JP2003243054A - Photo-electrode for photoelectric transducing element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photo-electrode for a photoelectric transducing element of such a structure that a direct touch of its transparent conductive film with an electrolyte layer or hole conveying layer can be avoided and that the output characteristic of the transducing element is prevented from dropping. <P>SOLUTION: The photo-electrode has a transparent base board 1, the transparent conductive film 2 formed on its one surface, and an oxide semiconductor porous film 3 formed on the transparent conductive film 2, and an insulating film 11 is formed on the transparent conductive film 2 in the region A in which oxide semiconductor particulates 33 constituting the oxide semiconductor porous film 3 are not in direct touch with the transparent conductive film 2. The insulating film 11 should favorably consist of a polymeride produced through electrolytic polymerization of monomers having two or more mercapt radicals in one molecule. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a photoelectrode used for a photoelectric conversion element such as a dye-sensitized solar cell.

[0002]

2. Description of the Related Art Dye-sensitized solar cells have been developed by Gretzell et al. In Switzerland and have advantages such as high photoelectric conversion efficiency and low manufacturing cost, and have been attracting attention as a new type of solar cell. FIG. 2 shows an example of this dye-sensitized solar cell (Japanese Patent Publication No. 8-15097).

In the figure, reference numeral 1 is a transparent substrate such as a glass plate, and a transparent conductive film 2 such as tin-doped indium oxide (ITO) or fluorine-doped tin oxide (FTO) is formed on one surface of the transparent substrate 1. There is. This transparent conductive film 2
An oxide semiconductor porous film 3 made of oxide semiconductor fine particles such as titanium oxide and niodymium oxide and having a photosensitizing dye carried thereon is formed on the upper side, and serves as a photoelectrode 4.

Further, reference numeral 5 in the drawing is a conductive glass substrate serving as a counter electrode, and between the photoelectrode 4 and the counter electrode 5, an electrolytic solution made of a non-aqueous solution containing a redox couple such as iodine / iodine ion. Are filled, and the electrolyte layer 6 is formed.
Also, instead of the electrolyte layer 6, there is also one in which a hole transport layer made of a p-type semiconductor such as copper iodide is provided. In this dye-sensitized solar cell, when light such as sunlight enters from the transparent substrate 1 side, an electromotive force is generated between the transparent conductive film 2 and the counter electrode 5.

In such a dye-sensitized solar cell, the oxide semiconductor porous film 3 is porous in order to increase the amount of the photosensitizing dye carried, and a dispersion liquid in which the above metal oxide fine particles are dispersed. It is produced by a method such as coating and sintering.

However, in the porous film 3 of such a sintered body of oxide semiconductor fine particles, as shown in FIG. 3, there is an area A where the fine particles 33 forming the porous film 3 do not directly contact the transparent conductive film 2. It will inevitably occur. In this region A, therefore, the transparent conductive film 2 is in direct contact with the electrolyte layer 6, which causes a disadvantage such as current loss and voltage loss such as reverse electron transfer and short circuit.

By the way, the transparent power transmission film 2 is made of ITO or F.
When the electrolyte is made of TO or the like and the electrolyte is a redox couple such as iodine / iodine ion, it is considered that the redox reaction of iodine-iodine ion is slow, and even if the transparent conductive film 2 comes into contact with the electrolyte layer 6, it is fatal. However, in consideration of the decrease in photoelectric efficiency, it cannot be ignored.

However, in the solid-state dye-sensitized solar cell in which the hole transport layer made of a p-type semiconductor such as copper iodide is replaced with the electrolyte layer 6, one end of the p-type semiconductor is transparent conductive film 2 In addition, since the other end is in direct contact with the counter electrode 5, a large number of partial short-circuit points occur, which leads to a fatal output reduction due to significant voltage and current loss.

As a means for avoiding such direct contact between the transparent conductive film 2 and the electrolyte layer 6 or the hole transport layer, a thin and dense oxide semiconductor film is provided on the entire surface of the transparent conductive film 2 to function as a shielding layer. Things have been proposed. However, in this method, since the transparent conductive film 2 is covered with the shielding layer before the oxide semiconductor porous film 3 is formed, a space between the oxide semiconductor porous film 3 and the transparent conductive film 2 is formed. Since the shielding layer is present on the whole, the shielding layer hinders the electron transfer from the oxide semiconductor porous film 3 to the transparent conductive film 2, thus deteriorating the output characteristics.

