking out electrode and the internal resistance in the semiconductor electrode, and enhance photoelectric transfer efficiency by increasing utilization efficiency of irradiation light energy in a wet solar cell having the pigment sensitizing semiconductor electrode. SOLUTION: A conducting substrate 5 for taking out electromotive force is oxidized, and pigment is carried on an oxidized film to produce a pigment sensitizing semiconductor electrode 4 integrated with the conducting substrate. As the oxidizing method, anodic oxidation is used, hydrothermal treatment is applied to the anodically oxidized film to make the oxidized film porous. Thereby, a large amount of pigment is adsorbed and utilization efficiency of irradiation light energy is enhanced. A wet solar cell is assembled by interposing an electrolyte layer 3 between the pigment sensitizing semiconductor electrode 4 and a transparent conducting film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet solar cell for directly converting light energy into electric energy.

[0002]

2. Description of the Related Art Conventionally, as a method for directly converting light energy into electric energy, a photochemical cell using a silicon semiconductor or a dye is known. Above all, a solar cell using a pn junction of semiconductor silicon is well known, and is already used as a field of weak power consumption, an independent power supply, and a space power supply. However, the silicon solar cell has a problem that the theoretical conversion efficiency is low and the conversion efficiency is deteriorated in practical use. In addition, a large amount of energy is required to produce amorphous silicon as well as silicon single crystal, so it is necessary to continue power generation for a long period of several decades in order to recover the energy used to make batteries. is there. Photochemical cells (wet solar cells) in which a semiconductor electrode is dye-sensitized have been studied for a long time, but this type of photochemical cell has a problem of low conversion efficiency. However, recently, the surface area of the semiconductor electrode has been increased to allow a large amount of dye to be adsorbed, and the conversion efficiency has been dramatically increased. The semiconductor electrode on which such a dye is adsorbed is called a dye-sensitized semiconductor electrode.

FIG. 3 is a cross-sectional view showing a schematic structure of a conventional photochemical cell using a dye-sensitized semiconductor electrode. The structure is such that a transparent conductive film 2 is attached to each of two transparent substrates 1,
An electrolyte layer 3 and a dye-sensitized semiconductor electrode 4 are sandwiched between transparent conductive films 2, and titania (TiO ₂ ) is used as a semiconductor electrode. However, since the concentration of carriers (charge carriers) is much lower than that of a metal when the semiconductor electrode is left as it is, it has been extremely difficult to smoothly transfer electrons.

[0004] Various dye-sensitized semiconductor electrodes have recently been devised in terms of chemical bonding between them so that electrons can be properly transferred at the interface between the titania fine particles and the dye.

[0005]

However, with respect to the photoelectric conversion efficiency of a wet type solar cell, the electric power between the conductive film and the titanium oxide film formed on the surface thereof and between the titania fine particles constituting the titanium oxide film is limited. Resistance has a significant effect.
Therefore, it is necessary to reduce the internal resistance generated at the interface between the conductive film and the titanium oxide film and between the titania fine particles as much as possible. However, the conventional dye-sensitized semiconductor electrode is a titanium oxide film obtained by applying a solution in which titania fine particles are dispersed on a transparent substrate with a transparent conductive film, and then drying and sintering at a high temperature. There was no room for improvement in the transfer of electrons at the interface.

[0006] The dye-carrying performance of the titanium oxide film is determined by the surface roughness of the titanium oxide film, but there is no room for controlling the surface roughness in the conventional manufacturing process. An object of the present invention is to provide a wet-type solar cell in which electrons are smoothly exchanged and which has high use efficiency of irradiation light.

[0007]

Means for Solving the Problems The present inventors have integrated a dye-sensitized semiconductor electrode and a conductive film (one electrode) provided in contact with the dye-sensitized semiconductor electrode, so that an electron at the interface is formed. Was found to be able to send and receive information smoothly.
That is, the present invention provides a `` transparent substrate with a transparent conductive film, a semiconductor electrode and an electrolyte layer carrying a dye between the transparent substrate and a conductive substrate forming a counter electrode, and the transparent conductive film is subjected to photoelectric conversion. In a wet battery that generates electric energy between the conductive substrate and the conductive substrate, the semiconductor electrode is an oxide film obtained by oxidizing at least a part of a metal that forms the conductive substrate. (Claim 1).

