JP2011040223A - Dye-sensitized solar cell, coating liquid for electrolyte layer forming, and solar cell module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell with high stability of an electrolyte layer with alkali metal salt or alkaline earth metal salt as a redox pair, and with excellent durability. <P>SOLUTION: The dye-sensitized solar cell is structured of a conductive base material, a porous semiconductor layer formed on the conductive base material with sensitizing dyes carried on a pore surface, an opposed electrode arranged in opposition to the porous semiconductor layer, and an electrolyte layer formed between the conductive material and the opposed electrode and containing alkali metal salt or alkaline earth metal salt and ionic liquid with anion as B(CN)<SB>4</SB><SP>-</SP>, Al(CN)<SB>4</SB><SP>-</SP>, C(CN)<SB>3</SB><SP>-</SP>, Si(CN)<SB>3</SB><SP>-</SP>, P(CN)<SB>2</SB><SP>-</SP>, OCN<SP>-</SP>, or SCN<SP>-</SP>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell, a coating solution used for forming an electrolyte layer in the solar cell, and a dye-sensitized solar cell module formed by connecting two or more solar cells. .

  In recent years, global warming caused by carbon dioxide has become a global problem. In recent years, active research and development of solar cells using solar energy has been promoted as an environmentally friendly and clean energy source. . Among them, a dye-sensitized solar cell has attracted attention as a solar cell with higher photoelectric conversion efficiency and lower cost.

  The dye-sensitized solar cell has, for example, a transparent substrate, a transparent conductive layer formed on the transparent substrate, an oxide semiconductor layer carrying a dye, a redox couple, and an electrolyte from the light incident side. The electrolyte layer and the substrate on which the counter electrode is formed are sequentially stacked to form a cell. In particular, the Gretcher cell is characterized by using a porous semiconductor layer obtained by firing titanium oxide, which is a nanoparticle, and by making the semiconductor layer porous, the adsorption amount of the sensitizing dye is increased and the light absorption ability is increased. It is improving. Further, as a technique for improving the battery performance of the Gretcher cell, it is known to increase the current value by using an alkali metal salt or alkaline earth metal salt such as lithium iodide as the redox pair of the Gretcher cell. (Patent Document 1, paragraphs 0004 to 0005).

  However, in the conventional dye-sensitized solar cell, since an organic solvent-based electrolyte is used, there is a problem of performance degradation due to evaporation of the liquid. On the other hand, a dye-sensitized solar cell using an ionic liquid that is relatively stable at room temperature as an electrolyte has been proposed.

  For example, Patent Document 2 discloses an electrolyte in which an ionic liquid whose anion is a fluorine-containing imide ion is used as a solvent. However, an ionic liquid in which the anion is a fluorine-containing imide ion has a problem that the battery performance of current value and photoelectric conversion efficiency is insufficient.

  For example, Patent Document 2 and Patent Document 3 disclose ionic liquids whose anion is a non-fluorine-containing material. However, many ionic liquids that are non-fluorine-containing materials have low solubility in alkali metal salts or alkaline earth metal salts. In an electrolyte layer using an ionic liquid with low solubility, a sufficient amount of alkali metal salt or alkaline earth metal salt cannot be added, and even if forcibly added, an alkali metal salt or alkaline earth metal salt is not present. There is a problem that it may be deposited, and the electrolyte layer lacks stability over time.

  Furthermore, in putting the dye-sensitized solar cell into practical use, it is an important issue to further improve the durability of the solar cell so that it can withstand long-term use in various environments. In order to improve the durability of the solar cell, the electrolyte layer needs to be stable over time and heat.

JP 2004-247158 A JP 2006-134615 A JP 2006-302531

  In view of the above situation, the present invention provides a dye-sensitized solar cell having high durability and excellent durability of an electrolyte layer using an alkali metal salt or an alkaline earth metal salt as a redox pair, and dye sensitization. An object is to provide a sensitive solar cell module. Another object is to provide a coating solution for forming such an electrolyte layer.

In the present inventor, the anion is B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ . The present invention has been completed by finding that the ionic liquid is highly soluble in alkali metal salts or alkaline earth metal salts.

Furthermore, the present inventor has found that the use of an ionic liquid having an anion of B (CN) ₄ ⁻ can prevent deterioration of the alkali metal salt or alkaline earth metal salt with the passage of time. Also completed.

That is, the gist of the present invention is as follows.
According to a first aspect of the present invention, there is provided a conductive substrate, a porous semiconductor layer formed on the conductive substrate and having a sensitizing dye supported on the pore surface, and disposed opposite the porous semiconductor layer. The counter electrode is formed between the conductive base material and the counter electrode, and an alkali metal salt or alkaline earth metal salt and anions of B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN ) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ , and an electrolyte layer, and a dye-sensitized solar cell.

The second invention is the first invention, the anion is B (CN) ₄ ^- is a dye-sensitized solar cell is.

  A third invention is a dye-sensitized solar cell according to the first or second invention, wherein the electrolyte layer contains a thermoplastic cellulose resin.

The fourth invention is a coating solution for forming an electrolyte layer of a dye-sensitized solar cell, wherein the alkali metal salt or alkaline earth metal salt and the anion are B (CN) ₄ ⁻ , Al (CN) ₄ ^−. , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ .

  A fifth invention is a dye-sensitized solar cell module formed by connecting two or more of the dye-sensitized solar cells of the first to third inventions in series or in parallel.

  According to the present invention, it is possible to obtain a dye-sensitized solar cell and a solar cell module in which an electrolyte layer containing an alkali metal salt or an alkaline earth metal salt as a redox pair has high stability and excellent durability. it can. Moreover, the coating liquid for forming such an electrolyte can be obtained.

It is sectional drawing which shows one Embodiment of the dye-sensitized solar cell of this invention.

