JP2008059851A - Dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell capable of suppressing deterioration of a photoelectric transfer performance due to short circuit by preventing leakage current, without requiring a high temperature treatment in a manufacturing process. <P>SOLUTION: The dye-sensitized solar cell is provided with an electrode layer 2, a photoelectric transfer layer 6 consisting of a porous semiconductor layer which is formed on the electrode layer to absorb dyes 5, a counter electrode 8 installed so as to be opposed to the electrode layer, and a charge transporting layer 7 to be arranged between the photoelectric transfer layer and the counter electrode. A short circuit preventative layer 3 consisting of fluorocarbon is installed between the charge transporting layer 7 and the electrode layer 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell, and relates to a dye-sensitized solar cell capable of preventing leakage current.

  As a new energy source to replace fossil fuels, solar cells that use solar light that is sustainable and have no environmental impact have attracted attention, and various studies have been conducted. As solar cells currently in practical use, those using single crystal silicon, polycrystalline silicon, or amorphous silicon as cells are the mainstream. However, these solar cells have problems such as high cost of silicon as a raw material and high energy cost in the manufacturing process.

  On the other hand, as a new type of solar cell, a dye-sensitized solar cell, which is a wet solar cell applying photoinduced electron transfer of an organic dye, has been proposed (Patent Document 1). These dye-sensitized solar cells are composed of an electrode including a porous semiconductor, a counter electrode, and an electrolyte layer sandwiched between these electrodes. On the surface of the porous semiconductor that is a photoelectric conversion material, A photosensitizing dye having an absorption spectrum in the visible light region is adsorbed. When light is irradiated to the porous semiconductor layer of such a solar cell, electrons are generated in the porous semiconductor layer, and the electrons move to the counter electrode through the electric circuit and are transported by ions in the electrolyte layer. Or, it returns to the electrode of the porous semiconductor layer through the P-type semiconductor. By repeating such a process, electric energy is extracted.

  However, in the dye-sensitized solar cell, since the electrolyte layer is in contact with the electrode layer in the portion where the electrode layer and the porous semiconductor layer are not in contact, leakage current is generated inside the solar cell, and the photoelectric conversion performance There are problems such as lowering.

  In Patent Document 2, a dye-sensitized solar cell having an undercoat layer for preventing a short circuit is disclosed. In this dye-sensitized solar cell, an undercoat layer of titanium oxide having a high resistivity formed by, for example, a spray pyrolysis method is provided on the entire surface of the electrode layer. Further, by forming a porous semiconductor layer thereon, contact between the carrier transport layer formed on the porous semiconductor layer and the electrode layer is prevented, and a short circuit inside the solar cell is prevented.

  However, although the undercoat layer described above can suppress a short circuit due to contact between the carrier transport layer and the electrode layer, the carrier generated by light must pass through the undercoat layer in the middle of moving from the porous semiconductor layer to the electrode layer. However, since this increases the internal series resistance, there is a problem that sufficient photoelectric conversion efficiency cannot be obtained. Further, since the substrate is heated to 400 ° C. when forming the undercoat layer, there is a problem that it cannot be applied to a flexible film substrate such as plastic.

  Moreover, in patent document 3, as a means to solve the increase problem of said internal series resistance, for example, the electrode layer and the photoelectric conversion layer are not in contact with each other by utilizing hydrolysis of an alkoxide of a metal oxide. A technique is disclosed in which this part is covered with a metal oxide such as magnesium oxide to function as a short-circuit prevention layer.

  However, in order to form this short-circuit prevention layer, annealing at 150 ° C. for 20 minutes is repeated 10 times or more, and further, for example, annealing at 500 ° C. for 1 hour must be performed, and it takes a very long time to form the short-circuit prevention layer. There is a problem. Moreover, since a high temperature process is performed, there also exists a problem that it cannot apply to flexible film substrates, such as a plastics.

