JP4721643B2 - Composition for forming conductive coating, electrode for dye-sensitized photovoltaic cell using the same, and photovoltaic cell using the electrode for dye-sensitized photovoltaic cell - Google Patents

Description

  The present invention relates to a composition for forming a conductive coating that is suitably used as an electrode, particularly as an electrode for a photovoltaic cell, an electrode using the conductive composition, and a photovoltaic cell using the electrode.

  In general, from the viewpoint of durability and efficiency, solid-state devices using silicon pn junction semiconductors or compound semiconductors are the mainstream in photoelectric conversion means, and even solar cells aiming at high energy conversion efficiency have so far been single. Many photovoltaic cells using solid junctions such as crystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride, and indium copper selenide are known.

  However, photovoltaic cells that use these solid junctions generally require high temperatures when manufacturing their elements, and require film formation and lamination using vacuum technology, so that a great deal of energy must be consumed. , The amount of carbon dioxide emission is large, and there is a big risk in terms of environmental load.

  In addition, amorphous silicon solar cells, which are promising in terms of cost in order to spread as consumer products, can use visible light up to 800 nm against sunlight, and also provide an energy conversion efficiency of nearly 10%. However, the risk similar to the above cannot be avoided in that the vacuum deposition technique is indispensable for the production.

On the other hand, photosynthesis by natural biomass is a complete environmental circulation type energy conversion system, and it is known to convert sunlight with an efficiency of up to about 1%. This system has the advantage that the energy conversion efficiency is lower than that of the amorphous silicon solar cell, but it does not pose a risk of environmental burden.
However, since this system depends on the biological cycle, it has a drawback that it cannot supply a stable output over a long period of time unlike an amorphous silicon solar cell.

  By the way, recently, a photoelectric conversion element using dye-sensitized semiconductor fine particles has been proposed (see Non-Patent Document 1 and Patent Document 1), and has attracted attention as a wet solar cell using photosynthesis as a model. In this photoelectric conversion element, for example, a titanium dioxide porous thin film sensitized with a dye such as ruthenium complex having excellent light resistance is used as a light absorber, and there is an advantage of low cost. Since the redox electrolyte solution is used, there is a drawback that the sustainability is inevitably lowered due to a reduction in the stability of the redox agent or an external leakage of the electrolyte solution.

  In addition, since this light absorber is carried on a hard transparent substrate such as a glass plate, it cannot be used as a bendable material, and the application is naturally limited. For these reasons, wet solar cells have not yet reached the stage of practical use, despite their great feasibility in terms of environmental load suppression and environmental circulation.

  By the way, a photovoltaic cell such as a solar cell is usually composed of two opposing electrodes and an electrolytic solution. Conventionally, an ITO-PET film having a low resistance value is used as an electrode material of the photovoltaic cell, and the photovoltaic cell is made into a plastic film. Attempts have been made to propose a method of forming an electrode by supporting a semiconductor layer on a plastic film electrode at a temperature lower than the softening temperature of the plastic (see Non-Patent Document 2).

  However, the types of plastic electrodes that can be used for the counter electrode of the dye-sensitized semiconductor electrode are limited, and plastic films in which a noble metal such as platinum that is chemically stable has been deposited on the surface are known so far. This has a cost disadvantage and is not suitable for practical use.

  By the way, among the plastic supports that can be coated as a conductive film at a relatively low temperature, a metal thin film such as aluminum or silver can give the lowest surface resistance. It is only known, especially when optical transparency is required in addition to low resistance, and this is used exclusively. For example, an ITO film having a resistance value of 50Ω / □ or less is supported on a transparent plastic support. A radio wave absorber has been proposed (see Patent Document 2).

  Although the transparent conductive film in which the ITO film having such a low resistance value is supported on a plastic film such as PET or PEN can be used for various applications as an electrode, the surface resistance value thereof is aluminum. Compared with metal thin films such as silver and silver, the electrode materials and current collecting materials are still not fully satisfactory.

  If this ITO film surface is coated with a metal thin film, it is possible to reduce the surface resistance value. However, if such a metal thin film is used for contact with an electrolyte such as a battery, surface oxidation by an electrochemical reaction may occur. And suffer from the disadvantage of causing corrosion.

