JP2955647B2 - Organic dye-sensitized oxide semiconductor electrode and solar cell including the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic dye-sensitized oxide semiconductor electrode and a solar cell including the same.

[0002]

2. Description of the Related Art A solar cell including an oxide semiconductor electrode sensitized with an organic dye is known. Nature, 261
(1976) According to P402, a zinc oxide powder is compression-molded and sintered at 1300 ° C. for one hour to form a solar disk using an oxide semiconductor electrode having rose bengal as an organic dye adsorbed on the surface of a sintered disk. Batteries have been proposed.
However, according to the current / voltage curve of this solar cell, the current value at the time of an electromotive voltage of 0.2 V is as low as about 25 μA, and therefore, this solar cell cannot be seen from the current / voltage curve. If so, it was judged that practical application was almost impossible. On the other hand, when the solar cell is evaluated in terms of its material, it is clear that the oxide semiconductor and the organic dye used for the solar cell are very advantageous because both are mass-produced and relatively inexpensive. is there.

[0003]

SUMMARY OF THE INVENTION The present invention relates to an organic dye-sensitized oxide semiconductor electrode which, when used as an oxide semiconductor electrode in a solar cell, gives a practical current / voltage curve, and an electrode having the same. It is an object to provide a solar cell including the same.

[0004] The present inventors have conducted intensive studies to solve the above-mentioned problems, and have tried many organic dyes and oxide semiconductors. As a result, by combining a specific organic dye and a specific oxide semiconductor electrode, an organic dye As a system, they found an oxide semiconductor electrode exhibiting the highest open-circuit voltage and short-circuit current, and a solar cell composed of the electrode. That is, modern blue 29 (MB) and indium oxide, eriochrome cyanine R (EC) and indium oxide, aurin tricarboxylic acid (Aa) and titanium oxide, naphthochrome green (NG) and zinc oxide or indium oxide, It has been found that a combination of coumarin 343 (C3) and zinc oxide or indium oxide, and a combination of proflavine (Pf) and titanium oxide or indium oxide have important meanings. A solar cell including such an oxide semiconductor electrode and a counter electrode, and a redox electrolyte in contact with these electrodes can be provided.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The oxide semiconductor used in the present invention includes conventionally known oxide semiconductors. Such materials include Ti, Nb, Zn, Sn, Zr, Y, L
a, Ta and other transition metal oxides, SrTiO ₃ , C
a perovskite-based oxide such as aTiO ₃ ; This oxide semiconductor powder is preferably as fine as possible, and has an average particle size of 5000 nm or less, preferably 50 nm or less. The specific surface area is
It is at least 5 m ² / g, preferably at least 10 m ² / g.

The organic dye used in the present invention has the following formula (1)
At least one selected from a dye having a triphenylmethane skeleton represented by the following formula, a dye having a coumarin skeleton represented by the following formula (2), and a dye having an acridine skeleton represented by the following formula (3) Organic dye.

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Embedded image The dye is one in which one or more polar groups such as a carboxyl group, a sulfonic acid group, a hydroxyl group, an amino group, a halogen atom, and NO ₂ are bonded to the skeleton carbon. Those having an acidic group such as a carboxyl group, a sulfonic acid group or a hydroxyl group or a water-soluble salt thereof have excellent adsorptivity to an oxide semiconductor. Such organic dyes are well known in the art, and specific examples thereof include the following.

(1) Dye having triphenylmethane skeleton Specific examples thereof include the following. (I) Modern To Blue 29 (MB)

Embedded image (Ii) Eriochrome cyanine R (EC)

Embedded image (iii) Naphthochrome green (NG)

Embedded image (Iv) Aurin tricarboxylic acid (Aa)

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(2) Dye having coumarin skeleton Specific examples thereof include the following. (I) Coumarin 343 (C3)

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(3) Dye having acridine skeleton Specific examples thereof include the following. (I) Proflavin (Pf)

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[0010] The shape of the oxide semiconductor electrode of the present invention is not particularly limited, and may be various shapes such as a film shape, a plate shape, a columnar shape, and a cylindrical shape. It is used in the form of a film formed on a substrate. In order to manufacture such a semiconductor electrode, first, a coating solution containing fine powder of an oxide semiconductor is prepared. The finer the primary particle diameter of this oxide semiconductor fine powder, the more preferable it is. The primary particle diameter is usually 1 to 5000 nm, preferably 2 to 50 nm. Coating solution (slurry solution) containing oxide semiconductor fine powder
Can be prepared by dispersing an oxide semiconductor fine powder in a solvent. The oxide semiconductor fine powder dispersed in the solvent is dispersed in the form of primary particles. The solvent is not particularly limited as long as it can disperse the oxide semiconductor fine powder. Such solvents include water, organic solvents, and mixtures of water and organic solvents. Examples of the organic solvent include alcohols such as methanol and ethanol, ketones such as methyl ethyl ketone, acetone and acetylacetone, and hydrocarbons such as hexane and cyclohexane. If necessary, a surfactant or a viscosity modifier (polyhydric alcohol such as polyethylene glycol) can be added to the coating solution. The concentration of the oxide semiconductor fine powder in the solvent is 0.1 to 70% by weight, preferably 0.1 to 30% by weight.