  In Patent Document 4, an N-type conductive polymer, fullerene, endohedral fullerene, or an N-type conductive polymer in which these are dispersed is formed between the electrode layer and the photoelectric conversion layer. Is disclosed.

However, since the short-circuit prevention layer is not an insulator, there is a problem that a short circuit occurs between the carrier transport layer and the short-circuit prevention layer, and the short circuit cannot be completely prevented.
Japanese Patent No. 2664194 JP 2001-156314 A JP 2004-87622 A JP 2005-108807 A

  An object of the present invention is to provide a dye-sensitized solar cell that does not require high-temperature treatment in the production process, prevents leakage current, and suppresses a decrease in photoelectric conversion performance due to a short circuit.

  An electrode layer, a photoelectric conversion layer made of a porous semiconductor layer adsorbed with a dye formed on the electrode layer, a counter electrode provided to face the electrode layer, and disposed between the photoelectric conversion layer and the counter electrode In the dye-sensitized solar cell including the charge transport layer, a short-circuit prevention layer made of fluorocarbon is provided between the charge transport layer and the electrode layer.

  In the present invention, a fluorocarbon layer is formed as a short-circuit prevention layer. The fluorocarbon layer can be formed by, for example, a CVD method. Therefore, according to the present invention, the short-circuit prevention layer can be formed in a short time at a low temperature, the leakage current can be suppressed, and the photoelectric conversion efficiency can be improved.

  In the present invention, the photoelectric conversion layer may be provided so as to be in contact with the electrode layer, and the short-circuit layer may be provided on a region of the electrode layer where the photoelectric conversion layer is not in contact with the electrode layer. Such a structure can be formed by forming a photoelectric conversion layer on the electrode layer and then forming a short-circuit prevention layer by a CVD method or the like.

  Moreover, in this invention, a short circuit prevention layer may be formed on an electrode layer, and a photoelectric converting layer may be formed after short circuit prevention layer formation. In such a structure, a region where a short-circuit prevention layer exists is formed between the photoelectric conversion layer and the electrode layer.

  In the present invention, the thickness of the short-circuit prevention layer is not particularly limited, but generally it is preferably in the range of 1 nm to 20 nm, more preferably in the range of 3 nm to 10 nm. In particular, when a photoelectric conversion layer is formed after forming a short-circuit prevention layer on the electrode layer, a region where the short-circuit prevention layer exists is generated between the electrode layer and the photoelectric conversion layer. The thickness of is preferably thinner, and specifically in the range of 3 nm to 7 nm. If the thickness of the short-circuit prevention layer is too thin, the effects of the present invention that suppress leakage current may not be sufficiently obtained. If the thickness of the short-circuit prevention layer is too thick, the internal resistance increases and the photoelectric conversion efficiency decreases. There is a case.

  In the present invention, the electrode layer, the photoelectric conversion layer composed of a porous semiconductor layer adsorbed with a dye, the counter electrode, and the charge transport layer are, for example, those used in conventionally known dye-sensitized solar cells as they are. can do.

  The electrode layer can be formed, for example, by depositing gold, silver, aluminum, indium, tin oxide, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), or the like on the substrate. it can. Similarly, the counter electrode can be formed by depositing the conductive thin film on a substrate. At least one of the electrode layer and the counter electrode is preferably transparent. In this case, it is preferable to use a transparent substrate as the substrate. As the substrate, a glass substrate, a transparent plastic sheet substrate, a metal substrate, or the like can be used. When a metal substrate is used, this metal substrate can be used as an electrode layer or a counter electrode.

  The photoelectric conversion layer can be formed by adsorbing a dye to the porous semiconductor layer.

