JP2012009840A - Method of forming composite film for solar cell and composite film formed by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a composite film for a solar cell and a composite film formed by the method, which can improve a power generation efficiency of the solar cell by reducing the contact resistance between a photoelectric conversion layer and a transparent conductive film, and between the transparent conductive film and a conductive reflection film so as to reduce a series resistance in the solar cell at the time of power generation.SOLUTION: The method comprises the following processes. A transparent conductive coating film is formed on a photoelectric conversion layer which is laminated over surface electrodes on a substrate by using a wet-coating method applying a dispersion liquid containing conductive oxide fine particles and a dispersion liquid containing binder component or applying a composition for forming a transparent conductive film containing both the conductive oxide fine particles and the binder component. A conductive reflection coating film is formed on the conductive coating film by using the wet-coating method applying a composition for a conductive reflection film. And a substrate having the both coating films is baked to form a composite film composed of the transparent conductive film and the conductive reflection film. The conductive oxide fine particles contain either particles having non-spherical anisotropic shapes or aggregates having anisotropic structures formed by aggregating a plurality of particles.

Description

  The present invention relates to a method for forming a composite film for a solar cell comprising a transparent conductive film and a conductive reflective film provided on a photoelectric conversion layer of the solar cell, and a composite film formed by the method. More specifically, the power generation efficiency can be improved by reducing the contact resistance between the photoelectric conversion layer and the transparent conductive film, between the transparent conductive film and the conductive reflective film, and reducing the series resistance in the solar cell during power generation. The present invention relates to a method for forming a composite film for a solar cell and a composite film formed by the method.

  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.

  For example, a thin film solar cell has been studied to increase power generation efficiency by adopting a structure in which a transparent electrode, amorphous silicon, polycrystalline silicon, and a back electrode are formed in this order (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 a photovoltaic cell is composed of a silicon-based material, the photoelectric conversion layer has a relatively small extinction coefficient, so that the photoelectric conversion layer is incident at a thickness of several micrometers. Part of the light passes 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.

  Conventionally, when such a thin film solar cell is manufactured, each layer is formed by a vacuum film forming method such as a sputtering method. However, in general, maintenance and operation of a large-scale vacuum film forming apparatus requires a great deal of cost, and therefore, development of a method for manufacturing at a lower cost is being promoted by replacing this with a wet film forming method as much as possible. (For example, refer to Patent Document 1). The method disclosed in Patent Document 1 discloses a method of replacing the formation of the transparent conductive film located on the substrate side, that is, the surface electrode 12 shown in FIG. 1, with a wet film forming method.

JP-A-10-12059 (paragraph [0028], paragraph [0029])

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)

  By the way, in the thin film solar cell, in order to improve the power generation efficiency, the electrical resistance of the layer constituting each electrode or the film itself is decreased, and the good contact property between the photoelectric conversion layer and the electrodes or between the electrodes. Or electrical conductivity is required. The present inventors examined a method for replacing the formation of the electrode located on the back side with a wet film forming method, and until now, in the formation of a transparent conductive film using a wet coating method, a transparent conductive material is formed on the photoelectric conversion layer. A method of coating with a liquid containing oxide fine particles and a binder component, and baking this, or first, applying transparent conductive oxide fine particles on the photoelectric conversion layer, and then fixing the binder with the binder component and baking. Methods have been proposed.

  However, when a transparent conductive film is formed by a wet coating method using general spherical fine particles as transparent conductive oxide fine particles, the presence of a binder component between the photoelectric conversion layer and the transparent conductive film causes the film to However, when the carrier density of the photoelectric conversion layer is low, it is easily affected by such a conductivity inhibiting effect, which is a harmful effect of improving the power generation efficiency. Turned out to be. For example, when the electrical conductivity between the photoelectric conversion layer 13 and the transparent conductive film 14a deteriorates, the contact resistance between the photoelectric conversion layer 13 and the transparent conductive film 14a during power generation increases, which increases the series resistance in the solar cell during power generation. As a result, it was a cause that hindered improvement in power generation efficiency.

  The purpose of the present invention is to reduce the contact resistance between the photoelectric conversion layer and the transparent conductive film, between the transparent conductive film and the conductive reflective film, and to reduce the series resistance in the solar cell during power generation, thereby generating power from the solar cell. It is an object of the present invention to provide a method for forming a composite film for a solar cell capable of improving efficiency and a composite film formed by the method.

  As shown in FIG. 1, the first aspect of the present invention is a dispersion containing conductive oxide fine particles on a photoelectric conversion layer 13 of a solar cell laminated on a substrate 11 via a surface electrode 12. A dispersion containing a binder component or a composition for forming a transparent conductive film containing both conductive oxide fine particles and a binder component is applied by a wet coating method to form a transparent conductive coating, and the conductive on the transparent conductive coating After applying the reflective film composition by a wet coating method to form a conductive reflective coating film, the transparent conductive film 14a and the conductive film 14a are electrically conductive by firing the transparent conductive coating film and the substrate 11 having the conductive reflective coating film. A method for forming a composite film 14 for a solar cell comprising a conductive reflective film 14b, wherein the conductive oxide fine particles are formed by agglomerating particles having a non-spherical anisotropic shape or a plurality of particles. Containing any aggregate having an anisotropic structure. The features.

  A second aspect of the present invention is an invention based on the first aspect, and is characterized in that the aspect ratio of the anisotropically shaped particles or the anisotropic structure aggregate is 3 or more.

  A third aspect of the present invention is the invention based on the first aspect, and when the anisotropically shaped particles or anisotropic structural aggregates are plate-like, the thickness of the plate-like particles or aggregates Is 50 to 1500 nm, and the width-thickness ratio is 2 to 100.

  A fourth aspect of the present invention is an invention based on the first to third 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 inkjet coating method. Or a screen printing method, an offset printing method, or a die coating method.

  A fifth aspect of the present invention is a composition for forming a transparent conductive film for forming a transparent conductive film constituting a composite film for a solar cell by applying and baking by a wet coating method, wherein the composition is A dispersion of conductive oxide fine particles not containing a binder component and a dispersion of binder components not containing a conductive oxide fine particle, or a dispersion containing both conductive oxide fine particles and a binder component And the conductive oxide fine particles include either non-spherical anisotropic particles or aggregates having an anisotropic structure formed by aggregation of a plurality of particles, To do.

  A sixth aspect of the present invention is the invention based on the fifth aspect, and is characterized in that the aspect ratio of the anisotropically shaped particles or the anisotropic structural aggregate is 3 or more.

