JP2008258011A - Dye-sensitized solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dye-sensitized solar cell increasing open circuit voltage (Voc) while keeping high short circuit current (Isc) in light irradiation by improving the composition of a light reflection layer/a light scattering layer. <P>SOLUTION: The dye-sensitized solar cell is composed of an anode 1 formed by laminating at least a conductive layer 12 and a porous film layer 2, a cathode 5 facing the porous film layer 2 of the anode 1, and an electrolyte sealed between the anode 1 and the cathode 5, placed on the surface of a light permeable substrate 11, the porous film layer 2 is composed of at least a light absorbing layer 21 including fine particles on which sensitized dye is adsorbed and a light reflection layer 22 from the light permeable base material side in order, and the light reflection layer 22 mainly includes shape-anisotropic fine particles having an aspect ratio of ≥5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a dye-sensitized solar cell. More specifically, the present invention relates to a dye-sensitized solar cell having a porous membrane electrode containing tabular grains.

  Dye-sensitized solar cells have a structure that can be manufactured in a general printing process, and are expected to greatly reduce costs in terms of both materials and processes, and are attracting attention as next-generation solar cells following silicon, GaAs, and CIS systems. Collecting.

  In this dye-sensitized solar cell, the dye molecules adsorbed on the semiconductor surface absorb the sunlight, and so-called spectral enhancement is caused by electron injection from the dye LUMO (lowest orbital) to the semiconductor CB (conduction band). Do a feeling.

  Since the dye molecule is bonded to the semiconductor surface via an adsorbing group, it is generally considered to be a monomolecular layer.

  That is, in order to convert light incident on the solar cell into electrons with high efficiency, a technique for improving the light absorption ability of the dye is required.

  On the other hand, a major breakthrough was achieved by forming titanium oxide ultrafine particles as a porous film containing appropriate pores (for example, Non-Patent Document 1).

  By adsorbing a single molecule of a dye molecule on the particle surface in this porous film, the specific surface area of the light absorption / electron injection site can be increased to several thousand times, and the sunlight incident on the solar cell is efficiently used. Can be converted to electrons well.

  Electrons injected from the dye diffuse efficiently in the titanium oxide porous film and reach the transparent electrode.

  On the other hand, a dye that has lost electrons receives electrons from iodine ions in the electrolyte.

  Furthermore, the iodine ions that have passed the electrons receive the electrons on the counter electrode Pt substrate. The dye-sensitized solar cell drives an external circuit through this series of light absorption / oxidation reduction processes.

  A semiconductor electrode used for a dye-sensitized solar cell generally has a nanoporous structure mainly composed of titanium oxide.

  This titanium oxide film has a characteristic that recombination of electrons and holes, which is an electron deactivation process, is very difficult to occur depending on the amount of dye adsorbed, and is convenient for providing a charge separation function to the nanoporous structure.

  However, in order to further improve the photoelectric conversion efficiency, a new device for improving the light absorption ability of the dye is required.

  For example, it is conceivable to further reduce the particle size of titanium oxide to increase the specific surface area. However, in practice, it is most efficient to use fine titanium oxide particles of around 20 nm, and the specific surface area increases when the particle size is further reduced. However, it becomes difficult to form a nanoporous structure, and there is a trade-off relationship that the electrolyte does not diffuse efficiently into the nanoporous.

  On the other hand, it is conceivable to improve the light absorption ability by laminating the nanoporous structure of titanium oxide and increasing the film thickness. However, in the titanium oxide nanoporous film that has a long electron lifetime, A film thickness of about 8 to 15 μm is appropriate, and even if the film thickness is thicker than that, not only will the photoelectric conversion efficiency reach its peak, but the chance of recombination of electrons and holes will increase, resulting in a decrease in open circuit voltage, resulting in a result. Conversion efficiency is lowered.

  On the other hand, the light that has passed through the nanoporous film mainly composed of titanium oxide is reflected / scattered by the newly provided light reflecting layer / light scattering layer, and the light is again guided to the nano-nanoporous film with high photoelectric conversion efficiency. Techniques for reducing photoelectric conversion loss have been introduced (see, for example, Patent Documents 1 to 3).

  In addition, the particle size distribution in the nanoporous film can be reduced by the same photoelectric conversion loss reduction by mixing small particle size particles with high photoelectric conversion efficiency without light scattering and large particle size particles for light scattering purposes. The achieved technique is disclosed (for example, Patent Documents 4 to 5).

  However, in the former technique, it is necessary to stack several layers of fine particles having a particle size of several hundred nm or more on a fine nanoporous film, and there is a problem that the conversion efficiency is limited for the above reason.

Moreover, since the latter technique mixes large particle size particles in the nanoporous film, it is difficult to achieve both excellent light absorption ability and improvement in photoelectric conversion efficiency.
Nature 353, 24 (1991) 737 JP-A-10-255863 JP 2001-93591 A JP 2002-222968 A JP 2001-196104 A JP 2002-93475 A

  The present invention has been made in order to solve the conventional problems as described above, and an object of the present invention is to devise the structure of the light reflection layer / light scattering layer, so that a high short-circuit current during light irradiation ( An object of the present invention is to provide a dye-sensitized solar cell in which the open circuit voltage (Voc) is improved while maintaining Jsc).

  The present invention solves the above-mentioned problems by optimizing the shape of the semiconductor fine particles forming the semiconductor porous film layer, and the technical disclosure is provided herein.

  Therefore, the object of the present invention is achieved by the following configuration.

  1. An anode electrode in which at least a conductive layer and a porous membrane layer are laminated on the surface of the light-transmitting substrate, a cathode electrode facing the porous membrane layer side of the anode electrode, and the anode electrode and the cathode electrode In a dye-sensitized solar cell having a configuration in which an electrolyte is sealed between electrodes, the porous film layer, in order from the light-transmitting substrate side, a light absorption layer made of fine particles adsorbing at least a sensitizing dye; and A dye-sensitized solar cell comprising a light reflecting layer, wherein the light reflecting layer mainly comprises shape anisotropic fine particles having an aspect ratio of 5 or more.

  2. 2. The dye-sensitized solar cell as described in 1 above, wherein the shape anisotropic fine particles have an aspect ratio of 10 to 100.