  On the other hand, in the case of a conductive electrode having a low activity for electrochemical redox reaction, for example, an electrode having tin oxide or indium tin oxide (ITO) as a conductive layer, the surface of the electrode is modified with a carbon material or a conductive polymer. It is known to be activated by this.

  For example, the performance of a dye-sensitized solar cell using an iodine redox electrolyte can be improved by using a counter electrode having carbon nanotubes supported on the surface (see Non-Patent Document 3), and a conductive polymer can be used as a counter electrode. It has been reported that the photoelectric conversion characteristics of a dye-sensitized solar cell are improved by coating the surface (see Non-Patent Document 4).

  Thus, the possibility of using low-cost carbon-based electrodes and conductive polymer electrodes instead of high-cost platinum electrodes is increasing. However, batteries using these electrode materials have high resistance at the electrode interface. Still, sufficiently high power and energy efficiency have not been obtained. The reason why the performance of these electrode materials is significantly inferior to that of platinum electrodes is considered to be due to the fact that the catalytic effect of the oxidation-reduction reaction is insufficient in addition to the low conductivity.

  For this reason, with respect to the carbon-based electrode material, it is an important issue to reduce the resistance at the electrode interface and to increase the catalytic effect of the oxidation-reduction reaction so as to have performance comparable to that of the platinum electrode.

US Pat. No. 4,927,721 (Claims and others) JP-A-11-150393 (Claims and others) “Nature”, Volume 353, 1991, p. 737-740 “Chemist Letters”, 2002, p1250. “Chemist Letters”, 2003, p. 28-29. "Chemist Letters", 2002, p1060-1061.

  In view of the circumstances described above, an object of the present invention is to provide a conductive coating forming composition having excellent surface adhesion to an electrode substrate for providing a carbon-based conductive material having high performance comparable to that of a platinum electrode. It was made as.

  As a result of intensive studies to improve the performance of the carbon-based electrode material, the present inventors have found that an inorganic fine particle component composed of a carbon material having a predetermined size and a metal chalcogenide having a predetermined size is used as a polymer binder. It has been found that a composition that provides a conductive coating with excellent electrode performance and good adhesion to the electrode substrate can be obtained by containing it together with the components, and the present invention has been made based on this finding.

  That is, the present invention is a composition for forming a conductive coating carried on a conductive electrode substrate of an electrode for a dye-sensitized photovoltaic cell, and (A) the sphere-converted average particle diameter of primary particles is 5 to 500 nm. A conductive coating-forming composition comprising: a carbon material; and (B) an inorganic fine particle component comprising a metal chalcogenide having a sphere-converted average particle diameter of primary particles of 5 to 500 nm, and (C) a polymer binder component, Electrode for dye-sensitized photocell characterized in that a thin layer of this composition is supported on a conductive electrode substrate, and electrode and dye-sensitized semiconductor in which a thin layer of this composition is supported on a plastic electrode substrate The present invention provides a photovoltaic cell having an ion conductive electrolyte layer interposed between electrodes.

  The “sphere-converted average particle diameter of primary particles” in the above component (A) and component (B) is a factor for specifying the size of the fine particle component, and each particle has a true spherical shape. When it is assumed, it means a size corresponding to the diameter of the particle. And in the case of spherical or the shape of fine granular graphite, the average value of the lengths in the x, y and z axis directions may be used, but in the case of elongated particles such as carbon nanotubes. Is obtained as follows.

That is, assuming that the cross-sectional area of this granule is S and the length is l, the volume V is S · l.
On the other hand, the volume of a sphere is V = (π / 6) d ^{3 where} d is its diameter.
Therefore, the sphere equivalent average particle diameter of the above-mentioned granules is
(Π / 6) d ³ = S · l
d = [(6 / π) · S · l] ^1/3
become.

Next, the present invention will be described in more detail.
The carbon material used as the component (A) of the present invention reduces the electrical resistance by imparting conductivity to the electrode surface, and increases the activity of the redox reaction when used at the interface in contact with the ionic electrolyte. belongs to. This carbon material also plays a role of protecting the electrode surface from chemically and electrochemically stable properties.