  Examples of the material for the porous semiconductor layer include inorganic semiconductors and organic semiconductors. Examples of the inorganic semiconductor include titanium oxide, zinc oxide, tungsten oxide, barium titanate, strontium titanate, cadmium sulfide, etc. Among these, titanium oxide is particularly preferable from the viewpoint of stability and safety. . Titanium oxide means anatase-type titanium oxide, rutile-type titanium oxide, amorphous titanium oxide, various titanium oxides such as metatitanic acid and orthotitanic acid, or titanium hydroxide and hydrous titanium oxide. These inorganic semiconductors can be used alone or in combination of two or more. Examples of organic semiconductors include porphine derivatives, phthalocyanine derivatives, and cyanine derivatives.

  As a method for forming a porous semiconductor layer, a conventionally known method can be used, a method of applying a suspension containing semiconductor particles and heating, a CVD method, a PVD method, a vapor deposition method, You may form by sputtering method etc. Further, it may be formed by a sol-gel method.

  The porous semiconductor layer preferably has a large specific surface area in order to adsorb more dye.

  The dye adsorbed on the surface of the porous semiconductor layer functions as a spectral sensitizer for improving the photoelectric conversion efficiency of the dye-sensitized solar cell. In particular, when an inorganic semiconductor such as a metal oxide is used as the porous semiconductor layer, it is preferable to adsorb a dye in order to increase sensitivity to light.

  The dye is a compound having an absorption spectrum in the visible light region and / or the infrared light region, and in order to firmly adsorb the dye to the porous semiconductor layer, a carboxyl group, an alkoxy group, a hydroxyl group in the dye molecule. Those having an interlock group such as a sulfonic acid group, an ester group, a mercapto group, and a phosphonyl group are preferred. The interlock group provides an electrical bond that facilitates electron transfer between the excited dye and the conductive band of the porous semiconductor.

  Examples of the above dyes include ruthenium bipyridine dyes, azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes. Porphyrin dyes, phthalocyanine dyes, perylene dyes, indigo dyes, naphthalocyanine dyes, and the like.

  Examples of the dye include Cu, Ni, Fe, Co, V, Sn, Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo, Y, Zr, Nb, Sb, Metals such as La, W, Pt, Ta, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au, Ac, Tc, Te, Rh And metal complex dyes.

  Examples of the method for adsorbing the dye on the porous semiconductor layer include a method of immersing the porous semiconductor layer in a solution containing the dye.

  The charge transport layer can be formed from a P-type semiconductor, an electrolytic solution, a solid electrolyte, a gel electrolyte, a molten salt gel electrolyte, an organic hole transport material, or the like.

Examples of the P-type semiconductor include compound semiconductors containing monovalent copper, and semiconductors of metal oxides such as GaP, NiO, CoO, FeO, Bi ₂ O ₃ , MoO ₂ , and Cr ₂ O ₃ . Compound semiconductor containing monovalent copper Among these are preferred, and _{specifically, CuI, CuSCN, CuInSe 2,} Cu (In, Ga) Se 2, CuGaSe 2, Cu 2 O, CuS, CuGaS 2, CuInS 2, CuAlSe ₂ and the like, particularly preferably CuI and CuSCN are, CuI (especially gamma-CuI) is more preferred.

  The electrolytic solution preferably contains an electrolyte, a solvent, and an additive.

As the electrolyte, LiI, NaI, KI, CsI, and an iodide such as iodine salt of CaI metal iodide such as _2, and tetraalkylammonium iodide, pyridinium iodide, imidazolium iodide and quaternary ammonium compounds, I combination of _{2; LiBr, NaBr, KBr,} CsBr, CaBr metal bromide such as _2, and tetraalkyl ammonium bromide, and bromide such as bromine salts of quaternary ammonium compounds such as pyridinium bromide, combination of Br _2; ferrocyanide acid Metal complexes such as salt-ferricyanate and ferrocene-ferricinium ions; sulfur compounds such as sodium polysulfide and alkylthiol-alkyldisulfides; viologen dyes and hydroquinone-quinones. Among these, LiI, pyridinium iodide, and a combination of imidazolium iodide and I ₂ are preferable. Two or more of the above electrolytes may be mixed and used.

