JP2011109069A - Conductive reflecting film and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive reflecting film that does not require a vacuum process, has a high reflection factor from the base material side, and shows a low specific resistance at the same level as a bulk that can be used as an electrode for a solar cells, and to provide its manufacturing method. <P>SOLUTION: The conductive reflecting film formed on a transparent conductive film formed on a photoelectric conversion layer of a super straight type thin film solar cell is characterized in forming a reflecting film to have an air layer in a part of an interface with the transparent conductive film by coating a composition containing metal nanoparticles on the transparent conductive film by a wet coating method and firing the base material having the coating film, the total area of the air layer being in a range from 5 to 70% to the area of the reflecting film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention is a conductive reflective film formed by applying and baking a composition containing metal nanoparticles by a wet coating method, and has a high reflectance when measured from the substrate side, and is comparable to that of a bulk. The present invention relates to a conductive reflection film exhibiting a low specific resistance and a method for manufacturing the same.

  Currently, clean energy research and development is underway from the standpoint of environmental protection. In particular, solar cells are attracting attention because of the infinite amount of sunlight, which is a resource, and no pollution. Conventionally, for solar power generation using a solar cell, a bulk solar cell in which a bulk crystal of single crystal silicon or polycrystalline silicon is manufactured and sliced to be used as a thick plate semiconductor has been used. However, the above silicon crystal used for bulk solar cells requires a lot of energy and time for crystal growth, and it is difficult to increase mass production efficiency because of the complicated manufacturing process required in the subsequent manufacturing process. It was difficult to provide solar cells.

  On the other hand, so-called thin film semiconductor solar cells (hereinafter referred to as thin film solar cells) using a semiconductor layer of amorphous silicon or the like having a thickness of several micrometers or less as a photoelectric conversion layer are formed on an inexpensive substrate such as glass or stainless steel. In addition, as many semiconductor layers as photoelectric conversion layers may be formed as necessary. Therefore, this thin film solar cell is considered to become the mainstream of future solar cells because it is thin and light, low in manufacturing cost, and easy to increase in area.

  Thin film solar cells are classified into a super straight type and a substrate type depending on the structure. In a super straight type solar cell in which light is incident from the translucent substrate side, the order is usually substrate-transparent electrode-photoelectric conversion layer-back electrode. The structure formed by is taken. For super straight solar cells with a photoelectric conversion layer formed of a silicon-based material, for example, it is considered to increase the power generation efficiency by taking a structure formed in the order of transparent electrode, amorphous silicon, polycrystalline silicon, and back electrode. (See, for example, Non-Patent Document 1). In the structure shown in this non-patent document 1, amorphous silicon or polycrystalline silicon constitutes a photoelectric conversion layer.

  In particular, when the photovoltaic layer is made of a silicon-based material, the photoelectric conversion layer made of the above material has a relatively small extinction coefficient. A part of the light is transmitted through the photoelectric conversion layer, and the transmitted light does not contribute to power generation. Therefore, the back electrode is used as a reflection film, or a reflection film is formed on the back electrode, and the light that has not been absorbed and has passed through the photoelectric conversion layer is reflected by the reflection film, and then returned to the photoelectric conversion layer, thereby generating power efficiently. It is generally done to improve.

  In the development so far in the thin film solar cell, the electrode and the reflective film have been formed by a vacuum film forming method such as a sputtering method. However, generally, a large cost is required to maintain and operate a large vacuum film forming apparatus. For this reason, it is considered that these forming methods are changed from the vacuum film forming method to the wet film forming method, and the change to the wet film forming method is expected to greatly improve the running cost.

  As an example of a conductive reflective film formed by a wet film forming method, it is disclosed that a reflective film formed on the back side of a photoelectric conversion element is formed using an electroless plating method (for example, Patent Document 1). reference.). In the method disclosed in Patent Document 1, it is described that productivity can be improved by forming a reflective film by using an electroless plating method. Specifically, a resist film serving as a plating protective film is formed on the entire surface of the substrate by printing, and then the back surface of the substrate is added to the pretreatment liquid for nonconductor at a ratio of 2 to 4% by mass. A reflective layer made of a copper plating film of about 3 μm is formed using an electroless plating solution and using an electroless plating solution. Next, the photoelectric conversion element is formed by ultrasonically cleaning the substrate in a solvent and removing the resist film.

  However, in the electroless plating method disclosed in Patent Document 1, after a plating protective film is formed on the surface side, the side to be plated is pretreated with an HF solution and then subjected to steps such as immersion in an electroless plating solution. Therefore, in addition to complicated processes, generation of waste liquid is also expected.

  As a simpler method, a method in which a solution in which ultrafine metal particles are dispersed in an organic solvent is applied and sintered at a low temperature of 100 to 250 ° C. is disclosed (for example, see Patent Document 2). By the method disclosed in Patent Document 2, a uniform metal electrode having a large area with high reflectance and conductivity can be formed without using a high vacuum process.

  However, in the metal film obtained by the method disclosed in Patent Document 2, the reflectance on the base material side tends to be lower than the reflectance on the exposed surface side that hits the opposite surface. This is because, in general, when a metal film is formed by applying and firing a dispersion of ultrafine metal particles, pores having an average diameter of 100 nm or less are generated between the metal film and the substrate on which the film is formed. When pores occur between the metal film and the substrate, the light that has entered the pores is attenuated by repeated reflection within the pores, and the reflected light that reaches the substrate side is also incident on the substrate surface. When the angle increases, the ratio of total reflection at the interface of the low refractive index medium (air of pores) / high refractive index medium (base material) increases, and light is attenuated according to the ratio. Guessed.

JP 05-95127 A (paragraphs [0015], [0020] and [0021] in the detailed description of the invention) JP 09-246577 A (paragraph [0035] in the detailed description of the invention)

Shozo Yanagida et al., “The Forefront of Thin-Film Solar Cell Development: Toward High Efficiency, Mass Production, and Popularization”, NTS Corporation, March 2005, p. 113 FIG. 1 (a)

  When a reflective film is formed by applying a dispersion of metal nanoparticles and firing, when the reflectance is evaluated from the side of a translucent substrate such as glass, the reflectance is evaluated from the exposed surface side, which is the opposite side. Compared with the case where it did, the tendency for a reflectance to fall remarkably is seen.

  An object of the present invention is to provide a conductive reflective film that does not require a vacuum process, has a high reflectivity from the base material side, and exhibits a low specific resistance comparable to a bulk that can be used as an electrode for a solar cell, and its production It is to provide a method.

  Another object of the present invention is to eliminate a vacuum process such as a vacuum deposition method and a sputtering method as much as possible, and to produce a conductive reflective film for a super straight type solar cell at a lower cost by using a wet coating method. It is to provide a method.

  As a result of earnestly examining the properties of the conductive reflective film obtained by the coating process in the super straight type thin film solar cell, the present inventors applied the metal nanoparticle dispersion liquid on the base material, and a certain level of a certain level or more. By heating and baking at a temperature rising rate, a part of the particles in the coating film is lifted, an air layer having a certain total area at a part of the interface with the transparent conductive film is formed, and this air layer is Unlike pores having an average diameter of 100 nm or less that appeared in large amounts at the interface in the conventional coating process, this air layer produces a reflection enhancement effect, resulting in an increase in reflectivity compared to the conventional reflective film. It has been found that high conversion efficiency can be obtained by mounting this reflective film on a solar cell, and the present invention has been completed.

  The 1st viewpoint of this invention is a conductive reflective film formed on the transparent conductive film formed on the photoelectric converting layer of a super straight type thin film solar cell. By applying a wet coating method on the substrate and firing the substrate having this coating film, a reflective film is formed so as to have an air layer at a part of the interface with the transparent conductive film. The total area with respect to the film area is in the range of 5 to 70%.

  A second aspect of the present invention is an invention based on the first aspect, further comprising that the height of the air layer is in the range of 5 to 200 nm and the width of the air layer is in the range of 10 to 300 nm. Features.

  The third aspect of the present invention is the invention based on the first or second aspect, and is further selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose in the reflective film. Or it contains 2 or more types of substances.