  Examples of such a carbon material include graphites (graphite), carbon black, coke, carbon fiber, carbon nanotube, and fullerene. These may be used singly or in combination of two or more. Examples of the graphite include natural graphite, fibrous graphite, artificial graphite such as mesophase carbon microbeads (MCMB), and non-graphitizable carbon such as polyacene. Carbon black includes channel black, furnace black, acetylene black, thermal black, ketjen black and the like.

  These carbon materials are used in the form of fine particles, but the fine particle size distribution may be monodispersed or polydispersed. Moreover, you may form the secondary particle which the primary particle with small size aggregated. Here, the primary particle means a carbon material particle or an aggregated carbon particle which exists alone without being aggregated. The primary particle of the carbon material in the present invention needs to have an average particle diameter in terms of sphere of each particle of 5 to 500 nm. The preferable range of the sphere-converted average particle diameter of this carbon material is 5 to 200 nm, particularly 5 to 100 nm.

  Preferred as the carbon material used as the component (A) in the present invention is graphite ultrafine particles, carbon nanotubes, and a mixture thereof. The ultrafine particles of graphite may be crystalline or may contain an amorphous carbon structure with low crystallinity. Carbon nanotubes may be single-walled or multi-walled. The carbon nanotubes preferably have a diameter of 1 to 50 nm and a length of 20 to 500 nm. In addition, carbon nanotubes that are partly modified with organic compounds, those that contain metal atoms or clusters in the structure, or those that are complex (hybrid) with various organic or inorganic compounds can be used. .

About these carbon materials, it is preferable that the specific surface area by BET method is 500-10000 m < ² > / g, especially 1000-10000 m < ² > / g. Moreover, about graphite (graphite), it is preferable that the specific surface area by BET method is 2000-10000 m < ² > / g.

  As the component (A) of the present invention, for the purpose of enhancing the activity as an electrode material, a metal material having a catalytic function such as platinum or palladium is added to the above carbon material, or a composite material is added. Can be used. So-called platinum activated carbon (such as platinum activated graphite) can be used.

  The metal chalcogenide used as the component (B) of the present invention increases the oxidation-reduction reaction at the interface between the ionic electrolyte and the electrode, or increases the transfer rate of electrons and holes, and promotes the reaction. These metal chalcogenides may have any shape such as a sphere, a polyhedron, a tube, and a porous body. The size of the component (B) may be monodispersed or polydispersed, but the primary particles have a sphere equivalent average particle diameter of 5 to 500 nm, preferably 5 to 200 nm, particularly 5 to 100 nm. A range of nanoparticles is selected.

  As a metal element constituting such a metal chalcogenide, an element capable of forming ultrafine particles or nanoparticles having a small average size is preferable, and typical elements such as Al, Ge, In, Sn, and B, Mg, Ca, In addition to transition metals such as alkali metals such as Sr, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Mo, Ru, W, Pd, and Ir, elements such as Ce, Nd, Sm, and Eu Can also be used.

Among metal chalcogenides, metal oxides, particularly metal oxides having properties as a semiconductor are preferable. Here, the term “semiconductor” means a material in which the concentration of carriers involved in conduction (electrons in the n-type) is in the range of 10 ¹⁴ to 10 ²⁰ / cm ³ .

Examples of such a metal oxide semiconductor include oxides such as Ti, Sn, Zn, Fe, Cu, W, Zr, Sr, In, Ce, Y, La, V, and Nb. Preferred examples of the metal oxide semiconductor include TiO ₂ , TiSrO ₃ , ZnO, Nb ₂ O ₃ , SnO ₂ , WO ₃ , V ₂ O ₅ , CuO, and In ₂ O ₃ . In the present invention, it is particularly preferable to use an n-type semiconductor among metal oxide semiconductors. Preferred as the n-type semiconductor of this metal oxide are titanium oxide, zinc oxide, and tin oxide, and more preferred is titanium oxide.

As the component (B) of the present invention, metal chalcogenides other than metal oxides can also be used. Preferred as such metal chalcogenides are those having semiconductor properties. Examples include sulfides of Cd, Zn, Fe, Cu, Pb, Ag, Sb, In, Bi, selenides of Zn, Sn, Cd, Pb, phosphides of Zn, Ga, In, Cd, etc. Is mentioned. Preferred semiconductors are CdS, CdSe, ZnS, ZnSe, SnSe, FeS ₂ , PbS, InP, GaAs, CuInS ₂ , CuInSe ₂ and the like. As the component (B), other inorganic fine particles, for example, a metal halide such as copper iodide can be added to the metal chalcogenide. Further, two or more of the above inorganic fine particles may be mixed or combined.

