JP4922568B2 - Dye-sensitized solar cell electrode - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an electrode for a dye-sensitized solar cell and a method for producing the same, and more specifically, a dye-sensitized solar cell capable of producing a dye-sensitized solar cell having high photovoltaic power generation performance even when a plastic substrate is used. The present invention relates to an electrode for use and a manufacturing method thereof.

  The dye-sensitized solar cell has been proposed since a photoelectric conversion element using dye-sensitized semiconductor fine particles was proposed (“Nature”, Vol. 353, pages 737-740, (1991)). It is attracting attention as a new solar battery that replaces batteries. In particular, dye-sensitized solar cells using a plastic film as a support can be made flexible and lightweight, and many studies have been made.

JP-A-11-288745 JP 2001-160426 A JP 2002-50413 A JP 2001-93590 A JP 2001-358348 A

  As the metal oxide semiconductor layer of the dye-sensitized solar cell, a porous body obtained by sintering fine particles of an oxide semiconductor is usually used in order to increase the adsorption amount of the dye.

  When a glass substrate is used as the support, a method can be used in which needle crystals are grown on the glass substrate while oxidizing the metal material to produce oriented needle crystals. However, this method cannot be applied when a plastic substrate is used because the processing temperature is high.

  By the way, JP 2001-93590 A and JP 2001-358348 A describe that the efficiency of charge transport is improved by using a needle-like crystal of a metal oxide for a solar cell electrode. However, in order to obtain a good porous structure and achieve high charge transport efficiency, it is necessary to appropriately control the crystalline state of the metal oxide, and the oxide semiconductor at a sufficiently high temperature using a glass substrate Even when the layers are sintered, the photovoltaic performance can be improved by about 10 to 20%.

  The present invention provides a dye-sensitized solar cell with high photovoltaic power generation capability that can adsorb a sufficient amount of dye and obtain high charge transport efficiency while using a flexible plastic substrate as compared with glass as a support. An object of the present invention is to provide a dye-sensitized solar cell electrode.

That is, the present invention relates to a dye-sensitized solar cell comprising a polyester film, a transparent conductive layer provided on one surface thereof, and a porous semiconductor layer comprising metal oxide particles provided on the transparent conductive layer. in use the electrode, the metal oxide particles become 5 to 95% by weight of crystalline particles a and the crystalline particles B from 5 to 95 wt%, crystalline particles a will satisfy all the following conditions, and the particles a The crystal size is 38 nm or more, and the crystalline particle B has a crystal size of 12 nm or less. The crystal size is a diffraction having the highest peak intensity among diffraction peaks derived from a crystal plane in X-ray diffraction measurement. This is an electrode for a dye-sensitized solar cell, which is obtained from the half width of the peak .
5 ≦ dla / dsa ≦ 20
50 ≦ dsa ≦ 250
(Here, dla average particle maximum diameter of the crystalline particles A (nm), dsa is Ri average particle minimum diameter (nm) der crystalline particles A, wherein an average particle maximum diameter is the average value of the particle maximum diameter The maximum particle diameter is a distance between parallel lines when the distance between two parallel lines circumscribing the particle outline is the widest in the plan view of the particles observed with an electron microscope, and the average particle minimum diameter is represented by the average value of the particle minimum diameter, Ru distance der between the parallel line when the distance between the two parallel lines is narrowest.)

  According to the present invention, a dye-sensitized dye having high photovoltaic power generation performance capable of adsorbing a sufficient amount of dye and obtaining high charge transport efficiency while using a flexible plastic substrate as compared with glass as a support. A dye-sensitized solar cell electrode capable of producing a solar cell can be provided.

Hereinafter, the present invention will be described in detail.
[Porous semiconductor layer]
As the metal oxide particles constituting the porous semiconductor layer, metal oxide semiconductor particles are used. As the metal oxide semiconductor, it is preferable to use titanium oxide (TiO ₂ ), zinc oxide (ZnO), or tin oxide (SnO ₂ ), which are n-type semiconductors. A composite of a plurality of these metal oxides may be used.
The porous semiconductor layer is formed by applying a coating liquid, which is a dispersion of metal oxide particles, on the transparent conductive layer, and is further fixed on the transparent conductive layer by heating and drying.

  The metal oxide particles comprise 5 to 95% by weight of the following crystal particles A and 5 to 95% by weight of the following crystalline particles B. The ratio of the crystalline particles A is preferably 20 to 80% by weight, more preferably 40 to 60% by weight. When the proportion of the crystalline particles A is less than 5% by weight, the effect of increasing the charge transport efficiency is not exhibited, and sufficient photovoltaic efficiency cannot be obtained when a dye-sensitized solar cell is produced. The proportion of the crystalline particles B is preferably 20 to 80% by weight, particularly preferably 40 to 60% by weight. By using in this range, the amount of dye adsorption can be increased.

[Crystalline Particle A]
The crystalline particles A satisfy all of the following conditions. This condition will be described later.
5 ≦ dla / dsa ≦ 20
50 ≦ dsa ≦ 250
Here, dsa is the average particle minimum diameter (nm) of the crystalline particles A, and dla is the average particle maximum diameter (nm) of the crystalline particles A.

[Average particle minimum diameter dsa]
The average particle minimum diameter dsa of the crystalline particles A is 50 to 250 nm, preferably 70 to 200 nm. If it is less than 50 nm, the crystallinity of the particles is lowered, so that the charge transport efficiency is lowered, and sufficient photovoltaic power generation efficiency cannot be obtained when a dye-sensitized solar cell is produced. If it exceeds 250 nm, the surface area becomes too large and the amount of dye adsorbed decreases, so that sufficient photovoltaic power generation efficiency cannot be obtained when a dye-sensitized solar cell is produced.

