JP2945955B2 - Method for producing niobium oxide porous electrode and solar cell using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a niobium oxide porous electrode and a solar cell using the same.

[0002]

2. Description of the Related Art There are several types of solar cells, but most of them are silicon solar cells. However, recently, dye-sensitized wet solar cells have attracted attention,
It is being studied for practical use. Dye-sensitized wet solar cells have been studied for a long time. Its basic structure is composed of an oxide semiconductor, a dye adsorbed thereon, an electrolyte solution, and a counter electrode. Although various types of dyes and electrolytic solutions are being studied, research on semiconductors is limited. In the early days, semiconductor single-crystal electrodes were used. The types include titanium oxide (TiO ₂ ) and zinc oxide (Zn
O), cadmium sulfide (CdS), tin oxide (Sn
O ₂ ). However, the single crystal electrode has the disadvantage that the efficiency of the single crystal electrode is very low due to the small amount of dye adsorbed and the cost is high. What has been devised is a high-surface-area semiconductor electrode in which fine particles are sintered and many pores are formed. Tsubomura et al. Report that a porous zinc oxide electrode having an organic dye adsorbed thereon has very high performance (Nat
ure, 261 (1976) p402). Since then, dyes have also been improved, and Graetzel et al. Have adsorbed ruthenium-based dyes on porous titanium oxide electrodes, and now have performance comparable to silicon solar cells (J. Am). Chem.Soc.115
(1993) 6382). However, for practical use to replace silicon solar cells, higher energy conversion efficiency, higher short-circuit current, open-circuit voltage, and form factor are required. At present, substances reported as porous semiconductor electrodes include ZnO, TiO ₂ ,
There is only zirconium oxide (ZrO ₂ ).

Since the manufacturing cost of the dye-sensitized wet solar cell is much lower than that of the silicon solar cell, various products using the current silicon solar cell (for example, calculators, solar panels, watches, Game machines). At that time, the characteristics of the solar cell according to the usage of these products become important. There are various characteristics of solar cells. Short circuit current 2. Open voltage 3. Form factor 4. Energy conversion efficiency5. The optical absorption spectrum is particularly important.

[0004] Solar cells are being used everywhere in life, but there are two main ways of using them. One of them is an energy use in which many solar battery panels are installed on a roof or a square, and the generated power is stored in a storage battery or converted into an easy-to-use current / voltage for use. The other is a case where electricity generated only when light is applied, such as a solar cell calculator, is used.
In the former case, the most important performance of the solar cell is how large the electric energy that can be finally obtained because both the current and the voltage are large. On the other hand, in the latter case, it is important that the current and the voltage exceed a certain threshold. When it is desired to increase the current, it changes by increasing the area of the battery or reducing the internal resistance as much as possible, but the voltage is almost determined by the material of the solar cell. Therefore, in order to increase the voltage, many solar cells must be connected in series. This is a major disadvantage when using the latter.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to the manufacture of a niobium oxide semiconductor electrode having a porous structure and a higher open voltage than the prior art, which is advantageously applied to a dye-sensitized wet solar cell.
It is an object to provide a method and a solar cell using the electrode.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the manufacturing method of the present invention, a porous semiconductor electrode made of niobium oxide is provided. Also,
According to the present invention, a solar cell having a semiconductor electrode made of niobium oxide having a dye adsorbed thereon is provided.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION A porous semiconductor electrode made by the manufacturing method of the present invention comprises niobium oxide having a high surface area. Since the electrode has a high surface area, the niobium oxide preferably has a small primary particle diameter. Specifically, the thickness is 1 to 200 nm, preferably 50 nm or less, but is too small to be amorphous. The surface area of niobium oxide itself is preferably ⁵ to 100 m ² / g. In order to treat niobium oxide as an electrode, the niobium oxide powder may be pelletized by itself and sintered, but it is easier to handle by fixing it on a conductive substrate. The substrate may be a stable metal such as titanium or tantalum, or conductive glass or carbon. The thickness of niobium oxide on the substrate is 200 to 200
00 nm, preferably 1000 nm or more.

