JPWO2009113342A1 - Dye-sensitized solar cell - Google Patents

Abstract

The dye-sensitized solar cell, which has excellent photoelectric conversion efficiency, particularly excellent photoelectric conversion efficiency even in a large area, and excellent durability, has a transparent conductive layer and a dye adsorbed on the surface of a transparent substrate. A dye-sensitized solar cell having a metal oxide semiconductor layer composed of a semiconductor film, a charge transfer layer, and a counter electrode in order, wherein the transparent conductive layer contains metal nanowires as a conductive material And

Description

  The present invention relates to a dye-sensitized solar cell. In particular, the present invention relates to a dye-sensitized solar cell having excellent photoelectric conversion efficiency and further improved durability.

  In recent years, a dye-sensitized solar cell has attracted attention as a solar cell using an organic material instead of a silicon-based solar cell, and research and development have been actively conducted.

  In a conventional dye-sensitized solar cell, a metal oxide thin film such as indium-doped tin oxide (ITO) or fluorine-doped tin oxide (FTO) is formed as a transparent conductive film on a substrate by vapor deposition or sputtering. ing.

  However, this transparent conductive film is expensive in material cost and manufacturing cost, and further, the metal oxide constituting the transparent conductive film has a drawback that the resistivity is remarkably higher than that of metal or the like, and the photoelectric conversion efficiency in the solar cell is high. It contributed to the decline. Although the resistivity can be lowered by increasing the thickness of the transparent conductive film, the light transmittance is lowered by this, which further increases the material cost and the manufacturing cost. As a result, a sufficiently satisfactory photoelectric conversion efficiency has not been obtained without increasing the thickness of the transparent conductive film.

A transparent conductive film containing conductive nanowires is disclosed, and it is described that it can also be applied to solar cells (for example, see Patent Documents 1 and 2). However, in Patent Document 1, only carbon nanotubes are specifically described as conductive nanowires, and organic solar cells are mainly intended as solar cells. Further, Patent Document 2 clearly discloses silver nanowires and describes that they can be applied to thin film solar cells. However, both of them refer to specific aspects particularly focusing on dye-sensitized solar cells. Not done.
US Patent Application Publication No. 2007-153353 US Patent Application Publication No. 2007-74316

  The present invention is for solving the conventional problems as described above, and the purpose thereof is to achieve excellent photoelectric conversion efficiency, and in particular, dye sensitizing type that exhibits excellent photoelectric conversion efficiency even in the case of a large area. It is to provide a solar cell. Furthermore, it is providing the dye-sensitized solar cell which is excellent also in durability.

  The problem of the present invention has been solved by providing a transparent conductive layer containing metal nanowires and improving the conductivity of the electrode. Specifically, it is as follows.

  1. A dye-sensitized solar cell having, on a transparent substrate, a transparent conductive layer, a metal oxide semiconductor layer having a dye adsorbed on its surface, a charge transfer layer, and a counter electrode in order, The dye-sensitized solar cell, wherein the conductive layer contains metal nanowires as a conductive material.

  2. 2. The dye-sensitized solar cell according to 1 above, wherein the metal nanowire is a silver nanowire or a metal nanowire containing silver.

  3. 3. The dye-sensitized solar cell as described in 1 or 2 above, wherein the metal nanowire has an average minor axis diameter of 30 nm to 200 nm and an average major axis diameter of 1 μm to 20 μm.

  4). 4. The dye-sensitized type according to any one of 1 to 3, further comprising a metal oxide intermediate layer composed of a metal oxide between the transparent conductive layer and the metal oxide semiconductor layer. Solar cell.

  5. 5. The dye-sensitized solar cell as described in 4 above, wherein the porosity of the metal oxide intermediate layer is 10% or less.

  6). 6. The dye-sensitized solar cell according to any one of 1 to 5, wherein the transparent conductive layer further contains a conductive polymer.

  According to the present invention, it is possible to provide a dye-sensitized solar cell that realizes excellent photoelectric conversion efficiency, expresses excellent photoelectric conversion efficiency even in the case of a large area, and has excellent durability.

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

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transparent conductive layer 20 Metal oxide semiconductor layer 30 Charge transfer layer 40 Conductive layer (counter electrode)
50 base material 50a transparent base material 60 metal oxide intermediate layer

  Hereinafter, the present invention will be described in detail.

<< Dye-sensitized solar cell >>
First, the dye-sensitized solar cell of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing the basic structure of the dye-sensitized solar cell of the present invention. As shown in FIG. 1, the dye-sensitized solar cell of the present invention has a transparent conductive layer 10 on a transparent substrate 50a as a conductive substrate, a metal oxide intermediate layer 60 thereon, and a dye on the surface. The metal oxide semiconductor layer 20 adsorbs the metal, the charge transfer layer (sometimes referred to as “electrolyte layer”) 30, and the conductive layer 40 on the surface of the substrate 50 as a counter electrode. is there. In the present invention, the part from the transparent substrate to the metal oxide semiconductor layer may be referred to as a semiconductor electrode.

  When producing the dye-sensitized solar cell of the present invention, it is preferable that the above-described configuration is housed in a case and sealed, or the whole is resin-sealed.

  When the dye-sensitized solar cell of the present invention is irradiated with sunlight or an electromagnetic wave equivalent to sunlight, the dye adsorbed on the metal oxide semiconductor layer 20 is excited by absorbing the irradiated sunlight or electromagnetic wave. Electrons generated by excitation move from the metal oxide semiconductor layer 20 to the transparent conductive layer 10 through the metal oxide intermediate layer 60, and then move to the conductive layer 40 of the counter electrode via an external circuit, The redox electrolyte of the charge transfer layer 30 is reduced.

  On the other hand, the dye that has moved the electrons is an oxidant, but when the electrons are supplied from the counter electrode via the redox electrolyte of the charge transfer layer 30, it is reduced and returned to the original state, and at the same time The redox electrolyte of the moving layer 30 is oxidized and returns to a state where it can be reduced again by electrons supplied from the counter electrode. In this way, electrons flow and the dye-sensitized solar cell of the present invention can be configured.

<Transparent conductive layer>
The dye-sensitized solar cell of the present invention has a transparent conductive layer containing metal nanowires as a conductive material on a transparent substrate.

As the metal nanowire, various known metal elements can be used, but it is preferable to use a metal element having a bulk conductivity of 1 × 10 ⁶ S / m or more.

  There is no restriction | limiting in particular as a metal composition of the metal nanowire which concerns on this invention, Although it can be comprised from the 1 type or several metal of a noble metal element and a base metal element, it is gold, platinum, silver, palladium, rhodium, iridium, ruthenium. It is preferable to contain a metal selected from osmium, iron, cobalt, copper, and tin, and more preferably at least silver from the viewpoint of conductivity. Furthermore, in order to achieve both conductivity and stability (sulfurization and oxidation resistance of metal nanowires and resistance to magnation), it is preferable to include at least one metal belonging to noble metal other than silver and silver.

  In the present invention, the minor axis diameter and major axis diameter of the metal nanowire are not particularly limited, but the minor axis diameter is preferably 30 nm or more and 200 nm or less mainly from the viewpoint of both conductivity and transparency. The diameter is preferably 1 μm or more and 20 μm or less. Further, the distribution of the short axis diameter is preferably 20% or less, and the distribution of the long axis diameter is preferably 40% or less.

  The average value of the short axis diameter and the long axis diameter of the metal nanowires, and further, the distribution thereof is taken at least 100 or more, or a sufficient number of metal nanowires of 300 or more. Can be obtained from the arithmetic average of The major axis diameter of metal nanowires should be measured in a linearly stretched state, but in reality it may be bent, so the projected diameter of metal nanowires can be measured using an image analyzer from an electron micrograph. The projected area may be calculated and calculated assuming a cylindrical body (length = projected area / projected diameter). The distribution of the major axis diameter and minor axis diameter is represented by a value obtained by multiplying 100 by the value obtained by dividing the standard deviation of the measured particle diameter by the average particle diameter.

Particle size distribution [%] = standard deviation of particle size / average particle size × 100
When the metal nanowire according to the present invention includes two or more kinds of metal elements, for example, the metal composition may be different between the inside and the surface of the metal nanowire, or the entire metal nanowire has the same metal composition. However, an embodiment in which a thin layer is formed of at least one metal belonging to a noble metal excluding silver on the surface of the silver nanowire is most preferable.