Next, the coating solution is applied to a substrate, dried, and then fired in air or an inert gas to form an oxide semiconductor film on the substrate. As the substrate, a substrate having at least its surface formed on a conductive surface is used. As such a substrate, a substrate formed by forming a conductive metal oxide thin film of In ₂ O ₃ or SnO ₂ on a heat-resistant substrate such as glass or a substrate made of a conductive material such as metal is used. Such a conductive substrate is conventionally well-known. The thickness of the substrate is not particularly limited, but is usually 0.3 to
5 mm. This conductive substrate can be transparent or opaque. The coating obtained by applying and drying the coating solution on the substrate is composed of an aggregate of oxide semiconductor fine particles, the particle diameter of which corresponds to the primary particle diameter of the used oxide semiconductor fine powder. It is. Since the oxide semiconductor fine particle aggregate film formed on the substrate in this manner has a low bonding strength with the substrate and a low bonding strength between the fine particles and a low mechanical strength, it is baked. A fired product film having increased mechanical strength and strongly adhered to the substrate.

In the present invention, the fired product film is a porous structure film having a thickness of at least 10 nm, preferably 100 to 10,000 nm, and a ratio of the actual surface area to the apparent surface area of 10 or more, preferably 100 or more.
Above. The upper limit of this ratio is not particularly limited, but is usually 1000 to 2000. The apparent surface area means a normal surface area. For example, when the surface shape is rectangular, it is represented by a vertical length × a horizontal length. The actual surface area is defined as B obtained from the amount of krypton gas absorbed.
ET means surface area. The specific measuring method is as follows. An oxide semiconductor film with a substrate having an apparent surface area of 1 cm ² is measured using a BET surface area measuring device (ASAP200 manufactured by Micromeritics Co., Ltd.
0) is a method of adsorbing krypton gas at the temperature of liquid nitrogen. The BET surface area is calculated based on the krypton gas adsorption amount obtained by this measurement method.

Such a porous structure film has fine pores inside and fine irregularities on its surface. When the thickness of the fired product film and the ratio of the actual surface area to the apparent surface area are smaller than the above ranges, when the organic dye is adsorbed on the surface as a monomolecular film, the surface area of the organic dye monomolecular film becomes small, An electrode with good absorption efficiency cannot be obtained. The fired product film having the porous structure as described above, a coating solution containing oxide semiconductor fine particles is applied on a substrate,
When the dried fine particle aggregate film is fired, it can be obtained by lowering the firing temperature and lightly sintering the fine particle aggregate film. In this case, the firing temperature is 1
It is lower than 000C, usually 300-800C, preferably 500-800C. If the firing temperature is higher than 1000 ° C., the sintering of the fired material film proceeds too much, the actual surface area becomes small, and a desired fired material film cannot be obtained. The ratio of the actual surface area to the apparent surface area can be controlled by the particle size and specific surface area of the oxide semiconductor fine particles, the firing temperature, and the like.

Next, the organic dye is adsorbed as a monomolecular film on the surface of the oxide semiconductor film on the substrate obtained as described above. For this purpose, the oxide semiconductor film and the substrate may be immersed in an organic dye solution formed by dissolving an organic dye in an organic solvent. In this case, the film is subjected to a reduced pressure treatment or a heat treatment prior to immersion in the organic dye solution so that the organic dye solution penetrates deep inside the oxide semiconductor film which is a porous structure film. It is preferable to remove the air bubbles contained in the water in advance. Immersion time is 30 minutes to 2
It is about 4 hours, but it is appropriately determined according to the type of the organic dye. Further, the immersion treatment can be repeated a plurality of times as necessary. After the immersion treatment, the oxide semiconductor film on which the organic dye has been adsorbed is dried at normal temperature to 80 ° C.