  As the solvent used in the electrolyte, a compound that has low viscosity, improves ion mobility, has a high dielectric constant, and exhibits excellent ion conductivity that improves effective carrier concentration is desirable.

  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, polyethylene Chain ethers such as 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, polyp Propylene glycol, polyhydric alcohols such as glycerin; acetonitrile, glutarodinitrile, methoxy acetonitrile, propionitrile, nitrile compounds such as benzonitrile; like water; dimethyl sulfoxide, aprotic polar substances such as sulfolane.

  The electrolyte concentration in the electrolytic solution is preferably about 0.1 to 5 mol / l. Further, the addition concentration when iodine is added to the electrolyte is preferably about 0.01 to 0.5 mol / l.

  Basic compounds such as ter-butylpyridine, 2-picoline, and 2,6-lutidine can also be added to the electrolytic solution. The addition concentration when adding the basic compound is preferably about 0.05 to 2 mol / l.

  As the solid electrolyte, a mixture of an electrolyte and an ion conductive polymer compound can be used. Examples of the ion conductive polymer compound include polar polymer compounds such as polyethers, polyesters, polyamines, and polysulfides.

  As a gel electrolyte, what was produced using electrolyte and a gelatinizer can be used. As the gelling agent, a polymer gelling agent is preferably used. Examples thereof include polymer gelling agents such as crosslinked polyacrylic resin derivatives, crosslinked polyacrylonitrile derivatives, polyalkylene oxide derivatives, silicone resins, and polymers having a nitrogen-containing heterocyclic quaternary compound salt structure in the side chain.

  As the molten salt gel electrolyte, a gel electrolyte material obtained by adding a room temperature molten salt can be used. As room temperature type molten salts, nitrogen-containing heterocyclic quaternary ammonium salt compounds such as pyridinium salts and imidazolium salts are preferably used.

  When a charge transport layer is formed using a solid electrolyte, a gel electrolyte, or a molten salt gel electrolyte, the photoelectric conversion efficiency deteriorates unless the polymer electrolyte is sufficiently injected into the porous semiconductor layer. It is preferable that a certain monomer solution is impregnated in the porous semiconductor layer and then polymerized. Examples of the polymerization method include photopolymerization and thermal polymerization.

  The organic hole transport material has a function of efficiently passing holes injected from the dye. Examples of such hole transport materials include high molecular weight hole transport materials such as polyvinyl carbazole, polyamine, and organic polysilane; for example, low molecular weight holes such as triphenylamine derivatives, stilbene derivatives, hydrazone derivatives, and phenamine derivatives. Examples include transport materials.

  According to the present invention, high-temperature processing is not required in the manufacturing process, leakage current can be prevented, and deterioration in photoelectric conversion performance due to short circuit can be suppressed.

  Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples.

(Example 1)
The dye-sensitized solar cell shown in FIG. 1 was produced. As shown in FIG. 1, an electrode layer 2 is formed on a substrate 1, and a porous semiconductor layer 4 is provided on the electrode layer 2 so as to be in contact therewith. The dye 5 is adsorbed on the surface of the porous semiconductor layer 4, thereby forming a photoelectric conversion layer 6.

  On the region of the electrode layer 2 where the photoelectric conversion layer 6 is not in contact with the electrode layer 2, the short-circuit prevention layer 3 is formed. A counter electrode 8 is provided so as to face the electrode layer 2, and a charge transport layer 7 is provided between the counter electrode 8 and the photoelectric conversion layer 6.

  In this embodiment, the dye-sensitized solar cell shown in FIG. 1 was specifically formed as follows.

  As the substrate 1 on which the electrode layer 2 was formed, a glass substrate (trade name: “A110U80” manufactured by Asahi Glass Co., Ltd.) on which FTO (fluorine-doped tin oxide) was formed was used. The glass substrate was subjected to ultrasonic cleaning with 2-propanol (IPA) for 5 minutes, and then surface-treated with UV ozone for 5 minutes.