  3. 3. The dye-sensitized solar cell as described in 1 or 2 above, wherein the shape anisotropic fine particles have a flat plate shape.

  4). Any one of the above 1-3, wherein the shape anisotropic fine particles in the light reflecting layer have an average particle size of 200 nm to 10 μm and are larger than the average particle size of the fine particles in the light absorbing layer. The dye-sensitized solar cell according to Item.

  5. The ratio of the film thickness of the light absorption layer of the porous film layer to the film thickness of the light reflection layer is 5: 1 to 15: 1, Dye-sensitized solar cell.

  The dye-sensitized solar cell according to the present invention improves the open-circuit voltage (Voc) while maintaining a high short-circuit current (Jsc) during light irradiation by devising the configuration of the light reflection layer / light absorption layer. And has an excellent effect.

  Hereinafter, the present invention will be described in more detail.

  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 includes a light-absorbing layer 21 and a light-reflecting layer 22 each having a conductive layer 12 on a light-transmitting substrate 11 and adsorbing dye molecules 3. It comprises an anode electrode 1 having a porous membrane layer 2, a charge transfer layer (sometimes referred to as “electrolyte layer”) 4, and a counter substrate 6 having a cathode electrode 5.

  In FIG. 1, + represents a positive electrode, and-represents a negative electrode.

  When constituting the dye-sensitized solar cell of the present invention, the porous membrane layer 2, the charge transfer layer 4 and the cathode electrode 5 of the anode electrode 1 are sealed in the case with a sealant indicated by 7 in the figure. It is preferable to house and seal, or to seal them entirely with resin.

  When the solar cell of the present invention is irradiated with sunlight or an electromagnetic wave equivalent to sunlight, the dye 3 adsorbed on the porous membrane layer 2 is excited by absorbing the irradiated sunlight or electromagnetic wave.

  The electrons generated by the excitation move to the semiconductor porous membrane layer 2 and are then supplied to the external circuit via the conductive layer 12.

  On the other hand, the electrons that have moved to the cathode electrode 5 by driving the external circuit reduce the redox electrolyte of the charge transfer layer 4.

  The dye 3 that has moved electrons to the porous membrane layer 2 is an oxidant, but is reduced by being supplied with electrons from the cathode electrode 5 via the redox electrolyte of the charge transfer layer 4 and is reduced to the original. At the same time, the redox electrolyte of the charge transfer layer 4 is oxidized and returned to a state where it can be reduced again by the electrons supplied from the cathode electrode 5.

  In this way, electrons flow and the dye-sensitized solar cell of the present invention can be configured.

  Hereinafter, these will be described in more detail.

<Semiconductor porous membrane layer>
(Light reflecting layer)
The porous film layer of the present invention has at least a light absorption layer and a light reflection layer in order from the light transmissive substrate side, and the light reflection layer mainly has an aspect ratio (hereinafter sometimes abbreviated as AR). It consists of five or more shape anisotropic fine particles.

  The shape-anisotropic fine particles are characterized by having shape anisotropy such as flat plate shape, flake shape, plate shape, needle shape, columnar shape, fiber shape, rugby ball shape, spindle shape, etc. Shape, flake shape, and plate shape, and the plate shape is most preferred from the viewpoint of light reflectivity.

  The semiconductor fine particles of the present invention are characterized by having an aspect ratio of 5 or more, preferably 5 to 200, and more preferably 10 to 100.

  The reflective layer preferably has an average particle diameter of 100 nm to 10 μm for reflecting sunlight, more preferably about 200 nm to 3 μm, and most preferably about 250 nm to 2 μm from the viewpoint of reflection efficiency and conversion efficiency.

  The average particle diameter of the present invention is a circle equivalent diameter when the projected area of particles observed with a transmission electron microscope (for example, JEM-2010F type manufactured by JEOL Ltd.) is converted into a perfect circle, and the number of observed particles is 500. The average equivalent circle diameter is shown above.

  In the present invention, the aspect ratio indicates a value obtained by dividing the average particle diameter by an average thickness obtained by observing 500 or more particles from the lateral direction.

  Moreover, it is preferable that the film thickness of a light reflection layer is 0.5 micrometer-10 micrometers, More preferably, they are 1 micrometer-5 micrometers, More preferably, they are 1 micrometer-3 micrometers.

  If the thickness of the light reflecting layer is too thin, sufficient light reflectivity cannot be obtained. Conversely, if the thickness is too thick, the thickness of the porous membrane layer itself becomes too thick to inhibit the diffusion of the electrolyte. There is a possibility that the recombination chance between the injected electron and the dye hole is increased and the Voc is lowered.

  The composition of the shape anisotropic fine particles forming the light reflecting layer of the present invention is not particularly limited as long as the desired shape anisotropy is obtained, and various compounds such as metal particles, inorganic particles, organic particles, and polymer particles are used. I can do it. Preferably, the semiconductor is not affected by the electrolyte, and for further performance enhancement, it is preferable to select a semiconductor capable of adsorbing the dye in order to perform photoelectric conversion even in the light reflection layer. Moreover, in order to reflect light efficiently, it is preferable to select a composition having a high refractive index because a high light reflection effect can be obtained with a thinner layer. Specifically, it is preferable to use semiconductor fine particles, for example, increasing titanium oxide, zinc oxide, tin oxide, indium oxide, niobium oxide, tungsten oxide, zirconium oxide, strontium titanate, barium titanate, calcium titanate, etc. Among them, titanium oxide, zinc oxide, tin oxide, niobium oxide, strontium titanate are preferable in consideration of the high refractive index, the energy level of the conduction band and the adsorptivity of the dye, and more preferably titanium oxide and zinc oxide. Titanium oxide is most preferred.

In the present invention, the light reflecting layer and the light absorbing layer do not need to have the same composition, and different compositions may be selected for the purpose of enhancing functionality.
(Light absorption layer)
The light absorption layer of the present invention preferably has an average particle diameter of 5 nm to 100 nm which does not substantially scatter sunlight, and more preferably 8 nm to 80 nm, and 10 nm to 30 nm from the specific surface area and void size.

  Here, the fact that sunlight is not substantially scattered means that visible light (mainly 400 nm to 780 nm light) contained in sunlight, ultraviolet light called UVA (315 nm to 400 nm light), near infrared light to far light. It means that it is difficult to scatter spectrum light including infrared rays (light of 780 nm or more).

