JP5637196B2 - Composite film for super straight type thin film solar cell and manufacturing method thereof - Google Patents

Description

  The present invention relates to a composite film composed of two layers of a transparent conductive film and a conductive reflective film. More specifically, the present invention relates to a composite film suitable for a super straight type thin film solar cell.

  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, a thin film semiconductor solar cell using a semiconductor such as amorphous silicon having a thickness of several micrometers or less (hereinafter referred to as a thin film solar cell) is a photoelectric conversion layer on an inexpensive substrate such as glass or stainless steel. It is only necessary to form as many semiconductor layers 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 photoelectric conversion layer is composed of a silicon-based material, the absorption coefficient of the photoelectric conversion layer is relatively small. Therefore, when the photoelectric conversion layer has a film thickness of the order of several micrometers, part of the incident light is the photoelectric conversion layer. 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 transmitted through the photoelectric conversion layer is reflected by the reflection film, and then returned to the photoelectric conversion layer again to generate power. 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, since a large cost is generally required for maintaining and operating a large-scale vacuum film forming apparatus, it is expected to develop a cheaper manufacturing method by replacing this with a wet film forming method.

  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 addition, as a simpler method, a method in which a metal having a high reflectance such as silver is used as a nanoparticle and this is applied has been studied (for example, see Patent Document 2). Moreover, the method of apply | coating a metal nanoparticle is mentioned as a method of forming the metal coating film which exhibits a high metal-tone metallic luster on the base-material surface (for example, refer patent document 3). Furthermore, in the super straight type solar cell, the transparent electrode located on the substrate side among the transparent electrodes of the super straight type solar cell taking a structure such as substrate-transparent electrode-photoelectric conversion layer-transparent electrode-back surface reflecting electrode, There is a method in which a coating liquid in which conductive oxide fine particles are dispersed in a dispersion medium is applied and then dried and cured by a heating method (for example, see Patent Document 4).

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)

JP 05-95127 A (Claim 1, paragraph [0015]) JP 09-246577 A (paragraph [0035]) JP 2000-239853 A (Claim 3, paragraph [0009]) JP-A-10-12059 (paragraph [0028], paragraph [0029])

  However, the electroless plating method described in Patent Document 1 includes a process of forming a plating protective film on the surface side, treating the side to be plated with a hydrofluoric acid solution, and then immersing it in an electroless plating solution. In addition to the complicated process, the generation of waste liquid is also expected. Moreover, in the method of applying the metal nanoparticles described in Patent Documents 2 and 3, the reflectance (hereinafter referred to as back surface reflectance) when evaluated from the substrate side of the reflective film applied to the substrate surface is opposite. It tends to be lower than the reflectance on the exposed surface side that hits the side surface (hereinafter referred to as surface reflectance). It is presumed that the porosity is reduced between the reflective film and the base material, and light is repeatedly reflected inside the holes, so that the reflectance is lowered. In addition, when the reflected light passing through the holes is incident on the base material at an incident angle larger than the critical angle, the reflected light is totally reflected at the interface between the holes and the base material, and the total reflected light increases. By doing so, it is estimated that the reflectance decreases. Moreover, in the said patent document 4, the wet film-forming method is used only about the transparent conductive film located in the base material side in a super straight type solar cell, About the transparent conductive film located in the back surface reflective electrode side from the former It is formed by sputtering, which is a vacuum process that has been used.

  An object of the present invention is to provide a composite film of a super straight type thin film solar cell composed of two layers of a transparent conductive film and a conductive reflective film formed by using a wet coating method without reducing the back surface reflectance. There is to do.

  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 composite film for a super straight type thin film solar cell at a lower cost by using a wet coating method. Is to provide.

According to claim 1 invention is a transparent conductive film on the photoelectric conversion layer is formed of a superstrate type thin film solar cell, in a composite film composed of two layers having conductive reflective film is formed on the transparent conductive film, transparent Both the conductive film and the conductive reflective film are formed by a wet coating method, and the transparent conductive film is formed by applying a composition for a transparent conductive film containing conductive oxide fine particles using the wet coating method. The reflective film is formed by applying a composition for a conductive reflective film containing metal nanoparticles using a wet coating method, and the average diameter of pores appearing on the contact surface on the substrate side of the conductive reflective film is 100 nm or less The average depth at which pores are located is 100 nm or less, the number density of pores is 30 / μm ² or less, and the conductive reflective film is made of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose It is a composite film for a super straight type thin film solar cell characterized by containing one or more selected substances.

The invention according to claim 2 is the invention according to claim 1, wherein the conductive reflective film is for a super straight type thin film solar cell in which the proportion of silver in the metal element contained in the film is 75% by mass or more. It is a composite membrane.

