JP5005177B2 - Dye-sensitized solar cell - Google Patents

Description

  The present invention relates to a dye-sensitized solar cell using porous oxide semiconductor fine particles.

  At present, solar cells using single crystal, polycrystalline, or amorphous silicon semiconductors are used for electric products such as calculators, houses, and the like. However, high-precision processes such as plasma CVD and high-temperature crystal growth processes are used in the manufacture of solar cells using such silicon semiconductors, which requires a lot of energy and is expensive and requires a vacuum. Manufacturing costs are high due to the need for equipment.

  Therefore, as a solar cell that can be manufactured at a low cost, for example, a dye-sensitized solar cell using a material in which a photosensitizing dye such as a ruthenium metal complex is adsorbed on an oxide semiconductor such as titanium oxide has been proposed. Yes.

  Specifically, the dye-sensitized solar cell has, for example, a dye composed of a ruthenium complex on the surface of a transparent substrate such as a transparent glass plate or a transparent resin plate provided with a transparent conductive layer such as ITO. There is a type in which an electrolyte solution is sealed between a negative electrode in which adsorbed titanium oxide or the like is formed as a semiconductor layer and a substrate provided with a metal layer or a conductive layer such as platinum as a positive electrode. When the dye-sensitized solar cell is irradiated with light, the electrons of the dye that absorbed the light are excited in the negative electrode, the excited electrons move to the semiconductor layer, and are further guided to the transparent electrode, and from the conductive layer in the positive electrode The electrolyte is reduced by electrons. The reduced electrolyte is oxidized by transferring electrons to the dye, and it is believed that the dye-sensitized solar cell generates electricity during this cycle.

  Currently, dye-sensitized solar cells have lower power generation energy efficiency with respect to irradiation light energy than silicon solar cells, and raising the efficiency is an important issue in producing effective dye-sensitized solar cells. ing. The efficiency of the dye-sensitized solar cell is considered to be influenced by the characteristics of each element constituting the dye-sensitized solar cell and the combination of these elements, and various attempts have been made.

  As a light incident side electrode used for a dye-sensitized solar cell, a transparent conductive material having high transmittance and low sheet resistance has been desired. As an electrode material satisfying this condition, indium oxide (ITO) doped with tin has been often used. However, ITO has a defect that it is inferior in stability in heat treatment in the process of producing a porous film in a dye-sensitized solar cell.

Fluorine-doped tin oxide film (FTO) with a specific resistance as low as 3.5 × 10 ^-4 (Ωcm) has been obtained. Thermal stability when heat-treating a titanium oxide porous layer compared to ITO This material has been widely used as a transparent electrode for dye-sensitized solar cells. However, since the resistance is higher than that of ITO, a thicker film is required to obtain good resistance. For this reason, the transmittance of the glass substrate having the transparent conductive film is reduced, and the amount of light incident on the titanium oxide porous layer having the dye is reduced, resulting in a decrease in light conversion efficiency.

JP 2002-151168 A JP 2005-19205 A JP2003-323818 JP-A-1-259572 Japanese Patent Laid-Open No. 2-181473

Patent Document 1 describes a semiconductor layer in which a dye functioning as a photosensitizer is adsorbed on a semiconductor such as titanium oxide, and this semiconductor layer becomes a photoelectric conversion layer. And the dye-sensitized solar cell comprised in order of the transparent substrate, the transparent conductive film, the photoelectric converting film, the electrolyte solution, the platinum film, and the electroconductive board | substrate is disclosed.

  Patent Document 2 discloses a transparent conductive film used for various types of solar cells, wherein the transparent conductive film provided on the substrate has an electric resistance of 50 Ω / □ or less, and is composed of tin oxide containing antimony laminated thereon. It is a transparent conductive film, and describes a two-layer transparent conductive film having a visible light transmittance of 70% or more. Patent Document 3 describes a transparent electrode substrate in which an ITO film is formed on a transparent substrate and an FTO film having high heat resistance is formed thereon.

  Patent Documents 4 and 5 describe that the photoelectric conversion efficiency is increased by controlling the chlorine concentration or the fluorine concentration in the transparent electrode used in the amorphous solar cell. However, this is not related to dye-sensitized solar cells. In addition to the above problems, the method of forming the ITO film has a problem that it is difficult to obtain indium.

  The present invention provides a dye-sensitized solar cell in which an electrolyte is disposed between a surface-side electrode formed by laminating a substrate, a transparent conductive film, and a sensitizing dye-adsorbing metal oxide in this order, and a counter-surface-side electrode provided to face the surface-side electrode. The purpose is to improve the energy conversion efficiency.