[0010]

Therefore, the object of the present invention is to avoid direct contact between the transparent conductive film of the photoelectrode for a photoelectric conversion element and the electrolyte layer or the hole transport layer, and further This is to prevent the output characteristics from deteriorating.

[0011]

In order to solve the above problems, the invention according to claim 1 provides a transparent substrate, a transparent conductive film formed on one surface of the transparent substrate, and a transparent conductive film formed on the transparent conductive film. A porous oxide semiconductor film, and an oxide film is formed on the transparent conductive film in a region where the oxide semiconductor fine particles forming the oxide semiconductor porous film are not in direct contact with the transparent conductive film. It is a photoelectrode for a photoelectric conversion element.

The invention according to claim 2 is the photoelectrode for a photoelectric conversion element according to claim 1, wherein the insulating film is made of a polymer of a monomer having two or more mercapto groups in the molecule. The invention according to claim 3 is characterized in that the insulating film is made of a polymer obtained by electrolytic polymerization of a monomer having two or more mercapto groups in the molecule.
Alternatively, it is the photoelectrode for a photoelectric conversion element described in 2.

According to a fourth aspect of the present invention, a transparent substrate on which a transparent conductive film and a porous oxide semiconductor film are formed has a molecular structure of 2
The method for producing a photoelectrode for a photoelectric conversion element is characterized in that electrolytic polymerization is carried out in an electrolytic solution containing a non-aqueous solution of the above-mentioned monomer having a mercapto group. The invention according to claim 5 is
A photoelectric conversion element comprising an electrolyte layer containing a redox pair provided between the photoelectrode according to any one of claims 1 to 3 and the counter electrode.

The invention according to claim 6 is a photoelectric conversion element comprising a hole transport layer made of a p-type semiconductor between the photoelectrode according to any one of claims 1 to 3 and the counter electrode. The invention according to claim 7 is the photoelectric conversion element according to claim 5 or 6, which is a dye-sensitized solar cell in which a photosensitizing dye is carried on the oxide semiconductor porous film.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail based on the embodiments. FIG. 1 schematically illustrates an example of a photoelectrode for a photoelectric conversion element of the present invention, and shows a photoelectric conversion element using this photoelectrode. Reference numeral 1 in the figure is a transparent substrate. The transparent substrate 1 includes a glass plate, polyethylene terephthalate, polyethylene naphthalate,
It is preferably made of a plastic sheet such as polycarbonate or polyethylene sulfide and has good light transmittance.

A transparent conductive film 2 is formed on one surface of the transparent substrate 1. This transparent conductive film 2 is made of tin oxide, IT
A conductive transparent thin film made of O, FTO, or the like, which is formed by means of vapor deposition, sputtering, CVD, or the like. Between the transparent substrate 1 and the transparent conductive film 2, a conductive thin film made of metal or carbon having a thickness that does not impair transparency may be inserted if necessary.

An oxide semiconductor porous film 3 is formed on the transparent conductive film 2. The oxide semiconductor porous film 3 is formed by combining metal oxide fine particles 33 having semiconductivity, such as titanium oxide, tin oxide, tungsten oxide, zinc oxide, zirconium oxide, and niobium oxide, which are innumerable inside. It is a porous film having fine pores and fine irregularities on the surface, and its thickness is about 150 μm.

The oxide semiconductor porous film 3 is formed by applying a colloidal solution or dispersion in which fine particles of the metal oxide having an average particle size of 1 to 1000 nm are dispersed on the surface of the transparent conductive film 2 of the transparent substrate 1. It is carried out by a method of applying by a coating means such as printing, inkjet printing, roll coating, doctor coating, spin coating, spray coating, and sintering.

In addition to the above, a method of applying the above colloidal solution or dispersion to which a foaming agent has been added and sintering, and mixing the above metal oxide fine particles and polymer microbeads to form a dispersion, It is also possible to employ a method in which the dispersion liquid is applied and sintered to incinerate the polymer microbeads or to dissolve and remove the polymer microbeads.

