JP3353054B2 - 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 capable of generating a large short-circuit current and a high release voltage, 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 in which rose bengal is adsorbed as an organic dye 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 provides a practical current / voltage curve capable of generating a large short-circuit current and a high release voltage, and an electrode for the same. It is an object to provide a solar cell including the same.

[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 fired 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 has a specific oxide semiconductor and a specific organic dye. The combination of the above provides an oxide semiconductor electrode having a practical current / voltage curve capable of generating a large short-circuit current and a high release voltage. Further, according to the present invention, there is provided a solar cell including the oxide semiconductor electrode, a counter electrode thereof, and a redox electrolyte in contact with the electrodes.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The oxide semiconductor used in the present invention includes conventionally known oxide semiconductors. Examples of such a material include oxides of transition metals such as Zn, Sn, and In. This oxide semiconductor powder is preferably as fine as possible, and has an average particle size of 5000 n.
m, preferably 50 nm or less. Further, its specific surface area is 5 m ² / g or more, preferably 10 m ² / g or more.

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 9-phenylxanthene skeleton in which 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 02 (2) Rhodamine B (Rh)

Embedded image 03 (3) Eosin B (EB)

Embedded image 04 (4) Dibromofluorescein (DB)

Embedded image 05 (5) Erythrosin B (Er)

Embedded image 06 (6) Eosin Y (EY)

Embedded image 07 (7) Dichlorofluorescein (DC)

Embedded image 08 (8) Pyrogallol (Py)

Embedded image 09 (9) Fluorescein (FI)

Embedded image 10 (10) Phloxine (Ph)

Embedded image 11 (11) Aminopyrogallol (AP)

Embedded image 12 (12) Fluorescin (Fn)

Embedded image 13 (13) Uranine (Ur)

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

Embedded image 15 (15) Fluoresceinamine I (I1)

Embedded image 16 (16) Fluoresceinamine II (I2)

Embedded image 17 (17) Rhodamine 123 (R3)

Embedded image 18 (18) Rhodamine 6G (R6)

Embedded image 19

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.
５5 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 oxide semiconductor fine powder used. 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 adsorbed.
ET means surface area. The specific measurement 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 measurement 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 and, ^Br - / Br ₃ ^- system, quinone / hydroquinone system. Such a redox electrolyte can be obtained by a conventionally known method, for example,
The I ⁻ / I ₃ ⁻ type 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 As such,
Platinum electrodes, those obtained by subjecting the surface of a conductive material to platinum plating or platinum vapor deposition, rhodium metal, ruthenium metal, ruthenium oxide, carbon and the like can be used.

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 used oxide semiconductor powder, a commercial 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 pyrolyzing 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) and In ₂ O ₃ (25 m ² / g) were commercially available products (Wako Pure Chemical Industries, Ltd.). Also, as an organic dye,
The aforementioned Ro (rose bengal), Rh (rhodamine B), EB (eosin B), DB (dibromofluorescein), Er (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 (R3) and rhodamine 6G (R6) were used.

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 in air at 500 ° C. for 1 hour 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, ZnO: 200, SnO ₂ : 50
0, In ₂ O ₃ : ₂₀₀ . Next, the fired product film together with the substrate is immersed in an organic dye solution,
Then, after performing a dye adsorption treatment while performing a return solution, the resultant was dried at room temperature. In this case, the organic dye solution, except for F1,
It was prepared by dissolving the organic dye in ethanol at a concentration of 100 mg / 100 ml. In addition, the F1 solution is 100% F1.
It was prepared by dissolving in dimethylformamide at a concentration of mg / 100 ml.