The invention according to claim 3 is the composite film for super straight type thin film solar cells according to claim 1, wherein the thickness of the conductive reflective film is in the range of 0.05 to 2.0 μm. .

The invention according to claim 4 is the invention according to claim 1, wherein the number of particles having a particle size in the range of 10 to 50 nm is 70% or more on the average with respect to the metal nanoparticles in which the conductive reflective film is contained in the film. This is a composite film for a super straight type thin film solar cell.

The invention according to claim 5 is the invention according to claim 1, wherein the composition for a conductive reflective film includes 75% by mass or more of silver nanoparticles as metal nanoparticles, and the metal nanoparticles have a carbon skeleton with a carbon number. For a super-straight type thin film solar cell that is chemically modified with a protective agent for organic molecular main chains of 1 to 3, and that the metal nanoparticles have a number average of 70% or more of metal nanoparticles having a primary particle size of 10 to 100 nm. It is a composite membrane.

The invention according to claim 6 is the invention according to claim 1, wherein the composition for the conductive reflective film is made of gold, platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and manganese. It is a composite film for a super straight type thin film solar cell containing 0.02% by mass or more and less than 25% by mass of metal nanoparticles composed of one or two or more mixed compositions or alloy compositions selected from the group consisting of:

The invention according to claim 7 is the invention according to claim 1, wherein the composition for a conductive reflective film contains 1% by mass or more of water and 2% by mass or more of alcohols as a dispersion medium. It is a composite film for solar cells.

The invention according to claim 8 is the invention according to claim 1, wherein the composition for the conductive reflective film is selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds, and silicone oils. This is a composite film for a super straight type thin film solar cell containing one or more additives.

The invention according to claim 9 is the invention according to claim 8 , wherein the organic polymer is one or more selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose. This is a composite film for a super straight type thin film solar cell.

The invention according to claim 10 is the invention according to claim 8 , wherein the metal oxide is aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium and It is a composite film for a super straight type thin film solar cell, which is an oxide or composite oxide containing at least one selected from the group consisting of antimony.

The invention according to claim 11 is the invention according to claim 8 , wherein the metal hydroxide is aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium. And a composite film for a super straight type thin film solar cell, which is a hydroxide containing at least one selected from the group consisting of antimony.

The invention according to claim 12 is the invention according to claim 8 , wherein the organometallic compound is silicon, titanium, aluminum, antimony, indium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum and It is a composite film for a super straight type thin film solar cell, which is at least one metal soap, metal complex or metal alkoxide selected from the group consisting of tin.

The invention according to claim 13 is a composition for transparent conductive film, which is a mixture of conductive oxide fine particles and other components on a photoelectric conversion layer of a superstrate thin film solar cell via a transparent conductive film on a substrate. A step of forming a transparent conductive film by applying a wet coating method, and a conductive reflective coating by applying a composition for a conductive reflective film containing metal nanoparticles on the transparent conductive film by a wet coating method And a transparent conductive film having a thickness of 0.03 to 0.5 μm and 0.05 by baking a substrate having a transparent conductive film and a conductive reflective film at 130 to 400 ° C. Forming a two-layered conductive reflective film having a thickness of up to 2.0 μm, and the composition for transparent conductive film is at least a dispersion medium and is cured by heating with a dispersion medium or a non-polymer as the other component One of mold binders Or it is the manufacturing method of the composite film for super straight type thin film solar cells containing both .

The invention according to claim 14 is the invention according to claim 13 , wherein 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 inkjet coating method, a screen printing method, It is the manufacturing method of the composite film for super straight type thin film solar cells which is either the offset printing method or the die coating method.

As described above, according to the present invention, a composite composed of two layers in which a transparent conductive film is formed on a photoelectric conversion layer of a super straight type thin film solar cell and a conductive reflective film is formed on the transparent conductive film. In the film, both the transparent conductive film and the conductive reflective film are formed by a wet coating method, and the transparent conductive film is formed by applying a composition for transparent conductive film containing conductive oxide fine particles using the wet coating method. Since the conductive reflective film is formed by applying a composition for conductive reflective film containing metal nanoparticles using a wet coating method, a transparent conductive film formed by a vacuum deposition method such as a sputtering method is used. In addition, a transparent conductive film having a low refractive index is formed, and thereby, a reflection enhancing effect is produced in the conductive reflective film, and a sufficient reflectivity is obtained. The conductive reflective film contains one or more substances selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose, and the conductive reflective film has a contact surface on the substrate side. A translucent substrate having a transmittance of 98% or more is obtained by having an average diameter of pores appearing of 100 nm or less, an average depth of pores of 100 nm or less, and a number density of pores of 30 / μm ² or less. When used, a high diffuse reflectance of 80% or more of the theoretical reflectance can be achieved in the wavelength range of 500 to 1200 nm.

