JP2011222953A - Composition for transparent conductive film formation, method for forming composite film for solar cell, and composite film formed by the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite film and a method for forming the composite film for a solar cell capable of improving conversion efficiency of the solar cell by decreasing the contact resistance between a photoelectric conversion layer and a transparent conductive film, and between the transparent conductive film and a conductive reflection film, decreasing the serial resistance of the solar cell in power generation, and provide a composition for transparent conductive film formation.SOLUTION: Conductive oxide fine particles are made of Sn- or Zn-doped indium oxide containing In, and Sn or Zn as constituent elements; or In-, Sn-, Al-, Ga-, or Ge-doped zinc oxide containing Zn, and In, Sn, Al, Ga, or Ge as constituent elements; or In-, Ga-, Al-, or Sb-doped tin oxide containing Sn, and In, Ga, Al or Sb as constituent elements. The conductive oxide fine particles further contain a different kind of additive element from the constituent elements, and the content rate of the additive element is 0.01 to 20 mol% for the total 100 mol% of the constituent elements and additive element in the conductive oxide fine 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 the photoelectric conversion layer of the solar cell, a composite film formed by the method, and formation of the transparent conductive film The present invention relates to a composition for forming a transparent conductive film used in the above. More specifically, the conversion 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 solar cells, a composite film formed by the method, and a composition for forming a transparent conductive film used for forming the transparent conductive film.

  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 have been studied to increase conversion efficiency by taking, for example, a structure formed of a transparent electrode, amorphous silicon, polycrystalline silicon, and back electrode 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 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, thereby converting the conversion efficiency. 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 conversion efficiency, the electrical resistance of the layer constituting each electrode or the film itself is decreased, or the good contact property between the photoelectric conversion layer and the electrodes or between the electrodes. Or electrical conductivity is required. The present inventors have examined a method of replacing the formation of the electrode located on the back side with a wet film forming method, and the surface of the transparent conductive film 14a shown in FIG. And the work function of the surface of the photoelectric conversion layer 13 on which the transparent conductive film 14a is formed or the work function of the surface of the conductive reflective film 14b formed on the transparent conductive film 14a. This has been found to be an adverse effect of improving conversion efficiency. For example, when the difference between the work function on the surface of the photoelectric conversion layer 13 and the work function on the surface of the transparent conductive film 14a increases, the contact resistance between the photoelectric conversion layer 13 and the transparent conductive film 14a during power generation increases, which is the power generation. As a result, the series resistance of the solar cell was increased, and as a result, the conversion efficiency was hindered.

  The purpose of the present invention is to convert solar cells 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. An object of the present invention is to provide a method for forming a composite film for solar cells that can improve efficiency, a composite film formed by the method, and a composition for forming a transparent conductive film used for forming the transparent conductive film.

  As shown in FIG. 1, the first aspect of the present invention is a transparent film used for forming the transparent conductive film 14a of a composite film 14 for a solar cell composed of a transparent conductive film 14a and a conductive reflective film 14b. In the composition for forming a conductive film, the composition for forming a transparent conductive film includes both conductive oxide fine particles and a binder component, and the conductive oxide fine particles are Sn or Zn doped with In and Sn or Zn as constituent elements. Indium oxide, Zn, and In, Sn, Al, Ga, or Ge-doped zinc oxide containing In, Sn, Al, Ga, or Ge as constituent elements, or Sn and In, Ga, Al, or Sb. In, Ga, Al, or Sb-doped tin oxide, the conductive oxide fine particles further contain an additive element of a different type from the constituent elements, and the content ratio of the additive element is the conductive oxide fine particles A total of 100 mole% of the constituent elements and the addition element in contrast, is characterized in that 0.01 to 20 mol%.

  The second aspect of the present invention is the invention based on the first aspect, and the additional elements are Na, K, Cs, Mg, Ca, Sr, Al, Cu, Ti, Nb, Si, P, Ga, One, two or more selected from the group consisting of Sn, In, Ge, Sb, La, Ce, Pr, Sm, Eu, Gd and Yb.