Further, the metal constituting the conductive substrate may be:
An oxide film selected from titanium, niobium, tantalum, and zirconium (claim 2), and constituting the semiconductor electrode,
The metal is anodized to have a porous structure (claim 3). Further, the conductive substrate,
The semiconductor substrate is a titanium substrate roughened by sandblasting, and the semiconductor electrode is a titanium anodic oxide film having a porous structure.

Further, the conductive substrate has a titanium layer formed by spraying titanium powder on at least a part thereof, and the semiconductor electrode is obtained by anodizing at least a part of the titanium layer. An anodic oxide film (claim 6).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The semiconductor electrode of the present invention comprises titanium,
Since it is obtained by oxidizing a metal selected from niobium, tantalum and zirconium, a metal oxide having a photoelectric conversion action and a metal used as an electrode are integrated.
Examples of the metal oxidation treatment include a method of heating the metal in an oxidizing atmosphere and a method of utilizing ionization in an electrolytic solution. The anodic oxidation method is particularly preferable for the following reasons. Since the anodic oxide film is formed by oxidizing the surface of the metal substrate, the adhesion between the substrate and the oxide film is extremely good, and the electric resistance at this interface is very small. Also, despite the oxide film being formed with relatively low energy,
Since the particles constituting the anodic oxide film are strongly bonded to each other, the electric resistance inside the anodic oxide film can be reduced. The time required to form the anodic oxide film is as short as several minutes, and the anodic oxide film can be formed in an aqueous solution at room temperature without requiring any special equipment, so that the energy consumption required for film formation is very small. Therefore, using an anodic oxide film for a wet solar cell is very advantageous for improving the conversion efficiency. The anodic oxidation performed in the present invention is a technique of forming an oxide film having a thickness of several μm on the surface of the metal on the anode side by applying an electric field with the above metal as an anode and any metal as a cathode in an electrolyte. is there. As the electrolyte used for anodization,
Phosphoric acid, sulfuric acid or a mixed acid thereof, or an aqueous solution in which glycerophosphate and metal acetate are dissolved are preferred. Examples of the glycerophosphate include sodium glycerophosphate and calcium glycerophosphate, and sodium glycerophosphate is most preferable because it is very soluble in water.
Any metal acetate can be used, but especially alkali metal (lithium, sodium, potassium, rubidium, cesium) acetate, alkaline earth metal (magnesium, calcium, strontium, barium) acetate, and lanthanum acetate are glyceroline. It is most preferable because it can be very well dissolved in an aqueous solution of an acid salt and can be stably anodized up to a high voltage. When titanium is anodized, for example, using these electrolytes, a titanium anodic oxide film is formed in which phosphorus ions or phosphate ions are taken in from phosphoric acid or glycerophosphate and metal ions are taken in from metal acetate. Before starting anodic oxidation using these electrolytes, the highest attainable voltage is set in advance. When the anodization is started, the voltage gradually increases. When the voltage reaches the maximum voltage, no current flows and the anodization is terminated. The time required for the anodic oxidation can be completed in a shorter time as the current density is increased and the pressure is increased more quickly.
Minutes and relatively short. Since the thickness of the film is proportional to the voltage, in order to increase the surface area per unit area of the anodic oxide film, it is preferable to increase the film thickness by anodizing at a high voltage.
However, if the film thickness is too large, anodic oxidation cannot be performed stably, so that about 500 V is the limit. When the voltage exceeds about 100 V, spark discharge occurs on the surface of the anodic oxide film, and the oxide film is locally heated to a high temperature. As a result of repeatedly heating the film innumerably, the entire anodic oxide film is crystallized, and an anodic oxide film having high crystallinity is formed. Further, anodic oxidation has the advantage that the film formation rate is faster than other methods of manufacturing a ceramic film, and that a uniform thickness can be formed even in a large area. In addition, since a film can be formed even when severe unevenness is formed on the substrate surface or the substrate has a complicated shape, it is an industrially useful method for forming a large-area ceramic film. Further, in order to further improve the conversion efficiency of the wet solar cell, in the present invention, a dye-sensitized semiconductor electrode having a dye adsorbed on the surface of the semiconductor electrode is used. In order to increase the amount of dye adsorbed and the amount of light absorbed per unit area of the dye-sensitized semiconductor electrode, it is effective to form fine irregularities on the electrode surface and increase the apparent surface area as much as possible. It has been known that when a metal substrate is anodized at a high voltage, a large number of discharge marks are formed by spark discharge generated on the surface, and the substrate becomes porous.
However, since the diameter of such a discharge trace is as large as about several μm, it does not contribute much to increasing the surface area of the anodic oxide film. In order to increase the surface area of the film, it is extremely effective to form very fine pores of about several tens nm in the film to make the film porous. In order to have such a porous structure, first, at the time of anodic oxidation, the ions are taken into the anodic oxide film from the electrolyte by heating by spark discharge,
Next, substances (ions) soluble in the liquid taken into the anodic oxide film may be eluted. After the soluble substance elutes, numerous pores are formed, the anodic oxide film becomes porous, and the surface area is significantly increased. As the elution method, a so-called hydrothermal method in which the anodic oxide film is heated in a range of 100 to 500 ° C. in a liquid or vapor in a closed vessel such as an autoclave is effective. If the heating temperature is lower than 100 ° C, the soluble substance hardly elutes. Also, set the autoclave to 5
Heating to a temperature higher than 00 ° C. is unusual because the equipment is very bulky. In general, pure water is used as the liquid, but the liquid is not limited to pure water, and may be made acidic or alkaline in order to promote elution of the soluble substance from the anodic oxide film. When the liquid is heated while being stirred, the elution is promoted. Further, if the surface of the metal substrate to be anodized is roughened in advance, the surface area per unit area can be further increased. In order to roughen the substrate surface, a method using sand blast or grit blast is preferable.
It is necessary to remove all the sand and grit pierced on the surface by this method by etching with a hydrofluoric acid solution or the like. If a powder of titanium, niobium, tantalum, zirconium, or the like is fixed to a substrate of any material such as ceramics, metal, and plastic by arc spraying, flame spraying, or plasma spraying, the roughened metal layer can be formed. Can be formed. If this is anodized, the same effect as the blasting can be obtained. Hereinafter, the present invention will be described in detail with reference to specific examples. Semiconductor electrodes used for wet solar cells include titanium, niobium, tantalum and zirconium oxides, as described above. Titanium oxide is particularly preferred because holes on the photoexcited surface have a very high oxidation potential. Attention has been paid. Therefore,
In the following embodiments, a wet solar cell using titanium and titanium oxide will be described.