Hereinafter, the present invention will be described in detail.
FIG. 1 is a cross-sectional view showing an embodiment of the dye-sensitized solar cell of the present invention. The dye-sensitized solar cell 1 includes a conductive substrate 10, a porous semiconductor layer 20 formed on the conductive substrate 10 and carrying a sensitizing dye on the pore surface, and a porous semiconductor layer 20. The counter electrode 40 is arranged roughly and is composed of a conductive substrate 10 and an electrolyte layer 30 formed between the counter electrode 40. The electrolyte layer 30 includes at least a redox pair having an alkali metal salt or an alkaline earth metal salt as a component, and anions of B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN ) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ .

(Conductive substrate)
As the conductive substrate 10, general conductive substrates such as various metal foils and metal plates can be used, or can be obtained by forming a conductive layer on a substrate such as glass or plastic. it can. The substrate may be transparent or opaque, but when it is located on the light receiving surface side, it is preferably a transparent substrate having excellent light transmittance. Furthermore, it is preferable that it is excellent in heat resistance, weather resistance, and gas barrier properties against water vapor and the like. Specifically, non-flexible transparent rigid materials such as quartz glass, Pyrex (registered trademark), and synthetic quartz glass, ethylene-tetrafluoroethylene copolymer film, polyethylene terephthalate film (PET), polyether Examples thereof include a sulfone film, a polyether ether ketone film, a polyether imide film, a polyimide film, and a plastic film such as polyethylene naphthalate (PEN).

  Among the above, when using a conductive base material in which a rigid material is used as a substrate and a conductive layer is formed thereon, a sintering process is performed at a few hundred degrees after forming a porous semiconductor layer described later on the conductive base material. It is preferable to carry out. The sintering process improves the retention function of the redox couple of the porous semiconductor layer, thereby preventing a decrease in photoelectric conversion efficiency due to the deterioration of the redox couple over time and increasing the durability of the solar cell.

  When using a conductive base material made of a flexible film with a conductive layer formed on a plastic film as a substrate, solar cells can be used for various applications. Cost reduction can be achieved. When a plastic film is used as a substrate, after the porous semiconductor layer is formed, the porous semiconductor layer is subjected to a press treatment of the porous semiconductor layer and / or a sintering treatment at a temperature that can withstand the plastic film. It is possible to improve the retention function of the redox pair. The plastic film may be used alone as a substrate, or may be used in a state where two or more different plastic films are laminated.

  The thickness of the conductive substrate or the substrate of the conductive substrate is preferably in the range of 10 μm to 500 μm.

The material of the conductive layer formed on the substrate is not particularly limited as long as it is excellent in conductivity, but the conductive layer located on the light receiving surface side is excellent in light transmission. Preferably there is. For example, as a material having excellent light permeability, can be cited SnO _2, ITO, FTO, ZnO, IZO, or the like. Among these, FTO and ITO are particularly preferably used because they are excellent in both conductivity and transparency.

Further, the material for the conductive layer formed on the substrate is preferably selected in consideration of each work function. For example, examples of materials having a high work function include Au, Ag, Co, Ni, Pt, C, ITO, FTO, SnO ₂ , and ZnO. On the other hand, examples of the material having a low work function include Li, In, Al, Ca, Mg, Sm, Tb, Yb, and Zr.

  Each conductive layer may be composed of a single layer, or may be composed of laminated materials having different work functions.

  The thickness of the conductive layer is in the range of 0.1 nm to 500 nm, preferably in the range of 1 nm to 300 nm.

  A method for forming such a conductive layer is not particularly limited, and examples thereof include a vapor deposition method, a sputtering method, and a CVD method. Among these, the sputtering method is preferably used.

(Porous semiconductor layer)
Next, the porous semiconductor layer 20 will be described. The porous semiconductor layer has metal oxide fine particles, on which a sensitizing dye is supported, and has a function of conducting charges generated from the sensitizing dye by light irradiation.

  The metal oxide fine particles are preferably porous having communication holes because the sensitizing dye is supported on the surface of the pores. By setting it as such a porous, the surface area of a porous semiconductor layer becomes large, and sufficient quantity of a sensitizing dye can be carry | supported. Moreover, a contact area with the electrolyte layer mentioned later becomes large, and energy conversion efficiency can be improved.

  The film thickness of the porous semiconductor layer is preferably in the range of 1 μm to 100 μm, and more preferably in the range of 5 μm to 30 μm. This is because the film resistance of the porous semiconductor layer can be reduced within the above range, and light absorption by the porous semiconductor layer is sufficiently performed.

The metal oxide fine particles forming the porous semiconductor layer are not particularly limited as long as the charge generated from the sensitizing dye can be conducted to the conductive substrate 10. _{Specifically, TiO 2, ZnO, SnO 2} , ITO, ZrO 2, SiO 2, MgO, Al 2 O 3, CeO 2, Bi 2 O 3, Mn 3 O 4, Y 2 O 3, WO 3, Ta ₂ O ₅ , Nb ₂ O ₅ , La ₂ O _{3 and the} like can be mentioned. Any one kind of these metal oxide fine particles may be used, or two or more kinds may be mixed and used. Among these, TiO ₂ can be preferably used. Further, a core-shell structure in which one of these is used as a core particle and the core particle is coated with another metal oxide fine particle to form a shell may be used.

  A resin can be added to the porous semiconductor layer as a binder for the metal oxide fine particles. As such a resin, it is preferable to use a cellulose-based resin described later.

  The content of the metal oxide fine particles in the porous semiconductor layer is preferably in the range of 40% by weight to 99.9% by weight, and more preferably in the range of 85% by weight to 99.5% by weight.

  The particle diameter of the metal oxide fine particles is preferably in the range of 1 nm to 10 μm, particularly in the range of 10 nm to 500 nm. When the particle diameter is smaller than the above range, it is difficult to produce such particles, and it is not preferable because each particle may aggregate to form secondary particles. On the other hand, when the particle diameter is larger than the above range, the porous semiconductor layer becomes thicker and the resistance becomes higher, which is not preferable.