  A seventh aspect of the present invention is the invention based on the fifth aspect, and when the anisotropically shaped particles or anisotropic structural aggregates are plate-like, the thickness of the plate-like particles or aggregates Is 50 to 1500 nm, and the width-thickness ratio is 2 to 100.

  An eighth aspect of the present invention is a composite film for a solar cell comprising a transparent conductive film and a conductive reflective film formed by a method based on the first to fourth aspects.

  A ninth aspect of the present invention is a solar cell including a composite film for a solar cell based on the eighth aspect.

  In the formation method of the 1st viewpoint of this invention, it is a method of forming the composite film for solar cells which consists of a transparent conductive film formed on the photoelectric converting layer of a solar cell, and an electroconductive reflective film, Comprising: The said transparent As a conductive fine particle dispersion used for forming a conductive film or a conductive oxide fine particle of a composition for forming a transparent conductive film, particles having a non-spherical anisotropic shape or a plurality of particles are formed by aggregation. Those containing any of the aggregates having an anisotropic structure are used. The anisotropic shaped particles and anisotropic structure aggregates can increase the contact area between the particles and increase the conductivity as compared with the case of using conventional spherical conductive oxide fine particles. This reduces the contact resistance between the photoelectric conversion layer and the transparent conductive film during power generation, between the transparent conductive film and the conductive reflective film, and reduces the series resistance in the solar cell during power generation, thereby Power generation efficiency can be improved. Moreover, since it forms by the wet coating method, it does not require vacuum processes, such as a vacuum evaporation method and a sputtering method, and it can manufacture more cheaply.

  In the composition for forming a transparent conductive film according to the fifth aspect of the present invention, the composition for forming a transparent conductive film for forming the transparent conductive film constituting the composite film for solar cells by applying and baking by a wet coating method. The composition is composed of a dispersion of conductive oxide fine particles not containing a binder component and a dispersion of binder components not containing conductive oxide fine particles, or conductive oxide fine particles and Consisting of a dispersion containing both binder components, as conductive oxide fine particles, particles having a non-spherical anisotropic shape, or aggregates having an anisotropic structure formed by aggregating a plurality of particles Use one containing either. The anisotropic shaped particles and anisotropic structure aggregates can increase the contact area between the particles and increase the conductivity as compared with the case of using conventional spherical conductive oxide fine particles. This reduces the contact resistance between the photoelectric conversion layer and the transparent conductive film during power generation, between the transparent conductive film and the conductive reflective film, and reduces the series resistance in the solar cell during power generation, thereby Power generation efficiency can be improved.

  Since the composite film for solar cells according to the eighth aspect of the present invention is formed by the method of the present invention, the conductive oxide fine particles of the conductive fine particle dispersion are used for forming the transparent conductive film constituting the composite film. As a non-spherical anisotropic particle or an aggregate having an anisotropic structure formed by agglomerating a plurality of particles, conventional spherical conductive oxide fine particles are used. Compared with the case where it contacted, the contact area between particle | grains can be enlarged and it can be set as the transparent conductive film which has high electroconductivity as a result. As a result, the contact resistance between the photoelectric conversion layer and the transparent conductive film during power generation, the contact resistance between the transparent conductive film and the conductive reflective film is reduced, the series resistance in the solar cell during power generation is reduced, and the power generation efficiency of the solar cell Can be further improved.

  Since the solar cell of the ninth aspect of the present invention includes the composite film for a solar cell of the present invention, the series resistance in the solar cell during power generation is small, and the power generation efficiency is very high.

It is sectional drawing which showed the laminated structure of the general solar cell typically.

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

  As shown in FIG. 1, the method for producing a composite film for a solar cell of the present invention has conductive oxide fine particles on a photoelectric conversion layer 13 of a solar cell laminated on a substrate 11 via a surface electrode 12. A transparent conductive coating film is formed by applying a dispersion containing a binder and a dispersion containing a binder component or a composition for forming a transparent conductive film containing both conductive oxide fine particles and a binder component by a wet coating method. After forming the conductive reflective coating film by applying the composition for the conductive reflective film on the film by a wet coating method, the substrate 11 having the transparent conductive coating film and the conductive reflective coating film is baked to be transparent. A composite film 14 for a solar cell composed of a conductive film 14a and a conductive reflective film 14b is formed.

  The substrate 11 is made of a light transmissive substrate made of glass, ceramics or a polymer material, or two or more kinds of light transmissive laminates selected from the group consisting of glass, ceramics, a polymer material and silicon. Can be used. Examples of the polymer substrate include a substrate formed of an organic polymer such as polyimide or PET (polyethylene terephthalate).

The surface electrode 12 is a transparent and conductive film that transmits light incident from the substrate 11 side to the photoelectric conversion layer 13 and functions as an electrode. As the surface electrode 12, for example, ITO (Indium Tin Oxide: Sn doped indium oxide), ATO (Antimony Tin Oxide: Sb doped tin oxide), SnO ₂ (tin oxide), ZnO (zinc oxide), IZO (Indium Zinc). Oxide: Zn-doped indium oxide) and the like. The surface electrode 12 is made of ZnO, In ₂ O ₃ , SnO ₂ , CdO, TiO ₂ , CdIn ₂ O ₄ , Cd ₂ SnO _4, or Zn ₂ SnO ₄ , and any of Sn, Sb, F, or Al. You may comprise by the 1 type (s) or 2 or more types of metal oxide chosen from the group of the metal oxide doped. Examples include AZO (Aluminum Zinc Oxide: Al-doped zinc oxide) and TZO (Tin Zinc Oxide: Sn-doped zinc oxide). The surface electrode 12 may be formed by a conventionally known method such as a thermal CVD method, a sputtering method, a vacuum deposition method, or a wet coating method, and is not particularly limited. When the surface electrode 12 is formed by a wet coating method, it can be performed in the same manner as when a transparent conductive film 14a constituting a composite film 14 described later is formed by a wet coating method. The ZnO is suitable as a material for the surface electrode 12 because it has high light transmittance, low resistance, and plasticity and is inexpensive.