  This wavelength region can be classified by Mie scattering, and the scattering characteristics are affected by the wavelength of light, particle diameter, and particle refractive index. In the case of inorganic fine particles, it is generally said that scattering occurs when a particle size comparable to the wavelength is present.

  Experimentally, it can be confirmed by evaluating the haze value of the porous film according to JIS-K-7136. A preferred haze value is 0.5% to 50%, more preferably 1% to 20%, and most preferably 1% to 10%. A haze value of 10 or less is preferable because it is substantially transparent by visual observation, and light sufficiently reaches not only near the surface of the light absorption layer but also in the thickness direction.

  Regarding the semiconductor porous membrane layer of the present invention, the film thickness of the light absorption layer is preferably 5 μm to 20 μm, more preferably 8 μm to 18 μm, and 11 μm to 15 μm is most preferable because of its highest conversion efficiency.

  The light-absorbing layer of the present invention is characterized in that it is a porous layer in which a sensitizing dye is adsorbed, and its composition is that semiconductor fine particles having a valence band (VB) and conduction band (CB) band gap of around 3 eV. A metal oxide is preferable because it is easy to form a nanoporous film.

  As typical metal oxides, for example, titanium oxide, zinc oxide, tin oxide, indium oxide, niobium oxide, tungsten oxide, zirconium oxide, strontium titanate, barium titanate, calcium titanate, etc. can be raised, Of these, titanium oxide, zinc oxide, tin oxide, niobium oxide, and strontium titanate are preferable in view of the energy level of the conduction band and the adsorptivity of the dye, more preferably titanium oxide and zinc oxide, and most preferably titanium oxide.

In addition, the semiconductor fine particles forming the light absorption layer of the present invention may be configured by laminating and / or mixing two or more kinds of the above-mentioned semiconductor fine particles for the purpose of improving the performance of the dye-sensitized solar cell. A core-shell fine particle formed by coating the surface of A with the semiconductor B, or a composite material that coats the surface of the semiconductor B after forming a porous film of the semiconductor A may be used.
(Porous membrane layer)
The total film thickness of the light absorption layer and the light reflection layer of the porous film layer (hereinafter also referred to as semiconductor porous film layer) of the present invention is preferably 10 μm to 20 μm, more preferably 13 μm to 17 μm, and more preferably 14 μm to 16 μm. Most preferred.

  The film thickness ratio between the light absorption layer and the light reflection layer is preferably light absorption layer: light reflection layer = 15: 1 to 4: 1, more preferably 12: 1 to 5: 1, and 10: 1 to 6: 1. Most preferred.

  In the present invention, the particle suspension (paste) is optimally designed so that the semiconductor porous film layer after firing is preferably formed in the above-mentioned film thickness range, and is repeatedly applied in the paste application step. For example, it is preferable to ensure the film thickness.

Furthermore, when laminating the light absorption layer and the light reflection layer of the present invention, it is preferable to form them by repeated coating in the same manner.
(Semiconductor fine particles)
The method for producing the semiconductor fine particles of the present invention can be performed using a generally known technique. Fine particle forming methods are roughly classified into a vapor phase method and a liquid phase method.

  The gas phase method is a method of forming crystals from a gaseous source material, and is suitable for mass production of low-cost, high-purity particles that are easy to construct a continuous process.

  On the other hand, the liquid phase method is a method in which one kind of raw material or two or more kinds are mixed in a solution and particles are formed by utilizing the solubility change of the raw material and the product. The single jet method, double jet method, sol -Gel method, hydrothermal method, and the like can be mentioned, and they are widely used as methods for synthesizing high-quality fine particles with uniform particle shapes that are not suitable for extreme mass production.

  In addition, it is a kind of liquid phase method, such as a melt method in which raw material is melted and particles are formed by utilizing the solubility change during cooling, and a method in which it is formed in a flux salt melted at a high temperature in the same manner as the melt method. Can be mentioned.

  The semiconductor fine particles used in the light absorption layer of the present invention may be formed by any of the above methods as long as the particle size is controlled, and the particle size and purity are limited to titanium oxide. From the viewpoint of cost, sufficient performance can be obtained by vapor phase titanium oxide (for example, P25 manufactured by Degussa).

  In the porous film layer of the present invention, a liquid phase method capable of stably obtaining a monodisperse and unique particle shape is particularly preferable as a method for producing high aspect ratio fine particles for forming a light reflecting layer. A metal alkoxide hydrolysis such as a so-called hydrothermal method, which is a gel method, can be preferably used. In the present invention, a melt method in which particles are formed by rapid cooling from a high-temperature molten state, or a flux method is preferable.

  The high aspect ratio fine particles used in the light reflecting layer of the present invention can be obtained by referring to, for example, the method described in JP-A-7-155731, taking titanium oxide as an example.

In this method, the heated melt of the raw material powder is cooled to produce fibrous potassium titanate crystals [K ₂ Ti ₂ O ₅ ], which are subjected to elution treatment of K ⁺ ions and wet pulverization treatment, followed by firing treatment. By performing this, a flake-shaped titanium oxide can be obtained.

The fibrous potassium titanate crystal has a layered structure crystal in which chains of TiO ₅ triangular bipyramids are stacked, and K ⁺ ions between the layers are replaced with H ⁺ or H ₃ O ^{+ in the} depotassification process with an acid aqueous solution. It causes swelling and decontamination.

  By applying a wet pulverization treatment to this, separation of fibers and delamination between layers are promoted, and a powder of hydrated titanium oxide having a uniform flake shape can be obtained in a high yield.

  The flake-shaped fine particles that can be used in the present invention can be monodispersed and stably obtained by controlling the temperature profile in the cooling process, and the flake thickness direction can be obtained by rapid cooling. Tends to be thinner.

  In addition, the wet pulverization treatment can stably obtain flake-shaped fine particles by using a bead mill disperser (for example, Ultra Apex Mill / 50 μm diameter zirconia beads manufactured by Sakai Kogyo Co., Ltd.) in the presence of a dispersant in an aqueous solution. it can.

  Next, the manufacturing method of the semiconductor porous film of this invention is demonstrated.