  Here, the average particle minimum diameter is an average value of the particle minimum diameter. The particle minimum diameter is a distance between parallel lines when the interval between two parallel lines circumscribing the particle outline in the plan view of the particles observed with an electron microscope is the smallest.

[Average maximum particle diameter dla]
The average particle maximum diameter dla of the crystalline particles A is preferably 500 to 4000 nm, more preferably 1000 to 2500 nm. If it is less than 500 nm, the charge transport efficiency is lowered, and the photovoltaic power generation efficiency is lowered, which is not preferable. If it exceeds 4000 nm, the amount of dye adsorbed decreases, and the photovoltaic power generation efficiency decreases, which is not preferable.

  Here, the average particle maximum diameter is an average value of the particle maximum diameter. The maximum particle diameter is a distance between parallel lines when the interval between two parallel lines circumscribing the outline of the particle is the largest in the plan view of the particle observed with an electron microscope.

[Dla / dsa]
The ratio dla / dsa between the average particle maximum diameter dla and the average particle minimum diameter dsa of the crystalline particles A is 5 to 20. If it is less than 5, the charge transport efficiency is lowered and the photovoltaic power generation efficiency is lowered. If it exceeds 20, the dispersion of the particles is inferior and a porous semiconductor layer having a uniform structure cannot be formed.

[Crystal size of crystalline particles A]
The average minimum particle diameter dsa of the crystalline particles A and the crystal size dxa of the crystalline particles A preferably satisfy the following conditions.
1.5 ≦ dsa / dxa ≦ 5.0
If the dsa / dxa is less than 1.5, the charge transport efficiency is undesirably lowered. If it exceeds 5.0, the amount of dye adsorbed is undesirably lowered. Here, dsa is the average minimum particle diameter (nm) of the crystalline particles A, and dxa is the crystal size (nm) of the crystalline particles A.

[Method for Producing Crystalline Particle A]
The crystalline particles A can be produced, for example, according to the method described in JP-A-7-2598. That is, a titanium tetrachloride aqueous solution is hydrolyzed by heating to produce a hydrous titanium oxide slurry containing free hydrochloric acid, and an alkali metal compound is added to the obtained slurry to form an alkali chloride metal salt, and then an oxyline compound Is added, then dehydrated, and then the dehydrated cake is baked at 700 to 1000 ° C. In this method, the average particle minimum particle size and the average particle maximum particle size can be adjusted by adjusting the pH of the hydrous titanium oxide slurry, and the crystal size is adjusted by the temperature and time for baking the dehydrated cake. be able to.

[Formation of porous semiconductor layer]
The coating liquid used for providing the porous semiconductor layer is a dispersion liquid in which metal oxide particles are dispersed in a dispersion medium. As the dispersion medium, water or an organic solvent can be used. As the organic solvent, alcohol is preferred. When dispersing in a dispersion medium, a small amount of a dispersion aid may be added as necessary. As the dispersion aid, for example, a surfactant, an acid, and a chelating agent can be used.

  Application | coating of a coating liquid can be performed using the arbitrary methods conventionally used in the case of application | coating process. For example, a roller method, a dip method, an air knife method, a blade method, a wire bar method, a slide hopper method, an extrusion method, and a curtain method can be exemplified. Further, a spin method or a spray method using a general-purpose machine may be used, and coating may be performed using wet printing such as intaglio, rubber plate, screen printing, as well as three major printing methods of letterpress, offset and gravure. Among these, a preferable film forming method can be used according to the liquid viscosity and the wet thickness.

Coating a porous amount of the semiconductor particles support 1 m ² per preferably 0.5 to 20 g / m ^2, more preferably performed such that 5 to 10 g / m ^2.

  After coating the coating liquid, heat treatment is performed to form a porous semiconductor layer. This heat treatment may be performed in the drying process at the time, or may be performed in a separate process after drying. The heat treatment is preferably performed at 170 to 250 ° C. for 1 to 120 minutes, more preferably 180 to 230 ° C. for 3 to 90 minutes, and particularly preferably 190 to 220 ° C. for 5 to 60 minutes. By performing this heat treatment, an increase in resistance of the porous semiconductor layer can be reduced while preventing deformation of the polyester film support due to heating.

  The final porous semiconductor layer has a thickness of preferably 1 to 30 μm, more preferably 2 to 10 μm. In particular, when the transparency is increased, 2 to 6 μm is most preferable.

  Furthermore, by irradiating the metal oxide particles constituting the porous semiconductor layer with ultraviolet light or the like that the particles strongly absorb, or by irradiating microwaves to heat the fine particle layer, You may perform the process which strengthens physical joining.

  For forming the porous semiconductor layer, a method of supporting a thin film of particles by electrodeposition can also be used. That is, the semiconductor fine particles are added to an appropriate low-conductivity solvent such as pure water, polar organic solvents such as alcohol, acetonitrile and THF, nonpolar organic solvents such as hexane and chloroform, or a mixed solvent thereof, so that there is no aggregation. The conductive resin sheet electrode to be electrodeposited and the counter electrode are made to face each other in parallel at a constant interval, the dispersion liquid is injected into the gap, and a DC voltage is applied between the electrodes. In this way, by selecting the concentration of the dispersion and the electrode interval, a porous semiconductor layer, which is an electrodeposition film having a constant and uniform thickness, is formed on the substrate electrode.