[0008] Niobium oxide particles are prepared by the decomposition of pure niobium hydroxide. It is desirable to use niobium hydroxide having as few impurities as possible, but it is also possible to purify the niobium salt or niobium alkoxide sufficiently and then hydrolyze to prepare pure niobium hydroxide. In order for the niobium oxide electrode to function sufficiently, electrical contact between the niobium oxide particles is important, and firing conditions are important for that. Preferably, niobium hydroxide or niobium oxide dehydrated and decomposed at a low temperature is pre-baked. 300 to 900 degrees in air, preferably 5
Slowly raise the temperature to 00-800 degrees and keep it for about 1 hour, then slowly lower the temperature. The pre-fired niobium oxide is fixed to the substrate at the thickness described above. For this purpose, the substrate may be dipped in a suspension of niobium oxide, or a slurry of niobium oxide may be applied. The viscosity of the niobium oxide slurry may be increased by using water or an aqueous solution of a surfactant, or by adding polyethylene glycol or the like. Then, it is slowly dried on the substrate. Next, the substrate is fired in air or under an inert atmosphere. The firing temperature is 300 to 900 degrees, preferably 400 to 800 degrees for 1 hour. However, the firing temperature must be lower than the temperature at which the substrate is not damaged.

Next, a method of manufacturing a solar cell using the niobium oxide electrode thus prepared will be described. To adsorb the dye on the niobium oxide electrode, place the electrode on a solution of the dye.
Soak for minutes to 2 hours. The temperature is preferably close to the boiling point of the solution as long as the decomposition of the dye does not occur. The solvent preferably dissolves the dye well, does not inhibit the adsorption of the dye to the electrode, and is electrochemically inactive even if it remains on the electrode surface. For example, ethanol, acetonitrile and the like can be mentioned. As a solvent for the electrolytic solution, a substance which is electrochemically inert and can dissolve a sufficient amount of the electrolyte is desired. For example, there are acetonitrile and propylene carbonate. As the electrolyte, a substance capable of transporting electric charges between the electrodes at a sufficient speed by a stable redox pair of ions is desired. Redox pairs include I ⁻ / I ₃ ⁻ , Br ⁻ / Br ₃ ⁻ , and quinone / hydroquinone pairs. For example, when forming an I ⁻ / I ₃ ⁻ pair, an ammonium salt of iodine and iodine are mixed. The cation is selected so that the electrolyte is easily dissolved in the solvent. Organic dyes such as rose bengal or metal complexes such as zinc porphyrin and ruthenium bipyridyl can be used as the dye.However, the oxides and reductants are stable and relatively stable, and the electron potential in the photoexcited dye is lower than that of the niobium oxide semiconductor. It is necessary to be more negative than the charge potential and more positive than the potential of a redox couple such as l ⁻ / I ₃ ⁻ ion. Material having a catalytic ability to perform a reduction reaction at a sufficient early as oxidized redox ion is desired ^- I ₃ for the counter electrode. For example, there is platinum or an electrode carrying the same on a conductive material. When a battery is finally manufactured, a redox-containing electrolytic solution is interposed between the niobium oxide electrode on which the dye is adsorbed and the counter electrode, and sealed with a sealant. It is desirable that the above operation be performed under such a condition that moisture and oxygen in the air are not touched as much as possible.

[0010]

Embodiments of the present invention will be described below.

Examples 1 to 7 The size of a battery to be measured was 1 × 1 cm.
The light source used was a 500 W xenon lamp. The filter is a 520 nm band pass filter (4 mW / cm ² )
Or a 390 nm cut-off filter (130 mW /
cm ² ). The measurement of short-circuit current, open-circuit voltage, and form factor used a potentiostat equipped with a non-resistance ammeter. Niobium oxide was prepared by thermal decomposition of niobium hydroxide (Central Glass). The pre-baking temperature for thermal decomposition was 500, 700, and 800 ° C. for 1 hour as shown in Table 1. The surface area of the niobium oxide thus prepared was 10 to 100 m ² / g. The niobium oxide powder was mixed with water, acetylacetone, and a surfactant to form a slurry. This slurry is mixed with conductive glass (F-Sn).
O ₂ , 10Ω / sq) so as to have a predetermined film thickness after firing. The firing was performed at 500 ° C. for 1 hour in the air to produce a niobium oxide electrode. The pigment is Gra
Ru ((bipy) (COO) reported by etzel
H) ₂ ) ₂ (SCN) ₂ was used. The dye was dissolved in ethanol, and a niobium oxide electrode was placed in the solution.
After refluxing for an hour, the dye was adsorbed on the electrode. Then, it was dried at room temperature. As a counter electrode, a conductive glass on which platinum was deposited with a thickness of 20 nm was used. The redox pair used was I ⁻ / I ₃ ⁻ . Solute is tetrapropylammonium
iodide (0.46M) and iodine (0.06M),
Solvent is ethyl carbonate (80v
ol%) and acetonitrile (20vol%)
Was used. Table 1 shows the characteristics of the solar cell using niobium oxide as an electrode.