  On the surface electrode 12, a photoelectric conversion layer 13 that generates power by light is formed. The photoelectric conversion layer 13 is composed of either one or both of amorphous silicon and microcrystalline silicon. In this embodiment, the photoelectric conversion layer 13 has a first photoelectric conversion layer formed of an amorphous silicon semiconductor and a second photoelectric conversion layer formed of a microcrystalline silicon semiconductor. Specifically, in the first photoelectric conversion layer, p-type a-Si (amorphous silicon), i-type a-Si (amorphous silicon), and n-type a-Si (amorphous silicon) are stacked in this order from the substrate 11 side. It is a p-i-n type amorphous silicon layer. The second photoelectric conversion layer includes p-type μc-Si (microcrystalline silicon), i-type μc-Si (microcrystalline silicon), and n-type μc-Si (microcrystalline silicon) in order from the first photoelectric conversion layer side. This is a stacked pin type microcrystalline silicon layer.

  As described above, the tandem solar cell using i-type a-Si (first photoelectric conversion layer) and i-type μc-Si (second photoelectric conversion layer) for the photoelectric conversion layer 13 has two different light absorption wavelengths. It is the structure which laminated | stacked these semiconductors, and can utilize a sunlight spectrum effectively. Here, in this specification, “microcrystal” means not only a complete crystal state but also a partially amorphous (amorphous) state.

  Note that the photoelectric conversion layer is either a single junction type composed of either an amorphous silicon layer or a microcrystalline silicon layer, or a multi-junction type including a plurality of either one or both of an amorphous silicon layer and a microcrystalline silicon layer. It can also take. Also, a structure such as p-type a-SiC: H (amorphous silicon carbide) / i-type a-Si / n-type μc-Si can be used. Although they are not particularly limited, they can be formed by a conventionally known method such as a plasma CVD method. Further, for example, in the example of the tandem structure, an intermediate layer is formed between the first photoelectric conversion layer (amorphous silicon photoelectric conversion unit) and the second photoelectric conversion layer (microcrystalline silicon photoelectric conversion unit). Also good. For this intermediate layer, it is preferable to use a material used for the transparent conductive film 14a constituting the surface electrode 12 and the composite film 14 described later.

  On the photoelectric conversion layer 13, a composite film 14 composed of a transparent conductive film 14a formed on the photoelectric conversion layer 13 and a conductive reflective film 14b formed on the transparent conductive film 14a is formed by a wet coating method. The transparent conductive film 14a constituting the composite film 14 has an effect of suppressing mutual diffusion between the photoelectric conversion layer 13 and the conductive reflective film 14b and increasing the reflection efficiency of the conductive reflective film 14b.

  In order to form the transparent conductive film 14a by a wet coating method, a method of applying a transparent conductive oxide fine particle and a binder component on the photoelectric conversion layer and baking it, or first, transparent conductive oxide fine particles Is applied to the photoelectric conversion layer, and then, for example, a method of firing after fixing with a binder component has been studied, but when using general spherical fine particles as transparent conductive oxide fine particles, The presence of the binder component between the photoelectric conversion layer and the transparent conductive film causes problems such as obstruction of conduction in the vertical direction with respect to the film. For this reason, when the electrical conductivity between the photoelectric conversion layer 13 and the transparent conductive film 14a deteriorates, the contact resistance between the photoelectric conversion layer 13 and the transparent conductive film 14a or between the photoelectric conversion layer 13 and the conductive reflective film 14b increases, As a result, the series resistance of the solar cell increases, and as a result, improvement in power generation efficiency of the solar cell is hindered.

  In the present invention, in order to increase the conductivity of the transparent conductive film 14a, the conductive oxide fine particles used for forming the transparent conductive film are formed by agglomerating particles having a non-spherical anisotropic shape or a plurality of particles. And those containing any of the aggregates having an anisotropic structure. The anisotropic shaped particles and anisotropic structure aggregates can increase the contact area between the particles compared to the case of using conventional spherical conductive oxide fine particles, and increase the conductivity of the transparent conductive film to be formed. be able to.

  The anisotropically shaped particles or anisotropic structure aggregates are preferably in the form of needles or rods having an aspect ratio of 3 or more. The aspect ratio here is a ratio when the longest side is divided by the shortest side. This is because when the aspect ratio is less than 3, there is no great difference from the conductivity of the transparent conductive film formed using conventional spherical fine particles, and the effect cannot be obtained sufficiently. Among these, a particularly preferable aspect ratio is 3 to 30. Also, the length of the minor axis side is preferably 5 to 100 nm.

For example, in the manufacturing method of rod-shaped indium tin oxide, first, an indium trichloride aqueous solution (InCl ₃ aqueous solution) and a tin tetrachloride aqueous solution (SnCl ₄ aqueous solution) are mixed, and an alkaline aqueous solution such as sodium hydrogen carbonate is added to this mixed solution. Then, the pH is adjusted to 5.0 to 8.5, preferably pH 6.0 to 8.0, and the precipitate is generated by reacting at a liquid temperature of 5 ° C. or higher, preferably 10 to 80 ° C. Let The precipitate is due to the coprecipitation phenomenon of indium hydroxide and tin hydroxide. Next, the produced precipitate is recovered by solid-liquid separation, dried by heating at 100 to 200 ° C. for 2 to 24 hours, and then at 250 ° C. or higher in the atmosphere, preferably at 400 to 800 ° C. for 1 to 6 hours. By baking by heating, a rod-shaped indium tin oxide powder having a minor axis of 5 to 50 nm and a major axis of 30 to 150 nm and an aspect ratio of 3 or more can be produced. The particle shape evaluation method is performed as follows. First, 5 fields or more of the powder were photographed with an SEM, and for 100 or more particles in the photographed image, the longest side and the shortest side were measured, average values were obtained, and these were measured as the major axis and minor axis, respectively. And Further, the ratio of the average major axis to the average minor axis is obtained to obtain the aspect ratio of the target powder.

  Further, when the anisotropically shaped particles or the anisotropic structure aggregates are plate-like, it is preferable that the plate-like particles or aggregates have a thickness of 50 to 1500 nm and a width-thickness ratio of 2 to 100. The width-thickness ratio here is a ratio when the width which is the longest length of the piece is divided by the thickness. This is because when the width-thickness ratio is less than 2, there is no significant difference from the conductivity of the transparent conductive film formed using conventional spherical fine particles, and the effect cannot be obtained sufficiently. Further, if the width-thickness ratio exceeds 100, a problem occurs in the dispersed state of the particles. Of these, a scaly shape having a thickness of 70 to 200 nm and a width to thickness ratio of 5 to 30 is preferable.

  For example, a method for producing scaly tin oxide is to first freeze a tin colloid solution obtained by adding hydrochloric acid to a gel obtained by neutralizing a tin chloride aqueous solution with ammonia, and then thawing the frozen product. By calcining scaly hydrous tin oxide obtained by performing freeze-drying to remove the solvent by performing normal vacuum drying while maintaining the temperature at 350 to 900 ° C., the thickness is 1 to 100 nm and the width A scaly tin oxide powder having a thickness ratio of 2 to 100 can be produced.