For the purpose of preventing the transparent conductive layer carrying the porous semiconductor from being electrically short-circuited with the counter electrode, an undercoat layer may be provided on the transparent conductive layer in advance. As the undercoat layer, TiO ₂ , SnO ₂ , ZnO, Nb ₂ O ₅ , particularly TiO ₂ is preferable. This undercoat layer can be provided by, for example, a sputtering method in addition to the spray pyrolysis method described in Electrochim, Acta 40, 643 to 652 (1995). The thickness of the undercoat layer is preferably 5 to 1000 nm or less, more preferably 10 to 500 nm.

[Polyester film]
In the present invention, the polyester constituting the polyester film is a linear saturated polyester synthesized from an aromatic dibasic acid or an ester-forming derivative thereof and a diol or an ester-forming derivative thereof.

  Specific examples of such polyesters include polyethylene terephthalate, polyethylene isophthalate, polyethylene isophthalate, polybutylene terephthalate, poly (1,4-cyclohexylenedimethylene terephthalate), polyethylene-2,6-naphthalate, and the like. It may be a blend of these copolymers or a small proportion of other resins. Among these polyesters, polyethylene terephthalate and polyethylene-2,6-naphthalate are preferable because of a good balance between mechanical properties and optical properties.

  In particular, polyethylene-2,6-naphthalate is most preferable because it is superior to polyethylene terephthalate in terms of mechanical strength, small thermal shrinkage, and a small amount of oligomer generated during heating.

  As the polyethylene terephthalate, those having an ethylene terephthalate unit of preferably 90 mol% or more, more preferably 95% or more, particularly preferably 97% or more are used. As the polyethylene-2,6-naphthalate, those having a polyethylene-2,6-naphthalate unit of preferably 90 mol% or more, more preferably 95% or more, particularly preferably 97% or more are used.

  The polyester may be a homopolymer or a copolymer obtained by copolymerizing the third component, but a homopolymer is preferred.

  The intrinsic viscosity of the polyester is preferably 0.40 dl / g or more, more preferably 0.40 to 0.90 dl / g. If the intrinsic viscosity is less than 0.40 dl / g, process cutting may occur frequently, which is not preferable, and if it exceeds 0.90 dl / g, melt extrusion becomes difficult because of high melt viscosity, and the polymerization time is long and uneconomical. Absent.

  Polyester can be obtained by a conventionally known method. For example, it can be obtained by a method of directly obtaining a low-polymerization degree polyester by reaction of dicarboxylic acid and glycol. Alternatively, it can be obtained by a method in which a lower alkyl ester of dicarboxylic acid and glycol are reacted with each other using a transesterification catalyst, and then a polymerization reaction is performed in the presence of a polymerization reaction catalyst.

  As the transesterification reaction catalyst, conventionally known compounds such as sodium, potassium, magnesium, calcium, zinc, strontium, titanium, zirconium, manganese, and cobalt can be used.

  Examples of the polymerization reaction catalyst include conventionally known ones, for example, antimony compounds such as antimony trioxide and antimony pentoxide, germanium compounds represented by germanium dioxide, tetraethyl titanate, tetrapropyl titanate, tetraphenyl titanate or a portion thereof. Titanium compounds such as hydrolysates, titanyl ammonium oxalate, potassium titanyl oxalate, and titanium trisacetylacetonate can be used.

  When polymerization is performed via a transesterification reaction, a phosphorus compound such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, or normal phosphoric acid is usually added for the purpose of deactivating the transesterification catalyst before the polymerization reaction. However, the content in the polyester as the phosphorus element is preferably 20 to 100 ppm from the viewpoint of thermal stability.

  The polyester may be converted into chips after melt polymerization, and further subjected to solid phase polymerization under heating under reduced pressure or in an inert gas stream such as nitrogen.

  It is preferable that the polyester film in the present invention contains substantially no particles. If the particles are contained, high transparency may be impaired, or the surface may become rough and it may be difficult to process the transparent conductive layer. The haze value of the film is preferably 1.5% or less, more preferably 1.0% or less, and particularly preferably 0.5% or less.

  The polyester film in the present invention preferably has a light transmittance at a wavelength of 370 nm of 3% or less and a light transmittance at 400 nm of 70% or more. This light transmittance can be obtained by using a polyester containing a monomer that absorbs ultraviolet rays, such as 2,6-naphthalenedicarboxylic acid, and by incorporating an ultraviolet absorber in the polyester.

  Examples of the ultraviolet absorber used in this case include 2,2′-p-phenylenebis (3,1-benzoxazin-4-one) and 2,2′-p-phenylenebis (6-methyl-3,1- Benzoxazin-4-one), 2,2′-p-phenylenebis (6-chloro-3,1-benzoxazin-4-one), 2,2 ′-(4,4′-diphenylene) bis (3 , 1-benzoxazin-4-one) and 2,2 ′-(2,6-naphthylene) bis (3,1-benzoxazin-4-one) and the like can be used.

  The polyester film in the present invention has a three-dimensional center line average roughness of preferably 0.0001 to 0.02 μm on both sides, more preferably 0.0001 to 0.015 μm, and particularly preferably 0.0001 to 0.010 μm. is there. In particular, it is preferable that the three-dimensional center line average roughness of at least one surface is 0.0001 to 0.005 μm because the transparent conductive layer can be easily processed. The most preferable surface roughness of at least one surface is 0.0005 to 0.004 μm.

  The thickness of the polyester film in the present invention is preferably 10 to 500 μm, more preferably 20 to 400 μm, and particularly preferably 50 to 300 μm.

  Next, the preferable manufacturing method of the polyester film of this invention is demonstrated. The glass transition temperature is abbreviated as Tg.

