JPH1092477A - Organic coloring matter intensified type oxide semi-conductor electrode and solar cell including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the solar cell including an electrode giving a practical current/voltage curve in an organic coloring matter intensified type oxide semi- conductor electrode. SOLUTION: An organic coloring matter intensified type oxide semi-conductor electrode is formed out of a transparent base provided with a conductive surface, an oxide semi-conductor film formed over the aforesaid conductive surface, and of organic coloring matter adsorbed by the surface of the oxide semi-conductor film, the aforesaid oxide semi-conductor film is formed out of the baked substance of aggrege of oxide semi-conductor fine particles, is thin as at least 10nm, concurrently, the ratio of actual surface area to its apparent surface area is more than 10, and the aforesaid organic coloring pigment is coloring pigment having 9-phenyl xanthene skeletons. The solar cell is formed out of the aforesaid oxide semi-conductor electrode, its opposite electrode, and of redox electrolyte coming in contact with these electrodes.

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 An object of the present invention is to provide, in an organic dye-sensitized oxide semiconductor electrode, an electrode giving a practical current / voltage curve and a solar cell including the electrode.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, a transparent 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 are provided. The film is formed from a baked product of an aggregate of oxide semiconductor fine particles, has a thickness of at least 10 nm, has a ratio of an actual surface area to an apparent surface area of 10 or more, and the organic dye has a 9-phenylxanthene skeleton. An oxide semiconductor electrode is provided which is a dye having the same. According to the present invention,
There is provided a solar cell including the oxide semiconductor electrode, a counter electrode thereof, and a redox electrolyte contacting the electrodes.

[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 is a dye having a 9-phenylxanthene skeleton represented by the following formula:

Embedded image The dye having a 9-phenylxanthene skeleton has a carboxyl group, a sulfonic acid group, a hydroxyl group, an amino group, a halogen atom, NO ₂
And one or more polar groups are bonded. 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) Rose Bengal (Ro)

Embedded image (2) Rhodamine B (Rh)

Embedded image (3) Eosin B (EB)

Embedded image (4) Dibromofluorescein (DB)

Embedded image (5) Erythrosin B (Er)

Embedded image (6) Eosin Y (EY)

Embedded image (7) Dichlorofluorescein (DC)

Embedded image (8) Pyrogallol (Py)

Embedded image (9) Fluorescein (FI)

Embedded image (10) Phloxine (Ph)

Embedded image (11) Aminopyrogallol (AP)

Embedded image (12) Fluorescin (Fn)

Embedded image (13) Uranine (Ur)

Embedded image (14) 4,5,6,7-tetrachlorofluorescein (Tf)

Embedded image (15) Fluoresceinamine I (I1)

Embedded image (16) Fluoresceinamine II (I2)

Embedded image (17) Rhodamine 123 (R3)

Embedded image (18) Rhodamine 6G (R6)

Embedded image

In order to manufacture the oxide semiconductor electrode of the present invention, first, a coating solution containing fine powder of an oxide semiconductor is prepared.
The finer the primary particle diameter of the oxide semiconductor fine powder is, the more preferable it is. The primary particle diameter is usually 1 to 5000 n.
m, preferably 2 to 50 nm. The coating liquid (slurry liquid) containing the oxide semiconductor fine powder can be prepared by dispersing the oxide semiconductor fine powder in a solvent. The oxide semiconductor fine powder dispersed in the solvent is
Disperse in the form of secondary particles. Any solvent may be used as long as it can disperse the oxide semiconductor fine powder,
There is no particular restriction. 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. Surfactants and viscosity modifiers (polyhydric alcohols such as polyethylene glycol, etc.), if necessary, in the coating solution
Can be added. 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 on 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 a porous structure as described above is obtained by applying a coating solution containing oxide semiconductor fine particles on a substrate, and firing the formed fine particle aggregate film formed by drying. It can be obtained by lightly sintering the body film. In this case, the firing temperature is lower than 1000 ° C, usually 300 to 800 ° C, preferably 500 to 80 ° C.
0 ° C. When the firing temperature is higher than 1000 ° C., the sintering of the fired product film proceeds too much, the actual surface area decreases,
The desired fired product 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, an 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 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.