Further, reference numeral 11 in the drawing is an insulating film.
As shown in the figure, the insulating film 11 has a region A on the surface of the transparent conductive film 2 which is not covered with the oxide semiconductor fine particles 33,
In other words, it is for covering the region A in direct contact with the electrolyte layer 6 and avoiding direct contact between the transparent conductive film 2 and the electrolyte layer 6. The photoelectrode 4 of this example is provided with the insulating film 11.

The insulating film 11 in this example has 2 molecules in the molecule.
By subjecting the above-mentioned monomer having a mercapto group to electrolytic oxidation polymerization, the polymer is deposited and deposited only on the region A of the transparent conductive film 2 to selectively cover the region A.

It is generally known that a molecule (monomer) having two or more mercapto groups in the molecule forms a polymer having a disulfide bond by an oxidation reaction.
This oxidation reaction proceeds not only by a chemical method but also by an electrochemical method. It is also known that most of the polymers thus obtained do not have electronic conductivity.

When such a monomer is electrochemically oxidized and polymerized, when the polymer progresses to a state where it cannot be dissolved in a solvent, it has a property of depositing as an insulating film on the working electrode. By utilizing the above, the polymer is selectively deposited only in the region A of the transparent conductive film 2 as described above, and the insulating film 1
1 can be formed.

Examples of the monomer having two or more mercapto groups in the molecule include compounds (1) to (3) represented by the following chemical formulas, and compounds obtained by substituting an alkali metal such as sodium for hydrogen in the mercapto group of these compounds. Etc. can be used. Further, in the case of a monomer having 3 or more mercapto groups in the molecule, the polymer obtained by electrolytic polymerization becomes a strong one having a three-dimensional structure, and therefore it is suitable as the insulating film 11, and a monomer of this type is selected. It is desirable to do.

[0025]

[Chemical 1]

Further, such a monomer can be used as an oligomer of a dimer or more as long as it can be dissolved in a solvent of an electrolytic bath at the time of electrolytic polymerization, and is previously oxidatively polymerized into an oligomer by a chemical method. Alternatively, this oligomer may be dissolved in a solvent and subjected to electrolytic polymerization.

The specific electrolytic polymerization of the above-mentioned monomer is carried out, for example, as follows. The above monomer is dissolved in a solvent such as acetonitrile, tetrahydrofuran, propylene carbonate, and salts such as lithium perchlorate, lithium tetrafluoroborate, and tetrabutylammonium perchlorate as a supporting electrolyte are added to this to prepare an electrolytic bath. To do. Then, the transparent substrate 1 on which the transparent conductive film 2 and the oxide semiconductor porous film 3 are formed is immersed in this electrolytic bath, and direct current electrolysis is performed using the transparent conductive film 2 as a working electrode.

The concentration of the monomer in the electrolytic bath is 0, 1 to 1
About 100 mmol / l is suitable, and the supporting electrolyte concentration is preferably about 0.1 to 2 mol / l. Conditions such as electrolysis voltage, electrolysis current, and electrolysis time depend on the material to be used, and are accordingly determined.

Reference numeral 5 is a counter electrode. This counter electrode 5
For this, a conductive substrate such as a metal plate or a non-conductive substrate such as a glass plate on which a conductive film of platinum, gold, carbon or the like is formed is used. When the p-type semiconductor is used as the hole transport layer, since the p-type semiconductor is solid, a conductive thin film of platinum or the like is directly formed on the p-type semiconductor by vapor deposition, sputtering, etc., and this conductive thin film is used as the counter electrode 5. You can also

An electrolyte solution is filled between the counter electrode 5 and the photoelectrode 4 to form an electrolyte layer 6. The electrolytic solution is not particularly limited as long as it is a non-aqueous electrolytic solution containing a redox couple. Examples of the solvent include acetonitrile, methoxyacetonitrile, propionitrile,
Ethylene carbonate, propylene carbonate, γ-butyrolactone, etc. are used.

As the redox pair, for example, a combination of iodine / iodine ion, bromine / bromine ion and the like can be selected. When adding this as a salt, the counter ion is a lithium ion or tetraalkyl ion in addition to the above redox pair. , Imidazolium ions, etc. can be used. Further, iodine or the like may be added if necessary. Alternatively, a solid electrolyte obtained by gelling such an electrolytic solution with a suitable gelling agent may be used.