  A fourth aspect of the present invention is an invention based on the first to third aspects, and is characterized in that the ratio of silver in the metal element contained in the reflective film is 75% by mass or more.

  A fifth aspect of the present invention is an invention based on the first to fourth aspects, and is characterized in that the thickness of the reflective film is in the range of 0.05 to 2.0 μm.

  The sixth aspect of the present invention is an invention based on the first to fifth aspects, and the metal nanoparticles contained in the reflective film further have a number average particle size of 70 to 50 nm. % Or more.

  A seventh aspect of the present invention is an invention based on the first to sixth aspects, wherein the coating after applying a wet coating method of a composition further containing metal nanoparticles has a thickness after firing of 0.05-2. The base material having a coating film is baked at a temperature rising rate of 100 to 300 ° C./min and a temperature of 130 to 400 ° C. for 10 to 60 minutes. It is characterized by that.

  The eighth aspect of the present invention is an invention based on the first to seventh aspects, and the wet coating method is a spray coating method, a dispenser coating method, a spin coating method, a knife coating method, a slit coating method, an ink jet method. It is one of a coating method, a screen printing method, an offset printing method, and a die coating method.

  A ninth aspect of the present invention is an invention based on the first to eighth aspects, wherein the composition containing metal nanoparticles further comprises metal nanoparticles in which the proportion of silver in the metal element is 75% by mass or more. Prepared by dispersing in a dispersion medium, the metal nanoparticles are chemically modified with a protective agent of an organic molecular main chain having 1 to 3 carbon atoms in the carbon skeleton, and the metal nanoparticles have a primary particle size in the range of 10 to 50 nm. It contains 70% or more of particles in number average.

  A tenth aspect of the present invention is an invention based on the first to ninth aspects, wherein the base material is either a glass, a ceramic containing a transparent conductive material, or a translucent substrate made of a polymer material, Alternatively, it is characterized in that it is a light-transmitting laminate of two or more types selected from the group consisting of glass, ceramics containing a transparent conductive material, a polymer material and silicon.

  An eleventh aspect of the present invention is an invention based on the first to tenth aspects, wherein the composition further comprising metal nanoparticles comprises an organic polymer, a metal oxide, a metal hydroxide, an organometallic compound, and It further comprises one or more additives selected from the group consisting of silicone oils.

  A twelfth aspect of the present invention is the invention based on the eleventh aspect, wherein the organic polymer is one or two selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose. It is characterized by being more than a species.

  A thirteenth aspect of the present invention is the invention based on the eleventh aspect, wherein the metal oxide is aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, It is an oxide or composite oxide containing at least one selected from the group consisting of tin, indium and antimony.

  A fourteenth aspect of the present invention is the invention based on the eleventh aspect, wherein the metal hydroxide is aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum. And a hydroxide containing at least one selected from the group consisting of tin, indium and antimony.

  A fifteenth aspect of the present invention is the invention based on the eleventh aspect, wherein the organometallic compound further comprises silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum and tin. It is a metal soap, metal complex or metal alkoxide containing at least one selected from the group consisting of

  A sixteenth aspect of the present invention is an invention based on the first to fifteenth aspects, and further contains 1% by mass or more of water and 2% by mass or more of alcohols as a dispersion medium. .

  According to a seventeenth aspect of the present invention, there is provided a substrate having a coating film, wherein a composition containing metal nanoparticles is applied on a transparent conductive film formed on a photoelectric conversion layer of a super straight type thin film solar cell by a wet coating method. By heating the material at a temperature of 100 to 300 ° C./minute and holding and firing at a temperature of 130 to 400 ° C. for 10 to 60 minutes, the film is formed so as to have an air layer at a part of the interface with the transparent conductive film. A method for producing a conductive reflective film, characterized in that a total area of the air layer formed and formed with respect to the reflective film area is within a range of 5 to 70%.

  An eighteenth aspect of the present invention is the invention based on the seventeenth aspect, wherein the composition containing metal nanoparticles further comprises metal nanoparticles having a silver content in the metal element of 75% by mass or more as the dispersion medium. Prepared by dispersion, the metal nanoparticles are chemically modified with a protective agent of an organic molecular main chain having 1 to 3 carbon atoms in the carbon skeleton, and the metal nanoparticles have a number of metal nanoparticles having a primary particle size in the range of 10 to 50 nm. It contains 70% or more on average, and the composition is applied on the transparent conductive film by a wet coating method so that the thickness after firing is in the range of 0.05 to 2.0 μm.

  According to a nineteenth aspect of the present invention, a transparent conductive film is formed on a photoelectric conversion layer of a superstrate solar cell, and the conductive reflective film according to the first to eighteenth aspects or the conductive film is formed on the transparent conductive film. A composite film for a super straight solar cell, characterized in that a conductive reflective film manufactured by a method for manufacturing a reflective film is formed.

  A twentieth aspect of the present invention is a laminate using a conductive reflective film based on the first to nineteenth aspects or a conductive reflective film manufactured by a method for manufacturing a conductive reflective film.

  According to a twenty-first aspect of the present invention, there is provided a solar cell using a conductive reflective film, a laminate, or a conductive reflective film produced by the method for producing a conductive reflective film according to the first to twentieth aspects as an electrode. It is.

  A twenty-second aspect of the present invention is a solar cell using the conductive reflective film based on the first to twenty-first aspects as an electrode.

  As described above, according to the present invention, the conductive reflective film formed on the transparent conductive film formed on the photoelectric conversion layer of the superstrate solar cell is transparent to the composition containing metal nanoparticles. By applying a wet coating method on a conductive film and firing a substrate having this coating film, the air layer is formed to have an air layer at a part of the interface with the transparent conductive film. The total area with respect to the area is in the range of 5 to 70%. In the reflection at the interface between the transparent conductive film and the conductive reflective film, although the reflectivity is high, the attenuation of light is large, and a sufficient reflectivity cannot be obtained with only the reflected light component by the conductive reflective film. When pores with a diameter of 100 nm or less appear, the light that has entered the pores attenuates due to repeated reflection in the pores, and the reflected light that reaches the substrate side also has a large incident angle with respect to the substrate surface. In this case, the ratio of total reflection at the interface of the low refractive index medium (pore air) / high refractive index medium (base material) increases, and light is attenuated according to the ratio. However, the reflection at the interface between the transparent conductive film and the air layer formed by the air layer of a certain size or more generated in the present invention results in less light attenuation. As a percentage of reflected light component Reflection effect occurs up El, sufficient reflectance can be obtained.

  In addition, the conductive reflective film of the present invention can obtain a specific resistance close to the specific resistance of the metal itself constituting the metal nanoparticles contained in the composition. That is, it shows a specific resistance as low as a bulk that can be used as an electrode for a solar cell.

  In addition, the conductive reflective film of the present invention is excellent in the long-term stability of the reflectance, adhesion, and specific resistance of the film as compared with a film formed by a vacuum process such as sputtering.

  Furthermore, a conductive reflective film and a composite film can be manufactured at low cost by eliminating vacuum processes such as vacuum deposition and sputtering as much as possible and using a wet coating method.

It is the figure which represented typically the cross section of the electroconductive reflective film for super straight type solar cells of this invention, and a composite film.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings.

  The conductive reflective film composition for forming the conductive reflective film of the present invention is a composition prepared by dispersing metal nanoparticles in a dispersion medium. In the metal nanoparticles, the proportion of silver in the metal element is 75% by mass or more, preferably 80% by mass or more. The reason why the ratio of silver in the metal element is in the range of 75% by mass or more is that when it is less than 75% by mass, the reflectance of the conductive reflective film formed using this composition is lowered. The metal nanoparticles are chemically modified with a protective agent having an organic molecular main chain having a carbon skeleton of 1 to 3 carbon atoms. The reason why the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent that chemically modifies the metal nanoparticles is in the range of 1 to 3 is that if the carbon number is 4 or more, the protective agent is desorbed by heat during firing or This is because decomposition (separation / combustion) is difficult, and a large amount of organic residue remains in the conductive reflective film, causing deterioration or deterioration, resulting in a decrease in conductivity and reflectivity of the conductive reflective film.