In this embodiment, a disk having a diameter of 20 mm is used as a substrate constituting a wet-type solar cell, but the size and shape are not limited. [First Embodiment] FIG. 1 is a sectional view showing a schematic configuration of a wet solar cell according to a first embodiment of the present invention. The structure is such that a transparent substrate 1, a transparent conductive film 2, an electrolyte layer 3, a dye-sensitized semiconductor electrode 4, and a conductive substrate 5 are sequentially laminated, and power is extracted from between the transparent conductive film 2 and the conductive substrate 5. . A glass substrate was used as the transparent substrate 1, an ITO film was used as the transparent conductive film 2, and a sputtering method was used to form the ITO film. In addition, a titanium substrate is used as the conductive substrate 5, and the dye-sensitized semiconductor electrode 4 is one in which a dye is carried on a titanium anodic oxide film formed by anodizing the titanium substrate. The anodic oxidation conditions for forming the titanium anodic oxide film on the surface of the titanium substrate were determined using a 40 ° C. electrolyte aqueous solution composed of sodium β-glycerophosphate at a concentration of 0.02 mol / l and strontium acetate at a concentration of 0.08 mol / l. , A DC voltage of 400 V, and a current density of 50 mA / cm ² . P and Sr are contained in the formed titanium anodic oxide film. These P and Sr are introduced into an autoclave by placing the titanium substrate on which the titanium anodic oxide film is formed in an autoclave.
Elution was carried out by a hydrothermal method in which heat treatment was performed in high-pressure water at 00 ° C. for 2 hours. As a result, the titanium anodic oxide film has a particle size of about 40
A porous structure was obtained in which fine pores were formed between titanium oxide fine particles of nm. This porous titanium anodic oxide film was immersed in an aqueous rhodamine B solution for 24 hours, and a dye was adsorbed on titanium oxide fine particles constituting the anodic oxide film, whereby a dye-sensitized semiconductor electrode 4 was produced. Lastly, between the transparent conductive film 2 and the dye-sensitized semiconductor electrode 4, an electrolyte solution obtained by dissolving tetraisopropyl iodide and iodine in a mixed solution of ethylene carbonate and acetonitrile was impregnated to form an electrolyte layer 3. The wet solar cell having the structure shown in FIG. 1 was completed. When the electromotive force when the wet solar cell of this embodiment was irradiated with light from a 500 W xenon lamp was measured, the current was 0.32 mA and the voltage was 0.33 V.