[0015]

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. 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 ₅ was used.
Used was prepared by thermally decomposing niobium hydroxide (manufactured by Central Glass Co., Ltd.) (500 ° C., 1 hour, 99 m ² / g). ^{ZnO (20m 2 / g),} SnO 2 (60m 2
/ G) and In ₂ O ₃ (25 m ² / g), commercial products (Wako Pure Chemical Industries, Ltd.) were used. Examples of the organic dye include Ro (rose bengal), Rh (rhodamine B), and EB.
(Eosin B), DB (dibromofluorescein), E
r (erythrosin B), EY (eosin Y), DC (dichlorofluorescein), Py (pyrogallol), F1
(Fluorescein), Ph (phloxine), AP (aminopyrogallol), Fn (fluorescin), uranine (Ur), 4,5,6,7-tetrachlorofluorescein (Tf), fluoresceinamine I (I1), fluoresceinamine II (I2), rhodamine 123 (R ₃ )
And Rhodamine 6G (R ₆ ).

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 contained 100 mg of the organic dye except for F1.
It was prepared by dissolving in ethanol at a concentration of 100 ml.
The F1 solution was prepared by dissolving F1 at a concentration of 100 mg / 100 ml in dimethylformamide.

A solar cell was constructed by bringing the oxide semiconductor electrode obtained as described above and its counter electrode into contact with an electrolyte solution. In this case, as a counter electrode, conductive glass in which platinum was deposited to a thickness of 20 nm was used. The distance between both electrodes is 1mm
And 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 open-circuit voltage of each battery obtained as described above, and the results of the experiment are discussed below.

[0018]

[Table 1]

(1) Rose Bengal (Ro) is made of TiO
_It adsorbed best on the _two electrodes and hardly adsorbed on Nb ₂ O ₅ . Sufficient short-circuit current except for Nb ₂ O ₅ electrode,
An open circuit voltage was obtained. In particular, a high current value was obtained with In ₂ O ₃ . It is considered that the reason why the performance is low with Nb ₂ O ₅ is that it is difficult to adsorb the dye and the potential of the conduction band is too high. (2) Rhodamine B (Ro) showed good adsorption on all electrodes. Sufficient short-circuit current and open-circuit voltage were obtained with any of the electrodes. In particular, an In ₂ in O ₃ high current value is obtained, an In ₂ O ₃ electrodes in the maximum value is obtained. As for Nb ₂ O ₅ , the largest current value was obtained in the Nb ₂ O ₅ electrode. (3) For erythrosin B (Er), the same results as Ro were obtained. (4) For Eosin Y (EY), results similar to Ro were obtained. In the TiO ₂ electrode, the highest current and voltage were obtained in the TiO ₂ electrode. This EY adsorbed TiO
_When a life test of the battery including the _two electrodes was performed, it was confirmed that the performance was not deteriorated for about 10 days under the condition that the water and oxygen in the cell were almost completely removed. The turnover number of the dye calculated from the total current value flowing at this time was 37.
Since the number reaches 10,000 or more, it can be said that such an organic dye can be stably used as long as it is not affected by decomposition by oxygen or the like. (5) Although the absorbance of the dye of fluorescein (F1) was small, the dye was sufficiently colored when adsorbed on the semiconductor electrode. The same behavior as that of EY was obtained as the battery behavior. (6) Phloxine (Ph) gave similar results as Ro. (7) Eosin B (EB) gave similar results as Ro. (8) Dibromofluorescein (DB) adsorbed best on the TiO ₂ electrode and hardly adsorbed on Nb ₂ O ₅ . With electrodes other than Nb ₂ O ₅ , sufficient short-circuit current and open-circuit voltage were obtained. In particular, ZnO and SnO ₂ showed the maximum values among those electrodes. (9) Dichlorofluorescein (DC) gave similar results as Ro. (10) In the case of pyrogallol (Py), although it was adsorbed to any of the electrodes, a long wavelength shift of the absorption wavelength was observed. Ti
Particularly high short-circuit currents were obtained for the O ₂ electrode. (11) Aminopyrogallol (AP) was adsorbed to any of the electrodes, especially to TiO ₂ . However, as for battery characteristics, high short-circuit current was obtained for electrodes other than TiO ₂ . (12) Fluorescein (Fn) exhibited the same battery characteristics as Ro. (13) As for uranine (Ur), the same results as Ro were obtained. (14) For 4,5,6,7-tetrachlorofluorescein (Tf), similar results to Ro were obtained. (15) Fluoresceinamine I (I1) is Ro
The same result as was obtained. (16) For fluoresceinamine II (I2), use Ro
The same result as was obtained. (17) Rhodamine 123 (R ₃ ) was very well adsorbed on the niobium oxide electrode, and obtained a higher current value than other dyes. The result was similar to that of Rh. (18) Rhodamine 6G (R ₆ ) was well adsorbed on the niobium oxide electrode, and a higher current value was obtained as compared with other dyes, but the performance was lower with electrodes other than niobium oxide. (19) The mixed dye of EY and Fn is well adsorbed on the TiO ₂ electrode to give a high-performance battery, and the short-circuit current is improved as compared with the case where EY and Fn are used alone. This is considered to be because the available light area was widened.