The fine particles of the metal chalcogenide used as the component (B) of the present invention may be prepared by a known method such as a sol-gel method, a high temperature hydrolysis method of a metal chloride, a sulfuric acid method, a chlorine method, a metal halide or a metal alkoxide in the gas phase. It can be produced by a gas phase synthesis method that thermally decomposes at a high temperature.
In the present invention, the content ratio of the component (A) and the component (B) is selected in the range of 1: 2 to 1:10.

  Next, as the polymer binder of the component (C) of the present invention, a hydrophilic or hydrophobic polymer or copolymer is used. Examples of such materials include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, polytrifluoroethylene chloride, acrylonitrile-butadiene-styrene copolymer, polyester, polyamide, and polycarbonate. Etc.

  Besides, thermoplastic resins such as polyvinyl chloride resin, polyethylene resin, polypropylene resin, polystyrene resin, ABS resin, vinyl chloride elastomer, polyolefin elastomer, polyester elastomer, styrene elastomer, chlorinated polyethylene, ethylene-ethyl acrylate Thermoplastic elastomers such as copolymers, ethylene-vinyl acetate copolymers or cross-linked products thereof, natural rubber, styrene butadiene rubber, butyl rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, chloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene Rubbers such as rubber, acrylic rubber, epichlorohydrin rubber, silicone rubber, fluororubber, or cross-linked products thereof can also be used.

  As the polymer binder component of the component (C) in the present invention, a conductive polymer can be used in addition to the insulating polymer. Examples of such a polymer include polyacetylene-based, polypyrrole-based, polythiophene-based, polyphenylene-based, and polyphenylene vinylene-based polymers.

  In the present invention, it is particularly preferable to use a conductive polymer as the component (C). And what is preferable as a conductive polymer is polythiophene and its derivatives. Of these, polyethylenedioxythiophene (PEDOT) and its derivatives are particularly preferable. Further, various copolymers including PEDOT, for example, a copolymer of PEDOT and polystyrene sulfonic acid (PEDOT-PSS) are preferable because of excellent solubility. In addition, PEDOT doped with a toluenesulfonic acid group (PEDOT-TsO) is also preferable because of its high electrode activation effect.

  The polymer binder used as the component (C) of the present invention is blended in the range of 5 to 65 mass%, preferably 10 to 50 mass%, based on the mass of the total composition.

  The conductive coating forming composition of the present invention is dispersed in a dispersing solvent and used in the form of a coating solution. In this case, water, alcohol or a mixture thereof is used as a dispersion solvent. In addition, carbonates such as propylene carbonate, nitriles such as propionitrile, γ-butyrolactone, α-methyl-γ-butyrolactone, Lactones such as β-methyl-γ-butyrolactone, γ-valerolactone, 3-methyl-γ-valerolactone, sulfoxides such as dimethyl sulfoxide and diethyl sulfoxide, amides such as dimethylformamide and diethylformamide, N-methylpyrrolidone Various polar organic solvents containing pyrrolidones such as pyrrolidones and the like, and nonpolar organic solvents containing aromatics such as alkyl halides and toluene can be used. If necessary, a surfactant may be added to the dispersing solvent as a dispersion aid.

Next, an electrode manufactured using the composition for forming a conductive coating will be described with reference to the accompanying drawings.
FIG. 1 and FIG. 2 show an example of a laminated structure of electrodes prepared by coating the surface of the electrode substrate with the above-described conductive coating forming composition. That is, a thin layer of the composition for forming a conductive coating is laminated on an electrode substrate in which a layer 2 of a conductive material having a sufficiently small electrical non-resistance is formed on a support 1 such as glass or plastic. ing. The thin layer of this composition has a structure in which fine particles 4 of metal chalcogenide are dispersed in a matrix 3 composed of a carbon material (A) and a polymer binder (C). In FIG. 1, the metal chalcogenide is uniformly distributed throughout the thin layer. In FIG. 2, the metal chalcogenide is distributed more on the surface of the thin layer. In the structure of FIG. 2, the surface of the electrode is uneven, and the surface roughness coefficient is high.