  The metal nanoparticles preferably contain 70% or more, preferably 75% or more of the number average of metal nanoparticles having a primary particle size of 10 to 50 nm. The content of the metal nanoparticles in the range of the primary particle size of 10 to 50 nm was set to a range of 70% or more with respect to 100% of all the metal nanoparticles on the number average. The specific surface area increases and the proportion of organic matter increases, and even organic molecules that are easily desorbed or decomposed (separated or burned) by the heat during firing have a large proportion of organic molecules, so conductive reflection Many organic residues remain in the film, and the residue is altered or deteriorated to reduce the conductivity and reflectivity of the conductive reflective film, or the particle size distribution of the metal nanoparticles is widened to reduce the density of the conductive reflective film. This is because the conductivity and reflectivity of the conductive reflective film are reduced. Furthermore, the primary particle diameter of the metal nanoparticles is within the range of 10 to 50 nm because the metal nanoparticles with the primary particle diameter within the range of 10 to 50 nm are stable over time (aging stability) according to statistical methods. This is because they are correlated. In the present invention, the primary particle size and number average measuring method of the metal nanoparticles are determined by the following method. First, the obtained metal nanoparticles are photographed at a magnification of about 500,000 times with a TEM (Transmission Electron Microscope). Next, a primary particle size is measured for 200 metal nanoparticles from the obtained image, and a particle size distribution is created based on the measurement result. Next, from the created particle size distribution, the ratio of the number of metal nanoparticles within the range of the primary particle size of 10 to 50 nm occupied by all metal nanoparticles is determined.

  One or more additives selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds and silicone oils in the composition for conductive reflective films containing the metal nanoparticles It is preferable that it is further included. An organic polymer, metal oxide, metal hydroxide, organometallic compound or silicone oil contained in the composition as an additive increases the chemical bond with the substrate or the anchor effect, or the metal nano in the firing process. By improving the wettability between the particles and the substrate, the adhesion to the substrate can be improved without impairing the conductivity.

  Moreover, when a conductive reflective film is formed using this composition, grain growth due to sintering between metal nanoparticles can be adjusted. In the formation of the conductive reflective film using this composition, a vacuum process is not required at the time of film formation, so that the process restrictions are small and the running cost of the manufacturing equipment can be greatly reduced.

The content of the additive is 0.1 to 20%, preferably 0.2 to 10% of the mass of the silver nanoparticles constituting the metal nanoparticles. If the additive content is less than 0.1%, the density of pores appearing at the interface with the transparent conductive film may be increased. If the content of the additive exceeds 20%, the conductivity of the formed conductive reflective film will be adversely affected, resulting in a problem that the volume resistivity exceeds 2 × 10 ⁻⁵ Ω · cm.

  As the organic polymer used as the additive, one or more selected from the group consisting of polyvinylpyrrolidone (hereinafter referred to as PVP), a PVP copolymer and water-soluble cellulose is used. Specifically, examples of the PVP copolymer include a PVP-methacrylate copolymer, a PVP-styrene copolymer, and a PVP-vinyl acetate copolymer. Examples of the water-soluble cellulose include cellulose ethers such as hydroxypropylmethylcellulose, methylcellulose, and hydroxyethylmethylcellulose.

  The metal oxide used as an additive is at least one selected from the group consisting of aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium and antimony An oxide or composite oxide containing is preferable. Specifically, the complex oxide is an indium oxide-tin oxide complex oxide (Indium Tin Oxide: ITO), an antimony oxide-tin oxide complex oxide (Antimony Tin Oxide: ATO), or an indium oxide-zinc oxide complex. An oxide (Indium Zinc Oxide: IZO) or the like.

  The metal hydroxide used as an additive is at least one selected from the group consisting of aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium and antimony. Species-containing hydroxides are preferred.

  As an organic metal compound used as an additive, metal soap, metal containing at least one selected from the group consisting of silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum and tin Complexes or metal alkoxides are preferred. Examples of the metal soap include chromium acetate, manganese formate, iron citrate, cobalt formate, nickel acetate, silver citrate, copper acetate, copper citrate, tin acetate, zinc acetate, zinc oxalate, and molybdenum acetate. Examples of the metal complex include an acetylacetone zinc complex, an acetylacetone chromium complex, and an acetylacetone nickel complex. Examples of the metal alkoxide include titanium isopropoxide, methyl silicate, isoanatopropyltrimethoxysilane, aminopropyltrimethoxysilane and the like.

  As the silicone oil used as the additive, both straight silicone oil and modified silicone oil can be used. The modified silicone oil further has an organic group introduced into part of the side chain of the polysiloxane (side chain type), an organic group introduced into both ends of the polysiloxane (both end type), and both ends of the polysiloxane. Those having an organic group introduced into one of them (one end type) and those having an organic group introduced into a part of both side chains and both ends of the polysiloxane (both side chain end type) can be used. The modified silicone oil includes a reactive silicone oil and a non-reactive silicone oil. Both types can be used as the additive of the present invention. Reactive silicone oil means amino modification, epoxy modification, carboxy modification, carbinol modification, mercapto modification, and heterogeneous functional group modification (epoxy group, amino group, polyether group). Indicates polyether modification, methylstyryl group modification, alkyl modification, higher fatty acid ester modification, fluorine modification, and hydrophilic special modification.

  On the other hand, among the metal nanoparticles constituting the conductive reflective film composition, metal nanoparticles other than silver nanoparticles are gold, platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and It is preferable to further contain metal nanoparticles composed of one kind of particles selected from the group consisting of manganese, or a mixed composition or alloy composition of two or more kinds. The metal nanoparticles other than silver nanoparticles are preferably 0.02% by mass or more and less than 25% by mass with respect to 100% by mass of all metal nanoparticles, and 0.03% by mass to 20% by mass. Is more preferable. The reason why the content of particles other than silver nanoparticles is in the range of 0.02% by mass or more and less than 25% by mass with respect to 100% by mass of all the metal nanoparticles However, within the range of 0.02% by mass or more and less than 25% by mass, the conductive reflective film after the weather resistance test (the test kept in a constant temperature and humidity chamber at a temperature of 100 ° C. and a humidity of 50% for 1000 hours) There is a feature that conductivity and reflectance are not deteriorated compared with those before the weather resistance test, and when it is 25% by mass or more, the conductivity and reflectance of the conductive reflective film immediately after firing is lowered, and the conductivity after the weather resistance test is also obtained. This is because the reflection film has lower conductivity and reflectance than the conductive reflection film before the weather resistance test.

  Moreover, content of the metal nanoparticle containing the silver nanoparticle in the composition for electroconductive reflective films contains 2.5-95.0 mass% with respect to 100 mass% of compositions which consist of a metal nanoparticle and a dispersion medium. The content is preferably 3.5 to 90% by mass. The content of the metal nanoparticles including silver nanoparticles is in the range of 2.5 to 95.0% by mass with respect to 100% by mass of the composition comprising the metal nanoparticles and the dispersion medium, and is less than 2.5% by mass. Then, although there is no effect on the properties of the conductive reflective film after firing, it is difficult to obtain a conductive reflective film having a required thickness. If it exceeds 95.0% by mass, ink or This is because the necessary fluidity as a paste is lost.

  The dispersion medium constituting the conductive reflective film composition is 1% by mass or more, preferably 2% by mass or more, and 2% by mass or more, preferably 3% by mass with respect to 100% by mass of all the dispersion media. It is preferable to contain a solvent compatible with at least% of water, for example, alcohols. For example, when the dispersion medium is composed of only water and alcohols, it contains 98% by mass of alcohol when it contains 2% by mass of water, and 98% by mass of water when it contains 2% by mass of alcohol. Further, the dispersion medium, that is, the protective molecule chemically modified on the surface of the metal nanoparticles contains one or both of a hydroxyl group (—OH) and a carbonyl group (—C═O). The reason why the content of water is preferably in the range of 1% by mass or more with respect to 100% by mass of all the dispersion media is obtained by applying the composition by a wet coating method when it is less than 1% by mass. It is difficult to sinter the film at a low temperature, and the conductivity and reflectance of the conductive reflecting film after firing are lowered, so that the content of the solvent compatible with water is 2% with respect to 100% by mass of all the dispersion media. The range of not less than 2% by mass is preferred because if it is less than 2% by mass, it is difficult to sinter the film obtained by applying the composition by the wet coating method at a low temperature as described above, and after firing. This is because the conductivity and reflectivity of the conductive reflective film are reduced. In addition, when a hydroxyl group (—OH) is contained in a protective agent that chemically modifies metal nanoparticles such as silver nanoparticles, the composition has excellent dispersion stability and has an effective effect on low-temperature sintering of the coating film. Yes, when a carbonyl group (—C═O) is contained in a protective agent that chemically modifies metal nanoparticles such as silver nanoparticles, the composition has excellent dispersion stability as described above, and the coating film is sintered at low temperature. Also has an effective action. As the solvent compatible with water used for the dispersion medium, alcohols are preferable, and among these alcohols, methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, glycerol, isobornyl hexanol and erythritol are preferable. It is particularly preferable to use one or more selected from the group consisting of:

  A method for producing a composition containing metal nanoparticles for forming the conductive reflective film of the present invention is as follows.