As a method for producing the semiconductor porous film, it is possible to apply a known method,
(1) A method of forming a semiconductor layer by applying a suspension containing semiconductor fine particles on a conductive substrate, drying and firing,
(2) Electrophoretic electrodeposition method in which a conductive substrate is immersed in a colloidal solution, and semiconductor fine particles are adhered to the conductive substrate by electrophoresis.
(3) A method in which a foaming agent is mixed and applied to a colloidal solution or dispersion and then sintered to make it porous.
(4) After the polymer microbeads are mixed and applied, 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 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 above method (1), the particle diameter of the semiconductor fine particles in the suspension is preferably finer and is preferably present as primary particles.

  The suspension containing the semiconductor fine particles can be prepared by dispersing the semiconductor fine particles in a solvent.

  The solvent is not particularly limited as long as it can disperse the semiconductor fine particles, and includes water, an organic solvent, and a mixed solution of water and an organic solvent.

  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. In the suspension, a surfactant, a viscosity modifier (polyhydric alcohol such as polyethylene glycol), a dispersant and the like can be added as necessary. The concentration range of the semiconductor fine particles in the solvent is preferably 0.1% by mass to 70% by mass, and more preferably 0.1% by mass to 30% by mass.

  The suspension containing the semiconductor fine particles obtained as described above is applied on a conductive substrate, dried, etc., and then baked in air or in an inert gas. A metal oxide semiconductor layer is formed.

  The semiconductor porous film layer obtained by applying and drying a suspension on a conductive substrate is composed of an aggregate of semiconductor fine particles, and the particle size of the fine particles is the primary particle size of the semiconductor fine particles used. It depends. The semiconductor porous membrane layer formed on the conductive substrate is a mechanically fragile film having a weak bonding force with the conductive substrate and a bonding force between the fine particles. It is preferable to increase the mechanical strength by baking treatment to obtain a fired product film that is strongly fixed to the substrate.

  By carrying out the firing process at the same time, so-called necking due to fusion adhesion is formed between the particles, and the effect of improving the electron conductivity in the semiconductor porous film is obtained.

  In the present invention, the fired product film may have any structure, but preferably has a porous structure (also referred to as a porous layer having voids).

  Here, the porosity of the semiconductor porous membrane layer is preferably 10% by volume or less, more preferably 8% by volume or less, and particularly preferably 0.01% by volume to 5% by volume.

  The porosity of the semiconductor porous film layer means a porosity that is penetrating in the thickness direction of the dielectric, and can be measured using a commercially available device such as a mercury porosimeter (for example, Shimadzu Polarizer 9220 type). I can do it.

  The firing temperature is about 300 ° C. to 1000 ° C. However, in the case of titanium oxide, care must be taken because the crystal phase obtained varies depending on the firing temperature.

  When titanium oxide is used in the present invention, it is generally preferable to use an anatase crystal formed at a temperature of 600 ° C. or lower in order to form a photocatalytically inactive rutile crystal at a firing temperature of 900 ° C. or higher.

  The semiconductor porous membrane layer of the present invention is, for example, titanium tetrachloride for the purpose of increasing the surface area of the semiconductor fine particles after the baking treatment, and for increasing the electron conductivity between the semiconductor fine particles and the substrate electrode, or between the semiconductor fine particles. Chemical plating using an aqueous solution or electrochemical plating using a titanium trichloride aqueous solution may be performed.

<Conductive substrate>
The conductive substrate 1 used in the present invention is preferably substantially transparent, and it is important that it is a so-called transparent conductive substrate.

  “Substantially transparent” means that the light transmittance is 10% or more, preferably 50% or more, and particularly preferably 80% or more.

  As the conductive substrate, a substrate having conductivity per se, or a substrate having a conductive layer on the surface thereof can be used.

  In the latter case, it is possible to use a glass plate, a ceramic polishing plate such as titanium oxide or alumina, and various known plastic sheets as the substrate.

  Specific examples of the plastic sheet include triacetyl cellulose (TAC), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyphenylene sulfide (PPS), syndiotactic polyester (SPS), and polycarbonate (PC). , Polyarylate (PA), polyetherimide (PEI), polysulfone (PSF), polyethersulfone (PES), cyclic polyolefin, phenoxy resin, brominated phenoxy and the like.

  In FIG. 1, the conductive material used for the conductive layer 12 provided on the light-transmitting substrate 11 is an inorganic conductive material, polymer-based conductive material, or inorganic-organic composite made of various known metals and metal oxides. Any type of conductive material can be used, such as a conductive material of a type, or a conductive material in which these are arbitrarily mixed.

Specific examples of the inorganic conductive material include metals such as platinum, gold, silver, copper, zinc, titanium, aluminum, rhodium, and indium, conductive carbon, tin-doped indium oxide (ITO), and tin oxide (SnO ₂ ). And metal oxides such as fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), and zinc oxide (ZnO ₂ ).

  Specific examples of the polymer-based conductive material include conductive polymers obtained by polymerizing various derivatives such as thiophene, pyrrole, furan, and aniline, and polyacetylene. Polythiophene is preferable from the viewpoint of high conductivity, Polyethylene dioxythiophene (PEDOT) is particularly preferable.

  As a method for forming a conductive layer on a substrate, a known appropriate method according to a conductive material can be used. For example, when a conductive layer made of a metal oxide such as ITO is formed, a sputtering method is used. And thin film forming methods such as CVD, SPD (spray pyrolysis deposition) and vapor deposition.

  Further, when forming a conductive layer made of a polymer-based conductive material, it is preferably formed by various known coating methods.

  The thickness of the conductive layer is preferably about 0.01 μm to 10 μm, more preferably about 0.05 μm to 5 μm.

The lower the surface resistance of the conductive substrate, the better. Specifically, it is preferably 50 Ω / cm ² or less, more preferably 10 Ω / cm ² or less.

  In addition, in order to improve the current collection efficiency of the conductive substrate and further increase the conductivity, the area ratio in a range that does not significantly impair the light transmittance, gold, silver, copper, platinum, aluminum, nickel, indium, titanium, A metal wiring layer made of tungsten or the like may be used in combination with the conductive layer.