  Moreover, a vacuum process such as a vacuum deposition method or a sputtering method is eliminated as much as possible, and a composite film can be manufactured at low cost by using a wet coating method.

It is the figure which represented typically the cross section of the composite film for super straight type thin film solar cells of this invention.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
As shown in FIG. 1, the super straight type thin film solar cell generally has a transparent conductive film 11b on a layer in which a transparent conductive film 13 and a photoelectric conversion layer 12 are laminated in this order on a base material 14. The conductive reflective film 11a is formed on the transparent conductive film 11b.
The present invention relates to a composite film 11 for a super straight type thin film solar cell comprising two layers of a transparent conductive film 11b formed on the photoelectric conversion layer 12 and a conductive reflective film 11a formed on the transparent conductive film 11b. It is about.

  The composite film 11 of the present invention is formed by applying a composition for a transparent conductive film in which the transparent conductive film 11b includes conductive oxide fine particles using a wet coating method. When the transparent conductive film 11b is formed by a vacuum film formation method such as sputtering, the refractive index of the film of the transparent conductive film 11b is determined by the material of the target material, and thus is formed by a vacuum film formation method such as sputtering. In the transparent conductive film 11b, it is difficult to obtain a desired refractive index. On the other hand, the transparent conductive film 11b formed using the wet coating method is formed by applying a composition for transparent conductive film, which is a mixture of conductive oxide fine particles and other components, so that the wet coating method is used. A desired low refractive index can be obtained for a film formed by using. The refractive index of the transparent conductive film 11b is 1.5-2. The transparent conductive film 11b having a low refractive index has a high refractive index formed by a vacuum film-forming method such as a conventional sputtering method in order to give a reflection enhancing effect on the optical design to the conductive reflective film 11a to be bonded. A higher reflectance than that of the conductive reflective film 11a bonded to the transparent conductive film 11b is obtained.

  Further, the composite film 11 of the present invention is obtained by applying a wet coating method to a conductive reflective film composition containing metal nanoparticles on a transparent conductive film 11b formed using the wet coating method. It is formed by using and applying. Therefore, the formed conductive reflective film 11a can obtain good film formability and high diffuse reflectance. When forming a film on a substrate such as glass, good film formability and high diffuse reflectance can be obtained even when the film is formed by a vacuum deposition method such as sputtering, but it is formed using a wet coating method. When a film is formed on the formed transparent conductive film 11b by a vacuum deposition method such as sputtering, the solvent remaining in the transparent conductive film 11b adversely affects the formed conductive reflective film 11a, and thus a high reflectance is obtained. It is difficult to form the conductive reflective film 11a.

  As described above, in the composite film 11 of the present invention, the optical reflective enhancement effect provided by the transparent conductive film 11b having a low refractive index, the good film formability and the high diffuse reflectance of the conductive reflective film 11a. High reflectance can be obtained.

Furthermore, the average diameter of pores appearing on the contact surface on the base material 14 side of the conductive reflective film 11a is 100 nm or less, the average depth at which the pores are located is 100 nm or less, and the number density of the pores is 30 / μm ² or less. Thus, when a translucent substrate having a transmittance of 98% or more is used, the conductive reflective film 11a capable of achieving a high diffuse reflectance of 80% or more of the theoretical reflectance in a wavelength range of 500 to 1200 nm; Become. This wavelength range of 500 to 1200 nm almost covers the convertible wavelengths when polycrystalline silicon is used as the photoelectric conversion layer. When the average diameter of the pores is set to 100 nm or less, the reflection spectrum generally shows items with high reflectance on the long wavelength side and low values on the short wavelength side, but when the average diameter of the pores exceeds 100 nm, the reflectance starts to decrease. This is because the inflection point is shifted to the longer wavelength side, so that a good reflectance cannot be obtained. The average pore depth is set to 100 nm or less because when the average pore depth exceeds 100 nm, the gradient (inclination) of the reflection spectrum increases and a good reflectance cannot be obtained. The reason why the number density of the pores is set to 30 / μm ² or less is that when the number density of the pores exceeds 30 / μm ² , the reflectance on the long wavelength side is lowered and a good reflectance cannot be obtained. is there.