  In the present specification, values such as sides, widths, and thicknesses of particles and aggregates are values calculated or measured by SEM image observation (Hitachi Electron Microscope S800). 5 fields or more are photographed with SEM, and the longest side and the shortest side are measured for 100 or more particles in the photographed image. The ratio of the average values is the aspect ratio of the target powder.

  As a method for forming the transparent conductive film 14a by the wet coating method, there are mainly two forming methods. The first method is to apply a transparent conductive film composition prepared by adding both conductive oxide fine particles and a binder component on the photoelectric conversion layer 13 by a wet coating method to form a transparent conductive coating film. Thereafter, firing is performed. The second method is to form a coating film of conductive oxide fine particles by applying a dispersion of conductive oxide fine particles not containing a binder component on the photoelectric conversion layer 13 using a wet coating method. This is a method of impregnating a binder dispersion containing no conductive oxide fine particles on the coating film of the conductive oxide fine particles using a wet coating method, and then baking.

  The composition for transparent conductive film in the first method is a composition containing the conductive oxide fine particles, and the conductive oxide fine particles are dispersed in a dispersion medium. As a dispersion medium, in addition to water, alcohols such as methanol, ethanol, isopropyl alcohol and butanol, ketones such as acetone, methyl ethyl ketone, cyclohexanone and isophorone, hydrocarbons such as toluene, xylene, hexane and cyclohexane, N and N -Amides such as dimethylformamide and N, N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, glycols such as ethylene glycol, glycol ethers such as ethyl cellosolve, and the like.

  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%.

  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. Examples of the non-polymer type binder include metal soap, metal complex, metal alkoxide, halosilanes, 2-alkoxyethanol, β-diketone, and alkyl acetate. 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 binder and non-polymer-type binder are cured by heating, thereby enabling formation of a transparent conductive film 14a 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 bonding property between the conductive oxide fine particles and the binder and the adhesion between the transparent conductive film 14a formed of the transparent conductive film composition and the photoelectric conversion layer 13 or the conductive reflective film 14b. 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.

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. .

  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.

  In order to form the transparent conductive film 14a using the transparent conductive film composition, first, the transparent conductive film composition has a thickness of 0.01 to 0.5 μm after firing. It apply | coats on the photoelectric converting layer 13 with a wet coating method so that it may exist in the range of 0.05-0.1 micrometer. Here, the reason why the thickness of the transparent conductive film 14a is limited to the range of 0.01 to 0.5 [mu] m is that when the thickness is less than 0.01 [mu] m or exceeds 0.5 [mu] m, the enhanced reflection effect cannot be obtained sufficiently. After apply | coating the composition for transparent conductive films on the photoelectric converting layer 13, it is dried for 1 to 10 minutes at the temperature of 20-100 degreeC, and a transparent conductive coating film is obtained.

  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.

  Thus, after forming a transparent conductive coating film on the photoelectric conversion layer 13, a conductive reflective coating film is formed on the transparent conductive coating film using a composition for conductive reflective film described later, The base material 11 having these coating films is fired under the conditions described below. Thereby, the transparent conductive film 14a is formed together with the formation of the conductive reflective film 14b.

  The dispersion liquid of conductive oxide fine particles not containing a binder component in the second method is a dispersion liquid in which the conductive oxide fine particles are dispersed in a dispersion medium. In addition, the dispersion medium used for preparation of the dispersion liquid of electroconductive oxide fine particles can use the same kind as the dispersion medium used with the composition for transparent conductive films in the said 1st method. The content ratio of the dispersion medium in the dispersion is preferably in the range of 50 to 99.99% by mass in order to obtain good film formability. The content ratio of the conductive oxide fine particles in the dispersion is preferably in the range of 0.01 to 50% by mass.

  It is preferable to add a coupling agent to the dispersion of the conductive oxide fine particles depending on the other components used. That is, the bonding property between the conductive oxide fine particles and the binder, and the adhesion between the transparent conductive film 14a formed of the conductive oxide fine particle dispersion and the binder dispersion, and the photoelectric conversion layer 13 or the conductive reflective film 14b. It is for improvement. In addition, the coupling agent used for preparation of the dispersion liquid of conductive oxide fine particles can be the same as the coupling agent used in the composition for transparent conductive film in the first method. It is preferable that the ratio of the coupling agent in the dispersion is in the range of 0.01 to 10% by mass based on the total of 100% by mass of the dispersion medium and the conductive oxide fine particles.

  Moreover, the dispersion liquid containing a binder component contains either or both of a polymer-type binder and a non-polymer-type binder that are cured by heating as a binder component. These polymer-type binder and non-polymer-type binder are cured by heating, thereby enabling formation of a transparent conductive film 14a having a low haze ratio and volume resistivity at low temperatures. The content of these binders in the binder dispersion is preferably in the range of 0.01 to 50% by mass, and particularly preferably in the range of 0.5 to 20% by mass. The polymer type binder and non-polymer type binder used for preparing the binder dispersion are the same type as the polymer type binder and non-polymer type binder used in the transparent conductive film composition in the first method. be able to.

  For the preparation of the binder dispersion, it is preferable to use the same dispersion medium as the dispersion medium used for the preparation of the dispersion of the conductive oxide fine particles. In order to form a uniform film, the content of the dispersion medium is preferably in the range of 50 to 99.99% by mass.

  Moreover, it is preferable to add a low resistance agent, a water-soluble cellulose derivative, etc. according to the component to be used. Examples of the low resistance agent include the same type as that used in the first method described above. The content ratio of these low resistance agents is preferably 0.1 to 10% by mass. Moreover, the transparency in the transparent conductive film formed improves by addition of a water-soluble cellulose derivative. Examples of the water-soluble cellulose derivative include the same types as those used in the first method described above. The addition amount of the water-soluble cellulose derivative is preferably in the range of 0.1 to 10% by mass.

  In the method of forming the transparent conductive film 14a using the conductive oxide fine particle dispersion and the binder dispersion, the first layer containing both the conductive oxide fine particles and the binder component is used as a lower layer, and the binder component is mainly used. There is a formation method in which the second layer made of the above is used as an upper layer, and a method in which the first layer containing both the conductive oxide fine particles and the binder component is the lower layer, and the second layer not containing the binder component is the upper layer.