  In the case of using a metal wiring layer, it is preferable that light is uniformly transmitted through the conductive base material as a pattern such as a lattice shape, a stripe shape, or a comb shape. When a metal wiring layer is used in combination, it is preferable to install the conductive layer on the substrate by vapor deposition, sputtering, or the like.

  In a dye-sensitized solar cell, in order to suppress a decrease in open circuit voltage due to a short circuit between the conductive layer provided on the light-transmitting substrate and the electrolyte sealed in the cell, It is preferable to form a metal oxide or the like on the order of several nm to several tens of nm.

  Specifically, titanium oxide, zinc oxide, tin oxide, indium oxide, niobium oxide, tungsten oxide, zirconium oxide, strontium titanate, barium titanate, calcium titanate, etc. can be raised, and these are mixed alone or in combination. It is desirable to form the film using a vacuum deposition method, a sputtering method, a CVD method, a dip coating method, or the like.

<Dye>
In the present invention, the dye 3 adsorbed on the surface of the semiconductor porous membrane layer 2 described above has absorption in various visible light regions and / or infrared light regions, and is the lowest higher than the conduction band of the metal oxide semiconductor. A dye having an empty level is preferable, and various known 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, and rhodanine dyes.

  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-11-86916, JP-A-11-97725, JP-A-11-158395, JP-A-11-163378, JP-A-11- No. 214730, JP-A-11-214731, JP-A-11-238905, JP-A-2004-207224, JP-A-2004-319202, European Patents 892411 and 911841, and the like. Can be mentioned. 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 the ruthenium complex dye include, for example, U.S. Pat. And complex dyes described in each specification such as JP-A No. 2000-26487, JP-A No. 2001-223037, JP-A No. 2001-226607, JP-A No. 3430254, and the like.

  These dyes preferably have a large extinction coefficient and are stable against repeated redox.

  The dye is preferably chemically adsorbed on the metal oxide semiconductor and has a functional group such as a carboxyl group, a sulfonic acid group, a phosphoric acid group, an amide group, an amino group, a carbonyl group, or a phosphine group. preferable.

  Further, 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.

  In the present invention, the method for adsorbing the dye to the semiconductor porous membrane layer is not particularly limited, and a known method can be used.

  For example, a method of dissolving a dye in an organic solvent to prepare a dye solution and immersing the semiconductor layer on the transparent conductive film in the obtained dye solution, or a method of applying the obtained dye solution to the surface of the semiconductor layer, etc. Can be mentioned.

  In the former, a dip method, a roller method, an air knife method or the like can be applied, and in the latter, a wire bar method, an application method, a spin method, a spray method, an offset printing method, a screen printing method, or the like can be applied.

  Prior to the adsorption of the dye, the semiconductor layer surface may be subjected to a treatment such as decompression treatment or heat treatment in advance to activate the surface and remove bubbles in the film.

  From the viewpoint of preferably obtaining a sensitizing effect on the semiconductor layer, the time for immersing the semiconductor film in the dye solution is preferably 3 hours to 48 hours, and more preferably 4 hours to 24 hours.

  In addition, the dye solution may be heated to a temperature at which it does not boil as long as the dye does not decompose.

  The preferred temperature range is 10 ° C. to 50 ° C., particularly preferably 15 ° C. to 35 ° C., but this is not the case when the solvent boils in the temperature range as described above.

  In addition, the dye solution in which the semiconductor film is immersed can be irradiated with ultrasonic waves.

  A commercially available apparatus can be used for the ultrasonic irradiation, and the irradiation time is preferably 30 minutes to 4 hours, more preferably 1 hour to 3 hours.

The solvent used for the dye solution may be any solvent that dissolves the dye, and a conventionally known solvent can be used. Also,
The solvent is preferably a solvent purified in accordance with a conventional method, or a higher-purity solvent that is distilled and / or dried as necessary prior to use of the solvent. For example, methanol, ethanol, butanol One or more hydrophobic solvents, aprotic solvents, hydrophobic and aprotic solvents or mixtures thereof.

Here, examples of the hydrophobic solvent include halogenated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; hydrocarbons such as hexane and cyclohexane;
Aromatic hydrocarbons such as benzene, toluene, xylene;
Halogenated aromatic hydrocarbons such as chlorobenzene and dichlorobenzene;
Examples thereof include esters such as ethyl acetate, butyl acetate, and ethyl benzoate, and mixed solvents thereof. Examples of the aprotic solvent include ketones such as acetone and methyl ethyl ketone; ethers such as diethyl ether, diisopropyl ether, and dimethoxyethane;
Nitrogen compounds such as acetonitrile, dimethylacetamide, hexamethylphosphoric acid triamide; sulfur compounds such as carbon disulfide and dimethyl sulfoxide;
Examples thereof include phosphorus compounds such as hexamethylphosphoramide, and combinations thereof. Solvents preferably used include alcohol solvents such as methanol, ethanol, n-propanol, n-butanol and t-butanol, ketone solvents such as acetone and methyl ethyl ketone, diethyl ether, diisopropyl ether, tetrahydrofuran and 1,4-dioxane. Ether solvents, halogenated hydrocarbon solvents such as methylene chloride and 1,1,2-trichloroethane, and nitrogen compounds such as acetonitrile, particularly preferably methanol, ethanol, acetone, methyl ethyl ketone, tetrahydrofuran, methylene chloride and acetonitrile. .

The density | concentration of the pigment | dye in a pigment | dye solution can be suitably adjusted with the pigment | dye to be used, the kind of solvent, and a pigment | dye adsorption process, for example, 1 * 10 < ^-5 > mol / liter or more, Preferably it is 5 * 10 < ^-5 > -1 *. About 10 ⁻² mol / liter is mentioned.

  Note that if the amount of dye adsorbed is small, the sensitizing effect will be insufficient. Conversely, if the amount of adsorbed is large, the dye not adsorbed on the oxide semiconductor will float, which will reduce the sensitizing effect and increase the photoelectric conversion efficiency. This is not preferable because it causes a decrease.

  From the above, it is preferable to quickly remove the unadsorbed dye by washing.

  As the cleaning solvent, a solvent having relatively low solubility of the dye and easy to dry is preferable. Moreover, it is preferable to perform washing in a heated state.