  You may mix and use the metal oxide fine particle from which a particle size differs. Thereby, the light scattering effect can be enhanced and more light can be confined in the porous semiconductor layer, so that light absorption by the sensitizing dye can be efficiently performed. For example, a case where metal oxide fine particles of 10 nm to 50 nm and metal oxide fine particles of 50 nm to 200 nm are mixed and used can be exemplified.

  The sensitizing dye supported on the metal oxide fine particles is not particularly limited as long as it can absorb light and generate an electromotive force. Specifically, an organic dye or a metal complex dye can be used. Examples of organic dyes include acridine, azo, indigo, quinone, coumarin, merocyanine, phenylxanthene, indoline, and squalium dyes. In particular, a coumarin system is preferably used.

  As the metal complex dye, a ruthenium dye, particularly a ruthenium bipyridine dye and a ruthenium terpyridine dye are preferably used. By carrying such a sensitizing dye on the pore surface of the metal oxide fine particles, it is possible to efficiently take in the visible light range and cause photoelectric conversion.

  The method for forming the porous semiconductor layer is not particularly limited, but it is preferably formed by a coating method. That is, using a known disperser such as a homogenizer, a ball mill, a sand mill, a roll mill, or a planetary mixer, a coating liquid in which metal oxide fine particles are dispersed in a solvent is prepared. It is applied to the top (the conductive layer side of the conductive substrate when a conductive layer is formed), dried, and further baked as necessary. Then, the porous semiconductor layer carrying the sensitizing dye can be formed by adsorbing the sensitizing dye on the surface of the metal oxide fine particles.

  The solvent used in the metal oxide fine particle coating solution is not particularly limited. Specifically, chlorine solvents such as chloroform, methylene chloride, dichloroethane, ether solvents such as tetrahydrofuran, aromatic hydrocarbon solvents such as toluene and xylene, ketone solvents such as acetone and methyl ethyl ketone, ethyl acetate, butyl acetate And ester solvents such as ethyl cellosolve acetate, alcohol solvents such as isopropyl alcohol, ethanol, methanol and butyl alcohol, N-methyl-2-pyrrolidone, and pure water.

  In addition, various additives may be used as necessary in order to improve the coating suitability of the coating liquid used for forming the porous semiconductor layer. As the additive, a surfactant, a viscosity adjuster, a dispersion aid, a pH adjuster and the like can be used. Examples of the pH adjuster include nitric acid, hydrochloric acid, acetic acid, ammonia and the like.

  The method for applying the coating liquid containing metal oxide fine particles is not particularly limited as long as it is a known coating method, specifically, die coating, gravure coating, gravure reverse coating, roll coating, reverse roll coating, Examples thereof include bar coating, blade coating, knife coating, air knife coating, slot die coating, slide die coating, dip coating, micro bar coating, micro bar reverse coating, and screen printing. Using such a coating method, the porous semiconductor layer is formed so as to have a desired film thickness by repeating coating and drying once or a plurality of times.

  After coating and drying, baking is performed as necessary. Thereby, the porous semiconductor layer can be homogenized and densified, and the binding property between the metal oxide fine particles can be increased, so that the charge conductivity can be improved. In addition, the adhesion between the conductive substrate and the porous semiconductor layer can be improved. The firing temperature and time vary depending on the film thickness of the porous semiconductor layer and are not limited, but are generally about 300 to 700 ° C. and about 5 to 120 minutes. Moreover, when a conductive base material is comprised from a plastic film, it is preferable to perform drying and baking below the heat-resistant temperature of a film.

As a method for supporting the sensitizing dye, for example, the dried and baked metal oxide fine particles are immersed in a sensitizing dye solution and then dried, or the sensitizing dye solution is applied onto the metal oxide fine particles. And a method of drying after permeation. The solvent used in the sensitizing dye solution is appropriately selected from an aqueous solvent and an organic solvent according to the type of the dye sensitizer used.
(Counter electrode)
As the counter electrode 40, it is possible to use various metal foils, metal plates, or the like, or those in which a conductive layer is formed on the surface of a substrate such as glass or plastic. The substrate may be transparent or opaque, but when it is located on the light receiving surface side, it is preferably a transparent substrate having excellent light transmittance. Furthermore, it is preferable that it is excellent in heat resistance, weather resistance, and gas barrier properties against water vapor and the like. Specifically, non-flexible transparent rigid materials such as quartz glass, Pyrex (registered trademark), and synthetic quartz glass, ethylene-tetrafluoroethylene copolymer film, polyethylene terephthalate film (PET), polyether Examples thereof include a sulfone film, a polyether ether ketone film, a polyether imide film, a polyimide film, and a plastic film such as polyethylene naphthalate (PEN).

  When a counter electrode made of a flexible film having a conductive layer formed on a plastic film as a substrate is used, solar cells can be used for various applications. Reduction can be achieved. The plastic film may be used alone as a substrate, or may be used in a state where two or more different plastic films are laminated.

  The thickness of the counter electrode or the substrate of the counter electrode is preferably in the range of 10 μm to 500 μm.

The material of the conductive layer formed on the substrate is not particularly limited as long as it is excellent in conductivity, but the conductive layer located on the light receiving surface side is excellent in light transmission. Preferably there is. For example, as a material having excellent light permeability, can be cited SnO _2, ITO, FTO, ZnO, IZO, or the like. Among these, FTO and ITO are particularly preferably used because they are excellent in both conductivity and transparency.

Further, the material for the conductive layer formed on the substrate is preferably selected in consideration of each work function. For example, examples of the material having a high work function include Au, Ag, Co, Ni, Pt, C, SnO ₂ , ITO, FTO, and ZnO. On the other hand, examples of the material having a low work function include Li, In, Al, Ca, Mg, Sm, Tb, Yb, and Zr.