  As a result of investigating the resistance value and transmittance of the FTO film and the characteristics of the dye-sensitized solar cell, the present inventors have found that the transmittance of the FTO film greatly affects the characteristics of the dye-sensitized solar cell. . Conventionally used transparent conductive films dope fluorine into the film in order to reduce the resistance value, but also contain residual chlorine derived from the raw material. The transmittance of the glass substrate with the transparent conductive film changes depending on the amount of these dopants in the film. The transmittance was considered to have a strong influence on the characteristics of the dye-sensitized solar cell. Therefore, the transparent conductive film does not contain fluorine and has a high resistance value but a high transmittance layer. A conventional FTO layer having a good resistance value is formed thereon, and a dye-sensitized solar cell is formed by using a substrate in which the interface resistance between the porous titanium oxide and the tin oxide transparent conductive film maintains the conventional value. As a result of examining the conversion efficiency, it was found that the efficiency of the solar cell formed on the film in which a layer containing no fluorine was present in the transparent conductive film was high, and the present invention was completed.

The present invention relates to a dye-sensitized solar in which an electrolyte is disposed between a surface-side electrode formed by laminating a transparent substrate, a transparent conductive film, and a sensitizing dye-adsorbing metal oxide in this order, and a counter-surface-side electrode provided opposite to the surface-side electrode. In the battery, the transparent conductive film is composed of two or more layers, the thickness of each layer is in the range of 0.05 to 1 μm, and the layer in contact with the sensitizing dye-adsorbing metal oxide is composed of tin oxide containing fluorine. One transparent conductive film is provided, and a layer in contact with the first transparent conductive film is provided with a second transparent conductive film made of a metal oxide film not containing fluorine, and the visible light transmittance of the transparent conductive film is 80%. This is a dye-sensitized solar cell having a sheet resistance of 10Ω / □ or less. Here, the amount of chlorine contained in the first transparent conductive film and the second transparent conductive film is 0.01 to 0.1 wt%, and the amount of fluorine contained in the first transparent conductive film is 0. 01-0.1 wt%.

  The surface side electrode of the dye-sensitized solar cell of the present invention is composed of a transparent substrate, a transparent conductive film, and a sensitizing dye-adsorbing metal oxide. And a transparent conductive film consists of two or more layers, and is called the 1st, 2nd transparent conductive film in an order from the layer which touches a sensitizing dye adsorption metal oxide.

  The first transparent conductive film is made of fluorine-containing tin oxide (FTO), the second transparent conductive film is made of fluorine-free tin oxide (TO), and 1) the first transparent conductive film and the second The amount of chlorine contained in the transparent conductive film is 0.01 to 0.1 wt%, or 2) the amount of fluorine contained in the first transparent conductive film is 0.01 to 0.1 wt% It is preferable. Furthermore, it is preferable that the transparent conductive film is attached on the transparent substrate by a thermal decomposition oxidation reaction.

  Furthermore, in the dye-sensitized solar cell of the present invention, the sensitizing dye-adsorbing metal oxide is preferably a sensitizing dye-adsorbing titanium oxide, and the average particle diameter is preferably 5 to 500 nm.

  According to the present invention, a highly efficient dye-sensitized solar cell can be provided.

Hereinafter, the dye-sensitized solar cell of this invention is demonstrated with reference to FIG.1 and FIG.2 which shows the layer structure.
The basic structure of the dye-sensitized solar cell of the present invention is that a surface electrode 10 in which a transparent conductive film 2 and a dye-adsorbing metal oxide layer 3 are laminated in this order on a substrate 1 and a conductive layer 5 on the substrate 4 are provided. The counter electrode 11 is provided, and the electrolyte 6 is disposed between the two electrodes. A dye adsorbing metal oxide layer 3 is provided on the inner surface side of the surface electrode 10 and is referred to as a semiconductor electrode. The dye-adsorbing metal oxide layer is composed of metal oxide particles such as titanium oxide particles and a sensitizing dye existing so as to fill a gap between the particles or to cover the surface of the particles. Light enters from the surface electrode 10 side.

  The substrate 1 used for the dye-sensitized solar cell is not particularly limited as long as it is a transparent insulating material, and examples thereof include a normal glass plate and a plastic plate, and the base material may be flexible. Well, for example, a PET resin can be mentioned, but it is preferably a heat-resistant material that can withstand the process of baking titanium oxide on a substrate at an upper limit of about 500 ° C., and a transparent glass plate can be mentioned.