  As a method for producing metal nanowires according to the present invention, metal ions are reduced to form metal nanoparticles, and metal nanowires are formed by Ostwald ripening between metal nanoparticles, or metal ions are first formed in a nucleation step. There is a method of forming metal nanowires by reducing particles to form nuclei nanoparticles and then reducing and depositing metal ions on the nuclei particles to grow nuclei particles in the particle growth step. Among these, from the viewpoint of improving the controllability of the form (diameter and length) of the metal nanowire and the metal composition, it is preferable to perform the nucleation step and the particle growth step separately.

  In the present application, the “nucleation step” means that at least one metal salt solution is added to a solution containing a reducing agent in a reaction vessel to reduce metal ions, which becomes a growth nucleus in the particle growth step. It means a step of forming metal fine particles (core particles). On the other hand, the “particle growth process” is a process in which at least one metal salt solution is added to a solution containing a reducing agent, a core particle, and a shape control agent in a reaction vessel to reduce metal ions. It means a step of growing the formed metal core particles into metal particles having a wire-like form.

  In order to improve the uniformity of the form (diameter and length) of the metal nanowires to be formed, it is important to control the reduction reaction of metal ions so that new metal fine particles are not generated in the particle growth process. Therefore, it is necessary to adjust the addition rate of the metal salt solution and the reduction rate of the metal ions in the particle growth process.

  Further, for example, as a method for producing metal nanowires containing silver and at least one metal other than silver, 1) In a solution containing a reducing agent and a protective colloid agent, at least one kind other than silver ions and silver is used. A method of producing metal nanowires containing at least one kind of metal other than silver and silver by a step of coexisting with metal ions, or 2) silver ions in a solution containing a reducing agent and a protective colloid agent. By mixing silver nanowires produced by reduction and at least one metal nanoparticle produced by reducing at least one metal ion other than silver in a solution containing a reducing agent and a protective colloid agent, A method of manufacturing a thin layer containing at least one metal other than silver on the surface of the silver nanowire can be applied.

  In the present invention, in order to control the addition rate of the metal salt solution, it is effective to use a single jet method or a multi jet method. In order to control the reduction reaction rate, it is effective to set the kind and concentration of the reducing agent, the reaction temperature, pH, and the like to preferable conditions.

  In the single jet method and the multi jet method according to the present invention, the amount of liquid fed is controlled as necessary using an appropriate liquid feeding device or the like, and one or a plurality of additive liquids are respectively added to the liquid in the reaction vessel. It is a method of reacting in the liquid in the container by dropping or spraying or injecting on the liquid surface or in the liquid, and in the present invention, a solution containing one or more metal salt solutions and a form control agent, It can be carried out by using a solution containing an anti-aggregation agent, a solution containing a reducing agent, or the like as the additive solution.

  In the present invention, the molar ratio of the metal salt (metal ion) used in the nucleation step and the particle growth step can be arbitrarily changed. In addition, the particle size and aspect ratio can be controlled by adjusting the molar ratio. For example, when forming metal nanowires having a high average aspect ratio, it is advantageous to reduce the molar ratio of the metal salt used in the nucleation step to the metal salt used in the entire particle production process. This is because the particle growth process greatly contributes to the formation of metal nanowires. Therefore, in this invention, it is preferable to set the molar ratio of the metal salt used at a nucleation process to 10 mol% or less, 5 mol% or less is more preferable, and it is still more preferable that it is 0.001-1 mol%.

  In the present invention, the type of metal salt used in the nucleation step and the particle growth step is not particularly limited, and metal halide, metal acetate, metal perhalogenate, metal sulfate, metal nitrate, metal carbonate Various metal salts such as salts and oxalic acid metal salts can be used. Usually, these metal salts can be dissolved in a solvent such as water and used as a metal salt solution. The concentration of the metal ions in the solution can be appropriately set to a preferred concentration, but reducing the concentration is preferable for uniforming the reduction reaction of the metal ions in the reaction solution and the formation reaction of the metal nanowires, On the other hand, increasing the concentration is preferable because the yield of metal nanowires can be increased. Therefore, the volume molar concentration of the metal salt solution added in the present invention is preferably 0.001 to 1M.

  In the present invention, when forming the metal nanowire by separating the nucleation step and the particle growth step, the type of metal salt used in the nucleation step and the type of metal salt used in the particle growth step are the same. It may be different or different.

  The “form control agent” used in the particle formation step according to the present invention is a compound having a function of defining the growth direction of metal particles in a one-dimensional manner, and is formed in the particle formation step by using the form control agent. The ratio of metal nanowires to be produced can be increased. In many cases, the shape control agent preferentially or selectively adsorbs on a specific crystal plane of a target particle to control the growth orientation by suppressing the growth of the adsorption plane.

  Examples of the shape control agent used in the particle forming step according to the present invention include hydrophilic polymers and amphiphilic molecules.

  Examples of the hydrophilic polymer include an amide group, a hydroxyl group, a carboxyl group, and / or an amino group such as polyvinyl pyrrolidone (for example, poly (N-vinyl-2-pyrrolidone)), polyvinyl alcohol, and poly (meth) acrylate. And natural products such as cyclodextrin, aminopectin, methylcellulose, gelatin and the like.

  Examples of amphiphilic molecules include various monofunctional or polyfunctional surfactants (any of anionic, cationic, nonionic, and amphoteric), such as sodium dodecyl sulfate, polyethylene glycol monolaurate, and the like. it can.

  The amount of the form control agent used is preferably 0.1 mol or more, more preferably 1 to 50 mol, relative to 1 mol of the metal. When the form control agent is a polymer, the molar amount means a value converted to the number of moles of the monomer unit.

  In the present invention, the aggregation preventing agent used in the particle forming step according to the present invention in the particle forming step is not particularly limited as long as it is a compound having a protective colloid function with respect to the target metal nanowire. And a conductive polymer, a metal coordinating molecule, an amphiphilic molecule, and an anionic compound.

  Examples of the hydrophilic polymer include an amide group, a hydroxyl group, a carboxyl group, and / or an amino group such as polyvinyl pyrrolidone (for example, poly (N-vinyl-2-pyrrolidone)), polyvinyl alcohol, and poly (meth) acrylate. In addition to polymers containing styrene or copolymers of monomers for forming these hydrophilic homopolymers, natural products such as cyclodextrin, aminopectin, methylcellulose, and gelatin can be used.

  Examples of metal coordinating molecules include organic molecules having one or more functional groups capable of coordinating to metals such as amino groups, thiol groups, disulfide groups, amide groups, carboxylic acid groups, phosphine groups, and sulfonic acid groups. And carbon monoxide and nitric oxide.

  Examples of amphiphilic molecules include various monofunctional or polyfunctional surfactants (any of anionic, cationic, nonionic, and amphoteric), such as sodium dodecyl sulfate, polyethylene glycol monolaurate, and the like. it can.

  Examples of the anionic compound include halides such as chlorides, perchlorates, various alkoxides, and salts of carboxylic acids such as oxalic acid, tartaric acid, citric acid, and the like. Examples thereof include metal salts, ammonium salts, and amine salts.

  In the particle forming step according to the present invention, among the above compounds, it is preferable to use a water-soluble polymer containing an amide group, a hydroxyl group, a carboxyl group and / or an amino group.

  Polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene glycol, and the like listed as exemplary compounds of the form control agent also function as an anti-aggregation agent for forming metal nanowires, and therefore can be preferably used in the present invention as an anti-coagulation agent. .

  In the present invention, the reducing agent for reducing metal ions is not particularly limited as long as it is a compound that can reduce the target metal, and at least one selected from general chemical reducing agents can be used. Examples of the reducing agent that can be preferably used in the present invention include primary or secondary alcohols, glycols, ethers in which a hydrogen atom is bonded to a carbon atom adjacent to an oxygen atom, ethanolamines, borohydride. And at least one selected from the group consisting of hydrazines.

  Furthermore, in this invention, it is preferable to have the process (form control agent removal process) which removes the form control agent used at the particle formation process using an ultrafiltration membrane etc. after a particle formation process.

  Moreover, in this invention, it is preferable to have a dispersion | distribution process for the purpose of preventing aggregation of metal nanowire.

  In the production method according to the present invention, as a method for suppressing the aggregation of the metal nanowires in the metal nanowire dispersion liquid and highly dispersing, a polymer-based dispersant or an active agent having a polar part and a nonpolar part can be used. A method of adsorbing on the surface and suppressing the formation of aggregates by the steric hindrance effect is effective.

  In the present invention, the structure of the dispersant is not particularly limited, and can be appropriately selected from phosphoric acid, sulfonic acid, carboxylic acid, nonionic, cationic, etc. It is preferable to use at least one dispersant having one or more functional groups capable of coordinating to a metal such as an amide group, a carboxylic acid group, a phosphine group, or a sulfonic acid group. The molecular weight of the dispersant is preferably 50,000 or less, more preferably 100 to 20,000, and most preferably 500 to 10,000. If the molecular weight is too large, the dispersant is not preferable because it forms bridging aggregates between the metal nanowires or inhibits the conductivity between the metal nanowires. If the molecular weight is too small, the molecular chain is short and sufficient steric hindrance effect cannot be obtained.