  Since the transparent conductive film formed by the former forming method is formed in a state where the entire surface of the conductive oxide fine particle layer is covered with the binder layer, there is an advantage that the change with time is small. In this forming method, first, the dispersion of the conductive oxide fine particles is applied onto the photoelectric conversion layer 13 by a wet coating method, and the temperature is 20 to 120 ° C., preferably 25 to 60 ° C., preferably 1 to 30 minutes. Forms a coating film of conductive oxide fine particles by drying for 2 to 10 minutes.

  Next, it coat | covers so that the whole surface of the coating film of electroconductive oxide fine particles may be coat | covered completely with a binder dispersion liquid. Moreover, the coating here is such that the mass of the binder component in the binder dispersion to be applied is 0.5 to 10 mass ratio with respect to the total mass of the fine particles contained in the coating film of the applied conductive oxide fine particles. It is preferable to apply so as to be (mass of binder component / mass of conductive oxide fine particles in binder dispersion to be applied). If it is less than the lower limit, sufficient adhesion is difficult to obtain, and if it exceeds the upper limit, the surface resistance tends to increase. The conductive oxide fine particle dispersion and the binder dispersion are applied such that the transparent conductive film 14a after baking has a thickness of 0.01 to 0.5 μm, preferably 0.03 to 0.1 μm. Apply to. After impregnating the binder dispersion, the transparent conductive coating film is formed by drying at a temperature of 20 to 120 ° C., preferably 25 to 60 ° C. for 1 to 30 minutes, preferably 2 to 10 minutes.

  After the transparent conductive coating film is formed on the photoelectric conversion layer 13, the substrate 11 having the transparent conductive coating film and the conductive reflective coating film is baked under the conditions described later, as in the first method. Thereby, the transparent conductive film 14a is formed together with the formation of the conductive reflective film 14b.

  On the other hand, the transparent conductive film 14a formed by the latter forming method is effective in increasing the fill factor, which is one of the factors that determine power generation efficiency. In this formation method, first, the conductive oxide fine particle dispersion is applied onto the photoelectric conversion layer 13 by a wet coating method to form a conductive oxide fine particle coating film. The application here is such that the transparent conductive film 14a after baking has a thickness of 0.01 to 0.5 μm, preferably 0.03 to 0.1 μm, and a temperature of 20 to 120 ° C., preferably A film of conductive oxide fine particles is formed by drying at 25 to 60 ° C. for 1 to 30 minutes, preferably 2 to 10 minutes.

  Next, the binder dispersion liquid is impregnated on the coating film of conductive oxide fine particles by a wet coating method. At this time, in the transparent conductive film 14a formed after firing, the binder dispersion is applied with conductive oxide fine particles so that the second layer not containing the binder component is exposed by 1 to 30% of the volume of the first layer. Complete impregnation to a predetermined depth of the membrane. Moreover, application | coating here is 0.05-0.5 with respect to the total mass of the microparticles | fine-particles contained in the coating film of the apply | coated conductive oxide microparticles | fine-particles in the binder component in the binder dispersion liquid to apply | coat. It is preferable to apply so as to be a mass ratio (the mass of the binder component in the binder dispersion to be applied / the mass of the conductive oxide fine particles). If it is less than the lower limit, it is difficult to obtain sufficient adhesion, and if it exceeds the upper limit, the surface resistance tends to increase. After impregnating the binder dispersion, the transparent conductive coating film is formed by drying at a temperature of 20 to 120 ° C., preferably 25 to 60 ° C. for 1 to 30 minutes, preferably 2 to 10 minutes.

  After the transparent conductive coating film is formed on the photoelectric conversion layer 13, the substrate 11 having the transparent conductive coating film and the conductive reflective coating film is baked under the conditions described later, as in the first method. Thereby, the transparent conductive film 14a is formed together with the formation of the conductive reflective film 14b.

  Since the conductive reflective film 14b plays a role of improving the power generation efficiency by reflecting the light that has not been absorbed and transmitted through the photoelectric conversion layer 13 and returning it to the photoelectric conversion layer 13, a high diffuse reflectance is required. For this reason, the conductive reflective film 14b is preferably a metal having a high reflectance. Examples of the metal include metals such as silver, iron, chromium, tantalum, molybdenum, nickel, aluminum, cobalt, and titanium, alloys of these metals, and alloys such as nichrome and stainless steel. The conductive reflective film 14b is formed by a wet coating method using a conductive reflective film composition in which metal nanoparticles are dispersed in a dispersion medium.

  The composition for conductive reflective film 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 if it is less than 75% by mass, the reflectivity of the conductive reflective film 14b formed using this composition for conductive reflective film decreases. Because it ends up. 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 number of carbon atoms in the carbon skeleton of the organic molecule main chain of the protective agent for chemically modifying the metal nanoparticles is in the range of 1 to 3 is that when the carbon number is 4 or more, the protective agent is desorbed or decomposed (separated) by heating. This is because it is difficult to burn), and a large amount of organic residue remains in the conductive reflective film 14b, which deteriorates or deteriorates, thereby reducing the conductivity and reflectance of the conductive reflective film 14b.

  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. When the content of the metal nanoparticles within the range of the primary particle size of 10 to 50 nm is less than 70% by mass with respect to 100% of all the metal nanoparticles, the specific surface area of the metal nanoparticles is increased and The proportion occupied is increased. For this reason, even if it is an organic molecule which is easily desorbed or decomposed (separated / burned) by heating, a large proportion of the organic molecule occupies, so that a large amount of organic residue remains in the conductive reflective film 14b. This residue may be altered or deteriorated to reduce the conductivity and reflectance of the conductive reflective film 14b, or the particle size distribution of the metal nanoparticles may be widened to reduce the density of the conductive reflective film 14b. Moreover, it is because the electroconductivity and reflectance of the electroconductive reflective film 14b will fall. Furthermore, the primary particle size of the metal nanoparticles was set within the range of 10 to 50 nm based on the correlation between the primary particle size and the stability over time (aging stability) of the metal nanoparticles.

  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. As the additive, an organic polymer, metal oxide, metal hydroxide, organometallic compound, or silicone oil contained in the composition for conductive reflective film is used. Thereby, the chemical bond with the base material or the anchor effect is increased, or the wettability between the metal nanoparticles and the base material is improved in the process of heating and firing, and the base material is not impaired. Adhesiveness can be improved. In addition, when the conductive reflective film 14b is formed using this conductive reflective film composition, grain growth due to sintering between metal nanoparticles can be adjusted. The formation of the conductive reflective film 14b using the composition for conductive reflective film does not require a vacuum process at the time of film formation, so that the process restrictions are small and the running cost of manufacturing equipment can be greatly reduced. it can.