Further, instead of the electrolyte layer 6, a hole transport layer made of a p-type semiconductor may be used. For this p-type semiconductor, for example, a monovalent copper compound such as copper iodide or copper thiocyanate or a conductive polymer such as polypyrrole can be used, and among them, copper iodide is preferable.

When such a photoelectric conversion element is used as a dye-sensitized solar cell, a photosensitizing dye is carried on the oxide semiconductor porous film 3. As the photosensitizing dye, ruthenium complexes containing ligands such as bipyridine structure and terpyridine structure, metal complexes such as porphyrin and phthalocyanine, and organic dyes such as eosin, rhodamine, and merocyanine are used. Can be appropriately selected according to the type of

In such a photoelectric conversion element photoelectrode 4, the polymer insulating film 11 made of a mercapto compound is selectively formed in the region A of the transparent conductive film 2, and the region A of the transparent conductive film 2 is formed. The direct contact with the electrolyte layer 6 or the hole transport layer in the above is prevented, and a short circuit is prevented. Further, in areas other than the region A, since the transparent conductive film 2 and the oxide semiconductor fine particles 33 of the oxide semiconductor porous film 3 are in direct contact,
Electron transfer between the two is not hindered.

Therefore, in the photoelectric conversion element such as the dye-sensitized solar cell made by using the photoelectrode 4, the deterioration of the output characteristics such as the open circuit voltage and the short circuit current is suppressed, and the photoelectric conversion efficiency becomes high. . Further, when the insulating film 11 is formed by electrolytic polymerization of a monomer having two or more mercapto groups in the molecule, the insulating film 11 can be selectively formed in the region A efficiently.

In the present invention, the insulating film 11 is also used.
In addition to the above-listed insulating materials for forming, the insulating film 11 can be selectively formed in the region A by electrolytically polymerizing aminopyrrole acid, aminopyridine acid, vinylpyridine acid and the like.

Specific examples will be shown below. (Example 1) A dispersion liquid of titanium oxide fine particles (average particle size 25 nm) was applied onto an FTO vapor-deposited glass plate, and the solvent was dried on a hot plate at 80 ° C, and then at 450 ° C, 6
It was baked for 0 minutes to obtain a titanium oxide porous film. An insulating solution was formed by electrolytic polymerization using an acetonitrile solution containing 1 mM of the above compound (1) and 0.1 M of LiClO ₄ as an electrolytic bath, and using the titanium porous film formed thereon as a working electrode.

Electropolymerization is performed at 1.70 V vs. Ag / Ag
A constant potential electrolysis of Cl was performed, and the process was terminated when the current value reached 10% of the initial value. This polymerization treatment was carried out in a vacuum glove bots, which had been replaced with argon. For the titanium porous membrane before the polymerization treatment, ferrocene (Fc / Fc ⁺ ) in an acetonitrile solution containing 10 mM ferrocene was used.
Although the redox response was confirmed, the redox response was not observed from the titanium porous membrane after the polymerization treatment. The semiconductor electrode after the polymerization treatment was dipped in an ethanol solution in which a ruthenium bipyridine complex was dissolved for about 8 hours to carry a sensitizing dye, thereby forming a photoelectrode.

As a counter electrode, an ITO vapor-deposited glass plate on which platinum was sputtered was used. Both electrodes were superposed, and an electrolytic solution was filled between them by a capillary phenomenon to obtain a test cell 1. Here, a methoxyacetonitrile solution containing 0.1 M lithium iodide, an iodine salt of 0.3 M quaternized imidazole, and 0.05 M iodine was used as the electrolytic solution.

Example 2 The above compound (3) was added to 1 mM,
An insulating film was formed by electrolytic polymerization using the prepared titanium porous film as a working electrode in an acetonitrile solution containing 0.1 M of LiClO ₄ . Electropolymerization is 1.85 V vs. Ag
/ AgCl was set to a constant potential, and the process was terminated when the current value reached 10% of the initial value. Further, a test cell 2 similar to that of Example 1 was prepared using the photoelectrode having this porous film formed.

(Example 3) An insulating film made of the compound (1) was prepared in the same manner as in Example 1, and the same dye was carried on the titanium porous film. Cu was prepared by preparing an acetonitrile solution saturated with copper iodide (CuI) and casting it little by little on the prepared dye-supporting titanium porous film.
The I film was deposited. This operation was performed on a hot plate heated to 80 ° C. After air-drying, the terminal portion of the FTO film on the glass plate was masked with a masking tape, and a platinum counter electrode was sputtered to obtain a test cell 3.