In addition, since the conductive reflective film constituting the composite film contains one or more substances selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose, the conductive reflective film The average diameter of pores appearing on the contact surface on the transparent conductive film side of the film can be easily reduced to 100 nm or less, the average depth to 100 nm or less, and the number density to 30 / μm ² or less. Moreover, in the electroconductive reflective film which comprises this composite film, since the ratio of silver in the metal element contained in a film | membrane is 75 mass% or more, a high reflectance is obtained. If it is less than 75% by mass, the reflectance of the conductive reflective film formed using this composition tends to decrease. Moreover, since the thickness of the electroconductive reflective film which comprises a composite film is 0.05-2.0 micrometers, the surface resistance value of an electrode required for a solar cell is obtained. Furthermore, with respect to the metal nanoparticles in which the conductive reflective film constituting the composite film is contained in the film, the particles having a particle size in the range of 10 to 50 nm are 70% or more in number average. Rate is obtained.

  The composition for transparent conductive film used for forming the transparent conductive film according to the present invention is a composition containing conductive oxide fine particles, and the conductive oxide fine particles are dispersed in a dispersion medium.

  Examples of the conductive oxide fine particles contained in the composition for transparent conductive film include ITO (Indium Tin Oxide), tin oxide powder of ATO (Antimony Tin Oxide), Al, Co, and Fe. Zinc oxide powder containing one or more metals selected from the group consisting of In, Sn, and Ti is preferable. Among these, ITO, ATO, AZO (Aluminum Zinc Oxide), Particularly preferred are IZO (Indium Zinc Oxide) and TZO (Tin Zinc Oxide). 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. The polymer binder may include aluminum, silicon, titanium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum or tin metal soap, metal complex or metal alkoxide hydrolyzate. preferable. 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, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium or antimony. These polymer-type binder and non-polymer-type binder are cured by heating, thereby enabling formation of a transparent conductive film 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 to improve the adhesion between the conductive fine particles and the binder and the adhesion between the transparent conductive film formed from the composition for transparent conductive film and the layer laminated on the substrate or the conductive reflective film. 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). Moreover, as a titanium coupling agent, the titanium coupling agent which has the dialkyl pyrophosphite group shown by following formula (2)-(4), and the dialkyl phosphite group shown by following formula (5) are used. The titanium coupling agent which has is mentioned.

カップリング剤の含有割合は、透明導電膜用組成物に占める固形分の割合として、０．２〜５質量％の範囲内が好ましく、このうち０．５〜２質量％の範囲内が特に好ましい。

The content of the coupling agent is preferably in the range of 0.2 to 5% by mass, particularly preferably in the range of 0.5 to 2% by mass, as the solid content in the transparent conductive film composition. .

  The dispersion medium constituting the composition for transparent conductive film includes water, alcohols such as methanol, ethanol, isopropyl alcohol and butanol, ketones such as acetone, methyl ethyl ketone, cyclohexanone and isophorone, toluene, xylene, hexane and cyclohexane. Hydrocarbons such as N, N-dimethylformamide, amides such as N, N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, glycols such as ethylene glycol, glycol ethers such as ethyl cellosolve, and the like. The content ratio of the dispersion medium is preferably in the range of 80 to 99% by mass in order to obtain good film formability.

  Moreover, it is preferable to add a low resistance agent, a water-soluble cellulose derivative, etc. according to the component to be used. The low resistance agent is preferably one or more selected from the group consisting of cobalt, iron, indium, nickel, lead, tin, titanium and zinc mineral salts and organic acid salts. For example, a mixture of nickel acetate and ferric chloride, zinc naphthenate, a mixture of tin octylate and antimony chloride, a mixture of indium nitrate and lead acetate, a mixture of titanium acetyl acetate and cobalt octylate, and the like can be mentioned. The content ratio of these low resistance agents is preferably 0.2 to 15% by mass with respect to the conductive oxide powder. The water-soluble cellulose derivative is a non-ionizing active agent, but it has a very high ability to disperse the conductive oxide powder even when added in a small amount compared to other surfactants, and it is formed by adding a water-soluble cellulose derivative. Transparency in the transparent conductive film is also improved. Examples of the water-soluble cellulose derivative include hydroxypropyl cellulose and hydroxypropyl methylcellulose. The addition amount of the water-soluble cellulose derivative is preferably in the range of 0.2 to 5% by mass.

  The conductive reflective film composition used for forming the conductive reflective film according to the present invention is a composition in which metal nanoparticles are dispersed in a dispersion medium. The metal nanoparticles contain 75% by mass or more, preferably 80% by mass or more of silver nanoparticles. The reason for limiting the content of silver nanoparticles to the range of 75% by mass or more with respect to 100% by mass of all metal nanoparticles is that the reflection of the conductive reflective film formed using this composition is less than 75% by mass. This is because the rate drops. Silver 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 number of carbons in the carbon skeleton of the organic molecular main chain of the protective agent that chemically modifies the metal nanoparticles was limited to the range of 1 to 3 because the protective agent was released by the heat during firing when the carbon number was 4 or more. Alternatively, it is difficult to be decomposed (separated / burned), and a large amount of organic residue remains in the film, which deteriorates or deteriorates and decreases the conductivity and reflectivity of the conductive reflective film.