  When the metal nanowire according to the present invention is dispersed in a non-aqueous solvent, a functional group capable of coordinating to a metal such as an amino group, a thiol group, a disulfide group, an amide group, a carboxylic acid group, a phosphine group, or a sulfonic acid group. It is preferable to use a dispersant having a compound having at least one group and having an affinity for a non-aqueous solvent.

  The dispersion operation in the production method according to the present invention can be carried out by using either an ultrasonic disperser or a high-speed stirring disperser, or a combination thereof.

  In the present invention, metal nanowires produced in an aqueous system can be subjected to a hydrophobization treatment as necessary. As a method for hydrophobizing metal nanowires, for example, JP-A-2007-500606 can be referred to.

  The transparent conductive layer according to the present invention may contain a binder as necessary. In that case, the mass ratio of the metal nanowires to the binder is preferably 7: 1 to 2: 1, and 5: 1 to 5: 1. 3: 1 is more preferred. When the ratio of the metal nanowires is high, the conductivity is sufficient but the adhesion is poor, and when the ratio of the metal nanowires is low, it is difficult to obtain sufficient conductivity.

  In the present invention, the type of binder is not particularly limited. For example, acrylic resin, alkyd resin, polyester resin, polyurethane resin, epoxy resin, phenol resin, melamine resin, vinyl chloride resin, silicone resin, rosin resin, etc. Contains water-soluble acrylic resins, water-soluble alkyd resins, water-soluble melamine resins, water-soluble urethane emulsion resins, water-soluble epoxy resins, water-soluble polyester resins, and other monomers with ethylenically unsaturated double bonds used for water-based inks And acrylic urethane resins, polyester acrylate resins, epoxy acrylate resins, polyol acrylate resins, and the like. In particular, the binder is preferably an acrylic resin, a polyurethane resin, or a phenol resin.

  As the solvent, toluene, xylene, butyl acetate, glycol ether solvent, ester solvent, alcohol solvent, water, glycol solvent, ketone solvent and the like can be used.

  Further, a dispersant may be contained, and the dispersant is not particularly limited. For example, anionic surfactants such as dialkylsulfosuccinates, alkylnaphthalenesulfonates, fatty acid salts, and the like, polyoxyethylene alkyl ethers , Nonionic surfactants such as polyoxyethylene alkyl allyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts Is mentioned.

  In addition, a polymeric surfactant can also be used, for example, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer, styrene. -Maleic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-methacrylic acid copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene- A maleic acid copolymer etc. can be mentioned.

  The transparent conductive layer according to the present invention preferably contains a conductive polymer. In that case, one kind of conductive polymer may be contained alone, or two or more kinds of conductive polymers may be contained in combination.

  The conductive polymer used in the present invention is preferably an organic polymer whose main chain is composed of a π-conjugated system. For example, polypyrroles, polythiophenes, polyacetylenes, polyphenylenes, polyphenylene vinylenes, polyanilines, polyacenes. , Polythiophene vinylenes, and copolymers thereof. Among these, a polymer selected from polypyrrole, polythiophene, poly (N-methylpyrrole), poly (3-methylthiophene), poly (3-methoxythiophene), poly (3,4-ethylenedioxythiophene), or A copolymer is preferably used. Polypyrrole, polythiophene, and poly (3,4-ethylenedioxythiophene) (PEDOT) are particularly preferable.

The conductive polymer used in the transparent conductive layer according to the present invention can be subjected to a doping treatment in order to further increase the conductivity. As a dopant for the conductive polymer, for example, a sulfonic acid having a hydrocarbon group having 6 to 30 carbon atoms (hereinafter also referred to as long-chain sulfonic acid) or a polymer thereof (for example, polystyrene sulfonic acid), a halogen atom, Lewis acid, proton acid, transition metal halide, transition metal compound, alkali metal, alkaline earth metal, MClO ₄ (M = Li ⁺ , Na ⁺ ), R ₄ N ⁺ (R = CH ₃ , C ₄ H ₉ , C ₆ H ₅ ), or at least one selected from the group consisting of R ₄ P ⁺ (R═CH ₃ , C ₄ H ₉ , C ₆ H ₅ ). Of these, the long-chain sulfonic acids are preferred.

Examples of the long chain sulfonic acid include dinonyl naphthalene disulfonic acid, dinonyl naphthalene sulfonic acid, and dodecylbenzene sulfonic acid. Examples of the halogen include Cl ₂ , Br ₂ , I ₂ , ICl ₃ , IBr, IF _{5 and the} like. Examples of the Lewis acid include PF ₅ , AsF ₅ , SbF ₅ , BF ₃ , BCl ₃ , BBr ₃ , SO ₃ , and GaCl ₃ . Examples of the protonic acid include HF, HCl, HNO ₃ , H ₂ SO ₄ , HBF ₄ , HClO ₄ , FSO ₃ H, ClSO ₃ H, CF ₃ SO ₃ H, and the like. The transition metal _{halide, NbF 5, TaF 5, MoF} 5, WF 5, RuF 5, BiF 5, TiCl 4, ZrCl 4, MoCl 5, MoCl 3, WCl 5, FeCl 3, TeCl 4, SnCl 4, SeCl ₄ , FeBr ₃ , SnI _{5 and the} like. The transition metal _{compound, AgClO 4, AgBF 4, La} (NO 3) 3, Sm (NO 3) 3 and the like. Examples of the alkali metal include Li, Na, K, Rb, and Cs. Examples of the alkaline earth metal include Be, Mg, Ca, Sc, and Ba.

Moreover, the dopant with respect to a conductive polymer may be introduce | transduced into fullerenes, such as hydrogenation fullerene, a hydroxylation fullerene, and a sulfonated fullerene. In the transparent conductive layer, the dopant is preferably contained in an amount of 0.001 part by mass or more with respect to 100 parts by mass of the conductive polymer. Furthermore, it is more preferable that 0.5 mass part or more is contained. The transparent conductive layer according to the present invention includes a long chain sulfonic acid, a polymer of long chain sulfonic acid (for example, polystyrene sulfonic acid), halogen, Lewis acid, proton acid, transition metal halide, transition metal compound, alkali Both at least one dopant selected from the group consisting of metals, alkaline earth metals, MClO ₄ , R ₄ N ⁺ , and R ₄ P ⁺ and fullerenes may be included.

  The transparent conductive layer containing the conductive polymer according to the present invention may contain a water-soluble organic compound. Among water-soluble organic compounds, compounds having an effect of improving conductivity by adding to a conductive polymer material are known. There is no restriction | limiting in particular in the water-soluble organic compound which can be used with the transparent conductive layer which concerns on this invention, It can select suitably from well-known things, For example, an oxygen containing compound is mentioned suitably.

  The oxygen-containing compound is not particularly limited as long as it contains oxygen, and examples thereof include a hydroxyl group-containing compound, a carbonyl group-containing compound, an ether group-containing compound, and a sulfoxide group-containing compound. Examples of the hydroxyl group-containing compound include ethylene glycol, diethylene glycol, propylene glycol, trimethylene glycol, 1,4-butanediol, and glycerin. Among these, ethylene glycol and diethylene glycol are preferable. Examples of the carbonyl group-containing compound include isophorone, propylene carbonate, cyclohexanone, and γ-butyrolactone. Examples of the ether group-containing compound include diethylene glycol monoethyl ether. Examples of the sulfoxide group-containing compound include dimethyl sulfoxide. These may be used alone or in combination of two or more, but it is particularly preferable to use at least one selected from dimethyl sulfoxide, ethylene glycol, and diethylene glycol.

  In the transparent conductive layer containing the conductive polymer according to the present invention, the content of the water-soluble organic compound with respect to 100 parts by mass of the conductive polymer is preferably 0.001 part by mass or more, and more preferably 0.01 to 50 parts by mass. Preferably, 0.01-10 mass parts is especially preferable.

  When the conductive polymer is contained in the transparent conductive layer according to the present invention, the metal nanowire and the conductive polymer may be mixed in one layer, but each layer is formed as a separate layer, and a multilayer structure is also formed. Good.