  In addition, after removing excess dye by washing, the surface of the oxide semiconductor fine particles may be treated with an organic basic compound to promote removal of unreacted dye in order to make the adsorption state of the dye more stable. Good.

  Examples of the organic basic compound include derivatives such as pyridine and quinoline.

  When these compounds are liquid, they may be used as they are, but when they are solid, they may be dissolved in a solvent, preferably the same solvent as the dye solution.

  When two or more kinds of dyes are used, the ratio of the dyes to be mixed is not particularly limited, and is selected and optimized from the respective dyes. In general, from about equimolar mixing, about 10% mol or more per dye. It is preferred to use.

  As a specific method when two or more kinds of dyes are used in combination, the dyes may be adsorbed on the semiconductor layer sequentially or may be mixed and dissolved.

  When the dye is adsorbed to the oxide semiconductor layer using a solution in which the dye to be used in combination is mixed and dissolved, the total concentration of the dye in the solution may be the same as when only one kind is supported.

  As a solvent in the case of using a mixture of dyes, the above-mentioned solvents can be used.

  Even when a solution is prepared for each dye to be used in combination and adsorbed to the semiconductor layer, the solvent described above can be used as the solvent, and the solvent for each dye to be used may be the same or different.

  In the case where a separate solution is prepared for each dye and is prepared by immersing in each solution in order, the effect of the present invention can be obtained regardless of the order in which the dye is adsorbed on the semiconductor layer.

  Moreover, you may produce by mixing the semiconductor fine particle which adsorb | sucked each pigment | dye independently.

  When the dye is supported on the thin film of oxide semiconductor fine particles, it is effective to support the dye in the presence of the inclusion compound in order to prevent the association between the dyes.

  Examples of inclusion compounds include steroidal compounds such as cholic acid, crown ether, cyclodextrin, calixarene, polyethylene oxide, and the like. Deoxycholic acid, dehydrodeoxycholic acid, chenodeoxycholic acid, methyl cholate are preferable. Examples include esters, cholic acids such as sodium cholate, polyethylene oxide, and the like.

  Further, after the dye is supported, the surface of the semiconductor layer may be treated with an amine compound such as 4-t-butylpyridine.

  As a treatment method, for example, a method in which a substrate provided with a semiconductor fine particle thin film carrying a dye in an ethanol solution of amine is immersed.

<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 that involve ions, electron transport materials and hole transport materials can also be used as materials whose carrier transport in solids is involved in electrical conduction, and these can be used in combination. Is possible.

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

Specifically, those containing an oxidation-reduction counter ion such as I ⁻ / I ₃ ⁻ series, Br ₂ ⁻ / Br ₃ ⁻ series, ferrocyanate / ferricyanate, ferrocene / ferricinium ion, cobalt Examples include 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 bromides of quaternary ammonium compounds such as tetraalkylammonium bromide and pyridinium bromide. 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, Polyhydric alcohols such as reethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, glycerin, nitrile compounds such as acetonitrile, glutarodinitrile, propionitrile, methoxypropionitrile, methoxyacetonitrile, benzonitrile, tetrahydrofuran, dimethylsulfur Aprotic polar substances such as foxide and sulfolane can be used.

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

  The molten salt electrolyte is preferable from the viewpoint of achieving both photoelectric conversion efficiency and durability.

  Examples of the molten salt electrolyte include pyridinium salts described in WO95 / 18456, JP-A-8-259543, JP-A-2001-357896, Electrochemistry, Vol. 65, No. 11, page 923 (1997), and the like. And electrolytes containing known iodine salts such as imidazolium salts and triazolium salts.

  These molten salt electrolytes are preferably in a molten state at room temperature, and it is preferable not to use a solvent.

  Gels prepared by adding an electrolyte or electrolyte solution to an oligomer or polymer matrix, polymer addition, addition of low-molecular gelling agent or oil gelling agent, polymerization including polyfunctional monomers, polymer crosslinking reaction, 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.

  Further, 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, a preferable crosslinkable reactive group is a nitrogen-containing heterocyclic ring (for example, a pyridine ring, an imidazole ring, a thiazole ring, an oxazole ring, a triazole ring, a morpholine ring, a piperidine ring, a piperazine ring), and a preferable crosslinking agent. Is a bifunctional or higher functional reagent (for example, alkyl halide, halogenated aralkyl, sulfonate ester, 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, and preferably about 0.1 to 90% by mass.

  In addition, 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, Polymer functional groups such as poly-β-propiolactone, polyethyleneimine, polyalkylene sulfide, or cross-linked products thereof, polyphosphazene, polysiloxane, polyvinyl alcohol, polyacrylic acid, polyalkylene oxide, Examples include those obtained by adding a polyether segment or oligoalkylene oxide structure as a side chain or a copolymer thereof. Among them, those having an oligoalkylene oxide structure as a side chain or a polyether segment as a side chain. Those with is preferable.

  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 which 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), its derivatives, polythienylene vinylene, 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 control of the oxide semiconductor surface ( A salt such as Li [(CF ₃ SO ₂ ) ₂ N] may be added to perform compensation of the space charge layer.

  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 eV or more and 5.5 eV or less, and more preferably 4.7 eV or more and 5.3 eV or less. . 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 cm ² / V · sec or more and 10 ⁴ cm ² / V · sec or less, and more preferably 10 ⁻³ cm ² / V · sec. sec to 10 ³ cm ² / V · sec.

The preferable conductivity of the charge transport layer is 10 ⁻⁸ S / cm or more and 10 ² S / cm or less, and more preferably 10 ⁻⁶ S / cm or more and 10 S / cm or less.

  In the present invention, the method for forming the charge transfer layer 4 between the semiconductor electrode and the cathode electrode 5 is not particularly limited. For example, the semiconductor electrode and the cathode electrode are disposed opposite to each other, and then both electrodes are disposed. A method of forming the charge transfer layer 4 by filling the above-described electrolyte solution and various electrolytes in between, and forming the charge transfer layer 4 by dropping or coating the electrolyte or various electrolytes on the semiconductor electrode or the cathode electrode, and then charge A method of superimposing the other electrode on the moving layer 4, a method of forming a hole for electrolyte injection in the electrode of the cell sealed except for the charge moving layer, and forming the charge moving layer 4 by injecting the electrolyte therefrom Can be used.