  Each conductive layer may be composed of a single layer, or may be composed of laminated materials having different work functions.

  The thickness of the conductive layer is in the range of 0.1 nm to 500 nm, preferably in the range of 1 nm to 300 nm.

  A method for forming such a conductive layer is not particularly limited, and examples thereof include a vapor deposition method, a sputtering method, and a CVD method. Among these, the sputtering method is preferably used.

  By further forming a catalyst layer on the conductive layer of the counter electrode, the power generation efficiency of the dye-sensitized solar cell can be further improved. Examples of the catalyst layer include a layer deposited with Pt and a catalyst layer made of an organic material such as polyaniline, polythiophene, polypyrrole, but are not limited thereto.

(Electrolyte layer)
Next, the electrolyte layer 30 will be described. The electrolyte layer 30 is formed between the conductive substrate 10 on which the porous semiconductor layer 20 is formed and the counter electrode 40, and an oxidation-reduction pair having an alkali metal salt or alkaline earth metal salt as a component and an anion of B ( CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ .

An alkali metal salt or alkaline earth metal salt used as a redox pair has an effect of lowering the conduction band of a metal oxide semiconductor such as titanium oxide, so that the current is increased, and as a result, battery performance can be improved. . Examples of the alkali metal salt include lithium salt, sodium salt, and potassium salt, and examples of the alkaline earth metal salt include calcium salt and magnesium salt. The alkali metal salt or alkaline earth metal salt is preferably iodide or bromide. Specific examples include lithium iodide, sodium iodide, potassium iodide, calcium iodide, lithium bromide, sodium bromide, potassium bromide, and calcium bromide. Of these, lithium iodide and potassium iodide have anions of B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , It is preferable because it is highly soluble in an ionic liquid that is OCN ⁻ or SCN ⁻ . These alkali metal salts or alkaline earth metal salts may be used in combination of two or more.

  As the oxidation-reduction pair, it is preferable to use iodine or bromine in combination on the condition that an alkali metal salt or an alkaline earth metal salt is contained.

  The concentration of the redox couple in the electrolyte layer 30 varies depending on the type of the redox couple and is not particularly limited, but the alkali metal salt or alkaline earth metal salt is iodide or bromide, and iodine or bromine When the redox couple of is used together, it is preferable that iodide or bromide is 0.1 mol / l to 5 mol / l, and iodine or bromine is 0.01 mol / l to 0.5 mol / l. Is set so that the molar ratio of the alkali metal salt or alkaline earth metal salt to iodine or bromine is about 10: 1.

  The ionic liquid lowers the viscosity of the electrolyte, improves the conductivity of ions, and improves the photoelectric conversion efficiency. Ionic liquids have a very low vapor pressure, and hardly evaporate at room temperature. There is no fear of volatilization or ignition like ordinary organic solvents, so it is possible to prevent deterioration of cell characteristics due to volatilization. .

As an ionic liquid, an anion (anion) is (1) B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , or P (CN) _2. ^- a is a cyanide ion boron atom, an aluminum atom, a carbon atom, a silicon atom, or a coordinating phosphorus atom and is formed by ion, (2) OCN ^- it can be cyanate ion, or (3) SCN ^- in An ionic liquid which is a certain thiocyanate ion is used. These anions have a covalent bond between a carbon atom and a nitrogen atom, and have a common or approximate coordination force. Cyanide ion, cyanate ion or thiocyanate ion is well coordinated to alkali metal ion or alkaline earth metal ion, so that the anion is B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) _{3 ^{-, Si (CN) 3 -}} , P (CN) 2 -, OCN -, or SCN ^- ionic liquid is, the higher the solubility of the redox pair whose components an alkali metal salt or alkaline earth metal salts In addition, the redox couple having an alkali metal salt or alkaline earth metal salt as a component can be favorably retained, and the electrolyte layer can be stabilized. Any one of these ionic liquids may be used alone, or a plurality of these ionic liquids may be used in combination.

In particular, it is more preferable to use an ionic liquid whose anion is B (CN) ₄ ⁻ (tetracyanoborate ion) (hereinafter sometimes referred to as “TCB-based ionic liquid”). By using TCB-based ionic liquid as an electrolyte, the battery performance is good, and there is little decrease in photoelectric conversion efficiency due to deterioration with time of alkali metal salt or alkaline earth metal salt, and dye sensitization with excellent durability. Type solar cell can be obtained.

  As the cation (cation) of the ionic liquid, 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-butyl-3- Methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-octadecyl-3-methylimidazolium, 1-methyl-2,3-dimethylimidazolium, 1-butyl- Imidazolium systems such as 2,3-dimethylimidazolium, 1-hexyl-2,3-dimethylimidazolium, 1-octyl-2,3-dimethylimidazolium, and 1-octadecyl-2,3-dimethylimidazolium; Pyridines such as 1-methyl-pyridium, 1-butyl-pyridium, and 1-hexyl-pyridium Um-based, alicyclic amine-based, and may include those aliphatic amine.

As the ionic liquid, the anion is B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ . On the condition that an ionic liquid is used, another ionic liquid may be used in combination, and it is preferable to use an iodide ionic liquid having iodine as an anion. Specifically, for example, 1,2-dimethyl-3-n-propylimidazolium iodide, 1-methyl-3-n-propylimidazolium iodide, 1-propyl-3-methylimidazolium iodide, 1 -Butyl-2,3-dimethylimidazolium iodide, 1-hexyl-3-methylimidazolium iodide, etc. can be mentioned. These iodide-based ionic liquids are a source of iodine ions and can also function as the above-described redox couple.