  A 150 μm spacer is attached to the surface-treated FTO substrate, and a titanium oxide paste (manufactured by Peccell, trade name: “PECC-K01”) is applied on the FTO substrate by the doctor blade method, and 30 at 120 ° C. in the atmosphere. The porous semiconductor layer 4 was formed by annealing for a minute.

  A fluorocarbon (CFx) film is formed as a short-circuit prevention layer 3 on the portion of the electrode layer 2 where the electrode layer 2 and the porous semiconductor layer 4 are not in contact with each other, and a thickness of 1 nm (deposition time: 15 seconds) using a plasma CVD apparatus. ).

  Thereafter, the whole substrate is immersed in a dye adsorption solution for 12 hours, and a dye 5 comprising a Ru complex dye (N719 dye) (trade name: “PECC-D07”, manufactured by Peccell) on the titanium oxide surface of the porous semiconductor layer 4. Was adsorbed to form a photoelectric conversion layer 6.

  The Ru complex dye has the following structure.

The dye adsorption solution was prepared by dissolving the Ru complex dye in a solvent in which acetonitrile and t-butyl alcohol were mixed at a ratio of 1: 1 to a concentration of 3 × 10 ⁻⁴ mol / l.

  After the dye 5 was adsorbed, a spacer was placed on the FTO substrate produced as described above, and an iodine redox electrolyte as a charge transport material was injected between the spacers.

  Next, a counter electrode 8 made of an FTO substrate having Pt deposited on the surface and having a catalytic function was placed thereon and bonded together to produce the dye-sensitized solar cell shown in FIG.

  The iodine redox electrolyte is an acetonitrile solution containing 0.5 mol / l iodine, 0.1 mol / l lithium iodide, 0.5 mol / l 4-tert-butylpyridine, 1,2-dimethyl-3-propyl. It was prepared by dissolving imidazolium iodide (having the structure shown below) at 0.6 mol / l.

(Example 2)
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that the thickness of the fluorocarbon film as the short-circuit preventing layer was 5 nm (film formation time: 75 seconds).

(Example 3)
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that the thickness of the fluorocarbon film as the short-circuit preventing layer was 17 nm (deposition time: 200 seconds).

(Comparative example)
A dye-sensitized solar cell was produced in the same manner as in Example 1 except that the fluorocarbon film as the short-circuit preventing layer was not formed.

[Evaluation of battery characteristics]
The dye-sensitized solar cells of Examples 1 to 3 and Comparative Example were evaluated by irradiating pseudo-sunlight with an intensity of 100 mW / cm ² using a solar simulator. Table 1 shows open circuit voltage (Voc), short circuit current density (Jsc), fill factor, and photoelectric conversion efficiency.

  As is apparent from the results shown in Table 1, according to the present invention, by providing a short-circuit prevention layer made of fluorocarbon between the charge transport layer and the electrode layer, leakage current can be suppressed and photoelectric conversion efficiency can be increased. it can.

  Further, as is clear from Table 1, the thickness of the short-circuit prevention layer having a thickness of 5 nm provides the highest photoelectric conversion efficiency. When the film thickness is thin, the leakage current suppressing effect is reduced. Since it acts as a resistance component on the quality semiconductor layer, the short circuit current density decreases. Therefore, the thickness of the short-circuit prevention layer is more preferably in the range of 3 to 10 nm.

  FIG. 2 is a graph showing the voltage-current density relationship in Examples 1 and 2 and the comparative example. As can be seen from FIG. 2, in the example according to the present invention, the leakage current was suppressed, and as a result, the short-circuit current density was increased, so that a high photoelectric conversion efficiency was obtained.