  This electrode is produced by adding the conductive coating forming composition to a dispersion solvent to form a paste, applying the paste to a conductive electrode substrate, and then evaporating and removing the dispersion solvent. As a coating method of the coating liquid at this time, a general coating method such as a coating method, a dip coating method, a spin coating method, a spray coating method, a screen printing method, an ink jet method, or the like can be used as a coating method.

About this coating liquid, it prepares so that the density | concentration of a polymer binder component may be 0.3-10 mass%, Preferably it is 0.5-5 mass%, More preferably, it is the range of 1-5 mass%.
The polymer binder component serves as an adhesive for fixing the carbon material (A) and the metal chalcogenide (B) with good adhesion on the substrate.

  In the above-mentioned composition for forming a conductive coating supported on an electrode substrate, the carbon material of component (A) is preferably selected from ultrafine graphite particles, carbon nanotubes, and mixtures thereof. The inorganic fine particles of component (B) are preferably metal chalcogenide semiconductors, particularly titanium oxide. The polymer binder of component (C) is preferably a conductive polymer material, particularly a polythiophene derivative, and the content thereof is preferably in the range of 5 to 65% by mass based on the mass of the total composition.

The surface of the thin layer of the conductive composition carried on the electrode substrate can be subjected to various surface modification treatments including hydrophilization treatment by methods such as plasma treatment, corona discharge treatment, and ultraviolet ozone treatment. . Furthermore, various organic compounds and inorganic compounds can be doped on the thin layer of the conductive composition, or the surface can be subjected to surface modification treatment by chemical bonding or physical and chemical adsorption on the surface of the conductive layer. .
In addition, the thin layer of the conductive composition is filled with processing aids, lubricants, conductivity-imparting agents, melt viscosity modifiers, plasticizers, liquid polymers, tacking agents, and fillers that are usually used in the rubber plastic field as desired. You may add compounding agents, such as an agent, in the range which can maintain electroconductivity.

The thin layer of the conductive composition carried on the electrode substrate has a surface roughness coefficient of 2 or more, preferably 5 or more, more preferably 20 or more. The surface roughness factor R of the electrode means the ratio of the actual surface area of the electrode material to the projected area of the electrode. This ratio is represented by R = SM using the specific surface area S (m ² / g) of the electrode material and the amount M (g / m ² ) of the electrode material supported on the electrode substrate.

The thin layer of the conductive composition carried on the electrode substrate preferably has a thickness of 0.02 to 100 μm, particularly 0.05 to 20 μm.
Moreover, it is particularly preferable that the thin layer of the conductive composition covers the surface of the conductive layer of the underlying electrode substrate with a coverage of 60% or more, particularly 80% or more. Most preferably, the coverage is substantially 100%. This coverage can be obtained by a method of observing the surface structure using a laser optical microscope, a scanning electron microscope (SEM), a probe microscope, etc., and calculating the ratio of the projected area where the carbon material covers the conductive film. . The coverage can also be evaluated by obtaining the elemental ratio of carbon by surface elemental analysis using SEM-EDX.

  Further, the thin layer of the conductive composition formed on the substrate preferably has a sheet resistance in the range of 2 to 500 Ω / □, particularly in the range of 2 to 200 Ω / □.

  The electrode thus obtained is suitable for use as an electrode of an electrochemical cell using an ionic electrolyte as an electrolyte, particularly as a cathode of an electrochemical cell. The cathode is an electrode that performs a reduction reaction with ions in the electrolytic solution, and means an electrode that acts as a positive electrode.

  In this case, the type of the electrode substrate to be used is not particularly limited, but the electrode activity can be enhanced by using an electrode made of a conductive material having a low oxidation-reduction activity. As an electrode substrate suitable for its purpose and application, an electrode using a metal oxide conductive layer such as tin oxide or indium tin oxide (ITO), a metal current collector using titanium, stainless steel, tantalum or the like can be mentioned. . Among these, an electrode substrate made of a transparent conductive layer whose conductive material is selected from tin oxide and indium tin oxide (ITO) is most suitable.