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] 20

(1) Rose Bengal (Ro) is made of TiO
₂Adsorbs best to electrodes, Nb₂O₅Hardly suck
I didn't wear it. Nb₂O₅Sufficient short circuit except for electrodes
The current and open circuit voltage were obtained. Especially In₂O₃Then high electricity
Flow values were obtained. Nb₂O₅The reason for the low performance
Adsorption is difficult and the conduction band potential is high.
It seems to be too much. (2) Rhodamine B (Ro) is good for any electrode
Showed poor adsorption. Sufficient short-circuit current and open
A discharge voltage was obtained. In particular, In₂O₃Now the high current value
Obtained, In₂O₃The maximum value in the electrode was obtained. Nb₂O
₅Also for Nb ₂O₅The largest current value in the electrode
Was. (3) Erythrosin B (Er) is the same as Ro
Results were obtained. (4) Eosin Y (EY) has the same conclusion as Ro.
The fruit was obtained. TiO₂In the electrode, TiO₂In the electrode
The maximum current and voltage were obtained. Ti which absorbed this EY
When the life test of the battery including the O2 electrode was performed,
10 days under conditions where water and oxygen are almost completely removed
It was confirmed that the performance did not deteriorate to the extent. At this time
The turnover number of the dye calculated from the total current value obtained was 3
Such organic dyes have acidity of 70,000 times or more.
It can be used stably as long as it is not affected by decomposition
It can be said that. (5) Fluorescein (F1) dye has low absorbance
However, when adsorbed on the semiconductor electrode, sufficient coloring was shown. Electric
Pond behavior was similar to EY. (6) Phloxine (Ph) gives similar results as Ro
Was. (7) Eosin B (EB) gives similar results as Ro
Was. (8) Dibromofluorescein (DB) is TiO₂Electric
Adsorbs best to the pole, Nb₂O₅Is almost absorbed
did not exist. Nb₂O₅Sufficient short-circuit voltage with other electrodes
Current and open circuit voltage were obtained. In particular, ZnO and SnO₂so
The maximum value was obtained among those electrodes. (9) Dichlorofluorescein (DC) is the same as Ro
Gave a good result. (10) In the case of pyrogallol (Py), any electrode
Although it was adsorbed, a long wavelength shift of the absorption wavelength was observed. Ti
O₂Particularly high short-circuit currents were obtained for the electrodes. (11) Aminopyrogallol (AP)
Also adsorb, especially TiO ₂ Was strongly adsorbed. Only
The battery characteristics are TiO₂High for other electrodes
A short circuit current was obtained. (12) Fluorescein (Fn) has the same behavior as Ro
Battery characteristics were shown. (13) For Uranine (Ur), the same results as Ro were obtained.
Obtained. (14) 4,5,6,7-tetrachlorofluorescein
Regarding (Tf), the same result as Ro was 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 (R₃About) Nio oxide
Adsorbs very well to the electrode, and has a higher charge than other dyes.
The streaming value was obtained. The result was similar to that of Rh. (18) Rhodamine 6G (R₆) For niobium oxide
Adsorbed well to the pole and obtained a higher current value than other dyes
However, the performance was low with electrodes other than niobium oxide. (19)
The mixed dye of EY and Fn is TiO₂Adsorbs well to the electrode,
With high-performance batteries, EY and Fn were used alone.
The short circuit current is improved as compared with the case. This is the available light
This is probably because the area has expanded.

Reference 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.

Reference 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 21 (MI)

Embedded image 22 (NF)

Embedded image 23

[0023]

[Table 2] 24

(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.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-24790 (JP, A) JP-A-55-124964 (JP, A) JP-A-4-58472 (JP, A) Table 6- 511113 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 14/00 H01L 31/04

Claims (4)

(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. Formed from a fired product of an aggregate of fine semiconductor particles, having a thickness of at least 10 nm, a ratio of the actual surface area to the apparent surface area of 10 or more, the oxide semiconductor is zinc oxide, and the organic dye Is at least one selected from dibromofluorescein, dichlorofluorescein, erythrosin B, and fluorescein. 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 oxide semiconductor film is oxidized. Formed at the thickness of at least 10 nm, the ratio of the actual surface area to the apparent surface area is 10 or more, the oxide semiconductor is tin oxide, and the organic dye is An oxide semiconductor electrode which is at least one selected from dibromofluorescein and rhodamine B. 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. The oxide semiconductor is formed from a baked product of the aggregate of 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 oxide semiconductor is 2 indium trioxide, and An oxide semiconductor electrode in which the dye is at least one selected from rhodamine B, phloxine, erythrosin B, rose bengal, dibromofluorescein, dichlorofluorescein, uranin, fluoresceinamine I, fluoresceinamine II, and rhodamine 123. 4. A solar cell comprising the oxide semiconductor electrode according to claim 1, a counter electrode thereof, and a redox electrolyte contacting the electrodes.