  Next, a transparent conductive film 2 is provided on the surface of the substrate 1 so as not to impair the transparency of the base material. The transparent conductive film 2 is composed of at least two layers. FIG. 2 is a diagram for explaining the layer structure of the surface electrode 10 in more detail. The first transparent conductive film 21 in contact with the dye-adsorbing metal oxide layer 3 is FTO, and the first transparent conductive film 21 The second transparent conductive film 22 in contact is TO. If necessary, a third transparent conductive film 23 in contact with the second transparent conductive film 22 can be provided, but this may be ITO, FTO, ATO, TO, or a combination of these, and further impairs transparency. It may be a metal layer with no thickness. A fourth and subsequent transparent conductive films can also be provided. In FIG. 2, the third transparent conductive film 23 is in contact with the substrate 1.

The method for providing these conductive layers is not particularly limited, and known methods such as spin coating, bar coating, and screen printing methods can be used if each material formed by sputtering, PVD, laser ablation, or pasting is used. . However, it is preferable that the thermal decomposition method such as the spray method or the CVD method described above is excellent in terms of the characteristics of the obtained film and is suitable as a film forming method having economic efficiency. As the tin raw material used in these methods, SnCl ₄ , (CnH _{2n + 1} ) ₄ Sn (where n = 1 to 4), C ₄ H ₉ SnCl ₃ , (CH ₃ ) ₂ SnCl _{2 and the} like are used. Good. In addition, as a raw material for doping fluorine for FTO, NH ₄ F in the case of spraying, HF, CCl ₂ F ₂ , CHClF ₂ , CH ₃ CHF ₂ , CF ₃ Br, etc. in the case of CVD Is good. Film formation of FTO and TO having a multi-layer structure using these raw materials is carried out by stopping the introduction of the fluorine dopant raw material under the film forming conditions not containing fluorine, and when introducing fluorine into the film, the fluorine dopant raw material By introducing a transparent conductive film having a two-layer or three-layer structure, an improvement in light transmittance can be achieved.

  The thickness of the first transparent conductive film 21 and the second transparent conductive film 22 is in the range of 0.05 to 1 μm, preferably 0.08 to 0.4 μm, and the total thickness of the transparent conductive film 2 is 0.2 to 1 μm, preferably 0.3. It is in the range of ~ 0.8 μm. The ratio of the thickness of the first transparent conductive film 21 and the second transparent conductive film 22 is preferably in the range of 0.5-5.

  Next, the dye adsorbing metal oxide layer 3, that is, the semiconductor electrode is provided. Usually, after a metal oxide layer is formed, a sensitizing dye is adsorbed thereto. As the metal oxide, a material known as a photoelectric conversion material can be used, and examples thereof include titanium oxide, zinc oxide, tungsten oxide, and the like, and titanium oxide is preferable. Titanium oxide may be titanium hydroxide such as anatase type or rutile type, titanium hydroxide or hydrous titanium oxide. Further, at least one of each element of Nb, V, or Ta may be doped so as to have a weight concentration (as a metal element) of 30 ppm to 5% with respect to titanium oxide.

  Such a metal oxide can be used in the present invention, but fine particles having an average particle diameter of 5 to 500 nm, preferably 10 to 200 nm are preferred. In the case of such a particle size, it is considered that the contact area between the conductive film subjected to the smoothing treatment and the metal oxide particles is increased, thereby reducing the resistance.

  The method of forming the metal oxide film on the transparent electrode 2 is not particularly limited, and for example, each method such as spin coating, printing, spray coating, or the like may be used for the paste of the metal oxide. . It is also possible to sinter for the purpose of sintering a metal oxide such as titanium oxide after film formation.

Next, a dye is adsorbed on the metal oxide to obtain a dye-adsorbed titanium oxide. As described above, in this adsorption, the dye enters the periphery of the metal oxide particles, but also enters the inside of the metal oxide particles if the metal oxide particles are porous. The type of sensitizing dye is not particularly limited, but cis-L ₂ -bis (2,2′-bipyridyl-4,4′-dicarboxylate) ruthenium (II) complex (where L is It is preferably a ruthenium complex such as halogen, CN or SCN.

  The method for adsorbing the dye is not particularly limited, but the so-called impregnation is performed by immersing the conductive film 2 and the metal oxide layer formed on the substrate 1 in a dye solution in which the dye is dissolved in an appropriate solvent. Law.