[Second Embodiment] The wet solar cell of the present embodiment is the same as the first embodiment except that the surface of the titanium substrate is provided with irregularities. After blasting the titanium substrate with # 36 alumina particles, the substrate was etched in a 30% hydrofluoric acid solution to remove the alumina particles sticking into the substrate, thereby forming irregularities on the surface of the substrate. As in the first embodiment, anodization, hydrothermal dye adsorption,
After a process of forming an electrolyte layer, a wet solar cell was assembled. When the electromotive force when the wet solar cell of this embodiment was irradiated with light from a 500 W xenon lamp was measured,
The current was 0.47 mA, and the voltage was 0.35 V. Both the current value and the voltage value were higher than the measured values in the first embodiment.

[Third Embodiment] FIG. 2 is a sectional view showing a schematic configuration of a wet solar cell according to a third embodiment of the present invention. The structure is such that a transparent substrate 1, a transparent conductive film 2, an electrolyte layer 3, a dye-sensitized semiconductor electrode 4, a titanium layer 6 and a substrate 7 are sequentially laminated, and the titanium layer 6 and the substrate 7 are combined to form a conductive substrate 5. And Therefore, electric power is extracted from between the transparent conductive film 2 and the titanium layer 6. A glass substrate is used as the transparent substrate 1, an ITO film is used as the transparent conductive film 2,
The sputtering method was used to form the ITO film.

A semiconductor electrode constituting the dye-sensitized semiconductor electrode 4 is a titanium anodic oxide film formed by anodizing a titanium layer formed by thermal spraying using stainless steel as a material of the substrate 7. In this case, the entire thickness of the titanium layer is not used as an anodic oxide film, but a part of the titanium layer that is not anodized is left and used as an extraction electrode.

The present embodiment is different from the first and second embodiments in that the metal layer for forming the anodic oxide film with the substrate 7 is different, and the metal layer for performing anodic oxidation is different from that of the first and second embodiments. The second point is that the substrate is formed on the substrate 7 by thermal spraying. In the present embodiment, titanium particles having a particle size of 10 to 45 μm are plasma-sprayed on a stainless steel substrate to form a titanium layer 6 having a thickness of about 50 μm and a surface roughness Rmax of 36 μm. The thickness of the titanium layer formed by plasma spraying is not limited to 50 μm, but may be thicker.

When the substrate 7 has conductivity, the entire titanium layer may be anodized. The conditions for forming the anodic oxide film on the surface of the titanium layer 6 are the same as those in the first and second embodiments. That is, concentration 0.02mol
/ l sodium β-glycerophosphate and concentration 0.08 mol / l
A DC voltage of 400 V and a current density of 50 mA / cm ² were set using an aqueous electrolyte solution of strontium acetate at 40 ° C. P and Sr are contained in the formed titanium anodic oxide film. These P and Sr are introduced into the autoclave by putting the conductive substrate 5 on which the titanium anodic oxide film is formed into an autoclave.
It was eluted by heat treatment in high-pressure water at 00 ° C for 2 hours. As a result, the titanium anodic oxide film has a particle size of about 40 nm.
It became a porous structure in which fine pores were formed between the titanium oxide fine particles. This porous titanium anodic oxide film was immersed in an aqueous rhodamine B solution for 24 hours, and a dye was adsorbed on titanium oxide fine particles constituting the anodic oxide film, whereby a dye-sensitized semiconductor electrode 4 was produced. Finally, the transparent conductive film 2
An electrolyte layer 3 was formed by impregnating an iodine electrolyte solution between the electrode and the dye-sensitized semiconductor electrode 4, and the periphery was sealed with a resin to complete a wet solar cell having the structure shown in FIG. When the electromotive force when the wet solar cell of this embodiment was irradiated with light from a 500 W xenon lamp was measured, the current was 0.54 mA and the voltage was 0.35 V. [Fourth Embodiment] This embodiment is different from the first embodiment in the conditions of hydrothermal treatment and the type of dye.
The conditions for forming the anodic oxide film on the surface of the titanium substrate are the same as in the above embodiments. That is, the concentration
0.02 mol / l β-glycerophosphate sodium and concentration 0.0
Using a 40 ° C. electrolyte aqueous solution comprising 8 mol / l strontium acetate, a DC voltage of 400 V and a current density of 50 mA / cm ²
Set to. P and Sr are contained in the formed titanium anodic oxide film. These P and Sr are introduced into the autoclave by placing the conductive substrate 5 shown in FIG. It was eluted by heat treatment in high-pressure water at ℃ for 4 hours. As a result, the titanium anodic oxide film had a porous structure in which fine pores were formed between titanium oxide fine particles having a particle diameter of about 30 nm. Immediately after vacuum drying this porous titanium anodic oxide film at 100 ° C., it is immersed in an ethanol solution containing eosin Y for 24 hours, and the dye is adsorbed on the titanium oxide fine particles constituting the anodic oxide film, thereby increasing the dye. A semiconductor sensitive electrode 4 was produced.