The concentration of the ionic liquid in the electrolyte layer 30 varies depending on the kind of the ionic liquid and the like, but it is preferable to contain 5 wt% to 95 wt%, particularly 10 wt% to 85 wt% in the electrolyte layer 30. Of all the ionic liquids contained in the electrolyte layer, the anions are B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN). _The ionic liquid which is ₂ ⁻ , OCN ⁻ or SCN ⁻ preferably occupies at least 10% by weight or more.
Note that an ionic liquid that also functions as a redox pair, such as an iodide ionic liquid, is contained as a redox pair instead of an ionic liquid in determining the concentration of the ionic liquid in the electrolyte layer 30 described above. The concentration described above for the redox couple is preferable, that is, 0.1 to 5 mol / l is preferably contained in the electrolyte layer 30. In that case, the total concentration of the iodide or bromide of the alkali metal salt or alkaline earth metal salt and the iodide ionic liquid may be 0.1 to 5 mol / l, but the alkali metal salt or alkaline earth metal may be used. It is preferable that the iodide or bromide of the salt occupies at least 0.2 mol / l or more.

  Furthermore, it is preferable that the electrolyte layer 30 contains a thermoplastic cellulose resin. Here, the cellulose-based resin refers to cellulose or a derivative thereof, and holds a redox couple and an ionic liquid to form a solid electrolyte layer. By solidifying the electrolyte, it is possible to prevent liquid leakage due to deterioration or damage of the sealing material.

In general, when solidifying an electrolyte using a polymer compound, it is difficult to directly dissolve the polymer compound in the ionic liquid. Therefore, the polymer compound, the ionic liquid, and the redox couple should be combined with an appropriate solvent. After preparing the coating solution dissolved in (2), the coating solution is applied onto the semiconductor layer by a coating method described later, and the solvent is evaporated to form a solid electrolyte layer. The cellulosic resin includes an oxidation-reduction pair comprising an alkali metal salt or an alkaline earth metal salt as a component, B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN). ^{_{) 3 -, P (CN)}} 2 -, OCN -, or SCN ^- a is liable solvent dissolved ionic liquid (methanol, ethanol, isopropanol, lower alcohols butanol, water, the solubility in NMP, etc.) Since it is high, the productivity of the coating liquid is excellent as a whole, and when the electrolyte layer is formed by application of the coating liquid, it is excellent in film formability and can form a thin film (for example, 4 μm). Suitable for electrolyte solidification. In addition, the electrolyte layer solidified with the cellulose resin includes a redox couple and B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN). Good retention of ionic liquids that are ₂ ⁻ , OCN ⁻ , or SCN ⁻ .

  Furthermore, since the cellulosic resin has high heat resistance, the electrolyte layer solidified with the cellulosic resin does not leak even at high temperatures and has high thermal stability. For example, in the manufacturing process of a solar cell, it may be necessary to heat seal the cell at about 150 ° C., and the temperature in the space may rise to about 80 ° C. in a sealed space under the hot sun. It is important to improve the thermal stability of the layer. In particular, by solidifying an electrolyte layer using a TCB-based ionic liquid with a cellulose-based resin, the stability of the electrolyte layer over time and heat can be increased, and the dye-sensitized solar with better durability A battery can be obtained.

  As such a cellulose resin, a thermoplastic resin (non-thermosetting resin) that does not use a reactive substance is used. This is because if a reactive substance is used, unreacted residues and by-products are generated in the electrolyte, adversely affecting the redox couple and the like, and impairing the durability of the solar cell. Specifically, cellulose acetate (CA) such as cellulose, cellulose acetate, cellulose diacetate, and cellulose triacetate, cellulose acetate butyrate (CAB), cellulose acetate propionate (CAP), cellulose acetate phthalate, cellulose such as cellulose nitrate, etc. Examples thereof include cellulose ethers such as esters, methylcellulose, ethylcellulose, benzylcellulose, cyanoethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and carboxymethylcellulose. Any of these cellulose resins may be used alone, or two or more thereof may be used in combination.

Among cellulose resins, a cationic cellulose derivative is particularly preferably used from the viewpoint of compatibility with the electrolyte solution. The cationic cellulose derivative means a product obtained by cationization by reacting a cellulose or an OH group of the derivative with a cationizing agent. By containing the cationic cellulose derivative, it is possible to obtain a solid electrolyte excellent in the retention of the electrolytic solution, and in particular, having no leakage of the electrolytic solution at a high temperature or under pressure, and excellent in thermal stability. In addition, since there is no leakage of electrolyte, a sealing material for sealing the electrolyte layer in the cell, which was an essential material in the past, is no longer necessary, reducing the manufacturing cost of the solar cell and simplifying the manufacturing process. Can be achieved. These effects are due to the fact that the electrolyte in the dye-sensitized solar cell is mainly composed of a solvent (organic solvent or ionic liquid), iodine salt (I ⁻ , I ₃ ⁻ ), etc., and is anionic. It is considered that the use of a cationized cellulose derivative improves the compatibility with the electrolytic solution and the adsorptivity of the electrolytic solution.

  Examples of cellulose to be cationized or derivatives thereof include cellulose and alkylcelluloses such as methylcellulose and ethylcellulose; hydroxyalkylcelluloses such as hydroxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose; and hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and hydroxyethylethylcellulose. And hydroxyalkylalkylcellulose in which the OH group of cellulose is substituted with an alkoxy group or a hydroxyalkoxy group. Among these, hydroxyalkyl cellulose such as hydroxyethyl cellulose is preferably used.

As the cationizing agent, a substance having a cation moiety such as a group that reacts with the OH group of cellulose or a derivative thereof and a quaternary ammonium group is used. The group that reacts with the OH group is not particularly limited as long as it is a reactive group that forms a covalent bond with the OH group, and examples thereof include an epoxy group, a halohydrin group, a halogen group, a vinyl group, and a methylol group. In particular, an epoxy group and a halohydrin group are preferable from the viewpoint of reactivity. Further, the quaternary ammonium group has a structure of —N ⁺ R ₃ (wherein R is an alkyl group, aryl group or heterocyclic group which may have a substituent). Preferable examples of such a cationizing agent include glycidyltrialkylammonium halides such as glycidyltrimethylammonium chloride and 3-chloro-2-hydroxypropyltrimethylammonium chloride and halohydrin type thereof.

