JP4655519B2 - Electrolyte for dye-sensitized solar cell and dye-sensitized solar cell - Google Patents

Description

  The present invention relates to an electrolyte solution for a dye-sensitized solar cell and a dye-sensitized solar cell using this electrolyte solution, and is particularly difficult to volatilize. Therefore, the present invention is effective in stabilizing battery performance and improving the battery property. The present invention relates to an electrolyte solution for a dye-sensitized solar cell that can also be used, and a dye-sensitized solar cell using the electrolyte solution.

  It is already known that a solar cell is configured using an oxide semiconductor adsorbed with a sensitizing dye as an electrode. FIG. 1 is a cross-sectional view showing a general structure of such a dye-sensitized solar cell. As shown in FIG. 1, a transparent conductive film 2 such as FTO (fluorine-doped tin oxide) or ITO (indium tin oxide) is provided on a substrate 1 such as a glass substrate, and a spectral sensitizing dye is formed on the transparent conductive film 2. As a result, the dye-sensitized semiconductor electrode 4 is formed. A counter electrode 5 is disposed opposite to the dye-adsorbing semiconductor film 3 with a space therebetween, and an electrolyte 7 is sealed between the dye-sensitized semiconductor electrode and the counter electrode 5 by a sealing material 6 ( For example, Unexamined-Japanese-Patent No. 2003-308893).

  The dye-adsorbing semiconductor film 3 is usually composed of a titanium oxide thin film to which a dye is adsorbed, and this titanium oxide film is formed by a sol-gel method. The dye adsorbed on the titanium oxide thin film is excited by visible light, and power is generated by passing the generated electrons to the titanium oxide fine particles.

  The counter electrode 5 has a transparent conductive film such as ITO or FTO formed on a substrate such as glass or plastic, and promotes the transfer of electrons between the transparent conductive film and the sensitizing dye on the transparent conductive film. The platinum film as the catalyst is formed to a thickness that does not decrease the transmittance. The counter electrode 5 may also be formed of a platinum plate.

As the electrolyte 7, redox substances, for example, LiI, NaI, KI, combinations of metal iodides and iodine, such as CaI _2, LiBr, NaBr, KBr, the metal bromide and bromine, such as CaBr ₂ combination, preferably Uses an electrolytic solution prepared by dissolving a redox substance comprising a combination of metal iodide and iodine in a solvent such as acetonitrile or nitrile compound such as methoxyacetonitrile. In this electrolyte solution, t-butylpyridine may be further blended for improving battery performance.
JP 2003-308893 A

  In conventional electrolytes, volatile solvents such as acetonitrile (boiling point 82 ° C.) and methoxyacetonitrile (boiling point 118 to 119 ° C.) are used. As a result, the solvent volatilizes over time, particularly in a high temperature environment. Since the electrolyte composition changes, there is a drawback that the battery performance is not stabilized.

  Conventionally, t-butylpyridine blended for improving battery performance has a problem of strong odor and poor working environment during battery assembly.

  The present invention solves the above-mentioned conventional problems, is less likely to volatilize, is effective for stabilizing battery performance, and can also improve battery performance without containing t-butylpyridine. An object is to provide an electrolytic solution and a dye-sensitized solar cell using the electrolytic solution.

The dye-sensitized solar cell electrolyte of the present invention is a dye-sensitized solar cell electrolyte containing a redox substance and a solvent, and contains a liquid imidazole compound as an electrolyte that also serves as the solvent, and a property improver As an electrolyte solution for a dye-sensitized solar cell to which alkylene carbonate is added as a solvent, γ-butyrolactone is further contained as a solvent .

  As a result of intensive studies to solve the above problems, the present inventors have found that the use of a non-volatile liquid imidazole compound for the electrolytic solution makes it difficult for the electrolytic solution to volatilize and stabilize the battery performance. It was. However, it has also been found that an electrolytic solution using a liquid imidazole compound tends to lower battery performance such as open-circuit voltage and conversion efficiency. Therefore, as a result of further investigations on the improvement of the battery performance, it is possible to improve the battery performance by adding alkylene carbonate, particularly ethylene carbonate, as a characteristic improver, without adding t-butylpyridine. The inventors have found that battery performance such as open-circuit voltage and conversion efficiency can be improved, and have completed the present invention.

  In the present invention, 1-methyl-3-propylimidazolium iodide (hereinafter referred to as “MPI”) is preferable as the imidazole compound, and ethylene carbonate is preferable as the alkylene carbonate. Further, as the redox substance, lithium iodide and iodine are preferable.