  In the polyester film of the present invention, the polyester is melt-extruded into a film form, cooled and solidified with a casting drum to form an unstretched film, and this unstretched film is once or twice or more in the longitudinal direction at Tg to (Tg + 60) ° The film is stretched so that the magnification is 3 to 6 times, and then stretched so that the magnification is 3 to 5 times in the width direction at Tg to (Tg + 60) ° C., and further 1 to 1 at Tm 180 ° C. to 255 ° C. if necessary. It can be obtained by performing a heat treatment for 60 seconds. In order to reduce the difference in thermal shrinkage between the longitudinal direction and the width direction of the polyester film and the thermal shrinkage in the longitudinal direction, a method of shrinking in the longitudinal direction in a heat treatment step as disclosed in JP-A-57-57628 Alternatively, a method of relaxing heat treatment of a film in a suspended state as disclosed in JP-A-1-275031 can be used.

[Transparent conductive layer]
Examples of the transparent conductive layer in the present invention include conductive metal oxides (fluorine-doped tin oxide, indium-tin composite oxide (ITO), indium-zinc composite oxide (IZO), metal thin films (for example, platinum, gold, etc.). , Silver, copper, aluminum, etc.), carbon materials can be used, and the transparent conductive layer may be a laminate or composite of two or more types, among which ITO and IZO have light transmittance. Is particularly preferable because of its high resistance and low resistance.

  The surface resistance of the transparent conductive layer is preferably 100Ω / □ or less, more preferably 40Ω / □ or less. If it exceeds 100Ω / □, the resistance in the battery becomes too large and the photovoltaic power generation efficiency is lowered, which is not preferable.

  The thickness of the transparent conductive layer is preferably 100 to 500 nm. If it is less than 100 nm, the surface resistance value cannot be lowered sufficiently, and if it exceeds 500 nm, the light transmittance is lowered and the transparent conductive layer is easily broken, which is not preferable.

  The surface tension of the transparent conductive layer in the present invention is preferably 40 mN / m or more, and more preferably 65 mN / m or more. When the surface tension is less than 40 mN / m, the adhesion between the transparent conductive layer and the porous semiconductor may be inferior, and when it is 65 mN / m or more, the porous material is coated with an aqueous coating liquid whose main component is water. The semiconductor layer can be easily formed, which is more preferable.

A transparent conductive layer having the above properties can be obtained by forming a transparent conductive layer using, for example, ITO or IZO and processing it by any of the following methods.
(1) Method of activating the surface of the transparent conductive layer with an acidic or alkaline solution (2) Method of activating by irradiating the surface of the transparent conductive layer with ultraviolet rays or an electron beam (3) Transparent conductivity by applying corona treatment or plasma treatment Method for activating layer surface Among these, the method for activating the surface by plasma treatment is particularly preferred because high surface tension can be obtained.

[Easily adhesive layer]
In order to improve the adhesion between the polyester film and the transparent conductive layer, it is preferable to provide an easy adhesion layer between the polyester film and the transparent conductive layer. The thickness of the easy adhesion layer is preferably 10 to 200 nm, more preferably 20 to 150 nm. If the thickness of the easy-adhesion layer is less than 10 nm, the effect of improving the adhesion is poor, and if it exceeds 200 nm, cohesive failure of the easy-adhesion layer tends to occur and the adhesion may be lowered.

  When providing an easy-adhesion layer, it is preferable to provide by coating in the manufacturing process of a polyester film, and it is preferable to apply | coat to the polyester film before orientation crystallization is completed further. Here, the polyester film before the crystal orientation is completed is an unstretched film, a uniaxially oriented film in which the unstretched film is oriented in either the longitudinal direction or the transverse direction, and further in two directions, the longitudinal direction and the transverse direction. And a film that has been stretched and oriented at a low magnification (a biaxially stretched film before being finally re-stretched in the machine direction or the transverse direction to complete oriented crystallization). In particular, it is preferable to apply the aqueous coating liquid of the above composition to an unstretched film or a uniaxially stretched film oriented in one direction, and perform longitudinal stretching and / or lateral stretching and heat setting as it is.

  The easy adhesion layer is preferably made of a material having excellent adhesion to both the polyester film and the transparent conductive layer. For example, a polyester resin, an acrylic resin, a urethane acrylic resin, a silicon acrylic resin, a melamine resin, or a polysiloxane resin is used. be able to. These resins may be used alone or as a mixture of two or more.

[Hard coat layer]
In order to improve the adhesion between the polyester film and the transparent conductive layer, particularly the durability of the adhesion, a hard coat layer may be provided between the easy adhesion layer and the transparent conductive layer. The thickness of the hard coat layer is preferably 0.01 to 20 μm, more preferably 1 to 10 μm.

  When providing a hard-coat layer, it is preferable to provide by coating on the polyester film which provided the easily bonding layer. The hard coat layer is preferably made of a material having excellent adhesion to both the easy adhesion layer and the transparent conductive layer, such as an acrylic resin, a urethane resin, a silicon resin, a UV curable resin, and an epoxy resin. A resin component or a mixture of these and inorganic particles can be used. As the inorganic particles, for example, alumina, silica, and mica particles can be used.

[Antireflection layer]
In the present invention, an antireflection layer may be provided on the surface opposite to the transparent conductive layer for the purpose of increasing the light transmittance and increasing the photovoltaic power generation efficiency.

  As a method for providing the antireflection layer, a method in which a material having a refractive index different from the refractive index of the polyester film is laminated in a single layer or two or more layers is preferable. In the case of a single layer structure, it is better to use a material having a refractive index smaller than that of the base film, and in the case of a multilayer structure of two or more layers, the layer adjacent to the laminated film is larger than the polyester film. It is preferable to select a material having a refractive index smaller than that of a material having a high refractive index and a layer laminated thereon.