  The method for producing the transparent conductive layer according to the present invention is not particularly limited. However, from the viewpoint of productivity and production cost, electrode quality such as smoothness and uniformity, and reduction of environmental load, the transparent conductive layer can be formed. Is preferably a liquid phase film forming method such as a coating method or a printing method. As coating methods, roll coating method, bar coating method, dip coating method, spin coating method, casting method, die coating method, blade coating method, bar coating method, gravure coating method, curtain coating method, spray coating method, doctor coating method Etc. can be used. As the printing method, a letterpress (letter) printing method, a stencil (screen) printing method, a lithographic (offset) printing method, an intaglio (gravure) printing method, a spray printing method, an ink jet printing method, and the like can be used.

  Moreover, a conductive material containing metal nanowires can be patterned on a transparent substrate to form a transparent wiring or a transparent circuit. In addition, physical surface treatments, such as a corona discharge process and a plasma discharge process, can also be given to the transparent base material surface as a preliminary process for improving adhesiveness and coating property as needed.

<Transparent substrate>
As a transparent substrate used in the dye-sensitized solar cell of the present invention, a glass plate or a resin film can be used.

  Specific examples of the resin film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate, polyolefins such as polyethylene (PE), polypropylene (PP), polystyrene and cyclic olefin resins, polyvinyl chloride, poly Vinyl resins such as vinylidene chloride, polyether ether ketone (PEEK), polysulfone (PSF), polyether sulfone (PES), polycarbonate (PC), polyamide, polyimide, acrylic resin, triacetyl cellulose (TAC), etc. are used. be able to.

  Among these, from the viewpoints of transparency, heat resistance, ease of handling and cost, a biaxially stretched polyethylene terephthalate film, an acrylic resin film, and a triacetyl cellulose film are preferable, and a biaxially stretched polyethylene terephthalate film is preferable. Most preferred.

<Metal oxide intermediate layer>
The dye-sensitized solar cell of the present invention preferably has a metal oxide intermediate layer composed of a metal oxide between the transparent conductive layer and the metal oxide semiconductor layer.

  As a metal oxide which comprises a metal oxide intermediate | middle layer, the thing similar to what is used for the metal oxide semiconductor layer mentioned later can be used. Among them, the reverse current at the time of light irradiation is small, the forward electron transfer is increased, and high photoelectric conversion efficiency can be obtained, so that it is the same as the conduction band bottom potential of the metal oxide used for the metal oxide semiconductor layer. It is preferable to use a metal oxide having a level or a lower potential of the lower end of the conduction band.

  Specifically, when the metal oxide constituting the metal oxide semiconductor layer is titanium oxide or zinc oxide, the metal oxide used for the metal oxide intermediate layer includes zirconium oxide, strontium titanate, niobium oxide, oxide Zinc is preferable, and strontium titanate and niobium oxide are more preferable.

  The thickness of the metal oxide intermediate layer is preferably 1 nm or more and 500 nm or less, and more preferably 5 nm or more and 100 nm or less. The porosity of the metal oxide intermediate layer is preferably smaller than the porosity of the metal oxide semiconductor layer, specifically 20% or less, more preferably 10% or less. When the porosity of the metal oxide intermediate layer is reduced, not only is it difficult for electrons to move in the reverse direction, but also adhesion and durability with the transparent conductive layer are improved. Further, the metal oxide intermediate layer may have a laminated structure of two or more layers, and the composition, thickness, porosity and the like of the metal oxide fine particles to be formed can be arbitrarily controlled.

  Here, the porosity means a porosity having penetrability in the thickness direction of the dielectric, and can be measured by using a commercially available apparatus such as a mercury porosimeter (Shimadzu Polarizer 9220 type).

  The method for producing the metal oxide intermediate layer is not particularly limited, and is a vacuum deposition method, ion sputtering method, cast method, coating method, spin coating method, spray method, aerosol deposition method (AD method), dipping method, electrolytic weight Various thin film forming methods such as a combination method, a photoelectrolytic polymerization method, and a pressure press method can be given.

  Among these, the vacuum vapor deposition method and the ion sputtering method can be performed under known conditions using a commercially available vapor deposition apparatus or sputtering apparatus. About the coating method etc., it can carry out according to the coating method of the semiconductor fine particle of the metal oxide semiconductor layer mentioned later. Moreover, when a transparent base material is not a glass plate but a resin film, methods, such as a pressure press method which does not require a high temperature heating process, can be applied preferably.

<Metal oxide semiconductor layer>
The metal oxide constituting the metal oxide semiconductor layer according to the present invention is not particularly limited as long as it is a semiconductor that receives electrons generated by light irradiation with a dye adsorbed on the semiconductor and transmits the electrons to the transparent conductive layer. Various metal oxides used in the dye-sensitized solar cell can be used.

  Specifically, various metal oxide semiconductors such as titanium oxide, zirconium oxide, zinc oxide, vanadium oxide, niobium oxide, tantalum oxide, tungsten oxide, strontium titanate, calcium titanate, magnesium titanate, barium titanate, niobium Various composite metal oxide semiconductors such as potassium oxide and strontium tantalate, transition metal oxides such as magnesium oxide, strontium oxide, aluminum oxide, cobalt oxide, nickel oxide, manganese oxide, cerium oxide, gadolinium oxide, samarium oxide, ytterbium oxide And metal oxides such as lanthanoid oxides, and inorganic insulators such as natural or synthetic silicate compounds represented by silica.

  Further, these materials can be used in combination. Furthermore, the metal oxide particles may have a core-shell structure or may be doped with a different metal element, and a metal oxide having an arbitrary structure and composition can be applied.

  The average particle diameter of the metal oxide particles is preferably 10 nm or more and 300 nm or less, and more preferably 10 nm or more and 100 nm or less. Further, the shape of the metal oxide is not particularly limited, and may be spherical, acicular, or amorphous crystals.

  The method for forming metal oxide particles is not particularly limited, and various liquid phase methods such as hydrothermal reaction method, sol-gel method / gel sol method, colloid chemical synthesis method, coating pyrolysis method, spray pyrolysis method, and chemical vapor phase It can be formed using various gas phase methods such as a precipitation method.

  Next, a method for manufacturing a metal oxide semiconductor layer according to the present invention will be described.

  As a method for producing the metal oxide semiconductor layer of the dye-sensitized solar cell of the present invention, a known method can be applied. (1) Suspension containing metal oxide fine particles or a precursor thereof A method of forming a semiconductor layer by coating the transparent conductive layer on the transparent conductive layer, and (2) immersing the transparent conductive layer in a colloidal solution and subjecting the metal oxide semiconductor particles to the transparent conductive property by electrophoresis. Electrophoretic electrodeposition method to deposit on the layer, (3) Method to mix and apply foaming agent to colloidal solution or dispersion, then sinter to make porous, (4) Mix and apply polymer microbeads Then, a method of removing the polymer microbeads by heat treatment or chemical treatment to form voids and making it porous can be applied.

  Among the above-described production methods, a known method can be applied particularly as a coating method, and examples thereof include a screen printing method, an ink jet method, a roll coating method, a doctor blade method, a spin coating method, and a spray coating method. Can do.

  In particular, in the case of the method (1), the particle diameter of the metal oxide fine particles in the suspension is preferably fine and is preferably present as primary particles. The suspension containing the metal oxide fine particles is prepared by dispersing the metal oxide fine particles in a solvent, and the solvent is not particularly limited as long as the metal oxide fine particles can be dispersed, and water, Organic solvents, mixtures of water and organic solvents are included. As the organic solvent, alcohols such as methanol and ethanol, ketones such as methyl ethyl ketone, acetone and acetyl acetone, hydrocarbons such as hexane and cyclohexane, and the like are used. A surfactant and a viscosity modifier (polyhydric alcohol such as polyethylene glycol) can be added to the suspension as necessary. The concentration range of the metal oxide fine particles in the solvent is preferably 0.1 to 70% by mass, more preferably 0.1 to 30% by mass.

  The suspension containing the metal oxide core fine particles obtained as described above is applied onto the transparent conductive layer, dried, etc., and then baked in air or in an inert gas to be transparent. A metal oxide semiconductor layer is formed over the conductive layer. The metal oxide semiconductor layer obtained by applying and drying the suspension on the transparent conductive layer is composed of an aggregate of metal oxide fine particles, and the particle size of the fine particles is the primary particles of the metal oxide fine particles used. It corresponds to the diameter. Since the metal oxide semiconductor layer formed on the transparent conductive layer has a low bonding strength with the transparent conductive layer and a bonding strength between the fine particles and a low mechanical strength, the metal oxide fine particles Preferably, the aggregate film is fired to increase mechanical strength and to be a fired product film that is strongly fixed to the substrate.