  As the support material for the electrode substrate of the electrode of the present invention, metal, plastic, resin and the like are used, and there is no particular limitation on the kind thereof, but a flexible substrate in that it is transported as a roll or supplied to the production process. Most preferably, is used. Such a support is a plastic support.

  The plastic support is also required when plasticizing these optical elements while using the electrode of the present invention in a photoelectric conversion element such as a dye-sensitized photovoltaic cell or an organic light emitting element. As the kind of the support, those excellent in heat resistance, chemical resistance, workability, and light transmittance are preferable, the glass transition point is 100 ° C. or higher, preferably 120 ° C. or higher, and the light transmittance is the wavelength. A plastic having 50% or more at 420 nm and 70% or more at a wavelength of 500 nm is preferable.

  Examples of such plastics include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), tetraacetyl cellulose (TAC), polyester sulfone (PES), polyphenylene sulfide (PPS), polycarbonate (PC), and polyarylate (PAr). ), Polysulfone (PSF), polyetherimide (PEI), polyacetal, transparent polyimide-based polymer, polyethersulfone, and the like. Of these, polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) are particularly preferred, including the cost.

  The plastic support constituting the electrode of the present invention has a thickness of 50 to 500 μm, preferably 100 to 200 μm. This plastic film electrode preferably has a total thickness of 50 to 500 μm.

  The electrode of the present invention is most effective when used as an electrochemical electrode in an electrochemical cell and bonded to an ion conductive electrolyte. Therefore, it is suitable for use as an electrode of an electrochemical cell. In particular, the electrode of the present invention is suitable as a counter electrode (cathode) for a dye-sensitized photovoltaic cell and a photovoltaic cell such as a dye-sensitized solar cell that are combined with an ion-conductive electrolyte and combined with a dye-sensitized semiconductor electrode. is there.

  According to the present invention, it is possible to form a conductive coating having an excellent catalytic effect on a high conductive redox reaction compared to conventional carbon-based conductive materials, and when used as an electrode of a photovoltaic cell, a sufficiently high output and Energy effect can be obtained.

  Next, the best mode for carrying out the present invention will be described by way of examples.

  Fine particle powder of graphite with a sphere-converted average particle diameter of primary particles of 30 nm, and crystalline nanoparticles of titanium dioxide with a sphere-converted average particle diameter of primary particles of 25 nm (made by Showa Denko KK, rutile content 20%) by a vibration mill The mixture was uniformly mixed, and the mixture was heat-treated in air at 300 ° C. for 20 minutes. A conductive polymer solution was prepared by adding 5 times the amount of t-butanol to an aqueous solution of the conductive polymer polythiophene derivative PEDOT-PSS and mixing them.

  The above mixture of graphite and titanium dioxide was added to this solution, and the mixture was uniformly dispersed and mixed using a rotating and rotating mixer to prepare a paste. The content of graphite fine particles in the paste was 0.8% by mass, and the content of titanium dioxide particles was 4.8% by mass. Moreover, the content of PEDOT-PSS was changed in the range of 0.1 mass% to 15 mass%.

  Next, in place of titanium dioxide, as inorganic ultrafine particles, aluminum oxide (average particle size: about 50 nm), tin dioxide (average particle size: about 40 nm), zinc oxide (average particle size: about 40 nm) Were used, and the particles were mixed in the same manner to prepare a paste containing graphite.

  For comparison, the primary particles have a sphere-converted average particle size of about 0.4 μm (400 nm), a graphite powder having a particle size of about 0.6 μm (600 nm), and the primary particles have a sphere-converted average particle size of about 0.001. A paste was prepared in the same manner using titanium dioxide of 3 μm (300 nm) and about 0.6 μm (600 nm).

  Multi-walled carbon nanotubes having an outer diameter of about 20 nm and an aspect ratio of about 30 were mechanically pulverized to prepare carbon nanotubes having a spherical equivalent particle diameter of about 50 nm. This nanotube was mixed with crystalline nanoparticles of titanium dioxide having a sphere-converted average particle diameter of primary particles of 25 nm (Showa Denko KK, rutile content 20%), and the mixture was heat-treated at 300 ° C. in air for 20 minutes. It was.