For example, as an example of a preferable cationic cellulose or a derivative thereof, ether obtained by reacting hydroxyethyl cellulose with 3-chloro-2-hydroxypropyltrimethylammonium chloride which is a cationizing agent can be mentioned. In this cationic cellulose derivative, some hydrogen atoms of the three OH groups of cellulose are substituted with hydroxyethyl groups (—CH ₂ CH ₂ OH), and the rate of substitution (substitution degree m) is as follows: 1 to 3 (that is, 1 to 3 OH groups are substituted in the repeating unit of cellulose), preferably about 1.3.

In addition, in the case of the cationic cellulose derivative described above, the ratio of cationization by a cationizing agent, that is, cationized with a quaternary ammonium salt among all —CH ₂ CH ₂ OH groups of hydroxyethyl cellulose— The proportion of CH ₂ CH ₂ OH groups varies depending on the molecular weight of the cellulose and is not particularly limited, but is preferably 20% to 50%, more preferably 30% to 40%. In addition, the numerical range about these substitution degrees m and the ratio to cationize is similarly applied also to cationic cellulose derivatives other than the above cationized hydroxyethyl cellulose.

  The cationic cellulose or derivative thereof can be produced according to a conventional method. Specifically, it is carried out by allowing cellulose or a derivative thereof to act on a cationizing agent and an alkali metal hydroxide as a catalyst. As a reaction solvent, 8 to 15 times by weight of water or lower alcohol such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol or water alone or water with respect to cellulose or a derivative thereof. And a mixed solvent can be applied. Examples of the alkali metal hydroxide include sodium hydroxide and potassium hydroxide. The amount of the cationizing agent and the catalyst varies depending on the solvent composition of the reaction system, the mechanical conditions of the reactor, and other factors, but the above-described ratio of cationization in the molecule of cellulose or its derivative is a desired value. It adjusts suitably so that it may become.

  Cellulose derivatives such as alkyl cellulose and hydroxyalkyl cellulose can be obtained, for example, by a method in which cellulose is alkali-treated and then a halogenated alkane such as methyl chloride or an alkylene oxide is added.

  After reacting with a cationizing agent, the remaining alkali metal hydroxide salt is neutralized with a mineral acid or an organic acid, washed with an organic solvent such as isopropyl alcohol or acetone, purified, and dried as appropriate. Alternatively, a derivative thereof can be obtained. When the dried product is an aggregated lump, it can be pulverized with a hammer mill or the like to improve the handling properties during use.

  The molecular weight of the cellulose resin as described above varies depending on the type of the cellulose resin and is not particularly limited. However, from the viewpoint of obtaining good film forming properties when forming the electrolyte layer, the weight average molecular weight is 10,000 or more ( Polystyrene conversion), particularly preferably in the range of 100,000 to 200,000. For example, when ethyl cellulose is used as the cellulosic resin, the value obtained by dissolving ethyl cellulose at 2% by weight in water and measuring the viscosity at 30 ° C. is 10 mPa · s to 1000 mPa · s, particularly 5 mPa · s to The molecular weight is preferably such that the viscosity is 500 mPa · s.

  In addition, the glass transition temperature of the cellulose resin is preferably 80 ° C. to 150 ° C. in order to obtain sufficient thermal stability of the electrolyte layer.

  If the concentration of the cellulose resin in the electrolyte layer 30 is too low, the thermal stability of the electrolyte layer is lowered. Conversely, if the concentration is too high, the photoelectric conversion efficiency of the solar cell is lowered. . Specifically, it is preferable to contain 5 wt% to 60 wt% in the electrolyte layer 30.

  In addition, the electrolyte layer 30 can contain various additives for the purpose of improving durability, improving open-circuit voltage value, and the like. Specific examples of the additive include guanidinium thiocyanate, tertiary butyl pyridine, N-methylbenzimidazole and the like. The concentration of these additives in the electrolyte layer 30 is preferably 1 mol / l or less in total of various additives.

  As a method for forming the electrolyte layer 30, the coating liquid used for forming the electrolyte layer is arranged such that the porous semiconductor layer 20 and the counter electrode 40 have a predetermined gap, and the coating liquid is injected into the gap. Examples thereof include a method of forming an electrolyte layer (hereinafter referred to as an injection method), a method of applying the electrolyte layer on the porous semiconductor layer 20 and drying it (hereinafter referred to as a coating method), and the like.

  When the electrolyte layer 30 is formed by an injection method, first, the counter electrode 40 on which a conductive layer is formed is prepared, and the porous semiconductor layer 20 and the counter electrode 40 are arranged to face each other with a predetermined gap. The gap at this time is preferably set so that the distance between the conductive substrate 10 and the counter electrode 40 is 2 μm to 150 μm. In order to arrange the counter electrode 40 with a predetermined gap, a spacer can be provided on either the conductive substrate 10 side or the counter electrode 40 side. Examples of such a spacer include known glass spacers and resin spacers.

  Next, a coating liquid used for forming the electrolyte layer is injected into the gap using a capillary phenomenon or the like, and cured by performing temperature adjustment, ultraviolet irradiation, electron beam irradiation, or the like to form the electrolyte layer 30. be able to. Thereby, a dye-sensitized solar cell can be obtained.

When the electrolyte layer 30 is formed by a coating method, first, the redox couple and the anions are B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P A coating solution containing at least an ionic liquid that is (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ is prepared.