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 14b 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 selected from the group consisting of aluminum, silicon, titanium, zirconium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum, tin, indium and antimony An oxide or composite oxide containing one kind is preferable. Specifically, the composite oxide is ITO, ATO, IZO, AZO or the like described above.

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

  As an organometallic compound used as an additive, a metal soap containing at least one selected from the group consisting of silicon, titanium, zirconium, chromium, manganese, iron, cobalt, nickel, silver, copper, zinc, molybdenum and tin Metal 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. When 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, it is maintained in a constant temperature and humidity chamber having a temperature of 100 ° C. and a humidity of 50% for 1000 hours. This is because the conductivity and reflectance of the conductive reflective film 14b after the test are not deteriorated as compared with those before the weather resistance test.

  Moreover, content of the metal nanoparticle containing the silver nanoparticle in the composition for electroconductive reflective films is 2.5-95 with respect to 100 mass% of composition for electroconductive reflective films which consists of a metal nanoparticle and a dispersion medium. The content is preferably 0% by mass, and more preferably 3.5 to 90% by mass. This is because if the content ratio with respect to 100% by mass of the composition for conductive reflective film exceeds 95.0% by mass, the required fluidity as an ink or paste is lost during wet coating of the composition for conductive reflective film. .

  Further, the dispersion medium constituting the composition for conductive reflection film for forming the conductive reflection film 14b is 1% by mass or more, preferably 2% by mass or more of water with respect to 100% by mass of all the dispersion media. It is preferable to contain 2% by mass or more, preferably 3% by mass or more of a solvent compatible with 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 water content is preferably in the range of 1% by mass or more with respect to 100% by mass of all the dispersion media. This is because when the water content is less than 2% by mass, it is difficult to sinter the film obtained by applying the composition for conductive reflective film by a wet coating method at a low temperature. Furthermore, the conductivity and reflectance of the conductive reflective film 14b after firing 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 for conductive reflective film is excellent in dispersion stability and can be used for low-temperature sintering of the coating film. There is an effective action. In addition, when a carbonyl group (—C═O) is contained in a protective agent that chemically modifies metal nanoparticles such as silver nanoparticles, it is excellent in dispersion stability of the conductive reflective film composition as described above. There is also an effective action for low-temperature sintering of the film. As the solvent compatible with water used for the dispersion medium, alcohols are preferable. Among these, as the alcohols, it is particularly preferable to use one or more selected from the group consisting of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, diethylene glycol, glycerol, isobornyl hexanol and erythritol. preferable.

A method for producing a composition for a conductive reflective film containing metal nanoparticles for forming the conductive reflective film 14b 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. Demineralize by. Further, it is subsequently substituted and washed with alcohols so that the metal (silver) content is 2.5 to 50% by mass. 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. Prepare to contain. That is, the ratio of the silver nanoparticles in the range of the primary particle diameter of 10 to 50 nm with respect to 100% of all silver nanoparticles is adjusted so that the number average is 70% or more. 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. Further, when an additive is further included in the composition for the conductive reflective film, the dispersion is selected from the group consisting of an organic polymer, a metal oxide, a metal hydroxide, an organometallic compound, and a silicone oil. One or two or more additives are added in a desired ratio. Content of an additive is adjusted so that it may exist in the range of 0.1-20 mass% with respect to 100 mass% of compositions for electroconductive reflective films obtained. Thereby, the composition for electroconductive reflective films in which the silver nanoparticle chemically modified with the protective agent of the organic molecule main chain whose carbon number of carbon skeleton is 3 was disperse | distributed to the 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 order to form the conductive reflective film 14b using the conductive reflective film composition, first, the conductive reflective film composition is applied onto the transparent conductive coating film before firing by a wet coating method. The conductive reflective film composition is applied so that the thickness after firing is 0.05 to 2.0 μm, preferably 0.1 to 1.5 μm. Subsequently, this 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, to form a conductive reflective coating film. Here, the thickness of the conductive reflective film 14b after baking is applied so as to be in the range of 0.05 to 2.0 μm. If the thickness is less than 0.05 μm, the surface resistance value of the electrode necessary for the solar cell is not good. This is enough. In addition, about the wet coating method, the method similar to the method at the time of apply | coating the said composition for transparent conductive films, etc. can be used.

  After forming the transparent conductive coating film and the conductive reflective coating film as described above, the substrate 11 having these coating films is preferably 130 to 400 in the air or in an inert gas atmosphere such as nitrogen or argon. The firing is performed at a temperature of 150 ° C., more preferably 150 to 350 ° C., preferably 5 to 60 minutes, more preferably 15 to 40 minutes. Thereby, the composite film 14 including the transparent conductive film 14a and the conductive reflective film 14b is formed.

  The reason why the firing temperature is in the range of 130 to 400 ° C. is that when the temperature is less than 130 ° C., the transparent conductive film 14 a constituting the composite film 14 has a problem that the surface resistance value becomes too high. This is because in the conductive reflective film 14b, the metal nanoparticles are not sufficiently sintered and are not easily detached or decomposed (separated / burned) by heating the protective agent. That is, a large amount of organic residue remains in the fired conductive reflective film 14b, and the residue is altered or deteriorated, so that the conductivity and reflectance of the conductive reflective film 14b are reduced. Moreover, if it exceeds 400 degreeC, the merit in a low temperature process cannot be utilized. That is, the manufacturing cost is increased and the productivity is lowered, and this affects the light wavelength range of photoelectric conversion particularly in amorphous silicon, microcrystalline silicon, or a hybrid silicon solar cell using these. Furthermore, the reason why the holding time is set to 5 to 60 minutes is that if the holding time is less than 5 minutes, the transparent conductive film 14a constituting the composite film 14 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 14b and are not easily detached or decomposed (separated / burned) by heating the protective agent, the conductive reflective film 14b after firing is organic. This is because a large amount of residue remains, and the residue is altered or deteriorated, so that the conductivity and reflectance of the conductive reflective film 14b are lowered.