The material constituting such an antireflection layer is not particularly limited as long as it satisfies the above-described refractive index relationship, regardless of whether it is an organic material or an inorganic material. Preferably, CaF ₂ , MgF ₂ , NaAlF ₄ , A dielectric selected from the group consisting of SiO ₂ , ThF ₄ , ZrO ₂ , Nd ₂ O ₃ , SnO ₂ , TiO ₂ , Ce, O ₂ , ZnS, and In ₂ O ₃ is used.

  As a method of laminating the antireflection layer, for example, a dry coating method such as a vacuum deposition method, a sputtering method, a CVD method, or an ion plating method can be used, and a wet coating such as a gravure method, a reverse method, or a die method is used. Can be used.

  Prior to the lamination of the antireflection layer, pretreatment such as corona discharge treatment, plasma treatment, sputter etching treatment, electron beam irradiation treatment, ultraviolet irradiation treatment, primer treatment, and easy adhesion treatment may be performed.

[Preparation of dye-sensitized solar cell]
In order to produce a dye-sensitized solar cell using the electrode of the present invention, a known method can be used. Specifically, for example, it can be created by the following method.
(1) A dye is adsorbed on the porous semiconductor layer of the electrode of the present invention. It has the property of absorbing light in the visible and infrared regions, such as organometallic complex dyes represented by ruthenium bipyridine complexes (ruthenium complexes), cyanine dyes, coumarin dyes, xanthene dyes, porphyrin dyes, etc. A dye solution is prepared by dissolving a dye in a solvent such as alcohol or toluene, and the porous semiconductor layer is immersed, or sprayed or applied to the porous semiconductor layer. (Electrode A)
(2) As the counter electrode, a thin platinum layer formed by sputtering on the transparent conductive layer side of the laminated film of the present invention is used. (Electrode B)
(3) The electrode A and the electrode B are overlapped by inserting a thermocompression-bondable polyethylene film frame spacer (thickness 20 μm), the spacer portion is heated to 120 ° C., and both electrodes are pressure-bonded. Further, the edge portion is sealed with an epoxy resin adhesive.
(4) An electrolyte aqueous solution containing lithium iodide and iodine (molar ratio 3: 2) and 3% by weight of nylon beads having an average particle diameter of 20 μm as a spacer through a small hole for injecting an electrolyte provided in the corner of the sheet in advance. inject. Thoroughly deaerate the inside and finally seal the small holes with an epoxy resin adhesive.

Next, the present invention will be described in more detail with reference to examples. In addition, each characteristic value in an example was measured with the following method.
(1) Intrinsic viscosity Intrinsic viscosity ([η] dl / g) was measured with an o-chlorophenol solution at 35 ° C.

(2) Film thickness Using a micrometer (K-402B type manufactured by Anritsu Co., Ltd.), measurement is performed at 10 cm intervals in the continuous film forming direction and the width direction of the film, and a total of 300 film thicknesses are measured. To do. The average value of the film thicknesses of the obtained 300 locations was calculated and used as the film thickness.

(3) Light transmittance The light transmittance at wavelengths of 370 nm and 400 nm was measured using a spectrophotometer MPC3100 manufactured by Shimadzu Corporation.

(4) Thickness of coating layer A small piece of film is embedded in an epoxy resin (Epomount manufactured by Refinetech Co., Ltd.), sliced to a thickness of 50 nm together with the embedded resin using Microtome 2050 manufactured by Reichert-Jung, and transmitted. The thickness of the coating layer was measured with a scanning electron microscope (Topcon LEM-2000) at an acceleration voltage of 100 KV and a magnification of 100,000.

(5) Surface resistance value Any five points were measured using a 4-probe type surface resistivity measuring device (Made by Mitsubishi Chemical Corporation, Loresta GP), and the average value was used as a representative value.

(6) Surface tension Contact angles: θw and θy of water having a known surface tension and water-containing methylene to the transparent conductive thin film were measured using a contact angle meter (“CA-X type” manufactured by Kyowa Interface Science Co., Ltd.) It measured on 25 degreeC and 50% RH conditions. Using these measured values, the surface tension γs of the transparent conductive thin film was calculated as follows.
The surface tension γs of the transparent conductive thin film is the sum of the dispersive component γsd and the polar component γsp. That is,
γs = γsd + γsp (Formula 1)
From the Young equation,
γs = γsw + γw · cos θw (Formula 2)
γs = γsy + γy · cos θy (Formula 3)
Here, γsw is the tension acting between the transparent conductive thin film and water, γsw is the tension acting between the transparent conductive thin film and methylene iodide, γw is the surface tension of water, and γy is the surface tension of methylene iodide. It is.
From the Fowkes equation,
γ _sw = γ _s + γ _w −2 × (γ _sd · γ _wd ) ^1/2 −2 × (γ _sp · γ _wp ) ^1/2 (Formula 4)
γ _sy = γ _s + γ _y −2 × (γ _sd · γ _yd ) ^1/2 −2 × (γ _sp · γ _yp ) ^1/2 (Formula 5)
It is. Where γ _wd is the dispersive component of the surface tension of water, γ _wp is the polar component of the surface tension of water, γ _yd is the dispersive component of the surface tension of methylene iodide, and γ _yp is the surface tension of methylene iodide. It is a polar component.

By solving the simultaneous equations of Equations 1 to 5, the surface tension γ _s = γ _sd + γ _sp of the transparent conductive thin film can be calculated. At this time, the surface tension of water (γ _w ): 72.8 mN / m, the surface tension of methylene iodide (γ _y ): 50.5 mN / m, the dispersive component of the surface tension of water (γ _wd ): 21. 8 mN / m, polar component of surface tension of water (γ _wp ): 51.0 mN / m, dispersive component of surface tension of methylene iodide (γ _y d): 49.5 mN / m, surface tension of methylene iodide Polar component (γ _yp ): 1.3 mN / m was used.