  In addition, in order to prevent electrolyte from leaking between the semiconductor electrode and the cathode electrode, the gap between the semiconductor electrode and the cathode 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 4 and the cathode electrode 5 in an appropriate 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 formation process such as a vacuum deposition method or a CVD method, and then a cathode electrode can be applied.

  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 ⁻¹ S / cm or more, and more preferably 1 × 10 ⁻⁵ S / cm or more.

<Cathode electrode>
As the cathode electrode that can be used in the present invention, a single-layer structure of a substrate having conductivity itself, or a substrate having a counter electrode conductive layer on the surface thereof can be used in the same manner as the conductive substrate described above. . In the latter case, the conductive material and the base material used for the counter electrode conductive layer, and the manufacturing method thereof are the same as those of the conductive base material 1 described above, and various known materials and methods can be applied.

Among them, I ₃ ^- is preferable to use those having a catalytic ability to perform a reducing reaction sufficient rate of oxidation and other redox ions such as ions, specifically platinum electrodes, the conductive material surface Examples include platinum-plated or platinum-deposited materials, rhodium metal, ruthenium metal, ruthenium oxide, and carbon. 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 counter electrode conductive layer is not particularly limited, but is preferably 3 nm to 10 μm. When the counter electrode 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 cathode electrode is preferably as low as possible. Specifically, the surface resistance is preferably 50Ω / m ² or less, more preferably 20Ω / m ² or less, and more preferably 10Ω / m ² or less. Is more preferable.

  Since light may be received from one or both of the conductive substrate 1 and the cathode electrode 5 described above, it is sufficient that at least one of the conductive substrate and the cathode electrode is substantially transparent.

  From the viewpoint of improving the power generation efficiency, it is preferable to make the conductive base material transparent so that light enters from the conductive base material side.

  In this case, the cathode electrode preferably has a property of reflecting light.

  As such a cathode electrode, glass or plastic deposited with a metal or a conductive oxide, or a metal thin film can be used.

  For the cathode electrode, a conductive material is directly applied, plated, or vapor deposited (PVD, CVD) on the above-described charge transfer layer, or a conductive layer side of a base material having a counter electrode conductive layer or a single conductive base material layer is pasted. That's fine.

  In addition, as in the case of the conductive base material, it is also one of preferred embodiments to use a metal wiring layer in combination, particularly when the cathode 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 deposited with platinum, carbon, rhodium, ruthenium, etc. and coated with conductive fine particles can be used.

  Hereinafter, the present invention will be specifically described with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1
<< Preparation of semiconductor porous membrane layer >>
As the semiconductor porous film layer, a paste containing semiconductor fine particles was prepared, applied onto a substrate by a screen printing method, dried and then fired to form a desired porous film layer.

  Examples of each layer will be described below.

1. Light Absorbing Layer [Production Method of Light Absorbing Layer Paste LAP1]
Light absorption layer paste formulation Gas phase method titania (Degussa P25, primary particle size 21 nm, BET value 50 m ² / g)
15% by mass
Polyethylene glycol (manufactured by Kanto Chemical Co., MW20,000) 10% by mass
Activator (Emulgen 120, manufactured by Kao Corporation) 2% by mass
73% by mass of pure water
The above dispersion is continuously dispersed for 30 minutes using an ultrasonic disperser UH-300 manufactured by SMT, and then pulverized and dispersed at a rotation speed of 10 m / sec using ultra apex mill / 50 μm diameter zirconia beads manufactured by Kotobuki Industries. For 3 hours to prepare a light absorbing layer paste LAP1.

  The above vapor phase titania had an average particle size of about 21 nm and an average aspect ratio of about 1 estimated from the projection layer of a transmission electron microscope (TEM).

  Moreover, the analysis of the X-ray-diffraction apparatus (XRD) showed most anatase crystals.

2. Light Reflective Layer [Production Method of Light Reflective Layer Paste LRP1]
The high aspect ratio particles used for the light reflecting layer were produced using the following method.

Titanium oxide powder (purity: 99.8%) and potassium carbonate powder (purity: 99%) are mixed in such a ratio that the molar ratio of TiO ₂ / K ₂ O is 2 and heated at 1100 ° C. in a platinum crucible for 40 minutes. To melt.

  Subsequently, a molten potassium titanate crystal is obtained through a cooling process in which the melt is poured into a copper cooling layer at room temperature and rapidly cooled.

  This fibrous crystal is sufficiently ground in a mortar-shaped pulverizer, immersed in 50 times the amount of pure water under stirring for a day and night, and then immersed in a 60% sulfuric acid aqueous solution having the same mass as the fibrous crystal over 4 hours with stirring. It was dripped at the liquid.

  After stirring as it is for 2 hours, it is continuously dispersed for 30 minutes using an ultrasonic disperser UH-300 manufactured by SMT, and pulverized and dispersed at a rotational speed of 8 m / sec using Ultra Apex Mill / 30 μm diameter zirconia beads manufactured by Kotobuki Industries. For 12 hours. After pulverization and dispersion, washing with filtered water and drying were performed to obtain a white powder.

  Subsequently, the white powder was put into an alumina crucible and subjected to a baking treatment for 3 hours in an electric furnace heated to 500 ° C., thereby obtaining a white titanium oxide powder A.

  The titanium oxide powder A was anatase-type titanium oxide powder as analyzed by X-ray photoelectron spectroscopy (XPS) and an X-ray diffraction apparatus (XRD).

  Further, when the aspect ratio was calculated from the average equivalent circle diameter of the projected area and the average thickness from an observation image of 500 or more particles by a transmission electron microscope (TEM), the average particle diameter was 1.5 μm, and the aspect ratio was 12 .7.

  A dispersion was prepared according to the following light reflection layer paste formulation, and continuously dispersed for 30 minutes using an ultrasonic disperser UH-300 manufactured by SMT, then 10 m using Ultra Apex Mill / 50 μm diameter zirconia beads manufactured by Kotobuki Industries. Crushing and dispersing treatment was performed for 3 hours at a rotation speed of / sec to prepare a light reflecting layer paste LRP1.