Moreover, it is preferable that the electrolyte solution of this invention contains 0.1-10 mol of MPI, 10-60 weight% of ethylene carbonate, and 0.1-20 mol of oxidation-reduction substances with respect to 1L of (gamma) -butyrolactone. . With such an electrolytic solution, excellent battery performance can be obtained even when t-butylpyridine is not contained.

  The dye-sensitized solar cell of the present invention includes a dye-sensitized semiconductor electrode, a counter electrode provided opposite to the dye-sensitized semiconductor electrode, and a space between the dye-sensitized semiconductor electrode and the counter electrode. In the dye-sensitized solar cell having the electrolyte solution disposed in the electrolyte, the electrolyte solution is the electrolyte solution for the dye-sensitized solar cell according to the present invention.

  The electrolyte solution for a dye-sensitized solar cell of the present invention hardly volatilizes and is effective for stabilizing the battery performance. In addition, battery performance such as open-circuit voltage and conversion efficiency can be improved. By not containing t-butylpyridine, the working environment at the time of battery assembly can be improved.

  The dye-sensitized solar cell of the present invention uses such a dye-sensitized solar cell electrolytic solution of the present invention as an electrolytic solution, and has excellent battery performance and long-term stability.

  Hereinafter, embodiments of the electrolyte solution for dye-sensitized solar cells and the dye-sensitized solar cell of the present invention will be described in detail.

  The dye-sensitized solar cell electrolyte of the present invention is a dye-sensitized solar cell electrolyte containing a redox substance and a solvent, and contains a liquid imidazole compound as an electrolyte that also serves as a solvent, and as a property improver. An alkylene carbonate is added.

  Especially as a liquid imidazole compound, MPI is used suitably. Note that MPI is non-volatile and the exact boiling point is unknown, but it is estimated that this temperature is the boiling point because it is about 400 ° C. at a 10% decomposition reduction temperature.

  Examples of the alkylene carbonate as the property improver include ethylene carbonate (boiling point 243 to 244 ° C.) and propylene carbonate (boiling point 240 ° C.), and ethylene carbonate is preferable.

The oxidation-reduction substance is not particularly limited as long as it can be generally used in a battery or a solar battery, but a combination of a metal iodide such as LiI, NaI, KI, and CaI ₂ and iodine (I ₂ ), A combination of a metal bromide such as LiBr, NaBr, KBr, or CaBr ₂ and bromine is preferable. Among these, a combination of metal iodide and iodine, particularly a combination of LiI and I ₂ is preferable.

Further, the electrolytic solution of the present invention, viewed contains more γ- butyrolactone (boiling point 203-204 ° C.) as a solvent, thereby lowering the viscosity of the electrolyte solution, it is possible to increase the electrolyte permeability into the semiconductor electrode.

In the present invention, the most preferable electrolyte solution configuration is as follows: 1 L of γ-butyrolactone Redox substances (LiI and I ₂ ): 0.1 to 5 mol Liquid imidazole compound such as MPI: 0.1 to 10 mol Ethylene carbonate Properties improver such as: 10 to 60% by weight
It is preferable that the electrolytic solution is substantially free of t-butylpyridine and substantially composed of γ-butyrolactone, MPI, ethylene carbonate, LiI, and I ₂ .

  If the amount of liquid imidazole compound such as MPI is too small than the above range, the effect of reducing volatility by adding MPI cannot be obtained sufficiently, and if too much, the electrolyte becomes highly viscous and penetrates into the semiconductor electrode. The ionic conductivity may be deteriorated and the ion conductivity may be lowered. The content of a liquid imidazole compound such as MPI is preferably 0.3 to 6 mol with respect to 1 L of γ-butyrolactone.

  Moreover, when content of characteristic improvers, such as ethylene carbonate, is less than the said range, the improvement effect of the battery performance by having mix | blended ethylene carbonate cannot be acquired, and when too much, it will precipitate easily and performance will also fall. The content of a property improver such as ethylene carbonate is preferably 30 to 60% by weight based on 1 L of γ-butyrolactone.

Further, the content of the redox substance (are preferably contained in a total .LiI a substantially finally amount and I ₂ with LiI and I _2.) To obtain sufficient power generation efficiency and smaller than the above range If the amount is too large, the viscosity of the electrolyte is increased, which is not suitable.

  The dye-sensitized solar cell according to the present invention uses such an electrolyte solution for a dye-sensitized solar cell according to the present invention as an electrolyte. The other configuration than the electrolyte is as shown in FIG. It is set as the structure similar to the conventional dye-sensitized solar cell.