(7) Average particle maximum diameter, average particle minimum diameter, average particle diameter Particle slurry is diluted with a mixed solvent of methanol and water, the particles are dispersed and fixed to a collodion membrane, and a transmission electron microscope (Topcon LEM-2000) At accelerating voltage 100KV, independent particles dispersed and observed in the range of 10,000 to 50,000 times depending on the size of the particles are observed. When drawing two parallel lines circumscribing the outline of the particle against the plan view of the observed particle, the distance between the parallel lines when the distance is the largest is the largest particle diameter and the smallest distance. The distance between the parallel lines was defined as the minimum particle diameter. The average value of the maximum particle diameter and the minimum particle diameter was defined as the particle diameter. Measurement was performed on 1000 particles arbitrarily selected, and the average value of the maximum particle size was defined as the average maximum particle size, the average value of the minimum particle size was defined as the average minimum particle size, and the average particle size was defined as the average particle size.

(8) Crystal size of particle It measured on condition of the following using the powder X-ray diffractometer (Rigaku Denki RINT2500HL). Using CuK-α as an X-ray source, diverging slit 1/2 °, scattering slit 1/2 °, light receiving slit 0.15 mm, scanning speed 1.000 ° / min from 2Θ angle 10 ° to 80 ° Measure and separate the diffraction peak derived from the crystal plane, the halo derived from the amorphous, and the background by a multiple peak separation method using the Pseudo Voice peak model. The crystal size was calculated from the half-width of the diffraction peak having the highest peak intensity among the diffraction peaks derived from the crystal plane, using the Scherrer equation below.

ここで、λはＸ線の波長（ｎｍ）、Ｂは回折ピークの半値幅（°）θはブラッグ角（°）である。

Here, λ is the X-ray wavelength (nm), B is the half-width (°) θ of the diffraction peak, and B is the Bragg angle (°).

(9) IV characteristics (photocurrent-voltage characteristics)
A 25 mm ² large dye-sensitized solar cell was formed, and the photovoltaic power generation efficiency was calculated by the following method. A 500 W xenon lamp (made by USHIO ELECTRIC CO., LTD.) Is equipped with a correction filter for sunlight simulation (AM1.5 Global made by Oriel), and simulated solar light with an incident light intensity of 100 mW / cm ² is applied to the above photovoltaic power generation device. Irradiation was performed by changing the incident angle with respect to the horizontal plane. The system was left indoors at a temperature of 18 ° C. and a humidity of 50%. Using a current-voltage measuring device (Keutley source measure unit 238 type), the DC voltage applied to the system is scanned at a constant speed of 10 mV / second, and the photocurrent output from the device is measured, so that photocurrent-voltage The characteristics were measured, and the photovoltaic power generation efficiency was calculated.

<Preparation of oxide semiconductor particles>
An aqueous solution of titanium tetrachloride having a TiO ₂ concentration of 207.9 g / liter, equivalent to 462.5 g based on the weight of TiO ₂ , was collected from a 5-liter four-necked flask, heated to 75 ° C. with stirring, and then dispersed in advance. An equivalent amount of 37.5 g of the rutile seed crystal slurry was added based on the weight of TiO _{2 and} hydrolyzed by heating at 75 ° C. for 2 hours to obtain 2941 ml of a rutile crystal titanium dioxide slurry having a TiO ₂ concentration of 163.2 g / liter.

This slurry was dispensed into 1-liter beakers of 500 ml each, and Na ₂ CO ₃ powder was added with stirring to adjust the slurry pH as shown in Table 1, and then Na ₄ P ₂ O ₇ powder was added to TiO ₂ respectively. _2. Add 30 parts by weight to 100 parts by weight, mix well, and filter and dehydrated cake is obtained. Each of the cakes was baked in a muffle furnace at the temperature and time shown in Table 1. The obtained fired product was pulverized, put into deionized water, mixed with a mixer for about 10 minutes, filtered, washed to remove soluble salts, and dried to obtain particles A1 to A3.
Table 1 shows the firing conditions of the particles A1 to A3 and the characteristics of the particles after firing.

In addition, for the particles A4 to B2, the following commercial products are fired at a temperature and time shown in Table 2 in a muffle furnace, pulverized, and then baked in a deionized water mixer for 10 minutes, followed by filtration and washing. Obtained.
Particle A4: Titanium oxide titanix JA-1 manufactured by Teika Co., Ltd.
Particle A5: titanium oxide PC-101A for photocatalyst manufactured by Titanium Industry Co., Ltd.
Particle B1: Titanium Co., Ltd. photocatalyst titanium oxide AMT-100
Particle B2: AEROXIDE® TiO ₂ P25 manufactured by Nippon Aerosil
Table 2 shows the firing conditions of particles A4 to B2 and the properties of the particles after firing.

[Example 1]
<Creation of polyester film>
Polyethylene-2,6-naphthalene dicarboxylate pellets having an intrinsic viscosity of 0.63 and containing substantially no particles are dried at 170 ° C. for 6 hours, then fed to an extruder hopper, and melted at a melting temperature of 305 ° C. Then, it was filtered through a stainless steel fine wire filter having an average opening of 17 μm, extruded through a 3 mm slit die on a rotary cooling drum having a surface temperature of 60 ° C., and rapidly cooled to obtain an unstretched film. The unstretched film thus obtained was preheated at 120 ° C., and further heated by an IR heater at 850 ° C. from above 15 mm between low-speed and high-speed rolls and stretched 3.1 times in the longitudinal direction. The following coating agent A was applied on one side of the film after the longitudinal stretching with a roll coater so that the coating thickness after drying was 0.25 μm, thereby forming an easy-contact layer.