(a) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent for chemically modifying the silver nanoparticles is set to 3 First, silver nitrate is dissolved in water such as deionized water to prepare an aqueous metal salt solution. On the other hand, the aqueous solution of sodium citrate having a concentration of 10 to 40% obtained by dissolving sodium citrate in deionized water or the like is mixed with granular or powdered sulfuric acid in a stream of inert gas such as nitrogen gas. Iron is directly added and dissolved to prepare an aqueous reducing agent solution containing citrate ions and ferrous ions in a molar ratio of 3: 2. Next, the aqueous metal salt solution is added dropwise to and mixed with the reducing agent aqueous solution while stirring the reducing agent aqueous solution in the inert gas stream. Here, by adjusting the concentration of each solution so that the addition amount of the metal salt aqueous solution is 1/10 or less of the amount of the reducing agent aqueous solution, the reaction temperature is 30 to 30 even when the metal salt aqueous solution at room temperature is dropped. It is preferable to keep the temperature at 60 ° C. The mixing ratio of the two aqueous solutions is adjusted so that the equivalent of ferrous ions added as a reducing agent is three times the equivalent of metal ions. That is, the number of moles of metal ions in the aqueous solution of metal salt × (valence of metal ions) = 3 × (number of moles of ferrous ions in the aqueous reducing agent solution) is adjusted. After the dropping of the aqueous metal salt solution is completed, the mixture is further stirred for 10 to 300 minutes to prepare a dispersion composed of metal colloid. This dispersion is allowed to stand at room temperature, and the aggregates of the precipitated metal nanoparticles are separated by decantation, centrifugation, etc., and then water such as deionized water is added to the separation to form a dispersion, followed by ultrafiltration. The metal (silver) content is adjusted to 2.5 to 50% by mass by performing desalting treatment by the above, followed by substitution washing with alcohols. Thereafter, by adjusting the centrifugal force of the centrifuge using a centrifuge to separate coarse particles, the silver nanoparticles having a primary particle size in the range of 10 to 50 nm are 70% or more in average number of silver nanoparticles. It adjusts so that the ratio for which the silver nanoparticle in the range of the primary particle size of 10-50 nm with respect to 100% of all the silver nanoparticles may account for 70% or more may be prepared. Thereby, a dispersion in which the carbon skeleton of the carbon skeleton of the organic molecular main chain of the protective agent for chemically modifying the silver nanoparticles is 3 is obtained.

  Subsequently, the obtained dispersion is adjusted so that the final metal content (silver content) with respect to 100% by mass of the dispersion is in the range of 2.5 to 95% by mass. When the dispersion medium is an alcohol-containing aqueous solution, it is preferable to adjust the solvent water and the alcohol to 1% or more and 2% or more, respectively. When the composition further contains an additive, the dispersion is one or two selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds, and silicone oils. The above additives are added at a desired ratio. Content of an additive is adjusted so that it may become in the range of 0.1-20 mass% with respect to 100 mass% of compositions obtained. As a result, a composition in which silver nanoparticles chemically modified with a protective agent for an organic molecular main chain having 3 carbon skeletons is dispersed in a dispersion medium is obtained.

(b) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent that chemically modifies the silver nanoparticles is 2, except that the sodium citrate used when preparing the reducing agent aqueous solution is replaced with sodium malate A dispersion is prepared in the same manner as in the above (a). As a result, a dispersion having 2 carbon atoms in the carbon skeleton of the organic molecular main chain that chemically modifies the silver nanoparticles can be obtained.

(c) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent for chemically modifying the silver nanoparticles is 1, except that sodium citrate used when preparing the reducing agent aqueous solution is replaced with sodium glycolate A dispersion is prepared in the same manner as in the above (a). Thereby, a dispersion in which the carbon skeleton of the carbon skeleton of the organic molecular main chain for chemically modifying the silver nanoparticles is 1 is obtained.

(d) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent for chemically modifying metal nanoparticles other than silver nanoparticles is 3, the metal constituting the metal nanoparticles other than silver nanoparticles is gold, Examples include platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and manganese. The silver nitrate used to prepare the aqueous metal salt solution is chloroauric acid, chloroplatinic acid, palladium nitrate, ruthenium trichloride, nickel chloride, cuprous nitrate, tin dichloride, indium nitrate, zinc chloride, iron sulfate, sulfuric acid A dispersion is prepared in the same manner as in the above (a) except that it is replaced with chromium or manganese sulfate. Thereby, the dispersion whose carbon number of the carbon skeleton of the organic molecular principal chain of the protective agent which chemically modifies metal nanoparticles other than silver nanoparticles is 3 is obtained.

  In addition, when the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent that chemically modifies the metal nanoparticles other than the silver nanoparticles is 1 or 2, the silver nitrate used when preparing the metal salt aqueous solution is the above kind. A dispersion is prepared in the same manner as in the above (b) and (c) except that the metal salt is replaced. Thereby, the dispersion whose carbon number of carbon skeleton of the organic molecular principal chain of the protective agent which chemically modifies metal nanoparticles other than silver nanoparticles is 1 or 2 is obtained.

  When the metal nanoparticles include metal nanoparticles other than silver nanoparticles together with silver nanoparticles, for example, a dispersion containing silver nanoparticles produced by the method of (a) is used as the first dispersion, When the dispersion containing metal nanoparticles other than the silver nanoparticles produced by the method (d) is used as the second dispersion, 75% by mass or more of the first dispersion and less than 25% by mass of the second dispersion are obtained. Mixing is performed so that the total content of the first and second dispersions is 100% by mass. The first dispersion is not limited to the dispersion containing the silver nanoparticles produced by the method (a), but the dispersion containing the silver nanoparticles produced by the method (b) or the above (c). You may use the dispersion containing the silver nanoparticle manufactured by the method.

  In the production method of the present invention, as shown in FIG. 1, first, a transparent conductive film 14 is further formed on the photoelectric conversion layer 13 of the superstrate solar cell laminated on the base material 11 via the transparent conductive film 12. Then, the conductive reflective film composition is applied onto the transparent conductive film 14 by a wet coating method, and the thickness after firing is 0.05 to 2.0 μm, preferably 0.1 to 1.5 μm. A conductive reflective coating film is formed so as to have a thickness of.

The substrate 11 is selected from the group consisting of glass, ceramics containing a transparent conductive material or a transparent substrate made of a polymer material, or glass, ceramics containing a transparent conductive material, a polymer material, and silicon. Two or more types of translucent laminates can be used. Moreover, you may use the base material which contains any 1 type of transparent conductive films, and the base material which formed the transparent conductive film on the surface. Examples of the transparent conductive film include indium oxide, tin oxide, and zinc oxide. Examples of indium oxide include indium oxide, ITO (Indium Tin Oxide), and IZO (Indium Zic Oxide). Examples of tin oxide include Nesa (tin oxide SnO ₂ ), ATO (Antimony Tin Oxide), and fluorine-doped tin oxide. Examples of the zinc oxide system include zinc oxide, AZO (aluminum doped zinc oxide), and gallium doped zinc oxide. The substrate is preferably either a solar cell element or a solar cell element with a transparent electrode. Examples of the transparent electrode include ITO, ATO, Nesa, IZO, AZO and the like. Furthermore, a dielectric thin film such as lead zirconate titanate (PZT) may be formed on the substrate surface. Examples of the polymer substrate include a substrate formed of an organic polymer such as polyimide or PET (polyethylene terephthalate). The said dispersion is apply | coated to the surface of the photoelectric conversion semiconductor layer of a solar cell element, or the surface of the transparent electrode of a solar cell element with a transparent electrode.