  The substrate 1 of the dye-sensitized solar cell is usually a glass plate and is usually silicate glass, but various plastic substrates and the like can be used as long as visible light transmittance can be secured. The thickness of the substrate is generally 0.1 to 10 mm, and preferably 0.3 to 5 mm. The glass plate is preferably chemically or thermally strengthened.

As the transparent conductive film 2, a conductive metal oxide thin film is used. Preferable examples of the conductive metal oxide include In ₂ O ₃ : Sn (ITO), SnO ₂ : Sb, SnO ₂ : F, ZnO: Al, ZnO: F, and CdSnO ₄ .

  Examples of the metal oxide semiconductor of the semiconductor film 3 on which the spectral sensitizing dye is adsorbed include titanium oxide, zinc oxide, tungsten oxide, antimony oxide, niobium oxide, tungsten oxide, indium oxide, barium titanate, strontium titanate, cadmium sulfide. 1 type, or 2 or more types of well-known semiconductors, such as these, can be used. In particular, titanium oxide is preferable from the viewpoint of stability and safety. Examples of titanium oxide include anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, various titanium oxides such as metatitanic acid, orthotitanic acid, titanium hydroxide, and hydrous titanium oxide. Titanium oxide is preferred. The semiconductor film 3 preferably has a fine crystal structure. A porous film is also preferred. The film thickness of the semiconductor film 3 is generally 1 to 20 μm or more, and preferably 5 to 15 μm.

  The organic dye (spectral sensitizing dye) adsorbed on the semiconductor film 3 has absorption in the visible light region and / or infrared light region, and uses one or more of various metal complexes and organic dyes. be able to. Those having a functional group such as a carboxyl group, a hydroxyalkyl group, a hydroxyl group, a sulfone group, and a carboxyalkyl group in the molecule of the spectral sensitizing dye are preferable because adsorption onto a semiconductor is fast. Moreover, since it is excellent in the effect of spectral sensitization and durability, a metal complex is preferable. As the metal complex, metal phthalocyanines such as copper phthalocyanine and titanyl phthalocyanine, chlorophyll, hemin, and ruthenium, osmium, iron, and zinc complexes described in JP-A-1-220380 and JP-A-5-504023 are used. Can do. As the organic dye, metal-free phthalocyanine, cyanine dye, merocyanine dye, xanthene dye, and triphenylmethane dye can be used. Specific examples of cyanine dyes include NK1194 and NK3422 (both manufactured by Nippon Sensitive Dye Research Co., Ltd.). Specific examples of merocyanine dyes include NK2426 and NK2501 (both manufactured by Nippon Sensitive Dye Research Laboratories). Specific examples of xanthene dyes include uranin, eosin, rose bengal, rhodamine B, and dibromofluorescein. Specific examples of the triphenylmethane dye include malachite green and crystal violet.

  In order to adsorb the organic dye (spectral sensitizing dye) to the semiconductor film, the oxide semiconductor film is immersed with the substrate in an organic dye solution prepared by dissolving the organic dye in an organic solvent at room temperature or under heating. Just do it. The solvent of the solution is not particularly limited as long as it can dissolve the spectral sensitizing dye to be used. Specifically, water, alcohol, toluene, and dimethylformamide can be used.

As the counter electrode 5, as long as it has conductivity, but any conductive material is used, the electrolyte of I ₃ ^- a reduction reaction of oxidation-type redox ions such as ion fast enough It is preferable to use those having catalytic ability. Examples of such a material include a platinum electrode, a surface of a conductive material subjected to platinum plating or platinum deposition, rhodium metal, ruthenium metal, ruthenium oxide, carbon, cobalt, nickel, chromium, and the like.

  The dye-sensitized semiconductor electrode 4 is formed by coating a transparent electrode (transparent conductive film) 2 on the substrate 1, forming a semiconductor film for photoelectric conversion material thereon, and adsorbing the dye as described above. Is done.

  The dye-sensitized solar cell of the present invention has a substrate such as a glass plate coated with another transparent conductive film as the counter electrode 5 facing the dye-sensitized semiconductor electrode 4 described above, and the present invention is interposed between these electrodes. The electrolytic solution may be sealed with the sealing material 6.

  Usually, the electrolyte 7 by the electrolytic solution is formed to a thickness of about 100 nm to 2 mm.

  In the dye-sensitized solar cell of the present invention, the dye-sensitized semiconductor electrode, the electrolyte, and the counter electrode are housed and sealed in a case, but the whole may be resin-sealed. In this case, the dye-sensitized semiconductor electrode has a structure that is exposed to light. In a battery having such a structure, when sunlight or a visible light equivalent to sunlight is applied to the dye-sensitized semiconductor electrode, a potential difference is generated between the dye-sensitized semiconductor electrode and the counter electrode. A current starts to flow through.