  Subsequently, it was supplied to the tenter and laterally at 140 ° C. 3. Stretched 3 times. The obtained biaxially oriented film was heat-set at a temperature of 245 ° C. for 5 seconds to obtain a polyester film having an intrinsic viscosity of 0.58 dl / g and a thickness of 125 μm. Thereafter, this film was heat-relaxed in a suspended state at a relaxation rate of 0.7% and a temperature of 205 ° C.

<Preparation of coating agent A>
66 parts of dimethyl 2,6-naphthalenedicarboxylate, 47 parts of dimethyl isophthalate, 8 parts of dimethyl 5-sodium sulfoisophthalate, 54 parts of ethylene glycol and 62 parts of diethylene glycol were charged into the reactor, and 0.05 parts of tetrabutoxy titanium Was added and heated under a nitrogen atmosphere while controlling the temperature at 230 ° C., and the produced methanol was distilled off to conduct a transesterification reaction. Subsequently, the temperature of the reaction system was gradually raised to 255 ° C., and the pressure inside the system was reduced to 1 mmHg to carry out a polycondensation reaction to obtain a polyester. 25 parts of this polyester was dissolved in 75 parts of tetrahydrofuran, and 75 parts of water was dropped into the resulting solution under high-speed stirring at 10,000 rpm to obtain a milky white dispersion. Then, this dispersion was subjected to a reduced pressure of 20 mmHg. Distillation was performed, and tetrahydrofuran was distilled off to obtain an aqueous dispersion of polyester having a solid content of 25% by weight.

  Next, 3 parts of sodium lauryl sulfonate as a surfactant and 181 parts of ion-exchanged water are charged into a four-necked flask and the temperature is raised to 60 ° C. in a nitrogen stream, and then 0.5% ammonium persulfate is used as a polymerization initiator. Part, 0.2 part of sodium hydrogen nitrite is added, and further monomers 30.1 parts of methyl methacrylate, 21.9 parts of 2-isopropenyl-2-oxazoline, polyethylene oxide (n = 10) methacrylic acid A mixture of 39.4 parts and 8.6 parts of acrylamide was added dropwise over 3 hours while adjusting the liquid temperature to 60 to 70 ° C. After completion of dropping, the reaction was continued with stirring while maintaining the same temperature range for 2 hours, and then cooled to obtain an acrylic aqueous dispersion having a solid content of 35% by weight.

On the other hand, 0.2% by weight of silica filler (average particle size: 100 nm) (trade name Snowtex ZL manufactured by Nissan Chemical Co., Ltd.), polyoxyethylene (n = 7) lauryl ether (Sanyo Chemical Co., Ltd.) as a wetting agent An aqueous solution containing 0.3% by weight of the trade name NAROACTY N-70) was prepared.
A coating agent A was prepared by mixing 8 parts by weight of the polyester aqueous dispersion, 7 parts by weight of the acrylic water dispersion and 85 parts by weight of the aqueous solution.

<Hard coat>
Using the obtained polyester film, a UV curable hard coat agent (Desolite R7501 manufactured by JSR) was applied to the easy-contact layer side so as to have a thickness of about 5 μm, and UV cured to form a hard coat layer.

<Transparent conductive layer formation>
A transparent conductive layer made of IZO having a film thickness of 260 nm was formed on one surface on which the hard coat layer was formed by a direct current magnetron sputtering method using an IZO target mainly made of indium oxide and added with 10% by weight of zinc oxide. Formation of the transparent conductive layer by sputtering is performed by evacuating the chamber to 5 × 10 ⁻⁴ Pa before plasma discharge, introducing argon and oxygen into the chamber to a pressure of 0.3 Pa, and applying 2 W to the IZO target. Electric power was applied at a power density of / cm 2. The oxygen partial pressure was 3.7 mPa. The surface resistance value of the transparent conductive layer was 15Ω / □.

  Next, using a normal pressure plasma surface treatment apparatus (AP-T03-L manufactured by Sekisui Chemical Co., Ltd.), the surface of the transparent conductive layer was subjected to plasma treatment at 1 m / min under a nitrogen stream (60 L / min). At this time, the surface resistance value was 16Ω / □, and the surface tension was 71.5 mN / m.

<Antireflection layer>
A Y ₂ O ₃ layer having a thickness of 75 nm and a refractive index of 1.89 is formed on the surface of the laminated film opposite to the surface on which the transparent conductive layer is formed, and a TiO ₂ layer having a refractive index of 2.3 and a thickness of 120 nm is formed thereon. Further, SiO ₂ having a thickness of 90 nm and a refractive index of 1.46 was formed thereon by high frequency sputtering to form an antireflection treatment layer. When forming each electrostatic thin film, the degree of vacuum was 1 × 10 ⁻³ Torr, and Ar: 55 sccm and O ₂ : 5 sccm were flowed as gases. The substrate was kept at room temperature without heating or cooling during the film forming process.

<Porous semiconductor layer formation>
A mixture of the above-mentioned particles A1: 10 g and particles B1: 5 g is dispersed in 130 ml of ethanol and stirred for 30 minutes. Thereafter, 5 g of tetraisopropyl titanate is dropped over 5 minutes while stirring, and the mixture is further stirred for 30 minutes. After the stirring, this coating solution was immediately applied with a bar coater, heat treated at 200 ° C. for 30 minutes in the atmosphere to form a porous titanium dioxide layer having a thickness of 6 μm, and the dye-sensitized solar cell. An electrode was created.