Comparative Example 1 A previously published paper (Nature, 261 (1976) p40)
A semiconductor powder obtained by sintering ZnO at 1300 ° C. was prepared as in the method of Example 2, 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. The short-circuit current and open-circuit voltage of these batteries are shown in Table 2, and consideration of the experimental results is shown below.

(A7)

Embedded image (MI)

Embedded image (NF)

Embedded image

[0023]

[Table 2]

(1) Acid Orange 7 (A7) is an azo dye, which was 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.

[0025]

The organic dye-sensitized semiconductor electrode of the present invention is
Having enhanced performance, solar cells of the present invention that include this electrode have 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.

Claims (8)

[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. Formed from a baked product of the aggregate of semiconductor fine particles, having a thickness of at least 10 nm, and having a ratio of the actual surface area to the apparent surface area of 10 or more,
In addition, the organic dye is a dye having a 9-phenylxanthene skeleton. 2. The oxide semiconductor is titanium dioxide, and the organic dye is eosin Y, dibromofluorescein, fluorescein, rhodamine B, pyrogallol, dichlorofluorescein, erythrosin B, fluorescin, uranine, rhodamine 123, fluorescein amine I, fluorescein amine II. 2. The oxide semiconductor electrode according to claim 1, wherein the oxide semiconductor electrode is at least one member selected from the group consisting of: 3. The oxide semiconductor electrode according to claim 1, wherein the oxide semiconductor is titanium dioxide, and the organic dye is a mixture of eosin Y and fluorescin. 4. The oxide semiconductor is 2 niobium pentoxide,
The oxide semiconductor electrode according to claim 1, wherein the organic dye is at least one selected from rhodamine B, aminopyrogallol, rhodamine 6G and rhodamine 123. 5. The oxide semiconductor is zinc oxide, and the organic dye is dibromofluorescein, eosin Y, dichlorofluorescein, erythrosin B, rhodamine B, fluorescein, aminopyrogallol, phloxine, fluorescin, rose bengal, uranine, tetrachlorofluorescein, 2. The oxide semiconductor electrode according to claim 1, wherein the oxide semiconductor electrode is at least one selected from fluoresceinamine I, fluoresceinamine I and fluoresceinamine II. 6. The oxide semiconductor is tin oxide, and the organic dye is at least one selected from dibromofluorescein, rhodamine B, eosin Y, phloxine, fluorescein, dichlorofluorescein, erythrosin B, uranine, rose bengal and rhodamine 123. 2. The oxide semiconductor electrode of claim 1, which is a seed. 7. The oxide semiconductor is indium trioxide and the organic dye is selected from rhodamine B, eosin B, phloxine, eosin Y, erythrosin B, rose bengal, dibromofluorescein, dichlorofluorescein, aminopyrogallol and uranine. 2. The oxide semiconductor electrode according to claim 1, which is at least one of the following. 8. A solar cell comprising: the oxide semiconductor electrode according to claim 1; a counter electrode thereof; and a redox electrolyte in contact with the electrode.