  In the present invention, the metal oxide semiconductor layer may have any structure, but is preferably a porous structure film (also referred to as a porous layer having voids). Here, the porosity of the metal oxide semiconductor layer is preferably 0.1 to 20% by volume, and more preferably 5 to 20% by volume. Note that the porosity of the metal oxide semiconductor layer means a porosity that is penetrating in the thickness direction of the dielectric, and can be measured using a commercially available apparatus such as a mercury porosimeter (Shimadzu porer 9220 type). The thickness of the metal oxide semiconductor layer is preferably at least 10 nm or more, and more preferably 100 to 10,000 nm.

  From the viewpoint of appropriately adjusting the actual surface area of the metal oxide semiconductor layer during the firing treatment and obtaining the metal oxide semiconductor layer having the above-described porosity, the firing temperature is preferably lower than 1000 ° C, and 200 to 800 ° C. More preferably, it is in the range.

  In the metal oxide semiconductor layer according to the present invention, after the metal oxide semiconductor layer is formed, the metal oxide semiconductor film is subjected to a surface treatment with a metal oxide as necessary for the purpose of improving electronic conductivity. Also good. The surface treatment composition is preferably the same type of composition as that of the metal oxide forming the metal oxide semiconductor layer, particularly from the viewpoint of electron conductivity between the metal oxide fine particles.

  As a method for performing this surface treatment, after forming a metal oxide semiconductor film on the transparent conductive layer, a metal oxide precursor to be surface treated is applied to the semiconductor film, or the semiconductor film is used as a precursor. A surface treatment made of a metal oxide can be performed by immersing in a body solution and further performing a firing treatment as necessary.

  Specifically, the surface treatment is performed by using an electrochemical treatment using a titanium tetrachloride aqueous solution or titanium alkoxide which is a precursor of titanium oxide, or using a precursor of an alkali metal titanate or an alkaline earth titanate metal. be able to. The firing temperature and firing time at this time are not particularly limited and can be arbitrarily controlled, but are preferably 200 ° C. or lower.

<Dye>
The dye used in the present invention will be described.

  In the present invention, the dye adsorbed on the surface of the metal oxide semiconductor layer described above has absorption in various visible light regions or infrared light regions, and has a lowest vacancy level higher than the conduction band of the metal oxide semiconductor. The pigment | dye which has is preferable and well-known various pigment | dyes can be used.

  For example, azo dyes, quinone dyes, quinone imine dyes, quinacridone dyes, squarylium dyes, cyanine dyes, cyanidin dyes, merocyanine dyes, triphenylmethane dyes, xanthene dyes, porphyrin dyes, perylene dyes Examples thereof include dyes, indigo dyes, phthalocyanine dyes, naphthalocyanine dyes, rhodamine dyes, rhodanine dyes, and the like.

  Metal complex dyes are also preferably used. In this case, Cu, Ni, Fe, Co, V, Sn, Si, Ti, Ge, Cr, Zn, Ru, Mg, Al, Pb, Mn, In, Mo Y, Zr, Nb, Sb, La, W, Pt, Ta, Ir, Pd, Os, Ga, Tb, Eu, Rb, Bi, Se, As, Sc, Ag, Cd, Hf, Re, Au, Ac Various metals such as Tc, Te, and Rh can be used.

  Among the above, polymethine dyes such as cyanine dyes, merocyanine dyes, and squarylium dyes are one of preferred embodiments. Specifically, JP-A-11-35836, JP-A-11-67285, JP-A-11- No. 86916, JP-A-11-97725, JP-A-11-158395, JP-A-11-163378, JP-A-11-214730, JP-A-11-214731, JP-A-11-238905 Examples thereof include dyes described in each specification such as JP-A No. 2004-207224, JP-A No. 2004-319202, European Patent Nos. 892,411 and 911,841.

  Furthermore, a metal complex dye is also one preferred embodiment, and a metal phthalocyanine dye, a metal porphyrin dye, or a ruthenium complex dye is preferable, and a ruthenium complex dye is particularly preferable.

  Examples of ruthenium complex dyes include U.S. Pat. Nos. 4,927,721, 4,684,537, 5,084,365, 5,350,644, 5,463,057, 5,525,440, JP-A-7-249790, JP-T-10-504512, WO98 / 50393, JP2000- Examples include complex dyes described in Japanese Patent No. 26487, Japanese Patent Application Laid-Open No. 2001-223037, Japanese Patent Application Laid-Open No. 2001-226607, Japanese Patent No. 3430254, and the like.

  In the present invention, it is particularly preferable to use a rhodanine dye as the dye adsorbed on the surface of the metal oxide. Any structure can be preferably used as long as it is a rhodanine-based dye. Among these, at least a compound represented by the following general formula (1) or a compound represented by the following general formula (2) is preferred. It is particularly preferable to use one type.

In the formula, R ₁₁ represents a substituent, and n represents an integer of 0 to 4. X _{11 to} X ₁₄ each represent an oxygen atom, a sulfur atom or a selenium atom, and R ₁₂ and R ₁₃ each represent a hydrogen atom or a substituent. R ₁₄ represents a carboxy group or a phosphono group, and L ₁₁ represents a divalent linking group. R ₁₅ represents an alkyl group.

In the formula, R ₂₁ represents a substituent, and n represents an integer of 0 to 4. X _{21 to} X ₂₆ each represents an oxygen atom, a sulfur atom or a selenium atom, and R ₂₂ and R ₂₃ each represents a hydrogen atom or a substituent. R ₂₄ and R ₂₆ each represent a hydrogen atom, a carboxy group or a phosphono group, and at least one of R ₂₄ and R ₂₆ represents a carboxy group or a phosphono group. L ₂₁ and L ₂₂ each independently represent a divalent linking group. R ₂₅ represents an alkyl group.

  Further, the compound represented by the general formula (1) (dye) and the compound represented by the general formula (2) (dye) are derived from the compound in addition to the compound represented by the general formula. Ions and salts. For example, when the molecular structure has a sulfonic acid group (sulfo group), it is formed by an anion generated by dissociation of the sulfonic acid group in addition to the compound, and the anion and a counter cation. Salt.

  Such a salt may be a salt formed with a metal ion such as sodium salt, potassium salt, magnesium salt, calcium salt, or the like, such as pyridine, piperidine, triethylamine, aniline, diazabicycloundecene, etc. It may be a salt formed with an organic base.

  Similarly, in the case of a compound having a basic group in the molecule, the cation produced by protonation of the compound, and the hydrochloride, sulfate, acetate, methylsulfonate, p-toluenesulfonate, etc. Also included are salts formed with acids.

  Below, the specific example of a compound represented by General formula (1) or General formula (2) preferably used for this invention is shown.

  The compound represented by the general formula (1) and the compound represented by the general formula (2) are, for example, “Cyanine Soybean and Related Compounds” (1964, Inter Science Published by Publishers), U.S. Pat. Nos. 2,454,629, 2,493,748, JP-A-6-301136, JP-A-2003-203684, etc. It can be synthesized with reference to the method.

  These compounds (pigments) preferably have a large extinction coefficient and are stable against repeated redox reactions.

  The compound (dye) is preferably chemically adsorbed on the metal oxide semiconductor, and has a functional group such as a carboxy group, a sulfonic acid group, a phosphoric acid group, an amide group, an amino group, a carbonyl group, or a phosphine group. It is preferable to have.

  In addition, two or more kinds of dyes can be used in combination or mixed in order to widen the wavelength range of photoelectric conversion as much as possible and increase the conversion efficiency. In this case, the dye to be used or mixed and the ratio thereof can be selected so as to match the wavelength range and intensity distribution of the target light source.

<Charge transfer layer>
The charge transfer layer is a layer containing a charge transport material having a function of replenishing electrons to the oxidant of the dye. Examples of typical charge transport materials that can be used in the present invention include a solvent in which a redox counter ion is dissolved, an electrolytic solution such as a room temperature molten salt containing the redox counter ion, and a solution of the redox counter ion as a polymer. Examples thereof include a gel-like quasi-solidified electrolyte impregnated with a matrix, a low-molecular gelling agent, and the like, and a polymer solid electrolyte. In addition to charge transport materials involving ions, electron transport materials and hole transport materials can also be used as materials in which carrier transport in solids is involved in electrical conduction, and these can be used in combination. is there.

  When using an electrolytic solution for the charge transfer layer, the redox counter ion to be contained is not particularly limited as long as it can be used in a generally known solar cell or the like.

Specifically, those containing a redox counter ion such as I ⁻ / I ³⁻ and Br ²⁻ / Br ^{3 −} , ferrocyanate / ferricyanate, ferrocene / ferricinium ion, cobalt Metal redox systems such as metal complexes such as complexes, organic redox systems such as alkylthiol-alkyldisulfides, viologen dyes, hydroquinone / quinone, and sulfur compounds such as sodium polysulfide and alkylthiol / alkyldisulfides. .