  EXAMPLES The present invention will be described more specifically with reference to the following examples and comparative examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

  For convenience of explanation, a comparative example is given first.

Comparative Examples 1-4
MPI, .gamma.-butyrolactone, LiI, an electrolyte solution was prepared by blending _{I 2} and t- butylpyridine in proportions shown in Table 1.

  Using this electrolytic solution, a dye-sensitized solar cell was produced as follows.

  An FTO (fluorine-doped tin oxide) film having a thickness of 9000 mm is formed on a glass substrate (thickness: 2 mm), a titanium oxide film having a thickness of 10 μm is applied thereon and dried, and then at 450 ° C. for 30 minutes. Baked.

As a spectral sensitizing dye, cis-di (thiocyanato) -bis (2,2′-bipyridyl-4-dicarboxylate-4′-tetrabutylammonium carboxylate) ruthenium (II) in ethanol solution is 3 × 10 ^−4. The substrate on which the above titanium oxide film was formed was put in a solution dissolved at a mol / L, and immersed for 18 hours at room temperature to obtain a dye-sensitized semiconductor electrode. The adsorption amount of the spectral sensitizing dye was 10 μg per 1 cm ² of the specific surface area of the titanium oxide film.

  Each dye solution is injected between this dye-sensitized semiconductor electrode and a transparent conductive glass plate carrying platinum as a counter electrode, sealed with resin, and a lead wire is attached. A solar cell was produced.

The obtained dye-sensitized solar cell was irradiated with light having an intensity of 100 mW with a solar simulator (cell area 1 cm ² ) and the battery performance was evaluated. Table 1 also shows the degree of volatility of each electrolytic solution (large volatility, medium volatility, small volatility).

  From Table 1, it can be seen that with the increase in the amount of MPI added, the boiling point of the electrolyte solution becomes higher and it is difficult to volatilize, but the open circuit voltage and conversion efficiency tend to decrease even when t-butylpyridine is used. .

Examples 1-5
An electrolyte solution was prepared in the same manner as in Comparative Example 2 except that the composition shown in Table 2 was used, and a dye-sensitized solar cell was similarly prepared and evaluated. The results are shown in Table 2 together with the results of Comparative Example 2. It was shown to.

  From Table 2, by adding ethylene carbonate, the battery performance can be improved without adding t-butylpyridine. In particular, the addition of 30 to 60% by weight of ethylene carbonate can increase the open-circuit voltage. I understand that I can do it.

  The electrolyte solutions of Examples 1 to 5 did not have a problem of odor caused by t-butylpyridine, and the batteries could be assembled in a good working environment.

It is sectional drawing which shows the structure of a dye-sensitized solar cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Transparent conductive film 3 Dye adsorption semiconductor film 4 Dye sensitized semiconductor electrode 5 Counter electrode 6 Sealing material 7 Electrolyte

Claims (7)

In the dye-sensitized solar cell electrolyte solution containing a redox substance and a solvent, along with containing liquid imidazole compound as an electrolyte which also functions as the solvent, the dye-sensitized alkylene carbonate is added as a property enhancing agent solar cell An electrolyte solution for a dye-sensitized solar cell , further comprising γ-butyrolactone as a solvent .   The electrolyte solution for a dye-sensitized solar cell according to claim 1, wherein the imidazole compound is 1-methyl-3-propylimidazolium iodide (hereinafter referred to as "MPI").   3. The dye-sensitized solar cell electrolyte solution according to claim 1, wherein the alkylene carbonate is ethylene carbonate.   The electrolyte solution for a dye-sensitized solar cell according to any one of claims 1 to 3, wherein the redox substance is lithium iodide and iodine. In any 1 item | term of Claim 1 thru | or 4, 0.1-10 mol of MPI, 10-60 weight% of ethylene carbonate, and 0.1-5 mol of oxidation-reduction substances are included with respect to 1L of (gamma ) -butyrolactone. An electrolyte solution for a dye-sensitized solar cell. 6. The electrolyte solution for a dye-sensitized solar cell according to claim 5 , which is free of t-butylpyridine. A dye-sensitized semiconductor electrode comprising: a dye-sensitized semiconductor electrode; a counter electrode provided opposite to the dye-sensitized semiconductor electrode; and an electrolyte solution disposed between the dye-sensitized semiconductor electrode and the counter electrode. A dye-sensitized solar cell, wherein the electrolyte is the electrolyte for a dye-sensitized solar cell according to any one of claims 1 to 6 .

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