<Creation of dye-sensitized solar cell>
This electrode was immersed in a 300 μM ethanol solution of ruthenium complex (Ru535bisTBA, manufactured by Solaronix) for 24 hours to adsorb the ruthenium complex on the surface of the photoactive electrode. A counter electrode was prepared by depositing a Pt film on the transparent conductive layer of the laminated film by sputtering. The electrode and the counter electrode are overlapped via a thermocompression-bondable polyethylene film frame spacer (thickness 20 μm), the spacer portion is heated to 120 ° C., and both electrodes are pressure-bonded. Further, the edge portion is sealed with an epoxy resin adhesive. After injecting an electrolyte solution (3-methoxypropionitrile solution containing 0.5% lithium iodide, 0.05M iodine, 0.5M tert-butylpyridine, 3% by weight of nylon beads having an average particle size of 20 μm) And sealed with an epoxy adhesive.

As a result of measuring the IV characteristics (effective area 25 mm ² ) of the completed dye-sensitized solar cell, the open-circuit voltage, short-circuit current density, and fill factor were 0.71 V, 8.4 mA / cm ² , 0, respectively. As a result, the photovoltaic power generation efficiency was 4.1%.

[Example 2 and Comparative Examples 1-3]
A polyester film was prepared in the same manner as in Example 1, and a hard coat, a transparent conductive layer, and an antireflection layer were formed. Except for using the particles shown in Table 3 when preparing the coating liquid, a porous semiconductor layer was formed in the same manner as in the Examples to prepare a dye-sensitized solar cell. Table 3 shows the results of measuring the IV characteristics of the dye-sensitized solar cell.

[Example 3]
Pellets of polyethylene terephthalate (intrinsic viscosity: 0.66) containing 1% by weight of an ultraviolet absorber represented by the following formula (A) are dried at 150 ° C. for 6 hours, then supplied to an extruder hopper, and melted at a melting temperature of 295 ° C. And filtered through a stainless steel fine wire filter having an average opening of 17 μm, extruded through a 3 mm slit die on a rotary cooling drum having a surface temperature of 20 ° C., and melt-extruded on a rotary cooling drum maintained at 20 ° C. by quenching. Thus, an unstretched film was obtained.

  The unstretched film thus obtained was preheated at 80 ° C., and further heated by an IR heater at 850 ° C. from above 15 mm between low-speed and high-speed rolls and stretched 3.2 times in the longitudinal direction. The following coating agent A was applied on one side of the film after the longitudinal stretching with a roll coater so that the coating thickness after drying was 0.25 μm, thereby forming an easy-contact layer.

  Subsequently, it was supplied to the tenter and laterally at 110 ° C. Stretched by a factor of 3.4. The obtained biaxially oriented film was heat-set at a temperature of 232 ° C. for 5 seconds to obtain a polyester film having an intrinsic viscosity of 0.60 dl / g and a thickness of 125 μm. Thereafter, the film was heat relaxed in a suspended state at a relaxation rate of 0.5% and a temperature of 150 ° C.

  In the same manner as in Example 1, a hard coat layer and a transparent conductive layer were formed in this order to obtain a laminated film. A porous semiconductor layer was formed in the same manner as in Example 1 except that the heat treatment temperature after coating was set to 150 ° C. when forming the oxide semiconductor layer, and an electrode of a dye-sensitized solar cell was formed.

Using this electrode, a dye-sensitized solar cell was prepared in the same manner as in Example 1. As a result of performing the IV measurement (effective area 25 mm ² ), the open circuit voltage, the short circuit current density, and the fill factor are 0.67 V, 8.1 mA / cm ² , and 0.60, respectively. Was 3.3%.

  The electrode for dye-sensitized solar cells of the present invention can be suitably used as an electrode for dye-sensitized solar cells.

Claims (4)

In a dye-sensitized solar cell electrode comprising a polyester film, a transparent conductive layer provided on one surface thereof, and a porous semiconductor layer comprising metal oxide particles provided on the transparent conductive layer, a metal The oxide particles comprise 5 to 95% by weight of the crystalline particles A and 5 to 95% by weight of the crystalline particles B. The crystalline particles A satisfy all of the following conditions, and the crystal size of the particles A is 38 nm or more. The crystalline particle B has a crystal size of 12 nm or less , and the crystal size is determined from the half-value width of the diffraction peak having the highest peak intensity among diffraction peaks derived from the crystal plane in the X-ray diffraction measurement. An electrode for a dye-sensitized solar cell, which is required .
5 ≦ dla / dsa ≦ 20
50 ≦ dsa ≦ 250
(Here, dla average particle maximum diameter of the crystalline particles A (nm), dsa is Ri average particle minimum diameter (nm) der crystalline particles A, wherein an average particle maximum diameter is the average value of the particle maximum diameter The maximum particle diameter is a distance between parallel lines when the distance between two parallel lines circumscribing the particle outline is the widest in the plan view of the particles observed with an electron microscope, and the average particle minimum diameter is represented by the average value of the particle minimum diameter, Ru distance der between the parallel line when the distance between the two parallel lines is narrowest.) 2. The dye-sensitized solar cell electrode according to claim 1, wherein the crystal size dxa and the average minimum particle diameter dsa of the crystalline particles A are polycrystalline particles satisfying the following formula.
1.5 ≦ dsa / dxa ≦ 5.0
(Where dsa is the average minimum particle size (nm) of the crystalline particles A,
dxa is the crystal size (nm) of the crystalline particles A. )   The electrode for a dye-sensitized solar cell according to claim 1, wherein the porous semiconductor layer is provided by applying a coating liquid, which is a dispersion of metal oxide particles, on the transparent conductive layer.   A dye-sensitized solar cell comprising the dye-sensitized solar cell electrode according to any one of claims 1 to 3.