More specifically as iodine, iodine and LiI, NaI, KI, CsI, a combination of a metal iodide such as CaI _2, tetraalkylammonium iodide, pyridinium iodide, quaternary ammonium compounds such as imidazolium iodide And combinations with iodine salts of quaternary imidazolium compounds. More specifically, bromine-based combinations include bromine and metal bromides such as LiBr, NaBr, KBr, CsBr, and CaBr ₂ , and combinations of tetraalkylammonium bromide, pyridinium bromide, and the like with quaternary ammonium compounds such as bromine salts. Can be mentioned.

  As a solvent, it is an electrochemically inert compound that has low viscosity and improved ion mobility, or has a high dielectric constant and improved effective carrier concentration, and can exhibit excellent ionic conductivity. Is desirable.

  Specifically, carbonate compounds such as dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, heterocyclic compounds such as 3-methyl-2-oxazolidinone, ether compounds such as dioxane, diethyl ether, ethylene glycol dialkyl ether, propylene glycol dialkyl Ethers, chain ethers such as polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, alcohols such as methanol, ethanol, ethylene glycol monoalkyl ether, propylene glycol monoalkyl ether, polyethylene glycol monoalkyl ether, polypropylene glycol monoalkyl ether, Ethylene glycol, diethylene glycol, triethylene Polyhydric alcohols such as glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin, nitrile compounds such as acetonitrile, glutaronitrile, propionitrile, methoxypropionitrile, methoxyacetonitrile, benzonitrile, tetrahydrofuran, dimethyl sulfoxide, An aprotic polar substance such as sulfolane can be used.

  A preferable electrolyte concentration is 0.1 to 15M, and more preferably 0.2 to 10M. Moreover, the preferable addition density | concentration of an iodine when using an iodine type is 0.01-0.5M.

  The molten salt electrolyte is preferable from the viewpoint of achieving both photoelectric conversion efficiency and durability. Examples of the molten salt electrolyte include WO95 / 18456 pamphlet, JP-A-8-259543, JP-A-2001-357896, Electrochemistry, Vol.65, No.11, p.923 (1997) and the like. And electrolytes containing known iodine salts such as pyridinium salts, imidazolium salts, and triazolium salts described in (1). These molten salt electrolytes are preferably in a molten state at room temperature, and it is preferable not to use a solvent.

  Gels obtained by adding an electrolyte or electrolyte solution to an oligomer or polymer matrix, adding polymers, adding low-molecular gelling agents or oil gelling agents, polymerization containing polyfunctional monomers, polymer cross-linking reactions, etc. (Pseudo-solidification) can also be used.

  In the case of gelation by adding a polymer, polyacrylonitrile and polyvinylidene fluoride can be preferably used. In the case of gelation by adding an oil gelling agent, a preferred compound is a compound having an amide structure in the molecular structure. When the electrolyte is gelled by a polymer crosslinking reaction, it is desirable to use a polymer containing a crosslinkable reactive group and a crosslinking agent in combination. In this case, preferred crosslinkable reactive groups are nitrogen-containing heterocycles (for example, pyridine ring, imidazole ring, thiazole ring, oxazole ring, triazole ring, morpholine ring, piperidine ring, piperazine ring, etc.), and preferred crosslinking agents Is a bifunctional or more functional reagent (for example, alkyl halide, halogenated aralkyl, sulfonate, acid anhydride, acid chloride, isocyanate, etc.) capable of electrophilic reaction with a nitrogen atom. The concentration of the electrolyte is usually 0.01 to 99% by mass, preferably about 0.1 to 90% by mass.

Further, as the gel electrolyte, an electrolyte composition containing an electrolyte and metal oxide particles and / or conductive particles can also be used. As the metal oxide particles, TiO ₂ , SnO ₂ , WO ₃ , ZnO, ITO, BaTiO ₃ , Nb ₂ O ₅ , In ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , La ₂ O ₃ , SrTiO ₃ , Y Examples thereof include one or a mixture of two or more selected from the group consisting of ₂ O ₃ , Ho ₂ O ₃ , Bi ₂ O ₃ , CeO ₂ , and Al ₂ O ₃ . These may be doped with impurities or complex oxides. Examples of the conductive particles include those made of a substance mainly composed of carbon.

  Next, the polymer electrolyte is a solid substance capable of dissolving the redox species or binding with at least one substance constituting the redox species, for example, polyethylene oxide, polypropylene oxide, polyethylene succinate, A polymer compound such as poly-β-propiolactone, polyethyleneimine, polyalkylene sulfide, or a cross-linked product thereof, polyphosphazene, polysiloxane, polyvinyl alcohol, polyacrylic acid, polyalkylene oxide, Examples include those obtained by adding an ether segment or an oligoalkylene oxide structure as a side chain, or a copolymer thereof. Among them, those having an oligoalkylene oxide structure as a side chain or having a polyether segment as a side chain are included. It is preferred.

  In order to contain the redox species in the solid, for example, a method of polymerizing in the coexistence of a monomer that becomes a polymer compound and a redox species, a solid such as a polymer compound is dissolved in a solvent as necessary. Then, the above-mentioned method of adding the redox species can be used. The content of the redox species can be appropriately selected according to the required ion conduction performance.

  In the present invention, instead of an ion conductive electrolyte such as a molten salt, a solid hole transport material that is organic or inorganic or a combination of both can be used. Organic hole transport materials include aromatic amines and triphenylene derivatives, polyacetylene and its derivatives, poly (p-phenylene) and its derivatives, poly (p-phenylene vinylene) and its derivatives, polythienylene vinylene and its Conductive polymers such as derivatives, polythiophene and derivatives thereof, polyaniline and derivatives thereof, polytoluidine and derivatives thereof can be preferably used.

In order to control the dopant level, the hole transport material may be added with a compound containing a cation radical such as tris (4-bromophenyl) aminium hexachloroantimonate, or the potential of the oxide semiconductor surface may be controlled. In order to perform (space charge layer compensation), a salt such as Li [(CF ₃ SO ₂ ) ₂ N] may be added. A p-type inorganic compound semiconductor can be used as the inorganic hole transport material.

  The p-type inorganic compound semiconductor for this purpose preferably has a band gap of 2 eV or more, and more preferably 2.5 eV or more. Also, the ionization potential of the p-type inorganic compound semiconductor needs to be smaller than the ionization potential of the dye-adsorbing electrode from the condition that the holes of the dye can be reduced. Although the preferable range of the ionization potential of the p-type inorganic compound semiconductor varies depending on the dye used, it is generally preferably 4.5 to 5.5 eV, and more preferably 4.7 to 5.3 eV.

A preferred p-type inorganic compound semiconductor is a compound semiconductor containing monovalent copper, preferably CuI and CuSCN, and most preferably CuI. The preferred hole mobility of the charge transfer layer containing the p-type inorganic compound semiconductor is 10 ⁻⁴ to 10 ⁴ m ² / V · sec, more preferably 10 ⁻³ to 10 ³ cm ² / V · sec. The preferred conductivity of the charge transfer layer is 10 ⁻⁸ to 10 ² S / cm, more preferably 10 ⁻⁶ to 10 S / cm.

  In the present invention, the method for forming the charge transfer layer between the semiconductor electrode and the counter electrode is not particularly limited. For example, after the semiconductor electrode and the counter electrode are arranged to face each other, between the both electrodes The charge transfer layer is formed by filling the electrolyte solution or various electrolytes described above to form a charge transfer layer, or by dropping or coating the electrolyte or various electrolytes on the semiconductor electrode or the counter electrode. A method of overlaying the other electrode on the top can be used.

  Also, in order to prevent electrolyte from leaking between the semiconductor electrode and the counter electrode, the gap between the semiconductor electrode and the counter electrode is sealed with a film or resin as necessary, or the semiconductor electrode and the charge transfer It is also preferable to store the layer and the counter electrode in a suitable case.

  In the case of the former forming method, as a method for filling the charge transfer layer, a normal pressure process using capillary action by dipping or the like, or a vacuum process in which the gas phase in the gap is replaced with a liquid phase at a pressure lower than normal pressure can be used. .

  In the latter forming method, microgravure coating, dip coating, screen coating, spin coating or the like can be used as a coating method. In the wet charge transfer layer, the counter electrode is provided in an undried state and measures for preventing liquid leakage at the edge portion are taken. In the case of a gel electrolyte, there is a method in which it is applied in a wet manner and solidified by a method such as polymerization. In this case, the counter electrode can be applied after drying and fixing.