Finally, the electrolyte layer 3 is impregnated between the transparent conductive film 2 and the dye-sensitized semiconductor electrode 4 by impregnating an electrolytic solution in which tetraisopropyl iodide and iodine are dissolved in a mixed solution of ethylene carbonate and acetonitrile. Made,
A wet solar cell having the structure shown in FIG. 1 was completed. When the electromotive force of the wet solar cell of this embodiment when irradiated with light from a 500 W xenon lamp through a filter that cuts light having a wavelength of 420 nm or less was measured, the current was 0.7
8 mA, voltage was 0.65V. Even if this electromotive force measurement was continued for one hour, stable generation of electricity was recognized in the wet solar cell of this embodiment. In the present embodiment, a titanium plate is used as the conductive substrate 5. However, the present invention can be applied to a titanium plate subjected to sandblasting and a substrate having a titanium layer formed by spraying titanium powder.

[0018]

As described above, the dye-sensitized semiconductor electrode of the present invention uses an oxide film formed by anodizing the metal constituting the conductive substrate, so that the conductive substrate and the oxide film are firmly bonded. A combined integral structure is provided to reduce the electrical resistance at the interface. Further, the electrical resistance between the particles constituting the anodic oxide film can be reduced by the heating effect of the anodic oxidation and the hydrothermal treatment. Further, the porous structure in which micropores are formed innumerably in the anodic oxide film dramatically increases the surface area. By adsorbing a dye on the porous structure, the utilization efficiency of irradiation light can be increased. Therefore, in the wet solar cell using the dye-sensitized semiconductor electrode of the present invention, electrons can be smoothly exchanged and the irradiation light can be sufficiently used, so that the energy conversion efficiency is improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a wet solar cell according to first and second embodiments of the present invention.

FIG. 2 is a cross-sectional view illustrating a schematic configuration of a wet solar cell according to a third embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of a conventional wet solar cell.

[Explanation of symbols]

 1 ... Transparent substrate 2 ... Transparent conductive film 3 ... Electrolyte layer 4 ... Dye-sensitized semiconductor electrode 5 ... Conductive substrate 6 ...・ Titanium layer 7 ・ ・ ・ ・ ・ Substrate

Claims (6)

[Claims] 1. A transparent substrate with a transparent conductive film, a semiconductor electrode carrying a dye between a transparent substrate and a conductive substrate serving as a counter electrode, and an electrolyte layer. In a wet-type solar cell that generates electric energy between itself and a conductive substrate, the semiconductor electrode is an oxide film obtained by oxidizing at least a part of a metal that forms the conductive substrate. Wet solar cells. 2. The wet solar cell according to claim 1, wherein the metal constituting the conductive substrate is one kind of metal selected from titanium, niobium, tantalum, and zirconium. 3. The oxide film forming the semiconductor electrode is a metal anodic oxide film obtained by anodizing the metal, and the metal anodic oxide film has a porous structure. Item 2. A wet type solar cell according to Item 1. 4. The liquid crystal display device according to claim 3, wherein the porous structure is formed by eluting a liquid-soluble substance contained in the anodic oxide film by anodic oxidation by hydrothermal treatment. The wet-type solar cell according to 1. 5. The conductive substrate is a titanium substrate, the titanium substrate has a rough surface by sandblasting, the semiconductor electrode is a titanium anodic oxide film, and the anodic oxide film is The wet solar cell according to claim 1, wherein the wet solar cell has a porous structure. 6. A transparent substrate with a transparent conductive film, a semiconductor electrode carrying a dye between a transparent substrate and a conductive substrate serving as a counter electrode, and an electrolyte layer. In a wet solar cell that generates electric energy between the conductive substrate and the conductive substrate, the conductive substrate has a titanium layer formed by spraying titanium powder on at least a portion thereof, and the semiconductor electrode includes a titanium layer formed of a titanium layer. A wet solar cell, which is a titanium anodic oxide film obtained by anodizing at least a part thereof.