  The silver nanoparticles contain 70% or more, preferably 75% or more, of silver nanoparticles having a primary particle size in the range of 10 to 50 nm in terms of number average. The content of the metal nanoparticles in the range of the primary particle size of 10 to 50 nm is limited to a range of 70% or more with respect to 100% of all metal nanoparticles on the number average. Since the specific surface area increases and the proportion of organic matter increases, even organic molecules that are easily desorbed or decomposed (separated and burned) by the heat during firing, the organic molecules occupy a large proportion. A large amount of organic residue remains, 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 and the density of the conductive reflective film is likely to decrease. This is because the conductivity and reflectivity of the conductive reflective film are lowered. Furthermore, the primary particle size of the metal nanoparticles is within the range of 10 to 50 nm because the metal nanoparticles with the primary particle size within the range of 10 to 50 nm correlate with stability over time (aging stability) by statistical methods. Because it is.

  On the other hand, the metal nanoparticles other than silver nanoparticles are one or a mixture of two or more selected from the group consisting of gold, platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and manganese. It is a metal nanoparticle which consists of a composition or an alloy composition, and metal nanoparticles other than this silver nanoparticle are 0.02 mass% or more and less than 25 mass% with respect to 100 mass% of all metal nanoparticles, Preferably it is 0.03. It is contained by mass% to 20 mass%. The reason why the content of metal nanoparticles other than silver nanoparticles is limited to the range of 0.02% by mass or more and less than 25% by mass with respect to 100% by mass of all metal nanoparticles is particularly less than 0.02% by mass. Although there is no major problem, within the range of 0.02 to 25% by mass, the conductivity of the conductive reflective film after a weather resistance test (a test held in a constant temperature and humidity chamber at a temperature of 100 ° C. and a humidity of 50% for 1000 hours) And 25% by mass or more, the conductivity and reflectivity of the conductive reflective film immediately after baking are lowered, and the conductive reflection after the weather resistance test is characteristic. This is because the film has lower conductivity and reflectance than the conductive reflection film before the weather resistance test.

  The conductive reflective film composition used for forming the conductive reflective film according to the present invention is one selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds, and silicone oils. Or 2 or more types of additives are included. The metal oxide, metal hydroxide, organometallic compound or silicone oil contained in the composition as an additive increases the chemical bond with the transparent conductive film or the anchor effect, or is transparent with the metal nanoparticles in the firing process. By improving the wettability with the conductive film, the adhesion with the transparent conductive film can be improved without impairing the conductivity.

  When a conductive reflective film is formed using a composition that does not contain the above metal oxide or the like, the surface roughness of the formed conductive reflective film increases, but the uneven shape on the surface of the conductive reflective film has a photoelectric conversion efficiency. It is said that there is a condition for optimizing the thickness, and it is impossible to form a conductive reflective film surface having excellent photoelectric conversion efficiency simply by having a large surface roughness. As in the composition of the present invention, it is possible to form a surface having an optimized surface roughness by adjusting the type, concentration, and the like of the metal oxide.

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 content of the additive is less than 0.1%, pores having a large average diameter may appear or the pore density 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 a composite oxide containing Specifically, the composite oxide is ITO, ATO, 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. Examples include hydroxides containing seeds.

  The organometallic compound used as the additive is at least one selected from the group consisting of silicon, titanium, aluminum, antimony, indium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum and tin. Metal soap, metal complex or metal alkoxide. 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.

  The dispersion medium constituting the conductive reflective film composition is preferably composed of an alcohol or an alcohol-containing aqueous solution. Examples of the alcohols used as the dispersion medium include one or more selected from the group consisting of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, glycerol, isobornyl hexanol and erythritol. The alcohol-containing aqueous solution contains 1% by mass or more, preferably 2% by mass or more of water, and 2% by mass or more, preferably 3% by mass or more of alcohols with respect to 100% by mass of all the dispersion media. Is preferred. 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. The reason why the water content is 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 for conductive reflective film by a wet coating method when the content is less than 1% by mass. It is difficult to sinter the film at a low temperature, and the conductivity and reflectance of the film after firing are reduced, so that the content of alcohols is in the range of 2% by mass or more with respect to 100% by mass of all dispersion media. If the amount is less than 2% by mass, it is difficult to sinter a film obtained by applying the composition by a wet coating method at a low temperature as described above, and the conductivity and reflectance of the electrode after firing are reduced. Because it will do.