  Next, as a means for applying the coating liquid on the porous semiconductor layer 20 in the application method, a known means can be used. Specifically, a die coat, a gravure coat, a gravure reverse coat, a roll coat, Examples thereof include reverse roll coating, bar coating, blade coating, knife coating, air knife coating, slot die coating, slide die coating, dip coating, micro bar coating, micro bar reverse coating, and screen printing.

In addition, in order to contain a cellulose resin, other additives, etc., or to adjust the applicability of the coating liquid, a solvent can be used in the coating liquid as necessary. Solvents include redox couples and anions of B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ^- ionic liquid and a volatile organic solvent of amide solvent such as an alcohol solvent such as ethanol indicating the target solubility, ketone solvents such as methyl ethyl ketone, N- methylpyrrolidone (NMP) is, pure water Is preferably used. Specifically, lower alcohols such as methanol, ethanol, isopropanol and butanol, and solvents such as water and NMP are preferably used from the viewpoints of the stability of the coating solution and the film forming property of the electrolyte. When a solvent is used, the electrolyte layer can be formed by coating and then drying appropriately to remove the solvent.

The dye-sensitized solar cell of the present invention can be obtained by bonding the conductive layer side of the counter electrode 40 to the electrolyte layer 30 thus formed.
(Solar cell module)
A dye-sensitized solar cell module can be obtained by connecting two or more dye-sensitized solar cells 1 obtained as described above in series or in parallel. Specifically, for example, a plurality of dye-sensitized solar cells are arranged in a planar shape or a curved shape, and non-conductive partition walls are provided between the cells to partition each cell. These members can be used for electrical connection, and a positive or negative electrode lead can be drawn from the end portion to form a module. The number of dye-sensitized solar cells constituting the module is arbitrary, and can be freely designed so as to obtain a desired voltage.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, it is not limited to this.

(Preparation of electrolyte layer forming coating solution)
Example 1
0.13 g of lithium iodide was added to 6.67 g of 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB), and dissolved by stirring. Subsequently, 1.74 g of 1-propyl-3-methylimidazolium iodide (PMIm-I) and 0.24 g of iodine (I ₂ ) were added to the solution and dissolved by stirring. Thereby, the coating liquid for electrolyte layer formation was adjusted. At this time, the concentration of EMIm-TCB in the coating solution (electrolyte layer) is about 26% by weight.

(Example 2)
Cationic hydroxyethyl cellulose cationized using 3-chloro-2-hydroxypropyltrimethylammonium chloride (manufactured by Daicel Chemical Industries, Ltd .; Gelner QH200; substitution degree m = 1.3, cationization ratio is —CH ₂ CH ₂ OH group) Of lithium iodide was added to a solution prepared by dissolving 2.9 g) in 57 g of methanol and dissolved by stirring. Subsequently, 3.6 g of 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB), 5.0 g of 1-propyl-3-methylimidazolium iodide (PMIm-I), and iodine ( 0.5 g of I ₂ ) was added and dissolved by stirring. Thereby, the coating liquid for electrolyte layer formation which can be apply | coated was prepared. At this time, the concentration of EMIm-TCB in the electrolyte layer after drying the coating liquid after coating and removing methanol is about 28% by weight, and the concentration of cationic cellulose is about 22% by weight.

(Comparative Example 1)
A coating solution for forming an electrolyte layer was prepared in the same manner as in Example 1 except that lithium iodide was not used in Example 1.

(Comparative Example 2)
In Example 1, 1-ethyl-3-methylimidazolium trifluorosulfonylimide (EMIm-TFSI) was used in place of 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB). In the same manner as in Example 1, an electrolyte layer forming coating solution was prepared.

(Comparative Example 3)
In Comparative Example 2, an electrolyte layer forming coating solution was prepared in the same manner as Comparative Example 2 except that lithium iodide was not used.

(Comparative Example 4)
In Example 2, except that 1-ethyl-3-methylimidazolium trifluorosulfonylimide (EMIm-TFSI) was used instead of 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB). In the same manner as in Example 1, an electrolyte layer forming coating solution was prepared.

(Formation of conductive substrate and porous semiconductor layer)
A titanium oxide ink in which titanium oxide (manufactured by Nippon Aerosil Co., Ltd .; P25) was dispersed in ethanol was prepared. Subsequently, a transparent conductive glass (manufactured by Nippon Sheet Glass Co., Ltd.) having a fluorine-doped tin oxide (FTO) film formed on a glass plate as a conductive substrate is prepared, and the titanium oxide ink is screen-printed on the conductive glass. It was applied by the method and baked at 550 ° C. to form a porous titanium oxide layer having a thickness of 10 μm. Next, the above-mentioned titanium oxide layer was added to a dye solution in which a ruthenium complex (manufactured by Solaronix; RuI ₂ (NCS) ₂ ) was dissolved in absolute ethanol so as to have a concentration of 3.0 × 10 ⁻⁴ mol / l. It was immersed for 20 hours. After the immersion, the pigment solution was pulled up and the pigment solution adhering to the titanium oxide layer was washed with acetonitrile and air-dried. Thereby, the porous semiconductor layer was formed on the conductive substrate.
(Preparation of counter electrode)
A counter electrode was produced by laminating platinum with a thickness of 150 mm on transparent conductive glass (manufactured by Nippon Sheet Glass Co., Ltd.) on which a fluorine-doped tin oxide (FTO) film was formed on a glass plate.
(Preparation of dye-sensitized solar cell)
A. Example 1, Comparative Examples 1-3
The porous semiconductor layer (4 mm × 4 mm) on the conductive substrate and the platinum film of the counter electrode were faced to each other and bonded using an ionomer resin having a thickness of 30 μm. And what was bonded together is immersed in each coating solution for forming an electrolyte layer in Example 1 and Comparative Examples 1 and 2, so that the ionomer resin is impregnated with the coating solution for forming an electrolyte layer to form an electrolyte layer. It was. This produced the desired dye-sensitized solar cell.
B. Example 2 and Comparative Example 3
On the porous semiconductor layer (4 mm × 4 mm) on the conductive substrate, each electrolyte forming coating solution in Example 2 and Comparative Example 3 was applied with a doctor blade, dried at 100 ° C., and an electrolyte having a thickness of 4 μm. A layer was formed. Next, the conductive base material on which the electrolyte layer and the porous semiconductor layer were formed and the counter electrode were bonded together and pressed with a clip. This produced the desired dye-sensitized solar cell.