  According to a third aspect of the present invention, a dispersion containing conductive oxide fine particles and a dispersion containing a binder component on a photoelectric conversion layer 13 of a solar cell laminated on a substrate 11 via a surface electrode 12 or A transparent conductive film-forming composition containing both conductive oxide fine particles and a binder component is applied by a wet coating method to form a transparent conductive film, and the conductive reflective film composition is wet on the transparent conductive film. After applying the coating method to form a conductive reflective coating film, the substrate 11 having the transparent conductive coating film and the conductive reflective coating film is baked to form a transparent conductive film 14a and a conductive reflective film 14b. A method of forming a composite film 14 for a solar cell, wherein the conductive oxide fine particles are Sn and Zn-doped indium oxide containing In and Sn or Zn as constituent elements, or Zn and In, Sn, Al, Ga or Ge as a constituent element In, Sn, Al, Ga or Ge doped zinc oxide or In, Ga, Al or Sb doped tin oxide with Sn and In, Ga, Al or Sb as constituent elements, conductive oxide The fine particles further contain a different type of additive element from the constituent elements, and the content of the additive elements is 0.01 to 20 mol% with respect to a total of 100 mol% of the constituent elements and additive elements in the conductive oxide fine particles. It is characterized by.

  A fourth aspect of the present invention is the invention based on the third aspect, and the additional elements are Na, K, Cs, Mg, Ca, Sr, Al, Cu, Ti, Nb, Si, P, Ga, One, two or more selected from the group consisting of Sn, In, Ge, Sb, La, Ce, Pr, Sm, Eu, Gd and Yb.

  The fifth aspect of the present invention is an invention based on the third or fourth aspect, 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.

  The sixth aspect of the present invention is a composite film for a solar cell comprising a transparent conductive film 14a and a conductive reflective film 14b formed by the methods of the third to fifth aspects.

A seventh aspect of the present invention is an invention based on the sixth aspect, and further has an average depth of 100 nm or less from the contact surface with the transparent conductive film 14a or the surface facing the contact surface in the conductive reflective film 14b. The average diameter of the pores appearing in the region is 100 nm or less, and the number density of the pores is 30 / μm ² or less.

  The 8th viewpoint of this invention is a solar cell provided with the composite film 14 for solar cells of the 6th or 7th viewpoint.

  The composition for forming a transparent conductive film according to the first aspect of the present invention contains both conductive oxide fine particles and a binder component, and the conductive oxide fine particles are Sn or Zn-doped with In and Sn or Zn as constituent elements. Indium oxide, Zn, and In, Sn, Al, Ga, or Ge-doped zinc oxide containing In, Sn, Al, Ga, or Ge as constituent elements, or Sn and In, Ga, Al, or Sb. In, Ga, Al, or Sb-doped tin oxide, and the conductive oxide fine particles further contain a different type of additive element from the constituent elements. And the content rate of an additive element is 0.01-20 mol% with respect to the sum total of 100 mol% of the constituent element and additive element in electroconductive oxide fine particles. As described above, in the composition for forming a transparent conductive film of the present invention, the conductive oxide fine particles further contain an additive element of a type different from the constituent elements at a predetermined ratio, thereby allowing the photoelectric conversion layer of the solar cell to have A transparent conductive film having a small difference from the work function of the photoelectric conversion layer can be formed. For this reason, in a solar cell provided with a transparent conductive film formed using this composition as a part of the composite film, between the photoelectric conversion layer and the transparent conductive film during power generation, between the transparent conductive film and the conductive reflective film Since contact resistance falls, the series resistance in the solar cell in the case of electric power generation falls, and conversion efficiency improves significantly.

  In the formation method of the 3rd viewpoint of this invention, it is the 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 For the formation of the conductive film, by using conductive oxide fine particles that further contain additional elements of a different type from the constituent elements in a predetermined ratio, the work function of the transparent conductive film in contact with the photoelectric conversion layer is reduced, and The difference between the work function of the conversion layer and the work function of the transparent conductive film can be reduced. 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 Conversion 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.