  Furthermore, it is preferable that the protective medium chemically modified on the surface of the dispersion medium, that is, the metal nanoparticle contains one or both of a hydroxyl group (—OH) and a carbonyl group (—C═O). 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 action for low-temperature sintering of a coating film. 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 can be used for low-temperature sintering of a coating film. There is an effective action.

The method for producing the composition for conductive reflective film to be used 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 such that the equivalent of ferrous ions added as a reducing agent is three times the equivalent of metal ions, that is, (number of moles of metal ions in the aqueous metal salt solution) × ( It is prepared so as to satisfy the formula of metal ion valence) = 3 × (ferrous ion in reducing agent aqueous solution). 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.

Next, the manufacturing method of the composite film of this invention is demonstrated.
In the method for producing a composite film of the present invention, first, the composition for a transparent conductive film is applied by a wet coating method onto a photoelectric conversion layer of a superstrate solar cell laminated on a substrate via a transparent conductive film. To do. The coating here is performed so that the thickness after firing is 0.03 to 0.5 μm, preferably 0.05 to 0.1 μm. Subsequently, the coating film is dried at a temperature of 20 to 120 ° C., preferably 25 to 60 ° C. for 1 to 30 minutes, preferably 2 to 10 minutes. In this way, a transparent conductive coating film is formed. Next, the conductive reflective film composition is applied onto the transparent conductive coating film by a wet coating method. The coating here is performed so that the thickness after firing is 0.05 to 2.0 μm, preferably 0.1 to 1.5 μm. Subsequently, the coating film is dried at a temperature of 20 to 120 ° C., preferably 25 to 60 ° C. for 1 to 30 minutes, preferably 2 to 10 minutes. Thus, a conductive reflective coating film is formed. The base material is either a light-transmitting substrate made of glass, ceramics or a polymer material, or two or more light-transmitting laminates selected from the group consisting of glass, ceramics, a polymer material and silicon. can do. Examples of the polymer substrate include a substrate formed of an organic polymer such as polyimide or PET (polyethylene terephthalate).

  Further, the wet coating method is particularly 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. Although it is preferable, 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.

  Finally, the substrate having the coating film is heated to 130 to 400 ° C., preferably 150 to 350 ° C. in the air or in an inert gas atmosphere such as nitrogen or argon, for 5 to 60 minutes, preferably 15 to 40 minutes. Hold and fire. Here, the reason for applying the transparent conductive film composition so that the thickness of the transparent conductive film after firing is in the range of 0.03 to 0.5 μm is that the thickness after firing is less than 0.03 μm, or This is because if the thickness exceeds 0.5 μm, the effect of increasing reflection cannot be obtained sufficiently. The reason for applying the composition for conductive reflection film so that the thickness of the conductive reflection film after firing is 0.05 to 2.0 μm is that the surface resistance value is too high if it is less than 0.05 μm. This is because sufficient conductivity as an electrode of a solar cell cannot be obtained sufficiently, and if it exceeds 2.0 μm, there is no problem in characteristics, but the amount of material used is more than necessary and the material is wasted. .

  The reason why the firing temperature of the base material having the coating film is in the range of 130 to 400 ° C. is that when the temperature is lower than 130 ° C., the transparent conductive film in the composite film has a problem that the surface resistance value becomes too high. In addition, since the metal nanoparticles are not sufficiently sintered in the conductive reflective film and are not easily detached or decomposed (separated / burned) by the heat during firing of the protective agent, This is because a large amount of organic residue remains, and the residue is altered or deteriorated, so that the conductivity and reflectivity of the conductive reflective film are lowered. On the other hand, when the temperature exceeds 400 ° C., the merit in the production 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 hybrid silicon solar cells using these are relatively weak against heat, and the conversion efficiency is reduced by the firing process.

  The reason why the firing time of the base material having the coating film is in the range of 5 to 60 minutes is that when the firing time is less than the lower limit value, the surface resistance value becomes too high in the transparent conductive film in the composite film. In addition, since the metal nanoparticles are not sufficiently sintered in the conductive reflective film and are not easily detached or decomposed (separated / burned) by the heat during firing of the protective agent, This is because a large amount of organic residue remains, and the residue is altered or deteriorated, so that the conductivity and reflectivity of the conductive reflective film are lowered. If the firing time exceeds the upper limit, the characteristics are not affected, but the manufacturing cost is increased more than necessary and the productivity is lowered. Furthermore, it is because the malfunction which the conversion efficiency of a photovoltaic cell falls arises.

  As described above, the composite film of the present invention can be formed. As described above, the manufacturing method of the present invention can eliminate a vacuum process such as a vacuum vapor deposition method and a sputtering method as much as possible by using a wet coating method, so that a composite film can be manufactured at a lower cost.