  In the case of a solid electrolyte or a solid hole transport material, a charge transfer layer can be formed by a dry film forming process such as a vacuum deposition method or a CVD method, and then a counter electrode can be provided. Specifically, it can be introduced into the electrode by techniques such as vacuum deposition, casting, coating, spin coating, dipping, electropolymerization, and photoelectropolymerization. It is formed by evaporating the solvent by heating to an arbitrary temperature.

The thickness of the charge transfer layer is preferably 10 μm or less, more preferably 5 μm or less, and further preferably 1 μm or less. The conductivity of the charge transfer layer is preferably 1 × 10 ⁻¹⁰ S / cm or more, and more preferably 1 × 10 ⁻⁵ S / cm or more.

<Counter electrode>
The counter electrode that can be used in the present invention can utilize a single-layer structure of a base material having conductivity as in the transparent conductive layer described above, or a base material having a conductive layer on the surface thereof. In the latter case, the conductive material and substrate used for the conductive layer, and the production method thereof are the same as those of the transparent conductive layer described above, and various known materials and methods can be applied.

Among them, it is preferable to use a catalyst having a catalytic ability that allows oxidation of I ^3- ions and other redox ions to be carried out at a sufficiently high rate. Specifically, a platinum electrode, a surface of a conductive material. Examples thereof include platinum plating or platinum deposition, rhodium metal, ruthenium metal, ruthenium oxide, carbon and the like. In view of cost and flexibility as described above, it is also one of preferred embodiments that a plastic sheet is used as a base material and a polymer material is applied as a conductive material.

  The thickness of the conductive layer is not particularly limited, but is preferably 3 nm to 10 μm. When the conductive layer is a metal, the thickness is preferably 5 μm or less, and more preferably in the range of 10 nm to 3 μm. The surface resistance of the counter electrode is preferably as low as possible. Specifically, the range of the surface resistance is preferably 50Ω / □ or less, more preferably 20Ω / □ or less, still more preferably 10Ω / □ or less. .

  Since light may be received from one or both of the transparent conductive layer and the counter electrode described above, it is sufficient that at least one of the transparent conductive layer and the counter electrode is substantially transparent. From the viewpoint of improving the power generation efficiency, it is preferable to make the transparent conductive layer transparent so that light is incident from the transparent conductive layer side. In this case, the counter electrode preferably has a property of reflecting light. As such a counter electrode, glass or plastic deposited with a metal or a conductive oxide, or a metal thin film can be used.

  The counter electrode may be formed by directly applying, plating, or vapor-depositing (PVD, CVD) a conductive material on the above-described charge transfer layer, or attaching the conductive layer side of the substrate or a single transparent conductive layer. In addition, as in the case of the transparent conductive layer, it is also a preferable aspect to use a metal wiring layer in combination, particularly when the counter electrode is transparent.

  The counter electrode is preferably conductive and has a catalytic action on the reduction reaction of the redox electrolyte. For example, glass or a polymer film obtained by evaporating platinum, carbon, rhodium, ruthenium, or the like or applying conductive fine particles can be used.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these.

Example 1
<< Preparation of transparent conductive layer coating liquid >>
<Preparation of coating solution TC-01>
20 parts by mass of high-purity single-walled carbon nanotubes (manufactured by Carbon Nanotechnology Inc .; hereinafter referred to as “SWNT”) was added to 80 parts by mass of a 20% aqueous solution of sodium dodecylbenzenesulfonate with stirring at 100 rpm. Subsequently, ultrasonic treatment was performed for 1 hour to prepare a 20% by mass carbon nanotube dispersion liquid, which was designated as transparent conductive layer coating liquid TC-01.

<Preparation of coating solution TC-02>
Oxidative polymerization of 3,4-ethylenedioxythiophene in an aqueous medium in the presence of polystyrene sulfonic acid (PSS) in an aqueous medium, followed by ultrafiltration treatment, 20% aqueous dispersion of PEDOT: PSS as a conductive polymer Got the body. At this stage, the aqueous dispersion contains 30% PSS and 20% ethylene glycol. Next, the same amount of a 20% aqueous dispersion of PEDOT: PSS was added to the transparent conductive layer coating solution TC-01 while stirring at 100 rpm. Concentration was performed by ultrafiltration treatment, followed by ultrasonic treatment for 1 hour to prepare a 20% by mass carbon nanotube dispersion, which was designated as transparent conductive layer coating solution TC-02.

<Preparation of coating solution TC-03>
Adv. Mater. Reference is made to the method described in 2002, 14, 833 to 837, ethylene glycol (EG) is used as a reducing agent, polyvinylpyrrolidone (PVP) is used as a protective colloid agent and form control agent, and silver nanowires are produced by the following method. Was made.

(Nucleation process)
While stirring 100 ml of the EG solution maintained at 170 ° C. in the reaction vessel, 10 ml of an EG solution of silver nitrate (silver nitrate concentration: 1.5 × 10 ⁻⁴ mol / L) was added at a constant flow rate for 10 seconds. Thereafter, aging was carried out at 170 ° C. for 10 minutes to form silver core particles. The reaction solution after completion of ripening exhibited a yellow color derived from surface plasmon absorption of silver nanoparticles, and it was confirmed that silver ions were reduced and silver nanoparticles were formed.

(Particle growth process)
The reaction solution containing the core particles after completion of the ripening is kept at 170 ° C. with stirring, and 100 ml of an EG solution of silver nitrate (silver nitrate concentration: 1.0 × 10 ⁻¹ mol / L) and an EG solution of PVP (PVP) (Concentration: 5.0 × 10 ⁻¹ mol / L) was added at a constant flow rate for 100 minutes using the double jet method. In the particle growth process, the reaction solution was collected every 20 minutes and confirmed with an electron microscope. As a result, the silver nanoparticles formed in the nucleation process grew mainly in the major axis direction of the nanowires over time. Thus, no new core particles were generated in the grain growth process.

(Washing process)
After completion of the particle growth step, the reaction solution was cooled to room temperature, filtered using a filter, and the silver nanowires separated by filtration were redispersed in water. Filtration of the silver nanowires with a filter and redispersion in water were repeated 5 times, and finally a 20% by mass aqueous dispersion of the silver nanowires was prepared to obtain a transparent conductive layer coating solution TC-03.

  When a small amount of the obtained dispersion was collected and confirmed with an electron microscope, it was confirmed that silver nanowires having an average minor axis diameter of 85 nm and an average major axis diameter of 7.4 μm were formed.

<Preparation of coating solution TC-04>
The same amount of a 20% aqueous dispersion of indium-doped tin oxide was added to the transparent conductive layer coating solution TC-03 while stirring at 100 rpm. Concentration was performed by ultrafiltration treatment, followed by ultrasonic treatment for 1 hour to prepare a 20% by mass silver nanowire dispersion liquid, which was designated as a transparent conductive layer coating liquid TC-04.

<Preparation of coating solution TC-05>
The same amount of the 20% aqueous dispersion of PEDOT: PSS was added to the transparent conductive layer coating solution TC-03 while stirring at 100 rpm. Concentration was performed by ultrafiltration treatment, followed by ultrasonic treatment for 1 hour to prepare a 20% by mass silver nanowire dispersion liquid, which was designated as transparent conductive layer coating liquid TC-05.

<Preparation of coating solution TC-06>
J. et al. Phys. Chem. With reference to the method described in B205, 109, 16326-16331, a gold ion was reduced and prepared in the presence of a PVP protective colloid, and a dispersion of PVP protected gold nanoparticles was prepared in advance. On the other hand, similarly to the production of the silver nanowire of the transparent conductive layer coating solution TC-03, the process up to the particle growth step was completed to produce a silver nanowire. Next, while maintaining the reaction liquid at 170 ° C. and stirring, an amount equivalent to 3 × 10 ⁻⁴ mol of a PVP-protected gold nanoparticle dispersion prepared in advance was added over 5 minutes, and further at 170 ° C. Aging for 10 minutes was performed. Through the same water washing step as the transparent conductive layer coating solution TC-03, a 20% by mass aqueous dispersion of silver / gold nanowires was finally prepared. A trace amount of the obtained dispersion was collected and confirmed with an electron microscope, and it was confirmed that silver / silver nanowires having an average minor axis diameter of 98 nm and an average major axis diameter of 7.5 μm were formed.

  Next, the same amount of the 20% aqueous dispersion of PEDOT: PSS was added to the 20% by mass aqueous dispersion of the silver / gold nanowire while stirring at 100 rpm. Concentration was performed by ultrafiltration treatment, followed by ultrasonic treatment for 1 hour to prepare a 20% by mass silver / gold nanowire dispersion liquid, which was designated as a transparent conductive layer coating liquid TC-06.