  A dye-adsorbing metal oxide layer is formed by an impregnation method or the like, and this is heated or dried as necessary to obtain a surface electrode 10 having a conductive film 2 and a dye-adsorbing metal oxide layer 3 on a substrate 1. The surface electrode 10 functions as a negative electrode. An electrode (counter electrode) 11 acting as the other positive electrode is disposed to face the surface electrode 10. The electrode serving as the positive electrode may be a conductive metal or the like, or may be a substrate 5 such as a normal glass plate or plastic plate provided with a conductive film 4 such as a metal film or a carbon film.

  An electrolyte layer 6 is provided between the surface electrode 10 serving as the negative electrode and the counter electrode 11 serving as the positive electrode. The type of the electrolyte layer is not particularly limited as long as it contains a redox species for reducing the dye after photoexcitation and electron injection into the semiconductor, and may be a liquid electrolyte, which is well known. It may be a gel electrolyte obtained by adding a gelling agent (polymer or low molecular weight gelling agent).

For example, examples of the electrolyte used in the solution electrolyte, iodine and iodide (LiI, NaI, KI, CsI, metal iodide such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, such as imidazolium iodide 4 Combination of bromine and bromide (metal bromide such as LiBr, NaBr, KBr, CsBr, CaBr _{2 and the} like, quaternary ammonium compound bromide salt such as tetraalkylammonium bromide, pyridinium bromide, etc.), poly Examples thereof include sulfur compounds such as sodium sulfide, alkyl thiol, and alkyl disulfide, viologen dyes, hydroquinone, and quinone. The electrolyte may be used as a mixture.

  When a solvent is used in the electrolytic solution, it is desirable that the compound has a low viscosity and high ion mobility and can exhibit excellent ionic conductivity. Examples of such solvents include carbonate compounds such as ethylene carbonate and propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, ether compounds such as dioxane and diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl ether , Chain ethers such as polyethylene glycol dialkyl ether and polypropylene glycol dialkyl ether, alcohols such as methanol, ethanol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether and polypropylene glycol monoalkyl ether, ethylene Glycol, propylene glycol, polyethylene glycol, polypropylene glycol Lumpur, polyhydric alcohols such as glycerin, acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile, dimethyl sulfoxide, aprotic polar substances such as sulfolane, water and the like. These solvents can also be used as a mixture.

Further, as the electrolyte, a molten salt electrolyte having a high boiling point is preferable. When the semiconductor electrode is composed of a dye-adsorbed titanium oxide layer, particularly excellent battery characteristics are exhibited by combining with a molten salt electrolyte. The molten salt electrolyte composition includes a molten salt. The molten salt electrolyte composition is preferably liquid at room temperature. The molten salt as the main component is an electrolyte that is liquid at room temperature or has a low melting point, and a general example thereof is “Electrochemistry”, 1997, Vol. 65, No. 11, p. Pyridinium salts, imidazolium salts, and triazolium salts described in No. 923. The molten salt may be used alone or in combination of two or more. Alkali metal salts such as LiI, NaI, KI, LiBF ₄ , CF ₃ COOLi, CF ₃ COONa, LiSCN, and NaSCN can also be used in combination. Usually, the molten salt electrolyte composition contains iodine. The molten salt electrolyte composition preferably has low volatility and preferably does not contain a solvent. The molten salt electrolyte composition may be used after gelation.

  The solar battery of the present invention exhibits excellent battery characteristics when combined with the negative electrode and a molten salt electrolyte comprising methylpropylimidazolium iodide, iodine, tert-butylpyridine, and lithium iodide. Moreover, it is also preferable to add a basic compound such as t-butylpyridine, 2-picoline, or 2,6-lutidine to the aforementioned solution electrolyte or molten salt electrolyte composition.

  The method for providing such an electrolyte layer is not particularly limited, and for example, a film-like spacer 7 may be disposed between both electrodes to form a gap, and an electrolyte may be injected into the gap, A method of stacking the positive electrode at an appropriate interval after applying an electrolyte to the inner surface of the negative electrode may be used. It is desirable to seal both electrodes and their surroundings so that the electrolyte does not flow out, but the sealing method and the material of the sealing material are not particularly limited.

  Hereinafter, the present invention will be described in more detail based on examples and comparative examples.