In the present invention, the organic dye to be adsorbed on the oxide semiconductor film does not need to be one kind, and preferably, a plurality of organic dyes having different light absorption regions are adsorbed. Thus, light can be used efficiently. In order to adsorb a plurality of organic dyes to the film, a method of immersing the film in a solution containing a plurality of organic dyes, a method of preparing a plurality of organic dye solutions, and sequentially immersing the film in these solutions can be used. . In a solution in which an organic dye is dissolved in an organic solvent, any organic solvent can be used as long as it can dissolve the organic dye. Such materials include, for example, methanol, ethanol, acetonitrile, dimethylformamide, dioxane and the like. The concentration of the organic dye in the solution is 1% in 100 ml of the solution.
It is about 10000 mg, preferably about 10-500 mg, and is appropriately determined according to the type of the organic dye and the organic solvent.

A solar cell according to the present invention comprises the above-mentioned oxide semiconductor electrode, a counter electrode, and a redox electrolyte in contact with those electrodes. As the redox electrolyte, I ⁻ / I ₃
^- system or, Br ^- / Br ₃ ^- system, quinone / hydroquinone system. Such a redox electrolyte can be obtained by a conventionally known method, for example, I ⁻ / I ₃ ^−.
The system electrolyte can be obtained by mixing iodine with an ammonium salt of iodine. The electrolyte can be a liquid electrolyte or a solid polymer electrolyte containing the same in a polymer substance. In the liquid electrolyte, an electrochemically inert solvent is used as the solvent, for example, acetonitrile, propylene carbonate, ethylene carbonate, or the like. The counter electrode, as long as it has conductivity, but any conductive material is used, I ₃ ^- with catalytic ability to perform fast enough the reduction reaction of the redox ions oxidized such as ion It is preferred to use Examples of such a material include a platinum electrode, a material obtained by subjecting a conductive material surface to platinum plating or platinum evaporation, rhodium metal, ruthenium metal, ruthenium oxide, carbon, and the like.

In the solar cell of the present invention, the oxide semiconductor electrode, the electrolyte and the counter electrode are housed in a case and sealed, or the whole is sealed with a resin. In this case, light is applied to the oxide semiconductor electrode. In a battery having such a structure, when sunlight or visible light equivalent to sunlight is applied to the oxide semiconductor electrode, a potential difference occurs between the oxide semiconductor electrode and the counter electrode, and a current flows between the two electrodes. become.

[0018]

Next, the present invention will be described in more detail by way of examples.
Each of the batteries manufactured in the following examples has an electrode area of 1 × 1 cm. A 500 watt xenon lamp was used as a light source for operating the battery, and light having a wavelength of 420 nm or less from the lamp was cut by a filter. In addition, a potentiostat equipped with a non-resistance ammeter was used for measuring the short-circuit current and the open-circuit voltage of the manufactured battery. In the oxide semiconductor powder used, a commercially available product (Nihon Air Aerosil, P-25, surface area 55 m ² / g) was used as TiO ₂ , and Nb ₂ O was used.
₅ was prepared by thermally decomposing niobium hydroxide (manufactured by Central Glass Co., Ltd.) (500 ° C., 1 hour, 99 m ² / g). ZnO (20 m ² / g), SnO ₂ (60 m ² / g)
² / g) and In ₂ O ₃ (25 m ² / g) used were commercial products (Wako Pure Chemical Industries, Ltd.). As organic dyes, Modern Blue 29 (MB), Eriochrome Cyanine R (E
C), naphthochrome green (NG), aurin tricarboxylic acid (Aa), coumarin 343 (C3), and proflavine (Pf).

Example 1 An oxide semiconductor electrode was manufactured as follows. A concentration of about 1 wt% of the metal oxide powder (having an average primary particle diameter of 50 nm or less) in a mixed solution (volume mixing ratio = 20/1) of water and acetylacetone containing a nonionic surfactant. To prepare a slurry liquid. next,
This slurry liquid was applied to a conductive glass substrate (F-
It was applied on SnO ₂ , 10Ω / sq) and dried, and the obtained dried product was fired at 500 ° C. for 1 hour in the air to form a fired product film having a thickness of 7 μm on the substrate. When the ratio of the actual surface area to the apparent surface area of the fired product film is shown in relation to the type of the oxide semiconductor, TiO ₂ : 500 and Nb ₂ O ₅ : 85
0, ZnO: 200, SnO ₂ : 500, In ₂ O ₃ : 2
00. Next, this baked product film together with the substrate is immersed in an organic dye solution, and the solution is returned at 80 ° C.
After performing the dye adsorption treatment, it was dried at room temperature. in this case,
The organic dye solution was prepared by dissolving the organic dye in ethanol at a concentration of 100 mg / 100 ml.