(Production of dye-sensitized solar cell)
<< Preparation of dye-sensitized solar cell SC-01 >>
<Formation of undercoat layer>
A 200 μm thick biaxially stretched PET support is subjected to a corona discharge treatment of 12 W · min / m ^{2 on} one side, and the undercoat coating solution B-1 is applied to a dry film thickness of 0.1 μm, and 12 W is applied thereon. · min / m subjecting ² of the corona discharge treatment was applied so that the lower引塗coating solution B-2 to a dry film thickness of 0.06 .mu.m. Thereafter, heat treatment was performed at 120 ° C. for 1.5 minutes to obtain an underdrawn PET film support.

(Undercoating liquid B-1)
Copolymer latex liquid of 20 parts by mass of styrene, 40 parts by mass of glycidyl methacrylate and 40 parts by mass of butyl acrylate (solid content: 30%) 50 g
SnO ₂ sol (A) 440g
Compound (UL-1) 0.2g
Finish with water 1000ml
(Undercoating liquid B-2)
10g gelatin
Compound (UL-1) 0.2g
Compound (UL-2) 0.2g
Silica particles (average particle size 3μm) 0.1g
Hardener (UL-3) 1g
Finish with water 1000ml
Preparation of SnO ₂ sol (A) 65 g of SnCl ₄ .5H ₂ O was dissolved in 2000 ml of distilled water to make a homogeneous solution, which was then boiled to obtain a precipitate. The produced precipitate is taken out by decantation and washed with distilled water many times. Silver nitrate is added dropwise to distilled water in which the precipitate has been washed, and after confirming that there is no reaction of chlorine ions, distilled water is added to the washed precipitate to make a total volume of 2000 ml. To this, 40 ml of 30% aqueous ammonia was added and heated to obtain a uniform sol. Further, while adding ammonia water, the solution was concentrated by heating until the solid content concentration of SnO ₂ reached 8.3 mass%, to obtain SnO ₂ sol (A).

<Formation of transparent conductive layer>
The transparent conductive layer coating solution TC-01 is applied onto the undercoated PET film support so as to have a dry film thickness of 100 nm, followed by heat treatment at 100 ° C. for 20 minutes. A layer was formed.

<Metal oxide semiconductor layer formation and subsequent steps>
A TiO ₂ paste (Solaronix Ti-Nanoxide T) was applied several times to a dry film thickness of 10 μm, dried, applied to a size of 10 cm × 10 cm square on the transparent conductive layer, and then 130 ° C. by a press molding machine. And 9.8 × 10 ⁸ Pa for 1 minute to form a porous metal oxide semiconductor layer.

  Next, after preparing a dye solution in which 0.1 part by weight of dye 2-1 was dissolved in 200 parts by weight of acetonitrile: t-butanol = 1: 1 solution, the metal oxide semiconductor layer was immersed in the substrate for 24 hours. Then, it was washed with an acetonitrile: t-butanol = 1: 1 solution and dried to prepare a semiconductor electrode in which a dye was adsorbed on the metal oxide semiconductor layer.

  As a counter electrode, a sheet resistance of 0.8 Ω / sq. Coated with a 10 nm thick platinum film on the ITO surface of a polyethylene terephthalate (PET) film having a thickness of 400 μm and a surface resistance of 15 Ω / sq. The conductive film of □ was used.

  The semiconductor electrode and the counter electrode are bonded to each other by using a 25 μm thick sheet-like spacer / sealing material (SX-1170-25 manufactured by SOLARONIX) having a 6.5 mm square hole, and provided on the cathode electrode. From the electrolyte injection hole, lithium iodide, iodine, 1,2-dimethyl-3-propylimidazolium iodide, and t-butylpyridine were prepared using acetonitrile as a solvent at a concentration of 0.1 mol / L,. A charge transfer layer containing a redox electrolyte dissolved so as to be 05 mol / L, 0.6 mol / L, and 0.5 mol / L is injected, the hole is closed with a hot bond, and the sealing agent is added from above. And sealed.

  An antireflection film (Konica Minolta Op hard coat / antireflection type cellulose film) was bonded to the light-receiving surface side of the base material having the metal oxide semiconductor electrode to prepare a dye-sensitized solar cell SC-01.

<< Preparation of dye-sensitized solar cell SC-02 >>
The production of the dye-sensitized solar cell SC-01 was performed in the same manner as the dye-sensitized solar cell SC-01 except that the transparent conductive layer coating solution was changed from TC-01 to TC-02. Solar cell SC-02 was produced.

<< Preparation of dye-sensitized solar cell SC-03 >>
In the production of the dye-sensitized solar cell SC-02, the dye-sensitized solar cell SC was formed except that a metal oxide intermediate layer was formed between the transparent conductive layer and the metal oxide semiconductor layer by the following formation method. Dye-sensitized solar cell SC-03 was produced in the same manner as in Example 02.

<Formation of metal oxide intermediate layer>
Using the apparatus described in Japanese Patent Application Laid-Open No. 2004-256920, a metal oxide intermediate layer made of titanium oxide having a size of 10 cm × 10 cm square was formed on the transparent conductive layer by an aerosol deposition method. The film thickness was 172 μm and the porosity was 16%.

<< Preparation of dye-sensitized solar cell SC-04-12 >>
When forming the transparent conductive layer coating solution and further the metal oxide intermediate layer, the composition and the porosity are changed as shown in Table 1, as in the dye-sensitized solar cells SC-01 to 03. It produced and dye-sensitized solar cell SC-04-12 was produced.

  The porosity of the metal oxide intermediate layer was controlled by adjusting the gas pressure of the gas cylinder and the exhaust amount of the exhaust pump.

[Evaluation]
<< Evaluation of photoelectric conversion characteristics of solar cells >>
Each of the solar cells SC-01 to SC-12 obtained above was irradiated with light having an intensity of 100 mW / m ² by a solar simulator (manufactured by JASCO (JASCO), low energy spectral sensitivity measuring device CEP-25). The short-circuit current density Jsc (mA / cm ² ), the open-circuit voltage value Voc (V), the shape factor (fill factor ff), and the conversion efficiency η (%) were determined and shown in Table 1. The indicated value was an average value of measurement results obtained by producing and evaluating three solar cells having the same configuration and production method.

<< Durability evaluation of solar cells >>
Each of the solar cells SC-01 to SC-12 obtained above was subjected to 5 cycles of temperature / humidity change (-40 ° C to 90 ° C, relative humidity 85%) corresponding to the temperature / humidity cycle test A-2 of JIS standard C8938. And before and after that, photoelectric conversion efficiency (eta) (%) was calculated | required with the above-mentioned measuring method. The photoelectric conversion efficiency after the temperature / humidity cycle execution relative to the photoelectric conversion efficiency before the temperature / humidity cycle execution was calculated for each solar cell and shown in Table 1. The indicated value was an average value of measurement results obtained by producing and evaluating three solar cells having the same configuration and production method.

  As is clear from Table 1, in the dye-sensitized solar cells SC-04 to SC-12 of the present invention, the photoelectric conversion efficiency is improved particularly by increasing the short-circuit current, and in the case of a large area (10 cm × A remarkable effect is also exhibited at 10 cm square). Furthermore, in the sample in which a thin layer other than silver is formed on the metal nanowire and the sample in which the metal oxide intermediate layer is provided, the durability is remarkably improved. In particular, a significant improvement was confirmed by optimally controlling the porosity of the metal oxide intermediate layer.

  As a result, the dye-sensitized solar cell of the present invention has excellent photoelectric conversion efficiency even when fired at a low temperature (press molding at 130 ° C.), and is suitable when a resin film substrate is used. It is clear that a remarkable effect is exhibited even in a large area.

Claims (6)

A dye-sensitized solar cell having, on a transparent substrate, a transparent conductive layer, a metal oxide semiconductor layer having a dye adsorbed on its surface, a charge transfer layer, and a counter electrode in order, The dye-sensitized solar cell, wherein the conductive layer contains metal nanowires as a conductive material. The dye-sensitized solar cell according to claim 1, wherein the metal nanowire is a silver nanowire or a metal nanowire containing silver. 3. The dye-sensitized solar cell according to claim 1, wherein the metal nanowire has an average minor axis diameter of 30 nm to 200 nm and an average major axis diameter of 1 μm to 20 μm. The metal oxide intermediate layer composed of a metal oxide is provided between the transparent conductive layer and the metal oxide semiconductor layer, according to any one of claims 1 to 3. The dye-sensitized solar cell described. The dye-sensitized solar cell according to claim 4, wherein the metal oxide intermediate layer has a porosity of 10% or less. The dye-sensitized solar cell according to any one of claims 1 to 5, wherein the transparent conductive layer further contains a conductive polymer.