  A transparent conductive film 14 is formed on the photoelectric conversion layer 13. The transparent conductive film 14 is not particularly limited, but may be formed by a conventionally known method such as sputtering, vacuum deposition, thermal CVD, or wet coating. Moreover, when forming this transparent conductive film 14 with a wet coating method, first, the composition for transparent conductive films is produced. This composition for transparent conductive films is a composition containing conductive oxide fine particles, and the conductive oxide fine particles are dispersed in a dispersion medium. As the conductive oxide fine particles contained in the composition for transparent conductive film, ITO (Indium Tin Oxide), ATO (Antimony Tin Oxide: antimony oxide-tin oxide composite oxide) A tin oxide powder containing one or more metals selected from the group consisting of Al, Co, Fe, In, Sn, Ga and Ti is preferred. Of these, ITO, ATO, AZO (Aluminum Zinc Oxide), IZO (Indium Zinc Oxide), TZO (Tin Zinc Oxide: Tin-containing zinc oxide composite oxide) Is particularly preferred. Moreover, it is preferable that the content rate of the electroconductive oxide fine particle which occupies for solid content contained in the composition for transparent conductive films exists in the range of 50-90 mass%. The reason why the content of the conductive oxide fine particles is within the above range is that the conductivity is lowered if the content is less than the lower limit, and the adhesiveness is lowered if the upper limit is exceeded. Among these, it is especially preferable that it exists in the range of 70-90 mass%. Further, the average particle diameter of the conductive oxide fine particles is preferably within a range of 10 to 100 nm in order to maintain stability in the dispersion medium, and particularly preferably within a range of 20 to 60 nm. .

  The composition for transparent conductive film is a composition containing one or both of a polymer binder and a non-polymer binder that are cured by heating. Examples of the polymer binder include acrylic resin, polycarbonate, polyester, alkyd resin, polyurethane, acrylic urethane, polystyrene, polyacetal, polyamide, polyvinyl alcohol, polyvinyl acetate, cellulose, and siloxane polymer. Polymeric binders include aluminum, silicon, titanium, zirconium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum or tin metal soaps, metal complexes or metal alkoxide hydrolysates. It is preferable. The hydrolyzate of the metal alkoxide includes sol-gel. Non-polymer type binders include metal soaps, metal complexes, metal alkoxides, halosilanes, 2-alkoxyethanol, β-diketones, and alkyl acetates. The metal contained in the metal soap, metal complex or metal alkoxide is aluminum, silicon, titanium, zirconium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium or antimony. These polymer type binders and non-polymer type binders are cured by heating, thereby enabling formation of the transparent conductive film 14 having a low haze ratio and volume resistivity at low temperatures. The content of these binders is preferably in the range of 5 to 50% by mass, particularly preferably in the range of 10 to 30% by mass, as a proportion of the solid content in the transparent conductive film composition.

  It is preferable to add a coupling agent to the composition for transparent conductive films according to the other components used. This is for improving the adhesion between the conductive fine particles and the binder and the adhesion between the transparent conductive film 14 formed of the composition for transparent conductive film and the photoelectric conversion layer 13 or the conductive reflective film 16. Examples of the coupling agent include a silane coupling agent, an aluminum coupling agent, and a titanium coupling agent.

  Examples of the silane coupling agent include vinyltriethoxyxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-methacryloxypropyltrimethoxysilane. Examples of the aluminum coupling agent include an aluminum coupling agent containing an acetoalkoxy group represented by the following formula (1). Further, as a titanium coupling agent, a titanium coupling agent having a dialkyl pyrophosphite group represented by the following formulas (2) to (4), or a titanium having a dialkyl phosphite group represented by the following formula (5): A coupling agent is mentioned.

上記透明導電膜用組成物を用いて透明導電膜１４を形成するには、先ず透明導電膜用組成物を光電変換層１３上に湿式塗工法により塗布して焼成後の厚さが０．０３〜０．５μｍ、好ましくは０．０５〜０．３μｍの範囲内となるように成膜する。ここで、透明導電膜１４の厚さを０．０３〜０．５μｍの範囲に限定したのは、０．０３μｍ未満又は０．５μｍを越えると増反射効果が十分に得られないからである。次にこの積層体を大気中若しくは窒素やアルゴンなどの不活性ガス雰囲気中で１２０〜４００℃の温度に５〜６０分間保持して焼成することにより透明導電膜１４が形成される。

In order to form the transparent conductive film 14 using the transparent conductive film composition, first, the transparent conductive film composition is applied onto the photoelectric conversion layer 13 by a wet coating method, and the thickness after firing is 0.03. The film is formed to be in the range of ˜0.5 μm, preferably 0.05 to 0.3 μm. Here, the reason why the thickness of the transparent conductive film 14 is limited to the range of 0.03 to 0.5 [mu] m is that if the thickness is less than 0.03 [mu] m or exceeds 0.5 [mu] m, the enhanced reflection effect cannot be obtained sufficiently. Next, the transparent conductive film 14 is formed by baking the laminated body in the air or in an inert gas atmosphere such as nitrogen or argon at a temperature of 120 to 400 ° C. for 5 to 60 minutes.

  The wet coating method is particularly preferably a spray coating method, a dispenser coating method, a spin coating method, a knife coating method, a slit coating method, an inkjet coating method, a screen printing method, an offset printing method or a die coating method. However, the present invention is not limited to this, and any method can be used.

  The spray coating method is a method in which the dispersion is atomized by compressed air and applied to the substrate, or the dispersion itself is pressurized and atomized to apply to the substrate. The dispenser coating method is, for example, a method in which the dispersion is injected into a syringe. The dispersion is discharged from the fine nozzle at the tip of the syringe and applied to the substrate by pushing the piston of the syringe. The spin coating method is a method in which a dispersion is dropped onto a rotating substrate, and the dropped dispersion is spread to the periphery of the substrate by its centrifugal force. The knife coating method leaves a predetermined gap from the tip of the knife. In this method, the substrate is provided so as to be movable in the horizontal direction, the dispersion is supplied onto the substrate upstream of the knife, and the substrate is moved horizontally toward the downstream side. The slit coating method is a method in which a dispersion is discharged from a narrow slit and applied onto a substrate, and the inkjet coating method is a method in which a dispersion is filled in an ink cartridge of a commercially available inkjet printer and ink jet printing is performed on the substrate. is there. The screen printing method is a method in which wrinkles are used as a pattern indicating material and a dispersion is transferred to a substrate through a plate image formed thereon. The offset printing method is a printing method utilizing the water repellency of ink, in which the dispersion attached to the plate is not directly attached to the substrate, but is transferred from the plate to a rubber sheet and then transferred from the rubber sheet to the substrate again. . The die coating method is a method in which a dispersion supplied in a die is distributed by a manifold and extruded onto a thin film from a slit to coat the surface of a traveling substrate. The die coating method includes a slot coat method, a slide coat method, and a curtain coat method.

  Next, a conductive reflective film 16 is formed on the transparent conductive film 14. Specifically, the substrate having a conductive reflective coating is heated at a rate of 100 to 300 ° C./min, preferably 150 to 250 ° C./min in the air or an inert gas atmosphere such as nitrogen or argon. And baking at a temperature of 130 to 400 ° C., preferably 150 to 200 ° C., for 10 to 60 minutes, preferably 15 to 40 minutes. In this firing, by raising the temperature at a speed within the above range, some particles in the conductive reflective coating film are lifted up, and the conductive layer has an air layer 15 at a part of the interface with the transparent conductive film 14. The reflective film 16 can be formed. The formed conductive reflective film 16 and the transparent conductive film 14 constitute a composite film 17. In addition, when the heating rate is less than 100 ° C./min, there is a problem that the particles in the conductive reflective coating film are not easily lifted, and it is difficult to form an air layer of a certain size or more. There is a problem that the adhesion between the transparent conductive film and the conductive reflective film is lowered because the particles in the reflective coating film are too lifted.