  Since the composite film for a solar cell according to the sixth aspect of the present invention is formed by the method of the present invention, the transparent conductive film constituting the composite film contains the constituent elements of the conductive oxide fine particles and the element. An additional element of a different type from the constituent elements is further included. Thereby, the contact resistance between a photoelectric converting layer and a transparent conductive film, and between a transparent conductive film and a conductive reflective film becomes small, and the series resistance in the solar cell during power generation can be reduced. For this reason, the conversion efficiency of a solar cell can be improved more.

The composite film for solar cells according to the seventh aspect of the present invention is formed by the above-described method of the present invention, so that the average of the contact surface with the transparent conductive film in the conductive reflective film or the surface facing the contact surface is averaged. The average diameter of pores appearing in a region having a depth of 100 nm or less is 100 nm or less, and the number density of pores is 30 / μm ² or less. For this reason, 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.

  Since the solar cell according to the eighth 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 conversion 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. The transparent conductive film 14a formed by the wet coating method tends to increase the work function of the surface of the transparent conductive film 14a due to the influence of a small amount of organic matter adsorbed on the surface. Therefore, the work function of the surface of the transparent conductive film 14a and the work function of the surface of the photoelectric conversion layer 13 on which the transparent conductive film 14a is formed or the work function of the surface of the conductive reflective film 14b formed on the transparent conductive film 14a. If a difference arises between these and becomes large, 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, and the series resistance in the solar cell during power generation increases. As a result, improvement of the conversion efficiency of the solar cell is hindered.

  In the present invention, in order to reduce the work function on the surface of the transparent conductive film 14a, the transparent conductive film is formed by using Sn or Zn-doped indium oxide having In and Sn or Zn as constituent elements as conductive oxide fine particles. Or Zn, In, Sn, Al, Ga, or Ge-doped zinc oxide having In, Sn, Al, Ga, or Ge as constituent elements, or Sn, In, Ga, Al, or Sb as constituent elements. An In, Ga, Al, or Sb-doped tin oxide that further includes a different type of additive element from the above constituent elements is used. By using such conductive oxide fine particles, the additive element can be further included in the transparent conductive film 14a of the composite film 14 to be formed in addition to the constituent elements of the conductive oxide fine particles. Thereby, the work function of the surface of the transparent conductive film 14a is lowered, the work function of the surface of the photoelectric conversion layer 13 on which the transparent conductive film 14a is formed, or the work function of the surface of the conductive reflective film 14b formed on the transparent conductive film 14a. And the difference can be reduced. The content ratio of the additive element is 0.01 to 20 mol% with respect to 100 mol% in total of the constituent elements and additive elements in the conductive oxide fine particles. If the content ratio of the additive element is less than the lower limit, the effect of lowering the work function by adding the additive element cannot be sufficiently obtained. On the other hand, if the upper limit is exceeded, the conductivity of the transparent conductive film 14a itself is lowered, and long-term reliability cannot be obtained.

  The additive element contained in the conductive oxide fine particles is a different type of element from the constituent elements of the conductive oxide fine particles used, and is Na, K, Cs, Mg, Ca, Sr, Al, Cu, Ti, Nb. , Si, P, Ga, Sn, In, Ge, Sb, La, Ce, Pr, Sm, Eu, Gd and Yb are preferably one or more selected from the group consisting of.