  Through the above steps, a composite film for a solar cell composed of the transparent conductive film 14a and the conductive reflective film 14b can be formed on the photoelectric conversion layer 13 of the solar cell. In the composite film 14 formed by this method, in forming the transparent conductive film constituting the composite film, as the conductive oxide fine particles of the conductive fine particle dispersion, particles having a non-spherical anisotropic shape, or a plurality of Since an aggregate having an anisotropic structure formed by agglomerating particles is used, the contact area between the particles can be increased compared to the case of using conventional spherical conductive oxide fine particles, and as a result A transparent conductive film having high conductivity can be obtained. For this reason, the contact resistance between the photoelectric conversion layer and the transparent conductive film and between the transparent conductive film and the conductive reflective film is small, and the series resistance in the solar cell during power generation is reduced, so that power generation efficiency can be improved.

In addition, when the composite film 14 is formed by the wet coating method in this way, a simple process can be completed in a short time, and a vacuum process is not required at the time of film formation, so the process restrictions are small and the running cost of manufacturing equipment is greatly increased. Can be reduced. Further, in the composite film 14 obtained by this method, the average diameter of pores appearing in an area having an average depth of 100 nm or less from the contact surface with the transparent conductive film 14a in the conductive reflective film 14b or the surface facing this contact surface. Was 100 nm or less, the average depth at which pores were located was 100 nm or less, and the number density of pores was 30 / μm ² or less. Thereby, when a translucent substrate having a transmittance of 98% or more is 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. This wavelength range of 500 to 1200 nm almost covers the convertible wavelengths when polycrystalline silicon is used as the photoelectric conversion layer. In addition, the conductive reflective film 14b has a specific resistance close to the specific resistance of the metal itself constituting the metal nanoparticles contained in the composition for conductive reflective film. That is, it shows a specific resistance as low as a bulk that can be used as an electrode for a solar cell module. In addition, the conductive reflective film 14b is excellent 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 film is formed in the air, so that it is less susceptible to the intrusion of moisture, oxidation and the like than the film formed in a vacuum.

  A barrier film may be formed on the conductive reflective film 14b via a back electrode reinforcing film (not shown) or without a back electrode reinforcing film.

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

<Examples 1 to 10, Comparative Examples 1 and 2>
The composition shown in Table 1 and Table 2 below, the conductive oxide fine particles, the dispersion medium, the binder, and the coupling agent in the proportions shown in Table 1 and Table 2, with the total amount being 60 g, Was placed in a 100 cc glass bottle and dispersed with a paint shaker for 6 hours using 100 g of zirconia beads having a diameter of 0.3 mm (Microhaika, Showa Shell Sekiyu KK) to obtain a transparent conductive film composition.

  Of the conductive oxide fine particles used above, ATO particles and ATO aggregates were produced by the following method. First, a solution of 500 g of stannic chloride pentahydrate and 10 g of antimony trichloride in 500 ml of 3N hydrochloric acid solution in 5 l of pure water at 90 ° C. and sodium hydroxide are used, and the pH of the system is adjusted to 7 to 7.5. Was added in parallel over 20 minutes to maintain a coprecipitate. Next, hydrochloric acid was added thereto to adjust the pH of the system to 3, and then the precipitate was filtered, and then washed with water until the specific resistance of the filtrate reached 15000 Ωcm. Next, after the obtained cake was dried at 110 ° C. for 12 hours, 136.5 g of borax was added to the dried product, and both were uniformly mixed and ground. And this mixture was baked at 900 degreeC with the electric furnace for 1 hour. Thereafter, the fired product obtained was immersed in a hydrofluoric acid aqueous solution to remove soluble salts, and then dried and pulverized to obtain the target acicular antimony-containing tin oxide fine powder. .

In addition, ITO particles and ITO aggregates are mixed with an indium trichloride aqueous solution (InCl ₃ aqueous solution) and a tin tetrachloride aqueous solution (SnCl ₄ aqueous solution), and an alkaline aqueous solution containing sodium hydrogen carbonate is added to the mixed solution. The pH was adjusted to 5 to 10, reacted at a liquid temperature of 20 to 60 ° C. for 30 to 300 minutes, the produced precipitate was recovered by solid-liquid separation, dried, and then fired in the air.

In addition, SnO ₂ particles and SnO ₂ aggregates consist of a tin colloid solution containing 10% by mass in terms of oxide of tin obtained by adding hydrochloric acid to a gel obtained by neutralizing an aqueous solution of tin chloride with ammonia. It was produced by baking for 1 to 10 hours at 350 to 800 ° C. with a scaly hydrous tin oxide obtained by freezing for 5 to 120 minutes and then freeze-drying.

  In Table 1 or Table 2, the first mixed liquid is a dispersion medium in which isopropanol, ethanol and N, N-dimethylformamide are mixed at a mass ratio of 4: 2: 1. The second mixed liquid is a dispersion medium in which ethanol and butanol are mixed at a mass ratio of 98: 2.

  Next, 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, and the additives shown in the following Tables 3 and 4 are further added to this dispersion. Were added so as to have the ratios shown in Tables 3 and 4 to obtain conductive reflective film compositions, 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 the above-described method for producing silver nanoparticles, except that a metal salt of a type that forms metal nanoparticles other than silver nanoparticles shown in Tables 3 and 4 below is used. A dispersion of this metal nanoparticle was prepared as a second dispersion, and before adding the additives, the first dispersion and the second dispersion were made to have the ratios shown in Tables 3 and 4 below. By mixing the dispersion, a composition for a conductive reflective film was obtained.

Next, a composite film was formed on the photoelectric conversion layer of the solar cell to form a solar cell. Specifically, first, as shown in FIG. 1, a thickness of 1.7 μm is formed as a photoelectric conversion layer 13 on a base material 11 having a surface electrode 12 (SnO ₂ film) having a texture structure by a plasma CVD method. A microcrystal silicon layer was formed. Then, after applying the composition for transparent conductive film prepared above by various film forming methods shown in Tables 3 and 4 so that the thickness after firing becomes the film thickness shown in Table 5 below, the temperature A transparent conductive coating film was formed by drying at 25 ° C. for 5 minutes. Subsequently, the prepared composition for conductive reflective film is shown in the following Tables 3 and 4 so that the thickness after firing on the formed transparent conductive coating film becomes the film thickness shown in Table 5 below. After applying by various film forming methods, the conductive reflective coating film was formed by drying at a temperature of 25 ° C. for 5 minutes. Next, by baking under the heat treatment conditions shown in Tables 3 and 4 below, the composite film 14 was formed on the photoelectric conversion layer 13 to obtain a solar cell substrate. In Tables 3 and 4, “PVP” represents polyvinylpyrrolidone having Mw of 360,000, and “PET” represents polyethylene terephthalate.