  The air layer 15 is different from pores having an average diameter of 100 nm or less, which appeared in a large amount at the interface in the conventional coating process, and is an interface between the transparent conductive film and the air layer formed by an air layer having a certain size or more. However, since the attenuation of light due to reflection is small, an increase reflection effect in which the ratio of the reflected light component is increased as a result. Therefore, the reflectance is increased as compared with the conventional reflection film.

  The height of the air layer 15 is 5 to 200 nm, preferably 30 to 100 nm, and the width of the air layer 15 is 10 to 300 nm, preferably 100 to 200 nm. The width of the air layer 15 here refers to an average value calculated from the measured value by measuring the longest diameter and the shortest diameter from the area of the air layer 15 at the interface with the transparent conductive film 14.

  The total area of the air layer 15 with respect to the reflective film area is in the range of 5 to 70%, preferably 30 to 50%.

  Here, the height of the air layer 15 is regulated within the range of 5 to 200 nm. If the thickness is less than 5 nm, a problem that the effect of increasing the reflectance is reduced occurs. If the height exceeds 200 nm, the transparent conductive film and the conductive reflective film are formed. This is because a decrease in the adhesion to the substrate occurs.

  The reason why the width of the air layer 15 is defined in the range of 10 to 300 nm is that if it is less than 10 nm, the effect of increasing the reflectance is reduced, and if it exceeds 300 nm, the transparent conductive film and the conductive reflective film This is because a decrease in adhesion occurs.

  Further, the total area of the air layer 15 with respect to the area of the reflective film is defined within a range of 5 to 70% because if the ratio is less than 5%, the reflection ratio at the interface between the transparent conductive film 14 and the air layer 15 is too low. This is because if the ratio of the light component does not increase and exceeds 70%, the contact area between the transparent conductive film 14 and the conductive reflective film 16 becomes too small, and the conductive reflective film 16 is easily peeled off.

  In addition, the measuring method of the total area with respect to the reflective film area of an air layer, the height of an air layer, the width | variety of an air layer, and the thickness of a reflective film in this invention is calculated | required with the following methods. First, the conductive reflective film in close contact with the transparent conductive film on the substrate is processed by a focused ion beam (FIB) method to expose a cross section. Next, by observing this cross section with a scanning electron microscope (SEM), the shape of the interface of the metal film / substrate is observed. And about this interface image, the thickness of a reflecting film, the average height of an air layer, the average width of an air layer are calculated | required, and also the total area with respect to the reflecting film area of an air layer is evaluated. Here, the diameter of the evaluated opening is determined by regarding the length of the opening in the sectional view as an average width.

  Here, the application by the wet coating method is such that the thickness after firing is in the range of 0.05 to 2.0 μm because the surface resistance value of the electrode necessary for the solar cell is less than 0.05 μm. This is because if the thickness exceeds 2.0 μm, there is no problem in characteristics, but the amount of material used is increased more than necessary and the material is wasted.

  In addition, the firing temperature of the base material having the conductive reflective coating film was set in the range of 130 to 400 ° C., if it is less than 130 ° C., the sintering between the metal nanoparticles becomes insufficient and the heat during firing of the protective agent. It is difficult to desorb or decompose (separate / combust) due to the above, so that a lot of organic residue remains in the conductive reflective film after baking, and this residue is altered or deteriorated, resulting in a decrease in the conductivity and reflectivity of the conductive reflective film. If the temperature exceeds 400 ° C., the production advantage of the low temperature process cannot be utilized, that is, the manufacturing cost increases and the productivity decreases. In particular, amorphous silicon, microcrystalline silicon, or a hybrid silicon solar using these. This is because the light wavelength range of photoelectric conversion in the battery is affected.

  Furthermore, the firing time of the base material having the conductive reflective coating was set in the range of 10 to 60 minutes because the sintering between the metal nanoparticles became insufficient and the heat during firing of the protective agent in less than 10 minutes. It is difficult to desorb or decompose (separate / combust) due to the above, so that a lot of organic residue remains in the conductive reflective film after baking, and this residue is altered or deteriorated, resulting in a decrease in the conductivity and reflectivity of the conductive reflective film. This is because, if the time exceeds 60 minutes, the characteristics are not affected, but the manufacturing cost is increased more than necessary and the productivity is lowered.

  Among additives, PVP, which is an organic polymer, a copolymer of PVP, and water-soluble cellulose are known to gradually begin thermal decomposition at about 200 to 300 ° C. in the atmosphere. The speed is extremely slow. However, decomposition proceeds rapidly when the temperature exceeds 400 ° C. For example, when the metal nanoparticle film is baked at 130 ° C. for 10 minutes, these organic molecules remain in the film by 90% or more before baking. On the other hand, when the metal nanoparticle film is baked at 400 ° C. for 10 minutes, these organic molecules remain in the film by 50% or more.

  Thus, the production method of the present invention is a simple process in which the conductive reflective film composition is applied onto the transparent conductive film 14 by wet coating, and the substrate having the conductive reflective coating film is baked. The conductive reflective film 16 can be formed so as to have the air layer 15 at the interface with the transparent conductive film 14. Since a vacuum process is not required at the time of film formation, process restrictions are small, and the running cost of manufacturing equipment can be greatly reduced.

  In the conductive reflective film 16 of the present invention, a specific resistance close to the specific resistance of the metal itself constituting the metal nanoparticles contained in the composition is obtained. That is, it shows a specific resistance as low as a bulk that can be used as an electrode for a solar cell.

  In addition, the conductive reflective film 16 of the present invention is superior in long-term stability such as film reflectivity, adhesion, and specific resistance as compared with a film formed by a vacuum process such as sputtering. The reason for this is that the conductive reflective film of the present invention formed in the atmosphere is less susceptible to moisture intrusion and oxidation than a film formed in vacuum.

  The conductive reflective film 16 of the present invention has a high reflectance from the substrate side and exhibits a specific resistance as low as that of the bulk, and therefore can be used as an electrode of a solar cell.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Examples 1-37>
The composition for transparent electrically conductive films was prepared with the component of the classification | category 1-8 shown in the following Table 1, and a content rate. The classification numbers in Table 1 of the composition for transparent conductive film used in each Example are shown in Tables 2 to 4.

  In category 1, as shown in Table 1 below, as conductive oxide powder, 15% by mass of IZO powder having an average particle size of 0.025 μm, 72.77% by mass of isopropanol as a dispersion medium, and 2 of non-polymer type binder as a binder. -10% by mass of a mixed solution of n-butoxyethanol and 3-isopropyl-2,4-pentanedione, and a mixture of indium nitrate and lead acetate (mass ratio 1: 1) as a low resistance agent in a ratio of 2.23% by mass. An amount of 60 g was placed in a 100 cc glass bottle and dispersed in a paint shaker for 6 hours using 100 g of zirconia beads having a diameter of 0.3 mm (Microhaika, manufactured by Showa Shell Sekiyu KK) to obtain a transparent conductive film composition. .

  In Category 2, as shown in the following Table 1, 7.5% by mass of ITO powder having an average particle size of 0.025 μm as a conductive oxide powder, and a mixed liquid of isopropanol, ethanol and N, N-dimethylformamide as a dispersion medium (Mass ratio 4: 2: 1) is the first mixed solution, which is 92.3% by mass, the binder is 0.038% by mass of 2,4-pentanedione of a non-polymer type binder, and the above formula ( A transparent conductive film composition was obtained in the same manner as in Category 1 at a ratio of 0.162% by mass of the titanium coupling agent shown in 4).

  In Category 3, as shown in Table 1 below, 5% by mass of ATO powder having an average particle size of 0.025 μm as the conductive oxide powder, 50.99% by mass of the first mixed liquid as the dispersion medium, and non-binder as the binder For a transparent conductive film in the same manner as in Category 1, with a polymer-type binder of 2-n-propoxyethanol of 44% by mass and a titanium coupling agent of 0.01% by mass represented by the above formula (4) as a coupling agent. A composition was obtained.