  To the solution containing the conductive polymer polythiophene derivative PEDOT-PSS prepared as described above as a binder, a mixture of carbon nanotubes and titanium dioxide is added and uniformly dispersed and mixed using a rotating and rotating mixer. A paste having a binder content of 0.2% by mass was prepared. The carbon nanotube content in the paste was 1.5% by mass, and the content of titanium dioxide particles was 6.0% by mass.

  A PET film (surface resistance 15Ω / □, thickness 190 μm) carrying a conductive ITO film on one side was used as an electrode substrate, the substrate was washed with acetone, and then the ITO surface was washed with an ultraviolet ozone cleaner. On the ITO film of this electrode substrate, the conductive composition containing carbon prepared as described above was applied by a doctor blade method, the coated film was dried at 60 ° C. for 20 minutes, and further, 20 ° C. at 150 ° C. on a hot plate. A heat treatment was performed for 5 minutes to form a thin conductive solid layer having a thickness of 5 to 7 μm.

  For comparison, instead of the ITO-PET film that does not carry these conductive thin layers and the conductive film containing carbon, a platinum film was deposited on the ITO film with a thickness of 100 nm by a vacuum sputtering method. An electrode was produced.

  FTO film of glass substrate (thickness 0.9 mm) coated with a conductive film of fluorine-doped tin dioxide (FTO) on a viscous commercial paste (Solaronix, Nanoxide D) containing titanium dioxide nanoparticles and polymer binder The coating was applied on top by a doctor blade method, and the coating film was dried at room temperature and then baked in an electric furnace at 550 ° C. for 30 minutes to form a porous titanium dioxide film having a thickness of 12 μm on FTO glass. This titanium dioxide FTO glass electrode was immersed in a 0.3 mM solution of Ru complex dye (Solaronix, Ru535bisTBA) (t-butanol: acetonitrile = 1: 1 mixed solvent) at 40 ° C. for 30 minutes with stirring. Dye sensitization was performed. The dye-sensitized electrode thus prepared was used as the working electrode (anode) of the solar cell.

  Next, an ITO-PET film electrode coated with various conductive films containing carbon prepared as described above is used as a counter electrode (cathode) and combined with the above common working electrode (anode), and dye-sensitized solar A battery was manufactured. In this case, the electrolyte solution is 0.1M lithium iodide as a reducing agent, 0.05M iodine as an oxidizing agent, 0.6M dimethylpropylimidazolium iodide as an additive, and methoxyacetonitrile containing 0.5M t-butylpyridine. The solution was used.

Next, the above dye-sensitized working electrode (anode) and the plastic counter electrode (cathode) are sandwiched through a thermocompression-bonding resin film having a thickness of 50 μm while the separator porous film is inserted between the electrode surfaces. After pouring electrolyte between the electrodes, both electrodes were sealed by thermocompression bonding. In this manner, a dye-sensitized photovoltaic cell having a light receiving area of 0.64 cm ² using a plastic ITO-PET electrode substrate as a counter electrode was manufactured.

The battery thus obtained was irradiated with white light having a light amount of 100 mW / cm ² using a xenon lamp simulated sunlight irradiation system, and the photocurrent-voltage characteristics were measured.
Table 1 shows the contents of various conductive compositions prepared in this example, and the performance of batteries made using the compositions on the surface of the counter electrode. Table 1 also shows the adhesion strength of the conductive film to the ITO surface in the ITO-PET counter electrode carrying the conductive composition as a conductive film, in addition to the photocurrent and energy conversion efficiency indicating the photoelectric conversion performance of the battery. The adhesion strength was evaluated in three stages of 1 (strong), 2 (medium), and 3 (poor) by a peel resistance test using an adhesive tape.

From this result, in the battery using the ITO-PET film electrode that does not carry the conductive coating forming composition of the present invention as a conductive film as a counter electrode (cathode), only a slight photocurrent can be obtained, and substantially. It turns out that it does not function as a photoelectric conversion element.
On the other hand, in all the batteries carrying the conductive coating forming composition of the present invention, the photocurrent was improved and a basic photoelectric conversion function was obtained.

  However, in the case of using a composition in which the average particle size of the carbon material and the average particle size of the inorganic fine particles (metal oxide) are outside the scope of the present invention, the photocurrent is small and the photoelectric conversion efficiency is comparative platinum. The level of the coated ITO-PET counter electrode has not been reached, or the adhesion strength of the conductive film to the ITO-PET surface is low.