＜比較試験及び評価＞
実施例１〜１０及び比較例１，２の光電変換層上に複合膜を形成した太陽電池セル基板について、複合膜における透明導電膜及び導電性反射膜の厚さ、導電性反射膜における気孔分布、直列抵抗について評価した。これらの結果を以下の表５に示す。

<Comparison test and evaluation>
About the photovoltaic cell substrate in which the composite film was formed on the photoelectric conversion layers of Examples 1 to 10 and Comparative Examples 1 and 2, the thickness of the transparent conductive film and the conductive reflective film in the composite film, the pore distribution in the conductive reflective film The series resistance was evaluated. These results are shown in Table 5 below.

  (1) Film thickness: Using an SEM (Hitachi, Ltd., electron microscope: S800), the film thickness was directly measured three times from the film cross section, and the average value was obtained.

  (2) Pore distribution: For the pore distribution on the contact surface side with the transparent conductive film, different measurement methods were used depending on whether the conductive reflective film could be peeled off from the transparent conductive film.

  In an example in which the conductive reflective film can be peeled off from the transparent conductive film, first, an adhesive is applied to a jig having a smooth surface to the conductive reflective film adhered on the transparent conductive film, and this is electrically conductive. After pressing onto the reflective film and holding until the adhesive is sufficiently dry and has high adhesive strength, this jig is attached to the substrate using a tensile tester (manufactured by Shimadzu Corporation: EZ-TEST). Pulled up vertically, the conductive reflective film was peeled off from the transparent conductive film.

  Next, using an atomic force microscope (AFM), an uneven image of the surface of the conductive reflective film that was peeled off from the transparent conductive film and exposed on the jig was contacted with the transparent conductive film. Observed. 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 regarded as an average value obtained by measuring the longest side and the shortest side for holes having a diameter of 20 nm or more in the captured image with respect to an AFM image having five or more fields of view. The average depth of an AFM image of 5 fields or more is measured for a hole having a diameter of 20 nm or more in the photographed image, and an average within a circle having a radius of 10 nm centering on the deepest position of the hole. The depth.

  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 transparent conductive film / conductive reflective film interface was observed. About this interface image, the diameter, average depth, and number density of the opening were evaluated. The diameter of the opening was regarded as an average value obtained by measuring the longest side and the shortest side of a hole having a diameter of 20 nm or more in a photographed image with respect to an SEM image having five or more fields of view. The average depth is measured with respect to a SEM image of 5 fields of view or more, and the depth is measured for holes having a diameter of 20 nm or more in the photographed image, and the average within a circle having a radius of 10 nm centered on the deepest position of the hole. The depth.

(3) Series resistance: I- when the lead wire is wired on the substrate after the solar cell line processing and irradiated with light of AM1.5, 100 mW / cm ² using a solar simulator and a digital source meter. A V (current-voltage) curve was obtained. Further, the current value (I) in the obtained IV (current-voltage) curve is divided by the surface area of the solar battery cell to obtain a JV curve (current density-voltage). The reciprocal of the slope in the vicinity of the voltage at 0) was taken as the series resistance.

表５から明らかなように、比較例１，２では、発電の際の直列抵抗が４０〜５０Ω／ｃｍ²と比較的高い値を示したのに対し、本発明によって形成された複合膜を備える実施例１〜１０では、いずれも、発電の際の直列抵抗が２３Ω／ｃｍ²以下という非常に低い値を示した。

As is clear from Table 5, in Comparative Examples 1 and 2, the series resistance during power generation showed a relatively high value of 40 to 50 Ω / cm ² , whereas the composite film formed according to the present invention was provided. In each of Examples 1 to 10, the series resistance during power generation showed a very low value of 23 Ω / cm ² or less.

  INDUSTRIAL APPLICABILITY The present invention is extremely suitable as a technique for producing a composite film for a solar cell that increases power generation efficiency during power generation. Further, by using the present invention, it is possible to replace a composite film composed of a transparent conductive film and a conductive reflective film, which has been conventionally formed by a vacuum film formation method, with a coating and baking process, which greatly increases the manufacturing cost. Reduction can be expected.

DESCRIPTION OF SYMBOLS 11 Base material 12 Surface electrode 13 Photoelectric conversion layer 14 Composite film 14a Transparent conductive film 14b Conductive reflective film

Claims (9)

On a photoelectric conversion layer of a solar cell laminated on a substrate via a surface electrode, a dispersion containing conductive oxide fine particles and a dispersion containing a binder component or both conductive oxide fine particles and a binder component are included. Applying the transparent conductive film forming composition by a wet coating method to form a transparent conductive coating film,
After forming the conductive reflective coating film by applying the composition for conductive reflective film on the transparent conductive coating film by a wet coating method,
A method for forming a composite film for a solar cell comprising a transparent conductive film and a conductive reflective film by firing a substrate having the transparent conductive film and the conductive reflective film,
The conductive oxide fine particle includes either a non-spherical anisotropic particle or an aggregate having an anisotropic structure formed by aggregating a plurality of particles. Of forming a composite film for use.   The method for forming a composite film for a solar cell according to claim 1, wherein an aspect ratio of the anisotropically shaped particles or the anisotropic structural aggregate is 3 or more. When the anisotropically shaped particles or anisotropic structure aggregates are plate-like,
The method for forming a composite film for a solar cell according to claim 1, wherein the plate-like particles or aggregates have a thickness of 50 to 1500 nm and a width-thickness ratio of 2 to 100.   4. 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 formation method of the composite film for solar cells of any one of Claims 1. A composition for forming a transparent conductive film for forming the transparent conductive film constituting the composite film for a solar cell by applying and baking by a wet coating method,
The composition is composed of a dispersion of conductive oxide fine particles not containing a binder component and a dispersion of binder component not containing the conductive oxide fine particles, or the conductive oxide fine particles and the Consists of a dispersion containing both binder components,
The conductive oxide fine particle includes either a non-spherical anisotropic particle or an aggregate having an anisotropic structure formed by aggregating a plurality of particles. Film forming composition.   The composition for forming a transparent conductive film according to claim 5, wherein an aspect ratio of the anisotropic shaped particle or the anisotropic structure aggregate is 3 or more. When the anisotropically shaped particles or anisotropic structure aggregates are plate-like,
The composition for forming a transparent conductive film according to claim 5, wherein the plate-like particles or aggregates have a thickness of 50 to 1500 nm and a width-thickness ratio of 2 to 100.   The composite film for solar cells which consists of the said transparent conductive film formed by the method of any one of Claim 1 thru | or 4, and the said electroconductive reflection film.   The solar cell provided with the composite film for solar cells of Claim 8.

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