  In Category 4, as shown in Table 1 below, 5% by mass of AZO powder having an average particle size of 0.025 μm as a conductive oxide powder, 74.64% by mass of the first mixed liquid as a dispersion medium, and 2% as a binder. , 2-dimethyl-3,5-hexanedione and isopropyl acetate mixed liquid (mass ratio 1: 1) 20 mass%, ratio of titanium coupling agent 0.36 mass% shown in the above formula (3) as a coupling agent Thus, a transparent conductive film composition was obtained in the same manner as in Category 1.

  In Category 5, as shown in Table 1 below, 5% by mass of TZO powder having an average particle size of 0.025 μm as a conductive oxide powder, 93.95% by mass of the first mixed liquid as a dispersion medium, and 2% as a binder. -Mixture of isobutoxyethanol, 2-hexyloxyethanol and n-propyl acetate (mass ratio 4: 1: 1) 0.8% by mass, titanium coupling agent represented by the above formula (5) as a coupling agent 0. A transparent conductive film composition was obtained in the same manner as in Category 1 at a proportion of 25% by mass.

  In Category 6, first, ATO powder having an average particle size of 0.010 μm was suspended in water to adjust the pH to 7, and treated with a bead mill for 30 minutes. An amount of 0.01% by mass of hydroxypropylcellulose as a water-soluble cellulose derivative with respect to ATO powder was added to the suspension to obtain a conductive water-acid solution. The conductive water-acid solution thus obtained was prepared to a solid content concentration of 18.5%, and 100 g of this dispersion and 100 g of a 13.2% by weight gelatin aqueous solution were mixed at 40 ° C. A composition for transparent conductive film was obtained.

In the classification 7, as shown in Table 1 below, 5.3% by mass of ATO powder having an average particle size of 0.025 μm as a conductive oxide powder, and a mixed liquid of ethanol and butanol as a dispersion medium (mass ratio 98: 2) Is used as a second mixed solution, and is mixed at a ratio of 85% by mass, 1.7% by mass of a SiO ₂ binder as a binder, and 8.0% by mass of a titanium coupling agent represented by the above formula (3) as a coupling agent. Thus, a composition for transparent conductive film was obtained. The SiO ₂ binder used as the binder was a 500 ml glass four-necked flask, 140 g of tetraethoxysilane and 240 g of ethyl alcohol were added, and 11.0 g of 12N-HC was dissolved in 25 g of pure while stirring. And then reacted at 80 ° C. for 6 hours.

In category 8, as shown in Table 1 below, the conductive oxide powder is 8.0% by mass of ITO powder having an average particle size of 0.025 μm, the second mixed liquid is 88% by mass as a dispersion medium, and the binder is SiO 2%. _The composition for transparent conductive films was obtained by mixing 2.0 mass% of 2 binders and 2.0 mass% of titanium coupling agents shown in the above formula (2) as a coupling agent. The SiO ₂ binder used as the binder was produced by the same method as in Category 7.

続いて、以下の手順により、導電性反射膜用組成物を調製した。

Subsequently, a conductive reflective film composition was prepared by the following procedure.

  First, silver nitrate was dissolved in deionized water to prepare an aqueous metal salt solution. In addition, sodium citrate was dissolved in deionized water to prepare an aqueous sodium citrate solution having a concentration of 26% by mass. Reduction in which aqueous ferric sulfate is directly added and dissolved in this sodium citrate aqueous solution in a nitrogen gas stream maintained at 35 ° C. to contain citrate ions and ferrous ions in a molar ratio of 3: 2. An aqueous agent solution was prepared.

  Next, with the nitrogen gas stream maintained at 35 ° C., a magnetic stirrer stirrer is placed in the reducing agent aqueous solution, the stirrer is rotated at a rotation speed of 100 rpm, and the reducing agent aqueous solution is stirred, The metal salt aqueous solution was added dropwise to the reducing agent aqueous solution and mixed. Here, the amount of the metal salt aqueous solution added to the reducing agent aqueous solution is adjusted so that the concentration of each solution is adjusted to 1/10 or less of the amount of the reducing agent aqueous solution. The reaction temperature was maintained at 40 ° C. The mixing ratio of the reducing agent aqueous solution to the metal salt aqueous solution is such that the molar ratio of citrate ions and ferrous ions in the reducing agent aqueous solution to the total valence of metal ions in the metal salt aqueous solution is 3 times the mole. It was made to become. After the addition of the aqueous metal salt solution to the reducing agent aqueous solution was completed, stirring of the mixed solution was further continued for 15 minutes to generate metal particles inside the mixed solution to obtain a metal particle dispersion in which the metal particles were dispersed. The pH of the metal particle dispersion was 5.5, and the stoichiometric amount of metal particles in the dispersion was 5 g / liter.

  The obtained dispersion was allowed to stand at room temperature to precipitate the metal particles in the dispersion, and the aggregates of the precipitated metal particles were separated by decantation. Deionized water was added to the separated metal agglomerated to form a dispersion, subjected to desalting by ultrafiltration, and further washed with substitution with methanol, so that the metal (silver) content was 50% by mass. Thereafter, the centrifugal force of the centrifuge is adjusted using a centrifuge to separate relatively large silver particles having a particle size exceeding 100 nm, thereby obtaining silver nanoparticles having a primary particle size of 10 to 50 nm. It adjusted so that it might contain 71% by a number average. That is, the ratio of the silver nanoparticles in the range of the primary particle diameter of 10 to 50 nm to the silver nanoparticles of 100% on the number average was adjusted to 71%. The obtained silver nanoparticles were chemically modified with a protective agent for an organic molecular main chain having a carbon skeleton of 3 carbon atoms.

  Next, 10 parts by mass of the obtained metal nanoparticles are dispersed by adding and mixing in 90 parts by mass of a mixed solution containing water, ethanol and methanol. Further, the additives shown in the following Tables 2 to 4 are added to this dispersion. Was added so that it might become a ratio shown in Table 2-Table 4, and the composition for electroconductive reflective films was obtained, respectively. In addition, the metal nanoparticle which comprises the composition for electroconductive reflective films contains 75 mass% or more of silver nanoparticles.

  In addition, when containing metal nanoparticles other than silver nanoparticles together with silver nanoparticles as metal nanoparticles, the dispersion of silver nanoparticles obtained by the above method is used as the first dispersion, and instead of silver nitrate, Metal nanoparticles other than silver nanoparticles are produced in the same manner as in the method for producing silver nanoparticles, except that a metal salt of a type that forms metal nanoparticles other than silver nanoparticles shown in the following Tables 2 to 4 is used. The dispersion of the metal nanoparticles is used as the second dispersion, and before adding the additive, the first dispersion and the second dispersion are made to have the ratios shown in Tables 2 to 4 below. By mixing the dispersion, a composition for a conductive reflective film was obtained.

The obtained composition for transparent conductive film was formed on various substrates shown in Tables 2 to 4 by various film forming methods so that the thickness after firing was 0.7 to 1.3 × 10 ² nm. After coating, the film is dried at a temperature of 25 ° C. for 5 minutes to form a transparent conductive coating film, and then the resulting conductive reflective film composition has a thickness of 0 after baking on the formed transparent conductive film. The film was applied by various film forming methods so as to have a thickness of 0.05 to 2.0 μm, and then dried at a temperature of 25 ° C. for 5 minutes to form a conductive reflective coating film. Subsequently, the composite film comprised from the transparent conductive film and the electroconductive reflective film was formed on the base material by baking on the heat processing conditions shown in the following Table 2-Table 4.

  In Tables 2 to 4, “PVP” represents polyvinylpyrrolidone having Mw of 360,000, and “PET” represents polyethylene terephthalate.

<Comparative Examples 1-3>
A transparent conductive film is formed by sputtering, which is a vacuum deposition method, so that the film thickness becomes 0.5 to 2 × 10 ² nm, and then the same composition for a conductive reflective film as in Example 1 is formed on this transparent conductive film. A conductive reflective coating film is formed by the same method as in Example 1 and fired under the heat treatment conditions shown in Table 4 below, so that a transparent conductive film and a conductive reflective film are formed on the substrate. A composite membrane was formed.