Example 4
In this example, the Ru complex dye was adsorbed on the titanium oxide surface of the porous semiconductor layer after forming the porous semiconductor layer and before forming the short-circuit prevention layer. After forming the photoelectric conversion layer in this manner, a fluorocarbon film as a short-circuit prevention layer was formed to a thickness of 5 nm (film formation time: 75 seconds) in the same manner as in Example 1. Other than that was carried out similarly to Example 1, and produced the dye-sensitized solar cell.

  FIG. 3 is a schematic cross-sectional view showing the produced dye-sensitized solar cell. Since the dye 5 is adsorbed to the porous semiconductor layer 4 before the short-circuit prevention layer 3 is formed, the dye 5 is adsorbed to the porous semiconductor layer 4 even in the vicinity of the electrode layer 2.

[Evaluation of battery characteristics]
About the dye-sensitized solar cell of Example 4, the battery characteristic was evaluated similarly to the said Example. The evaluation results are shown in Table 2.

  As apparent from the results shown in Table 2, even when the short-circuit prevention layer is formed after the photoelectric conversion layer is formed, the leakage current can be suppressed and the photoelectric conversion efficiency can be improved.

(Example 5)
In this embodiment, before forming the porous semiconductor layer, a fluorocarbon film as a short-circuit prevention layer is formed by plasma CVD so as to have a thickness of 5 nm (film formation time: 75 seconds), and then the porous semiconductor layer is formed. Layer 4 was formed, and dye 5 was adsorbed thereto to form photoelectric conversion layer 6. Other than that was carried out similarly to Example 1, and produced the dye-sensitized solar cell.

  FIG. 4 is a schematic cross-sectional view showing the produced dye-sensitized solar cell. A short-circuit prevention layer 3 is formed on the electrode layer 2, and a photoelectric conversion layer 5 is formed on the short-circuit prevention layer 3.

[Evaluation of battery characteristics]
About the dye-sensitized solar cell of Example 5, the battery characteristic was evaluated similarly to the said Example. The evaluation results are shown in Table 3.

  As is apparent from the results shown in Table 3, it can be seen that even when a short-circuit prevention layer is provided between the photoelectric conversion layer and the electrode layer, the leakage current can be suppressed and the photoelectric conversion efficiency can be increased.

The typical sectional view showing the dye-sensitized solar cell of one example according to the present invention. The figure which shows the relationship of the voltage-current density in Example 1 and 2 and a comparative example. Typical sectional drawing which shows the dye-sensitized solar cell of the other Example according to this invention. Typical sectional drawing which shows the dye-sensitized solar cell of other Example according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Electrode layer 3 ... Short-circuit prevention layer 4 ... Porous semiconductor layer 5 ... Dye 6 ... Photoelectric conversion layer 7 ... Charge transport layer 8 ... Counter electrode

Claims (5)

An electrode layer, a photoelectric conversion layer formed on the electrode layer and made of a porous semiconductor layer on which a dye is adsorbed, a counter electrode provided to face the electrode layer, the photoelectric conversion layer and the counter electrode In a dye-sensitized solar cell comprising a charge transport layer disposed between,
A dye-sensitized solar cell, wherein a short-circuit prevention layer made of fluorocarbon is provided between the charge transport layer and the electrode layer.   The photoelectric conversion layer is provided so as to be in contact with the electrode layer, and the short-circuit prevention layer is provided on a region of the electrode layer where the photoelectric conversion layer is not in contact with the electrode layer. The dye-sensitized solar cell according to claim 1.   The dye-sensitized solar cell according to claim 1, wherein the short-circuit prevention layer is formed on the electrode layer, and the photoelectric conversion layer is formed on the short-circuit prevention layer.   The dye-sensitized solar cell according to any one of claims 1 to 3, wherein a thickness of the short-circuit preventing layer is in a range of 1 nm to 20 nm.   The dye-sensitized solar cell according to any one of claims 1 to 4, wherein the short-circuit prevention layer is formed by a CVD method.

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