Next, examples of the present invention will be described in detail together with comparative examples.
<Examples 1-32>
The composition for transparent conductive films in the composite film of the present invention was prepared with components and proportions of classifications 1 to 8 shown in Table 1 below. The classification numbers in Table 1 of the composition for transparent conductive film used in each Example are shown in Tables 2 and 3.
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.

  Next, the composition for conductive reflective films in the composite film of the present invention 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 10 on the formed transparent conductive coating film after firing. After applying by various film forming methods so as to be ^{2 to} 2 × 10 ³ nm, it was dried at a temperature of 25 ° C. for 5 minutes to form a conductive reflective coating film. Subsequently, the composite film was formed on the base material by baking under the heat treatment conditions shown in the following Tables 2 to 4.

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

<Comparative Example 1>
After forming a transparent conductive film by sputtering, which is a vacuum deposition method, so that the film thickness becomes 0.7 × 10 ² nm, the same composition for conductive reflective film as in Example 1 is formed on this transparent conductive film. A composite film was obtained by forming a conductive reflective film by the same method as in Example 1.

<Comparative example 2>
After forming the transparent conductive film by sputtering, which is a vacuum deposition method, so that the film thickness becomes 2.0 × 10 ² nm, the same composition for conductive reflective film as in Example 1 is formed on this transparent conductive film. A composite film was obtained by forming a conductive reflective film by the same method as in Example 1.

＜比較試験１＞
実施例１〜３７及び比較例１〜２で得られた複合膜における透明導電膜及び導電性反射膜の膜厚を評価した。評価結果を次の表５及び表６にそれぞれ示す。先ず、焼成後の透明導電膜及び導電性反射膜の厚さをＳＥＭ（日立製作所社製の電子顕微鏡：Ｓ８００）を用いて膜断面から直接計測した。

<Comparison test 1>
Were evaluated thickness of the transparent conductive Maku及 beauty conductive reflective film of the obtained composite film in Examples 1 to 37 and Comparative Examples 1 and 2. The evaluation results are shown in the following Table 5 and Table 6, respectively. First, the thicknesses of the transparent conductive film and the conductive reflective film after firing were directly measured from the film cross section using an SEM (Hitachi, Ltd., electron microscope: S800).

<Comparison test 2>
About the base material which formed the electroconductive reflection film obtained in Examples 1-37 and Comparative Examples 1-2, the distribution of the pores in the contact surface on the base material side and the back surface reflectance were evaluated. The evaluation results are shown in the following Table 5 and Table 6, respectively.

  As a method for measuring the pores, different measurement methods were used depending on whether or not the conductive reflective film can be peeled off from the transparent conductive film.

  In an example where the transparent conductive film can be peeled off from the base material, first, an adhesive is applied to a jig having a smooth surface to the conductive reflective film in close contact with the transparent conductive film, and this is applied to the conductive reflective film. After pressing onto the membrane and holding until the adhesive is sufficiently dry and has high adhesive strength, this jig is placed perpendicular to the substrate using a tensile tester (manufactured by Shimadzu Corporation: EZ-TEST). The conductive reflective film was pulled off from the transparent conductive film.

  Next, the surface of the conductive reflective film that was peeled off from the transparent conductive film and exposed on the jig was the contact surface on the base material side, and an uneven image of this surface was observed using an atomic force microscope (AFM). did. The observed concavo-convex image was analyzed, and the average diameter, average depth and number density of vacancies appearing on the film surface were evaluated. The average diameter was determined by measuring the longest diameter and the shortest diameter of each opening and calculating the average value.

  As another method of peeling the conductive reflective film from the transparent conductive film, a method of peeling the conductive reflective film from the transparent conductive film by sticking a double-sided tape on the conductive reflective film and pulling up one end thereof. Was also used.

  In an example in which the conductive reflective film cannot be peeled off from the transparent conductive film, first, the conductive reflective film adhered on the transparent conductive film was processed by the focused ion beam (FIB) method to expose the sample cross section. . By observing the cross section of this sample with a scanning electron microscope (SEM), the shape of the metal film / substrate interface was observed. About this interface image, the diameter, average depth, and number density of the opening were evaluated. Here, the diameter of the evaluated opening was determined by regarding the length of the opening in the cross-sectional view as the diameter.

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 .

<Comparison test 3>
The adhesion of the composite films obtained in Examples 1-37 and Comparative Examples 1-2 to the substrate was evaluated. The evaluation results are shown in Table 5 and Table 6 below. Qualitatively evaluated by the adhesive tape peeling test on the base material on which the composite film is formed. “Good” indicates that only the adhesive tape is peeled from the base material. “Neutral” indicates that the adhesive tape is peeled off. And the state where the substrate surface is exposed are mixed, and “defect” indicates a case where the entire surface of the substrate surface is exposed by peeling off the adhesive tape.