＜比較試験１＞
実施例１〜３７及び比較例１〜３で得られた基材上に形成した透明導電膜及び導電性反射膜から構成された複合膜について、透明導電膜との界面に出現する気孔の分布、空気層及び導電性反射膜の裏面反射率を評価した。評価結果を次の表５及び表６にそれぞれ示す。

<Comparison test 1>
About the composite film composed of the transparent conductive film and the conductive reflective film formed on the substrates obtained in Examples 1 to 37 and Comparative Examples 1 to 3, the distribution of pores appearing at the interface with the transparent conductive film, The back surface reflectance of the air layer and the conductive reflective film was evaluated. The evaluation results are shown in the following Table 5 and Table 6, respectively.

  The average height, average width, and area occupancy of the air layer are measured using a focused ion beam (FIB) method on a conductive reflective film that is in close contact with the transparent conductive film on the substrate to expose the sample cross section. The cross section of this sample was observed with a scanning electron microscope (SEM) to observe the shape of the metal film / substrate interface. And about this interface image, the average height of the opening part and the average width were calculated | required, and also the area occupation rate was evaluated. Here, the diameter of the evaluated opening was determined by regarding the length of the opening in the cross-sectional view as the average width.

  The back surface reflectance of the conductive reflective film was evaluated by measuring the diffuse reflectance of the conductive reflective film at wavelengths of 500 nm and 1100 nm using a combination of an ultraviolet-visible spectrophotometer and an integrating sphere.

表５及び表６から明らかなように、焼成において１００℃／分未満の速度で昇温した比較例１〜３では、１１００ｎｍの反射率は８５％以上と高かったが、５００ｎｍの反射率が８０％未満と低く、波長によって反射率にばらつきが生じてしまう結果が確認された。

As is clear from Tables 5 and 6, in Comparative Examples 1 to 3 where the temperature was raised at a rate of less than 100 ° C./min during firing, the reflectance at 1100 nm was as high as 85% or more, but the reflectance at 500 nm was 80%. As a result, it was confirmed that the reflectance varies depending on the wavelength.

  On the other hand, in Examples 1 to 37 in which the temperature was increased at a rate of 100 to 300 ° C./min during baking, the reflectances at both wavelengths of 500 nm and 1100 nm were as high as 80% or higher.

  INDUSTRIAL APPLICABILITY The present invention is extremely suitable as a technique for manufacturing an electrode provided on the opposite side of a light receiving surface suitable for a super straight type solar cell characterized by using a transparent substrate such as glass as a light receiving surface. It is.

  In addition, by using the present invention, it is possible to replace the transparent conductive film and the conductive reflective film, which have been conventionally formed by the vacuum film formation method, with a coating and baking process, and a significant reduction in manufacturing cost is expected. it can.

DESCRIPTION OF SYMBOLS 11 Base material 12 Transparent electrically conductive film 13 Photoelectric converting layer 14 Transparent electrically conductive film 15 Air layer 16 Conductive reflective film 17 Composite film

Claims (22)

In the conductive reflective film formed on the transparent conductive film formed on the photoelectric conversion layer of the super straight type thin film solar cell,
A composition containing metal nanoparticles is applied onto the transparent conductive film by a wet coating method, and a base material having the coating film is baked to have an air layer at a part of the interface with the transparent conductive film. A reflective film is formed on
The conductive reflective film, wherein the total area of the generated air layer with respect to the reflective film area is in the range of 5 to 70%.   The conductive reflective film according to claim 1, wherein the height of the air layer is in the range of 5 to 200 nm, and the width of the air layer is in the range of 10 to 300 nm.   The conductive reflective film according to claim 1 or 2, wherein the reflective film contains one or more substances selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose.   The conductive reflective film according to any one of claims 1 to 3, wherein a ratio of silver in the metal element contained in the reflective film is 75% by mass or more.   5. The conductive reflective film according to claim 1, wherein the thickness of the reflective film is in a range of 0.05 to 2.0 μm.   The conductive reflective film according to any one of claims 1 to 5, wherein the metal nanoparticles contained in the reflective film have a number average particle size of 70% or more in a range of 10 to 50 nm.   Application by the wet coating method of the composition containing metal nanoparticles is applied so that the thickness after baking is in the range of 0.05 to 2.0 μm, and baking of the substrate having a coating film is performed. The conductive reflective film according to any one of claims 1 to 6, wherein the conductive reflective film is carried out at a temperature rising rate of 100 to 300 ° C / min and a temperature of 130 to 400 ° C for 10 to 60 minutes.   The wet coating method is any one of a spray coating method, a dispenser coating method, a spin coating method, a knife coating method, a slit coating method, an ink jet coating method, a screen printing method, an offset printing method or a die coating method. The conductive reflective film according to any one of the above.   A composition containing metal nanoparticles is prepared by dispersing metal nanoparticles having a silver content in a metal element of 75% by mass or more in a dispersion medium, and the metal nanoparticles have a carbon skeleton of 1 to 3 carbon atoms. The chemical modification by the protective agent of an organic molecular principal chain, The said metal nanoparticle contains the metal nanoparticle of the range of primary particle size 10-50nm in number average 70% or more of any one of Claim 1 thru | or 8 Conductive reflective film.   2 selected from the group consisting of glass, ceramics containing a transparent conductive material or a translucent substrate made of a polymer material, or glass, ceramics containing a transparent conductive material, a polymer material and silicon. The conductive reflective film according to any one of claims 1 to 9, wherein the conductive reflective film is a translucent laminate of more than one type.   The composition containing metal nanoparticles further comprises one or more additives selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds, and silicone oils. The conductive reflective film according to any one of Items 10 to 10.   The electroconductive reflective film according to claim 11, wherein the organic polymer is one or more substances selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer, and water-soluble cellulose.   An oxide or composite in which the metal oxide includes at least one selected from the group consisting of aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium, and antimony The conductive reflective film according to claim 11, which is an oxide.   A hydroxide in which the metal hydroxide contains at least one selected from the group consisting of aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium and antimony The conductive reflective film according to claim 11.   The organometallic compound is a metal soap, metal complex, or metal alkoxide containing at least one selected from the group consisting of silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, and tin. The conductive reflective film according to claim 11.   The electroconductive reflective film according to any one of claims 1 to 15, comprising 1% by mass or more of water and 2% by mass or more of alcohols as a dispersion medium.   A composition containing metal nanoparticles is applied onto a transparent conductive film formed on a photoelectric conversion layer of a super straight type thin film solar cell by a wet coating method, and a substrate having the coating film is applied at 100 to 300 ° C./min. The film was formed to have an air layer at a part of the interface with the transparent conductive film by firing at a temperature of 130 to 400 ° C. for 10 to 60 minutes and firing. A method for producing a conductive reflective film, wherein the total area of the air layer with respect to the reflective film area is in the range of 5 to 70%. The composition containing metal nanoparticles is prepared by dispersing metal nanoparticles in which the proportion of silver in the metal element is 75% by mass or more in a dispersion medium,
The metal nanoparticles are chemically modified with an organic molecular main chain protective agent having a carbon skeleton of 1 to 3 carbon atoms,
The metal nanoparticles contain 70% or more of average number of metal nanoparticles having a primary particle size in the range of 10 to 50 nm,
The method for producing a conductive reflective film according to claim 17, wherein the composition is applied onto the transparent conductive film by a wet coating method so that the thickness after firing is in the range of 0.05 to 2.0 μm.   A transparent conductive film is formed on a photoelectric conversion layer of a super straight type solar cell, and the conductive reflective film according to any one of claims 1 to 18 or the method for producing a conductive reflective film on the transparent conductive film. A composite film for a super straight type solar cell, wherein the manufactured conductive reflective film is formed.   A laminate using the conductive reflective film according to any one of claims 1 to 19, or a conductive reflective film manufactured by the method for manufacturing a conductive reflective film.   A solar cell using the conductive reflective film and laminate produced by the method for producing a conductive reflective film, laminate or conductive reflective film according to any one of claims 1 to 20 as an electrode.   A solar cell using the conductive reflective film according to any one of claims 1 to 21 as an electrode.

Images