(Comparative Example 1) A test cell 4 having the same structure as in Example 1 was prepared. However, the insulating film treatment with the compound (1) was not performed here. (Comparative Example 2) A test cell 5 having the same structure as in Example 3 was prepared. However, the insulating film treatment with the compound (1) was not performed here. Each test cell was evaluated for photoelectric characteristics when irradiated with pseudo sunlight (energy density 100 mW / cm ² , AM 1.5). Open circuit voltage in each cell,
The short-circuit current values are shown in Table 1.

[0043]

[Table 1]

As shown in Table 1, in the electrolytic solution type test cells 1 and 2 filled with the electrolytic solution, the short circuit current and the open circuit voltage were improved as compared with the test cell 4. Further, comparing the solid test cell 3 having the hole transport layer using the p-type semiconductor with the test cell 5, the output characteristics of the test cell 3 are significantly improved in both current and voltage as compared with the test cell 5. You can see that The output characteristics of the solid test cell 3 are
Although it is inferior to the electrolyte solution test cell, this is due to various reasons peculiar to the solid-state battery, for example, the deposited crystal size of copper iodide.

[0045]

As described above, the photoelectrode for a photoelectric conversion element of the present invention is one in which the region where the transparent conductive film is in direct contact with the electrolyte layer or the hole transport layer is selectively covered with an insulating film. Therefore, direct contact between the transparent conductive film and the electrolyte layer or the hole transport layer is prevented, and transfer of electrons between these layers can be prevented.

Therefore, in the photoelectric conversion element using this photoelectrode, the output characteristics such as open circuit voltage and short circuit current are improved. In particular, in the solid-state photoelectric conversion element using the hole transport layer made of the p-type semiconductor, the effect of improving the output characteristics becomes remarkable.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a main part of an example of a photoelectrode of the present invention.

FIG. 2 is a schematic sectional view showing an example of a dye-sensitized solar cell.

FIG. 3 is a schematic sectional view showing a main part of a conventional photoelectrode.

[Explanation of symbols]

1 ... Transparent substrate, 2 ... Transparent conductive film, 3 ... Oxide semiconductor porous film, 33 ... Oxide semiconductor fine particles, 4 ... Photoelectrode, 5 ... Counter electrode, 6 ... Electrolyte layer, A ··region

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Okada             1-5-1 Kiba Stock Market, Koto-ku, Tokyo             Inside Fujikura F term (reference) 5F051 AA07 AA14 AA20 CB13 CB30                       FA03 FA04 FA06 FA18 FA30                       GA03                 5H032 AA06 AS06 AS16 BB07 EE04                       EE07 EE16

Claims (7)

[Claims] 1. A transparent substrate, a transparent conductive film formed on one surface of the transparent substrate, and an oxide semiconductor porous film formed on the transparent conductive film, to form an oxide semiconductor porous film. A photoelectrode for a photoelectric conversion element, characterized in that an insulating film is formed on the transparent conductive film in a region where the oxide semiconductor fine particles are not in direct contact with the transparent conductive film. 2. The photoelectrode for a photoelectric conversion element according to claim 1, wherein the insulating film is made of a polymer of a monomer having two or more mercapto groups in the molecule. 3. The photoelectrode for a photoelectric conversion element according to claim 1, wherein the insulating film is made of a polymer obtained by electrolytic polymerization of a monomer having two or more mercapto groups in the molecule. 4. A transparent substrate on which a transparent conductive film and a porous oxide semiconductor film are formed is subjected to electrolytic polymerization in an electrolytic solution containing a non-aqueous solution of a monomer having two or more mercapto groups in the molecule. A method of manufacturing a photoelectrode for a photoelectric conversion element. 5. A photoelectric conversion element comprising an electrolyte layer containing a redox pair between the photoelectrode according to claim 1 and a counter electrode. 6. A photoelectric conversion device comprising a hole transport layer made of a p-type semiconductor between the photoelectrode according to claim 1 and a counter electrode. 7. The photoelectric conversion device according to claim 5, wherein the dye-sensitized solar cell comprises a porous oxide semiconductor film carrying a photosensitizing dye.