(Evaluation method of power generation performance)
Evaluation of the power generation performance of the solar cell is performed by using pseudo-sunlight (AM1.5, incident light intensity of 100 mW / cm ² ) as a light source and entering from the side of the conductive substrate having a porous semiconductor layer on which a sensitizing dye is adsorbed. A voltage was applied using a source measure unit (type 2400, manufactured by Keithley) to measure the current-voltage characteristics of the solar cell, and the photoelectric conversion efficiency was obtained. The area of the porous semiconductor layer used for the measurement is 0.16 cm ² (4 mm × 4 mm).

(Durability evaluation method)
The durability of the solar cell was evaluated by an accelerated deterioration test and a thermal stability test. In the accelerated deterioration test, photoelectric conversion is performed in the same manner as the above-described evaluation method of power generation performance for solar cells after storage for 500 hours and 1000 hours in an oven set at a temperature of 60 ° C. and without humidity control. We asked for efficiency. On the other hand, in the thermal stability test, the solar cell was stored for 15 minutes in an oven set at a temperature of 120 ° C. or 150 ° C. and humidity not controlled, and then visually checked for the presence of liquid leakage. Photoelectric conversion efficiency was determined by the same method as the method for evaluating power generation performance.

(Evaluation results)
Tables 1 and 2 show the evaluation results of the dye-sensitized solar cells prepared in the above examples and comparative examples.

  In Table 1, by comparing Example 1 and Comparative Example 1, a dye-sensitized solar cell having high short-circuit current density and high photoelectric conversion efficiency and good battery characteristics by including lithium iodide in the electrolyte layer. It turns out that was obtained.

  In Comparative Example 2, when the electrolyte layer contained lithium iodide and EMIm-TFSI was used, the photoelectric conversion efficiency significantly decreased (0.74 times) after the accelerated deterioration test. On the other hand, in Comparative Example 3, when lithium iodide was not included in the electrolyte layer, a significant decrease in photoelectric conversion efficiency was similarly observed (0.86 times). There were few. This indicates that in Comparative Example 2, deterioration with time of lithium iodide occurred in the accelerated deterioration test. On the other hand, in Example 1, by using EMIm-TCB for the electrolyte layer, even if lithium iodide was included in the electrolyte layer, the decrease in photoelectric conversion efficiency after the accelerated deterioration test could be reduced. (0.95 times). Therefore, it can be seen that by using EMIm-TCB for the electrolyte layer, a dye-sensitized solar cell excellent in durability can be obtained, in which deterioration of lithium iodide over time can be prevented, photoelectric conversion efficiency can be relatively maintained. .

  In Comparative Example 1, when EMIm-TCB was used in the electrolyte layer, when lithium iodide was not included in the electrolyte layer, the photoelectric conversion efficiency did not decrease even when an accelerated deterioration test was performed (1 .02 times). On the other hand, when EMIm-TFSI was used in Comparative Example 3, the photoelectric conversion efficiency decreased after the accelerated deterioration test A (0.86 times) even if lithium iodide was not included in the electrolyte layer. This indicates that when EMIm-TFSI is used, the performance is deteriorated due to factors other than the deterioration with time of lithium iodide. By comparing Comparative Example 1 and Comparative Example 3, it can be seen that the use of EMIm-TCB for the electrolyte layer can prevent a decrease in photoelectric conversion efficiency due to factors other than the deterioration of lithium iodide over time.

  In Table 2, by comparing Example 1 and Example 2, by solidifying the electrolyte layer using cationic hydroxyethyl cellulose, liquid leakage does not occur after the thermal stability test, and excellent thermal stability It can be seen that an electrolyte layer was formed. Further, by comparing Example 2 and Comparative Example 4, even in the electrolyte layer having excellent thermal stability, by using EMIm-TCB, the decrease in photoelectric conversion efficiency due to deterioration with time of lithium iodide and the like is reduced. It can be seen that a dye-sensitized solar cell superior in durability was obtained.

1 Dye-sensitized solar cell 10 Conductive substrate 20 Porous semiconductor layer 30 Electrolyte layer 40 Counter electrode

Claims (5)

A conductive substrate;
A porous semiconductor layer formed on the conductive substrate and having a sensitizing dye supported on the pore surface;
A counter electrode disposed to face the porous semiconductor layer;
Formed between the conductive substrate and the counter electrode, an alkali metal salt or alkaline earth metal salt and anions B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si An electrolyte layer comprising an ionic liquid that is (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ⁻ ;
A dye-sensitized solar cell comprising: Anion B (CN) ₄ ^- dye-sensitized solar cell according to claim 1, characterized in that a.   The dye-sensitized solar cell according to claim 1 or 2, wherein the electrolyte layer contains a thermoplastic cellulose resin. A coating solution for forming an electrolyte layer of a dye-sensitized solar cell,
Alkali metal salt or alkaline earth metal salt and anions of B (CN) ₄ ⁻ , Al (CN) ₄ ⁻ , C (CN) ₃ ⁻ , Si (CN) ₃ ⁻ , P (CN) ₂ ⁻ , OCN ⁻ , or SCN ^- coating liquid comprising an ionic liquid is. A dye-sensitized solar cell module comprising two or more dye-sensitized solar cells according to any one of claims 1 to 3 connected in series or in parallel.

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