  On the other hand, a counter electrode produced using a conductive coating forming composition comprising particles having a sufficiently small average particle size has performance equivalent to or better than that of a platinum-coated counter electrode. In particular, the highest photoelectric conversion performance can be obtained with a composition using titanium dioxide nanoparticles as inorganic fine particles (metal oxide) and a composition for forming a conductive coating using ultrafine particles of graphite and nanotubes as carbon materials.

  A conductive coating composition comprising an ultrafine particle of a carbon material having an average particle size of 5 to 500 nm and an ultrafine particle of an inorganic material composed of a metal oxide or a metal chalcogenide, in particular, a nanoparticle dispersed in a polymer binder material, Provided is an electrode that is useful as a conductive paste, activates the surface of an electrode when used on an electrode substrate, and provides high redox activity particularly in an electrochemical cell.

Sectional drawing which shows an example of the structure of the electrode obtained using the composition for conductive coating formation of this invention. Sectional drawing of the example different from FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Support body 2 Conductive film 3 Conductive thin layer 4 Inorganic fine particle

Claims (18)

A composition for forming a conductive coating carried on a conductive electrode substrate of an electrode for a dye-sensitized photovoltaic cell, comprising: (A) a carbon material having a sphere-converted average particle diameter of primary particles of 5 to 500 nm; 1) A composition for forming a conductive coating, comprising an inorganic fine particle component composed of a metal chalcogenide having a sphere-converted average particle size of primary particles of 5 to 500 nm and (C) a polymer binder component.   The composition for forming a conductive coating according to claim 1, wherein the content of the component (C) is in the range of 5 to 65% by mass based on the mass of the total composition.   The composition for forming a conductive coating according to claim 1, wherein the component (A) is finely divided graphite, carbon nanotubes, or a mixture thereof.   The composition for forming a conductive coating according to any one of claims 1 to 3, wherein the component (B) is a metal oxide.   The composition for forming a conductive coating according to claim 4, wherein the metal oxide is a semiconductor.   The composition for forming a conductive coating according to claim 4 or 5, wherein the metal oxide is titanium oxide.   The composition for forming a conductive coating according to claim 1, wherein the component (C) is a conductive polymer.   The composition for forming a conductive coating according to claim 7, wherein the conductive polymer is a polythiophene derivative. (A) An inorganic fine particle component comprising a carbon material having a sphere-converted average particle diameter of primary particles of 5 to 500 nm, and (B) a metal chalcogenide having a sphere-converted average particle diameter of 5 to 500 nm of primary particles, and (C) a polymer binder component. An electrode for a dye-sensitized photovoltaic cell , wherein a thin layer of a composition for forming a conductive coating containing s is supported on a conductive electrode substrate. The dye-sensitized photovoltaic cell electrode according to claim 9, wherein the content of the component (C) is in the range of 5 to 65% by mass based on the mass of the total composition. The dye-sensitized photovoltaic cell electrode according to claim 9 or 10, wherein the component (A) is fine-grained graphite, carbon nanotube, or a mixture thereof. The dye-sensitized photovoltaic cell electrode according to any one of claims 9 to 11, wherein the component (B) is a metal oxide. The dye-sensitized photovoltaic cell electrode according to claim 12, wherein the metal oxide is a semiconductor. The dye-sensitized photovoltaic cell electrode according to claim 12 or 13, wherein the semiconductor is titanium oxide. The electrode for a dye-sensitized photovoltaic cell according to any one of claims 9 to 14, wherein the component (C) is a polythiophene derivative. The dye-sensitized photovoltaic cell electrode according to any one of claims 9 to 15, wherein the conductive electrode substrate is a transparent conductive layer selected from tin oxide and indium tin oxide (ITO). The electrode for a dye-sensitized photovoltaic cell according to claim 9 to 16, wherein the conductive electrode substrate is a plastic electrode having a plastic as a support. Between the plastic electrode and a dye-sensitized semiconductor electrode, in the fabricated dye-sensitized photovoltaic cell by interdigitated the ionic conducting electrolyte layer, a dye-sensitized photovoltaic cell electrode according to claim 17, wherein as the plastic electrode A photovoltaic cell characterized by being used.

Images