Examples 1-4 and Comparative Examples 1-2
A borosilicate glass having a size of 30 mm × 30 mm and a thickness of 1 mm was sufficiently washed and dried to obtain a glass substrate. A transparent conductive film was formed on this substrate as follows.
In the case of forming a fluorine-doped layer (FTO layer) in a mixed solution of n-butyltin trichloride, water and ethanol, when ammonium fluoride is added and a layer not containing fluorine (TO layer) is formed. By using a mixed solution without adding ammonium fluoride, the mixing ratio of water and ethanol, nitrogen gas and oxygen gas is changed by a spray method using a mixed gas of nitrogen gas and oxygen, while changing the heating temperature of the glass while changing the heating temperature of the glass. An FTO film was prepared.

The glass with a transparent conductive film thus obtained was thoroughly washed and dried, and then the titanium oxide fine particle paste was applied to an area of 0.5 cm × 1 cm by a squeegee method, and heat-treated at 450 ° C. for 1 hour in an electric furnace to oxidize. A titanium porous membrane was formed. The obtained titanium oxide porous membrane had a thickness of approximately 16 μm.
This porous membrane is immersed in an ethanol solution containing N3 (RuL ₂ (NCS) ₂ , L: 4,4'-dicarboxy-2,2'-bipyridine) dye for about 13 hours to modify the dye on the titanium oxide fine particles. Thus, a surface electrode was obtained.

  On the other hand, ITO or FTO having platinum formed on the substrate by sputtering was used as the counter electrode of the surface electrode and sealed with a 50 μm spacer. Into this cell, an electrolyte containing 0.5M LiI, 0.5M t-butylpyridine in acetonitrile and 0.05M iodine as main components was injected to form a solar cell.

Table 1 shows the structure, film thickness, fluorine concentration, and chlorine concentration of the transparent conductive film obtained in each Example and Comparative Example.
When two or more types are described in the column of the transparent conductive film configuration, the first transparent conductive film, the second transparent conductive film, and the third transparent conductive film are sequentially shown from the bottom.

The characteristics of the solar cell were obtained by irradiating the dye-sensitized solar cell with pseudo solar light of AM 1.5 and 100 mW / cm ² using a solar simulator. Table 2 shows the conversion efficiency of the solar cell (relative to the conventional product comprising a single layer containing fluorine) and various characteristics of the FTO film.

Schematic diagram for explaining the layer structure of a solar cell Schematic diagram for explaining the layer structure of the transparent conductive film

Explanation of symbols

1: substrate, 2: transparent conductive film, 3: dye adsorption metal oxide layer, 4: substrate, 5: conductive film, 6: electrolyte, 7: spacer, 10: surface electrode, 11: counter electrode, 21: first One transparent conductive film, 22: second transparent conductive film, 23: third transparent conductive film

Claims (5)

In a dye-sensitized solar cell in which an electrolyte is disposed between a surface-side electrode that is laminated in the order of a transparent substrate, a transparent conductive film, and a sensitizing dye-adsorbing metal oxide, and a counter-surface-side electrode that is provided to face the electrode. The conductive film is composed of two or more layers, the thickness of each layer is in the range of 0.05 to 1 μm, and the layer in contact with the sensitizing dye adsorbing metal oxide is a first transparent conductive film made of tin oxide containing fluorine. A film is provided, and a layer in contact with the first transparent conductive film is provided with a second transparent conductive film made of tin oxide not containing fluorine, and is contained in the first transparent conductive film and the second transparent conductive film. The chlorine content is 0.01-0.1 wt%, the fluorine content contained in the first transparent conductive film is 0.01-0.1 wt%, and the visible light transmittance of the transparent conductive film is 80%. A dye-sensitized solar cell having a sheet resistance of 10Ω / □ or less . The dye-sensitized solar cell according to claim 1, wherein the transparent conductive film is attached to the transparent substrate by a thermal decomposition oxidation reaction . The first transparent conductive film is attached to the transparent substrate by the thermal decomposition oxidation reaction of n-butyltin trichloride and ammonium fluoride, and the second transparent conductive film is the thermal decomposition of n-butyltin trichloride. The dye-sensitized solar cell according to claim 1 or 2, which is attached on a transparent substrate by an oxidation reaction.   The dye-sensitized solar cell according to claim 1 or 2, wherein the sensitizing dye-adsorbing metal oxide is sensitizing dye-adsorbing titanium oxide and has an average particle diameter of 5 to 500 nm. The dye-sensitized solar cell according to any one of claims 1 to 4, wherein a layer in contact with the second transparent conductive film is further provided with a third transparent conductive film made of tin oxide containing fluorine.

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