  As is clear from Tables 5 and 6, in Comparative Examples 1 and 2 in which the transparent conductive film was formed by sputtering, which is a vacuum deposition method, Comparative Example 2 had poorer adhesion than Examples 1 to 37. As a result. In Comparative Example 1, the reflectance at 500 nm was as low as 70%, and the reflectance at 1100 nm also tended to be low. In Comparative Example 2, the reflectivity at 1100 nm was as high as 90%, but the reflectivity at 500 nm was as low as 75%, and it was confirmed that the reflectivity varies depending on the wavelength. On the other hand, in Examples 1 to 37, 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 Composite film 11a Conductive reflective film 11b Transparent conductive film 12 Photoelectric conversion layer 14 Base material

Claims (14)

In a composite film composed of two layers in which a transparent conductive film is formed on a photoelectric conversion layer of a super straight type thin film solar cell, and a conductive reflective film is formed on the transparent conductive film,
Both the transparent conductive film and the conductive reflective film are formed by a wet coating method,
The transparent conductive film is formed by applying a composition for transparent conductive film containing conductive oxide fine particles using a wet coating method,
The conductive reflective film is formed by applying a composition for conductive reflective film containing metal nanoparticles using a wet coating method,
The conductive reflective film includes one or more substances selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose,
The average diameter of pores appearing on the contact surface on the substrate side of the conductive reflective film is 100 nm or less, the average depth at which the pores are located is 100 nm or less, and the number density of the pores is 30 / μm ² or less. A composite film for a super straight type thin film solar cell.   The composite film for a super-straight type thin film solar cell according to claim 1, wherein a ratio of silver in the metal element contained in the conductive reflective film is 75% by mass or more.   The composite film for a super straight type thin film solar cell according to claim 1, wherein the thickness of the conductive reflective film is in the range of 0.05 to 2.0 µm.   2. The super straight-type thin film solar cell according to claim 1, wherein the metal nanoparticles contained in the conductive reflective film have a number average particle size of 70% or more in a range of 10 to 50 nm. Composite membrane. The conductive reflective film composition contains 75% by mass or more of silver nanoparticles as metal nanoparticles,
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 composite film for a super-straight type thin film solar cell according to claim 1, wherein the metal nanoparticles contain 70% or more of metal nanoparticles having a primary particle diameter in the range of 10 to 100 nm in number average.   One or two or more mixed compositions or alloys selected from the group consisting of gold, platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and manganese as the conductive reflective film composition The composite film for a super-straight type thin film solar cell according to claim 1, containing metal nanoparticles having a composition of 0.02% by mass or more and less than 25% by mass.   The composite film for a super straight type thin film solar cell according to claim 1, wherein the composition for conductive reflective film contains 1% by mass or more of water and 2% by mass or more of alcohols as a dispersion medium.   The said composition for electroconductive reflection films contains the 1 type (s) or 2 or more types of additive chosen from the group which consists of an organic polymer, a metal oxide, a metal hydroxide, an organometallic compound, and a silicone oil. Composite film for super straight type thin film solar cells.   The composite film for a super straight type thin film solar cell according to claim 8, wherein the organic polymer is one or more selected from the group consisting of polyvinylpyrrolidone, polyvinylpyrrolidone copolymer and water-soluble cellulose.   The metal oxide is an oxide or composite containing 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 composite film for a super straight type thin film solar cell according to claim 8, which is an oxide.   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 composite film for a super straight type thin film solar cell according to claim 8.   The organometallic compound is at least one metal soap or metal complex selected from the group consisting of silicon, titanium, aluminum, antimony, indium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum and tin Alternatively, the composite film for a super straight type thin film solar cell according to claim 8, which is a metal alkoxide. A composition for transparent conductive film, which is a mixture of conductive oxide fine particles and other components, is applied onto a photoelectric conversion layer of a super straight type thin film solar cell via a transparent conductive film on a substrate by a wet coating method. Forming a transparent conductive coating film,
Applying a conductive reflective film composition containing metal nanoparticles on the transparent conductive film by a wet coating method to form a conductive reflective film;
By baking the substrate having the transparent conductive film and the conductive reflective film at 130 to 400 ° C., the transparent conductive film having a thickness of 0.03 to 0.5 μm and 0.05 to 2.0 μm Forming two layers of a conductive reflective film having a thickness ,
A method for producing a composite film for a super straight type thin film solar cell, wherein the composition for transparent conductive film includes at least one of a dispersion medium and a polymer binder or a non-polymer binder that is cured by heating as the other component. .   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 inkjet coating method, a screen printing method, an offset printing method, or a die coating method. A method for producing a composite film for a super straight type thin film solar cell.

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