[0012]

[Table 1] Example 520 nm band pass> 390 nm cut-off Pre-baking temperature Film thickness Open voltage Short circuit current Open voltage Short circuit current Form factor Semiconductor ℃ μm V mA V mA% 1 Nb ₂ O ₅ 500 6 0.61 0.29 0.72 6.02 58 2 Nb ₂ O ₅ 500 11 0.56 0.31 0.68 7.00 3 Nb ₂ O ₅ 700 3 0.60 0.10 0.84 4.2 4 Nb ₂ O ₅ 700 8 0.58 0.31 0.74 8.26 61 5 Nb ₂ O ₅ 700 10 0.57 0.22 0.73 5.04 6 Nb ₂ O ₅ 800 4 0.71 0.11 0.86 3.60 7 Nb ₂ O ₅ 800 8 0.63 0.21 0.80 5.45 60

Comparative Examples 1 to 9 Table 2 shows characteristics of solar cells using various oxide semiconductors instead of niobium oxide. For Comparative Example 1, Grae
zel et al. (J. Am. Chem. So
c. 115 (1993) 6382). P-25 (manufactured by Nippon Aerosil) was shown to be excellent as a titanium oxide material, and the same material was compared as an electrode by the same preparation method. In the results shown in Table 2, the preparation conditions were changed little by little before and after the conditions shown in the paper, and data having optimum values and reproducibility were placed. Comparing the results of Comparative Example 1 and Table 1, it can be seen that the open-circuit voltage of the niobium oxide electrode is much higher than that of the titanium oxide electrode in each case. The short-circuit current was higher for the titanium oxide electrode, but the form factor was slightly better for the niobium oxide electrode.

In Comparative Examples 2 to 9, as the semiconductor material, an oxide powder was prepared from various metal salts and alkoxides of commercially available oxides or hydroxides, and this was formed into an electrode in the same manner as the niobium oxide electrode. A battery was manufactured. The optimum values are listed in Table 2 by changing some preparation conditions. as a result,
It can be seen that the performance of the niobium oxide electrode greatly exceeds all of these various semiconductor electrodes in terms of open-circuit voltage, short-circuit current, and shape factor.

[0015]

[Table 2] Comparative example 520 nm band pass> 390 nm cut-off Pre-baking temperature Film thickness Open voltage Short circuit current Open voltage Short circuit current Form factor Semiconductor ℃ μm V mA V mA% 1 TiO ₂ 500 7 0.52 0.73 0.66 13.72 57 2 ZnO 500 7 0.49 0.11 0.54 0.63 25 3 ZrO ₂ 500 8-tr 0.15 tr 21 4 In ₂ O ₃ 500 7 0.30 0.05 0.41 0.74 31 5 SnO ₂ 500 7 0.46 0.12 0.60 1.61 30 6 La ₂ O ₅ 500 7-tr 0.15 tr-7 Ta ₂ O ₅ 500 6-tr 0.12 tr-8 WO ₃ 500 7 0.31 0.11 0.56 0.59-9 SrTiO ₃ 500 6 0.27 tr 0.31 tr 34

[0016]

According to the present invention, the open-circuit voltage can be increased as compared with a conventional wet-type solar cell using titanium oxide. When incorporated in a product, the number of batteries in series can be reduced, so that the manufacturing cost is reduced.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Takamasa Hanaoka 1-1-1, Higashi, Tsukuba, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (72) Inventor Hiroshi Ushijima 1-1-1, Higashi, Tsukuba, Ibaraki, Japan Inside the Research Institute of Engineering, Industrial Technology (72) Inventor Toshikazu Takahashi 1-1-1, Higashi, Tsukuba, Ibaraki Pref. Technical Research Institute (56) References JP-A-5-59562 (JP, A) JP-A-7-249790 (JP, A) JP-A-6-511113 (JP, A) JP-A-6-507999 (JP, A) A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 14/00

Claims (2)

(57) [Claims] (1) Niobium hydroxide or dehydrated and decomposed at low temperature
Niobium oxide slowly rises in air at 300-900 ° C
Warm it, keep it at that temperature for about an hour,
The manufactured niobium oxide having a particle size of 1 to 200 nm is placed on a substrate.
After fixing to the predetermined thickness and gently drying on the substrate,
300 ~ 900 ℃ in air or under inert atmosphere with substrate
Niobium oxide porous semiconductor electrode characterized by firing
Polar manufacturing method. 2. An acid produced by the production method according to claim 1.
A high-voltage solar cell having a niobium fluoride porous semiconductor electrode .