A solar cell was formed by bringing the oxide semiconductor electrode obtained as described above and its counter electrode into contact with an electrolyte solution. As a counter electrode, conductive glass in which platinum was deposited to a thickness of 20 nm was used. The distance between both electrodes was 1 mm.
As an electrolyte solution, a mixed solution of ethylene carbonate containing tetrapropylammonium iodide (0.46M) and iodine (0.6M) and acetonitrile (volume mixing ratio = 80/20) was used. Table 1 shows the short-circuit current and release voltage for each battery obtained as described above.
As can be seen from the results shown in Table 1, The combination of Modern Blue 29 (MB) and indium oxide resulted in a large short-circuit current. 2. The combination of Eriochrome Cyanine R (EC) and Indium Oxide resulted in a large short-circuit current. 3. The combination of aurin tricarboxylic acid (Aa) and titanium oxide provided a high release voltage. 4. The combination of naphthochrome green (NG) and zinc oxide or indium oxide resulted in a large short-circuit current and a high release voltage (zinc oxide). 5. With the combination of coumarin 343 (C3) and titanium oxide, zinc oxide or indium oxide, a large short-circuit current and a high release voltage (titanium oxide, zinc oxide) were obtained. 6. The combination of proflavin (Pf) and titanium oxide, zinc oxide or indium oxide resulted in a high release voltage (titanium oxide, zinc oxide).

[0021]

[Table 1]

Comparative Example 1 A previously published paper (Nature, 261 (1976) p40)
A semiconductor powder obtained by sintering ZnO at 1300 ° C. as in the method of Example 2 was prepared, and then a film was formed on conductive glass in the same manner as in Example 1, and a ZnO electrode (the ratio of the actual surface area to the apparent surface area <10) was formed. ) Was prepared. Thereafter, Rose Bengal (Ro) was adsorbed in the same manner as in Example 1. However, comparing the amount of adsorption with the absorbance, it was found to be 1/5 of the value of Example 1.
It was about. Next, when the battery characteristics were examined, the results shown in Table 2 were obtained, and the short-circuit current and the open-circuit voltage were smaller in the case of Example 1.

Comparative Examples 2 to 4 As an organic dye, Acid Orange 7 having the following structure was used.
A battery was constructed in the same manner as in Example 1 except that (A7), Modan Orange 1 (M1) and Clear Fast Red (NF) were used. Table 2 shows the short circuit current and open circuit voltage for these batteries.

(A7)

Embedded image (MI)

Embedded image (NF)

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[0025]

[Table 2]

(1) Acid Orange 7 (A7) is an azo dye, which adsorbed on TiO ₂ but hardly adsorbed on other electrodes. Battery performance was also very poor. (2) Modant Orange 1 (M1), which is an azo-based dye, exhibited good adsorption to all copper electrodes. However, the battery characteristics were very poor.
(3) Nuclear fast red (NF) is a quinone dye, which showed good adsorption to all semiconductor electrodes. However, the battery characteristics were very poor.

[0027]

The organic dye-sensitized semiconductor electrode of the present invention is
The solar cell of the present invention having enhanced performance and including the same has enhanced battery performance. The solar cell of the present invention can be produced relatively inexpensively because its material is mass-produced and is relatively inexpensive and highly safe, and after its use, it is disposable. Things.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-249790 (JP, A) JP-A-59-197831 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 14/00 H01L 31/04

Claims (7)

(57) [Claims] 1. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye adsorbed on the surface of the oxide semiconductor film, wherein the organic dye is modern blue 29. An oxide semiconductor electrode wherein the oxide semiconductor is indium oxide. 2. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye adsorbed on the surface of the oxide semiconductor film, wherein the organic dye is eriochrome cyanine. R is an oxide semiconductor electrode in which the oxide semiconductor is indium oxide. 3. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye adsorbed on the surface of the oxide semiconductor film, wherein the organic dye is aurin tricarboxylic acid Wherein the oxide semiconductor is titanium oxide. 4. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye adsorbed on the surface of the oxide semiconductor film, wherein the organic dye is naphthochrome green. An oxide semiconductor electrode, wherein the oxide semiconductor is zinc oxide or indium oxide. 5. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye adsorbed on the surface of the oxide semiconductor film, wherein the organic dye is a coumarin 343. Yes, the oxide semiconductor is titanium oxide,
An oxide semiconductor electrode which is zinc oxide or indium oxide. 6. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye adsorbed on the surface of the oxide semiconductor film, wherein the organic dye is proflavine. An oxide semiconductor electrode in which the oxide semiconductor is titanium oxide, zinc oxide, or indium oxide; 7. A solar cell comprising the oxide semiconductor electrode according to any one of claims 1 to 6, a counter electrode thereof, and a redox electrolyte in contact with the electrodes.