Light reflection layer paste formulation White titanium oxide powder A 15% by mass
Polyethylene glycol (manufactured by Kanto Chemical Co., MW20,000) 10% by mass
Activator (Emulgen 120, manufactured by Kao Corporation) 2% by mass
73% by mass of pure water
[Production Method of Light Reflective Layer Paste LRP2]
In the method for producing the light reflecting layer paste LRP1, the LRP1 was used except that the titanium oxide powder B formed by cooling in the cooling layer heated to 150 ° C. in the cooling step was used instead of the titanium oxide powder A. In the same manner as above, LRP2 was produced.

  Titanium oxide powder B used for LRP2 had an average particle diameter of 1.1 μm and an aspect ratio of 5.4 from an observation image of 500 or more particles by a transmission electron microscope (TEM).

<Production of dye-sensitized solar cell>
A 10 nm semiconductor film was formed on a transparent conductive glass substrate coated with fluorine-doped tin oxide as a conductive layer, using a high-frequency magnetron sputtering apparatus and titanium oxide as a target material.

  Then, the paste was applied by a screen printing method, naturally dried, and then fired at 500 ° C. for 60 minutes to form a semiconductor porous film layer made of titanium oxide on the substrate.

  The film thickness was adjusted by overcoating according to the samples shown in Table 1.

  Also, a sample having a light absorption layer and a light reflection layer was laminated and coated in the same manner.

Next, it was immersed in a 3.0 × 10 ⁻³ mol / L, acetonitrile: t-butanol = 1: 1 solution of the following ruthenium complex dye N719 for dye-sensitized solar cells for 24 hours. Excess dye was sufficiently washed away with an acetonitrile: t-butanol solution and vacuum-dried to prepare a semiconductor porous film layer on which the dye was adsorbed.

  As a cathode electrode, a hole for depositing platinum on a glass substrate and injecting an electrolyte was provided.

  The semiconductor porous membrane layer and the cathode electrode are bonded to each other using a 25 μm-thick sheet-like spacer / sealing material (SX-1170-25 manufactured by SOLARONIX) having a 1 cm square hole, and the electrolyte provided on the cathode electrode From the injection hole, tetrapropylammonium iodide, iodine, and t-butylpyridine were mixed in a mixed solvent of acetonitrile: ethylene carbonate having a volume ratio of 1: 4, respectively at concentrations of 0.46 mol / liter, 0.06 mol. A charge transfer layer containing a redox electrolyte dissolved so as to be 0.50 mol / liter is injected, the hole is closed with a hot bond, and a cover glass is pasted from above using a sealing agent, A sensitized solar cell encapsulated cell was produced.

  Each sample shown in Table 1 was produced in the same manner as described above. However, a titanium oxide paste having a particle diameter of 400 nm (PST-400C manufactured by Catalyst Kasei Co., Ltd.) was used for the light reflecting layer of the comparative example. The titanium oxide particles used in this paste consist of particles having various shapes, and there are many rod-shaped octahedrons, and the aspect ratio was 3 or less.

<< Evaluation of photoelectric conversion characteristics of solar cells >>
About the photovoltaic cell shown in Table 1 produced by the above method, a solar simulator (manufactured by JASCO Corporation, Low Energy Spectral Sensitivity Measurement Device CEP-25) was used, and the 0.25 cm ² mask, AM 1.5 filter, 100 mW / m ² The IV characteristics when irradiated with intense light were measured, the short-circuit current Jsc (mA / cm ² ) and the open-circuit voltage value Voc (V) were evaluated for three cells manufactured by the same configuration and method, and the average value was expressed. It was shown in 1.

  Table 1 shows that the total film thickness of LAP1 that is the light absorption layer and LRP of the light reflection layer greatly affects the open-circuit voltage (Voc), and that a higher voltage can be extracted as the film thickness is thinner.

  This is presumably because the increase in the film thickness increases the chance of recombination of the electrons injected into the semiconductor and the holes of the dye, resulting in a decrease in Voc.

  Further, as the thickness of the light absorption layer is increased, the light absorption ability of the dye is improved, so that Jsc is improved. However, when the thickness is too thick, the diffusion of the iodine electrolyte becomes rate-limiting or the behavior becomes a peak.

  In the cell using the high aspect ratio particle LRP1 in the light reflection layer, even if the film thickness of the light reflection layer is made thinner than that of the comparative example, the drop in Jsc is small and Voc is improved at the same time, so high conversion efficiency is expected. The

  The same can be said for LRP2 having a slightly low aspect ratio, and the effect of the present invention appears.

  From the above results, it was possible to provide a dye-sensitized solar cell with an improved open-circuit voltage (Voc) while maintaining a high short-circuit current (Jsc) during light irradiation by implementing the present invention.

FIG. 1 is a schematic cross-sectional view showing the basic structure of the dye-sensitized solar cell of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Anode electrode 11 Light transmissive substrate 12 Conductive layer 2 Porous membrane layer 21 Light absorption layer 22 Light reflection layer 3 Dye 4 Charge transfer layer 5 Cathode electrode 6 Counter substrate 7 Sealing material

Claims (5)

An anode electrode in which at least a conductive layer and a porous membrane layer are laminated on the surface of the light-transmitting substrate, a cathode electrode facing the porous membrane layer side of the anode electrode, and the anode electrode and the cathode electrode In a dye-sensitized solar cell having a configuration in which an electrolyte is sealed between electrodes, the porous film layer, in order from the light-transmitting substrate side, a light absorption layer made of fine particles adsorbing at least a sensitizing dye; and A dye-sensitized solar cell comprising a light reflecting layer, wherein the light reflecting layer mainly comprises shape anisotropic fine particles having an aspect ratio of 5 or more. 2. The dye-sensitized solar cell according to claim 1, wherein an aspect ratio of the shape anisotropic fine particles is 10 to 100. 3. The dye-sensitized solar cell according to claim 1 or 2, wherein the shape anisotropic fine particles have a flat plate shape. 4. The shape anisotropic fine particles in the light reflecting layer have an average particle size of 200 nm to 10 μm and are larger than the average particle size of the fine particles in the light absorbing layer. 2. A dye-sensitized solar cell according to item 1. The ratio of the film thickness of the light absorption layer of the said porous membrane layer and the film thickness of a light reflection layer is 5: 1-15: 1, The any one of Claims 1-4 characterized by the above-mentioned. Dye-sensitized solar cell.

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