JP3309131B2 - Organic dye-sensitized niobium 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 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 An object of the present invention is to provide a niobium oxide electrode which gives a practical current / voltage curve in an organic dye-sensitized oxide semiconductor electrode, and a solar cell containing the same. And

[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 directly adsorbed on the surface of the oxide semiconductor film, The semiconductor film is formed from a fired product of an aggregate of niobium oxide semiconductor fine particles, and has at least 10 n
m, the ratio of the actual surface area to the apparent surface area is 10 or more, and the organic dye is 9
-An oxide semiconductor electrode having an organic dye having a phenylxanthene skeleton and having an amino group is provided. Further, according to the present invention, there is provided a solar cell including the niobium 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 those conventionally known. As such, niobium Nb is used. The niobium 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. 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 has a 9-phenylxanthene skeleton and has an amino group. For comparison, a dye having a 9-phenylxanthene skeleton represented by the following formula is used for comparison. Here are some typical examples.

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. 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 (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 (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 niobium oxide semiconductor electrode of the present invention, first, a coating solution containing fine powder of a niobium oxide semiconductor is prepared. The finer the primary particle diameter of the oxide semiconductor fine powder is, the more preferable it is.
000 nm, preferably 2 to 50 nm. The coating liquid (slurry liquid) containing the niobium oxide semiconductor fine powder can be prepared by dispersing the oxide semiconductor fine powder in a solvent. The niobium 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 niobium oxide semiconductor fine powder. Such solvents include water, organic solvents, and mixtures of water and organic solvents. Organic solvents include alcohols such as methanol and ethanol, methyl ethyl ketone, acetone,
Ketones such as acetylacetone and hydrocarbons such as hexane and cyclohexane are used. 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 niobium oxide semiconductor fine powder in the solvent is 0.1 to 70% by weight, preferably 0.1 to 30% by weight.

Next, the coating liquid is applied on a substrate, dried, and then fired in air or an inert gas to form a niobium 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 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 niobium oxide semiconductor fine particles, the particle diameter of which corresponds to the primary particle diameter of the niobium oxide semiconductor fine powder used. Is what you do. 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,
This is fired to form a fired material film having increased mechanical strength and firmly fixed to the substrate.

In the present invention, the fired product film is a porous structure film, the thickness is 10 nm, and the ratio of the actual surface area to the apparent surface area is 10 or more. Although the upper limit of this ratio is not particularly limited, it is usually 1000 to 20.
00. 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 means a BET surface area obtained from the amount of krypton gas adsorbed. A specific measuring method is a method in which a krypton gas is adsorbed on a substrate-equipped oxide semiconductor film having an apparent surface area of 1 cm ² at a liquid nitrogen temperature using a BET surface area measuring device (ASAP2000, manufactured by Micromeritics). 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 is obtained by applying a coating solution containing niobium oxide semiconductor fine particles on a substrate, and firing the fine particle aggregate film formed by drying. It can be obtained by lightly sintering the assembly film.
In this case, the firing temperature is lower than 1000 ° C., usually 30
The temperature is 0 to 800 ° C, preferably 500 to 800 ° C. 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 niobium oxide semiconductor fine particles, the firing temperature, and the like.

Next, an organic dye having a 9-phenylxanthene skeleton and having an amino group is adsorbed as a monomolecular film on the surface of the niobium 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. The immersion time is about 30 minutes to 24 hours, but 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 having a 9-phenylxanthene skeleton and an amino group to be adsorbed on the niobium oxide semiconductor film does not need to be one kind of organic dye.
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 100 ml
Medium, 1 to 10000 mg, preferably 10 to 500 mg
And determined appropriately according to the type of the organic dye and the organic solvent.

The solar cell of the present invention is characterized in that the niobium oxide half
Conductor electrode, counter electrode, and redox electrodes in contact with those electrodes
It consists of decomposing. As a redox electrolyte, I
⁻/ I ₃ ⁻System and Br⁻/ Br₃ ⁻System, quinone / high
Droquinone type and the like can be mentioned. Such redox
The electrolyte can be obtained by a conventionally known method.
For example, I⁻/ I₃ ⁻The system electrolyte is iodine ammonia.
Can be obtained by mixing iodium salt and iodine
You. The electrolyte may be a liquid electrolyte or a liquid electrolyte contained in a polymer substance.
It can be a solid polymer electrolyte. Liquid electricity
In the decomposition, the solvent is electrochemically inert
For example, acetonitrile,
Pyrene, ethylene carbonate and the like are used. Opposite pole
As long as it has conductivity, any conductive
Materials are used,₃ ⁻Oxidized red such as ions
Catalytic ability to carry out the reduction reaction of x-ions at a sufficient speed
It is preferable to use those having As such
Uses platinum plating or platinum deposition on the surface of a platinum electrode or conductive material.
Treated, rhodium metal, ruthenium metal, ruthenium oxide
And carbon.

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 niobium oxide semiconductor powder used, niobium hydroxide (manufactured by Central Glass Co., Ltd.) was thermally decomposed as Nb ₂ O ₅ (500 ° C., 1 hour, 99 hours).
m ² / g). The organic dyes include Rh (rhodamine B), AP (aminopyrogallol), and fluoresceinamine I (I
1), fluoresceinamine II (I2), rhodamine 123 (R ₃ ) and rhodamine 6G (R ₆ ).

Example 1 A niobium oxide semiconductor electrode was manufactured as follows.
A liquid mixture of water and acetylacetone containing a nonionic surfactant (volume mixing ratio = 20 /
In 1), a slurry liquid was prepared by dispersing at a concentration of about 1 wt%. Next, this slurry liquid was applied on a conductive glass substrate (F-SnO ₂ , 10Ω / sq) having a thickness of 1 mm and dried, and the obtained dried product was fired at 500 ° C. for 1 hour in air. Then, a fired product film having a thickness of 7 μm was formed on the substrate. The ratio of the actual surface area to the apparent surface area of the fired product film was Nb ₂ O ₅ : 850 when expressed in relation to the type of the oxide semiconductor. Next, the fired product film together with the substrate was immersed in an organic dye solution, dye-adsorbing treatment was performed at 80 ° C. while returning the solution, and then dried at room temperature. In this case, the organic dye solution contains 100 mg / 100 of the organic dye except F1.
It was prepared by dissolving in ethanol at a concentration of ml. Also,
The F1 solution was prepared by dissolving F1 at a concentration of 100 mg / 100 ml in dimethylformamide.

The niobium oxide semiconductor electrode obtained as described above and its counter electrode were brought into contact with an electrolyte solution to form a solar cell. 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 1
mm. As the electrolyte solution, tetrapropylammonium iodide (0.46M) and iodine (0.6M)
Of a mixture of ethylene carbonate and acetonitrile (volume mixing ratio = 80/20). 9 for reference
An organic dye having a phenylxanthene skeleton but not having an amino group, specifically, Ro (rose bengal), EB (eosin B), DB (dibromofluorescein), Er (erythrosin B), EY (eosin Y) , DC (dichlorofluorescein), Py (pyrogallol), F1 (fluorescein), Ph (phloxine), Fn (fluorescin), uranine (Ur), 4,
For 5,6,7-tetrachlorofluorescein (Tf), a niobium oxide semiconductor electrode was prepared in the same procedure. 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 Nb₂
O₅Had almost no adsorption. Nb₂O₅Sex
The reason for the low performance is the difficulty in adsorbing the dye and its conduction.
This is probably because the potential of the belt is too high. (2) Rhodamine B (Ro) has sufficient short-circuit current and open
Voltage is obtained and Nb₂O ₅Also for Nb₂O₅In the electrode
The maximum current value was obtained. (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. (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 Nb₂O
₅Had almost no adsorption. (9) Dichlorofluorescein (DC) is the same as Ro
Gave a good result. (10) In the case of pyrogallol (Py), it adheres well to the electrode
However, a long wavelength shift of the absorption wavelength was observed. (11) Aminopyrogallol (AP) adsorbs well to electrodes
However, high short-circuit current was obtained as battery characteristics. (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), R
The same result as in o 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
Adsorbs well to the pole and obtains a higher current value than other dyes
Was.

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.

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 release voltage for these batteries, and the results of the experiment are discussed below.

(A7)

Embedded image 21 (MI)

Embedded image 22 (NF)

Embedded image 23

[0023]

[Table 2]

(1) Acid Orange 7 (A7) is an azo dye, but hardly adsorbed to the niobium oxide semiconductor electrode. Very poor battery characteristics
Result. (2) Modant Orange 1 (M1), which is an azo dye, showed good adsorption to the niobium oxide semiconductor electrode. However, the battery characteristics were very poor. (3) Nuclear fast red (NF) is a quinone-based dye, which exhibited good adsorption to the niobium oxide semiconductor electrode. However, the battery characteristics were very poor.

[0025]

The organic dye-sensitized semiconductor electrode of the present invention is
This served as a step toward practical use of the niobium oxide semiconductor electrode, and a solar cell using the niobium oxide semiconductor electrode could be provided. 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.

Continuation of the front page (56) References JP-A-7-249790 (JP, A) JP-A-55-124964 (JP, A) JP-A-4-58472 (JP, A) Table 6-511113 (JP) , A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 14/00 H01B 1/16 H01L 21/28 301 H01L 31/04

Claims (3)

(57) [Claims] 1. A substrate having a conductive surface, an oxide semiconductor film formed on the conductive surface, and an organic dye directly adsorbed on the surface of the oxide semiconductor film. It is formed from a fired product of the niobium oxide semiconductor fine particle aggregate, has a thickness of at least 10 nm, has a ratio of the actual surface area to the apparent surface area of 10 or more, and the organic dye has a 9-phenylxanthene skeleton. And an organic dye having an amino group. 2. An organic dye having a 9-phenylxanthene skeleton and having an amino group is one of the group consisting of rhodamine B, aminopyrogallol, fluoresceinamine I, fluoresceinamine II, rhodamine 123, and rhodamine 6G. The oxide semiconductor electrode according to claim 1, wherein 3. A solar cell comprising the oxide semiconductor electrode according to claim 1 or 2, a counter electrode thereof, and a redox electrolyte contacting the electrodes.