A method for obtaining the conductive oxide fine particles will be described as a representative of conductive oxide fine particles in which, for example, Sn-doped indium oxide containing In and Sn as constituent elements contains an additive element. Specifically, a mixed aqueous solution of indium chloride InCl ₃ and tin chloride SnCl ₄ is dropped into an aqueous solution of ammonium carbonate such as ammonium carbonate, ammonium bicarbonate, or ammonium carbamate, or a mixed aqueous solution thereof. A conventional method obtained by coprecipitation of hydroxide, solid-liquid separation of the obtained precipitate by decantation or centrifugal separation, and washing of the separated precipitate with water, drying, firing and pulverization can be applied. In this method, in the case where an additive element such as chloride, for example, Mg, is added as an additive element to a mixed aqueous solution of indium chloride InCl ₃ and tin chloride SnCl ₄ , magnesium chloride MgCl ₂ may be added. Similarly, when the additive element is other than Mg, the chloride of each element may be added to the mixed aqueous solution of indium chloride InCl ₃ and tin chloride SnCl ₄ . The temperature of the coprecipitation reaction is preferably in the range of 5 ° C to 95 ° C. The calcination is preferably performed within a range of 400 ° C. to 950 ° C. within a range of 30 minutes to 8 hours, preferably within a range of 500 ° C. to 850 ° C. within a range of 1 hour to 6 hours.

The average particle diameter of the conductive oxide fine particles is preferably in the range of 2 to 100 nm in order to obtain sufficient conductivity and good film formability, and of these, in the range of 5 to 50 nm. It is particularly preferred. In the present specification, the average particle diameter is a 50% average particle diameter (D) measured by a laser diffraction / scattering particle size distribution measuring device (LA-950, manufactured by Horiba, Ltd.) and calculated based on the particle diameter standard. ₅₀ ).

  As a method for forming the transparent conductive film 14a by the wet coating method, there are mainly two forming methods. In the first method, a transparent conductive film is formed by applying the transparent conductive film forming composition of the present invention, which is prepared by containing both the conductive oxide fine particles and the binder component, onto the photoelectric conversion layer 13 by a wet coating method. In this method, a coating film is formed and then fired. In the second method, a coating film of conductive oxide fine particles was formed on the photoelectric conversion layer 13 by applying the dispersion of the conductive oxide fine particles not containing a binder component using a wet coating method. Thereafter, a binder dispersion containing no conductive oxide fine particles is impregnated on the coating film of the conductive oxide fine particles using a wet coating method, followed by firing.

  The composition for forming a transparent conductive film of the present invention used in the first method is a composition containing the above-described conductive oxide fine particles and the conductive oxide fine particles 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 the solid content contained in the composition for transparent conductive film formation 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 forming a transparent conductive film is a composition containing one or both of a polymer type binder and a non-polymer type 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, and particularly preferably in the range of 10 to 30% by mass as a proportion of the solid content in the composition for forming a transparent conductive film.

  It is preferable to add a coupling agent to the composition for forming a transparent conductive film according to other components to be used. This is for improving the adhesion between the conductive oxide fine particles and the binder and the adhesion between the transparent conductive film 14a formed of the transparent conductive film forming 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、透明導電膜形成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 in the range of 0.5 to 2% by mass, as the solid content of the transparent conductive film forming composition. preferable.

  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 of these low resistance agents is preferably 0.2 to 15% by mass with respect to the conductive oxide fine particles. A water-soluble cellulose derivative is a non-ionizing active agent, but it has a very high ability to disperse conductive oxide fine particles even when added in a small amount compared to other surfactants, and is formed by the addition of 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 composition for forming a transparent conductive film, first, the composition for forming a transparent conductive film has a thickness of 0.01 to 0.5 μm after baking, Preferably, it coats on the photoelectric conversion layer 13 by a wet coating method so that it may become 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 film formation 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. The dispersion medium used for the preparation of the dispersion of conductive oxide fine particles should be the same type as the dispersion medium used in the composition for forming a transparent conductive film of the present invention used in the first method. Can do. 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. The coupling agent used for the preparation of the conductive oxide fine particle dispersion is the same as the coupling agent used in the transparent conductive film forming composition of the present invention used in the first method. can do. It is preferable that the ratio of the coupling agent in the dispersion is in the range of 0.1 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 the preparation of the binder dispersion are the polymer-type binder and non-polymer-type binder used in the transparent conductive film forming composition of the present invention used in the first method. The same kind can be used.

  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 the conversion 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 conversion efficiency by reflecting the light that cannot be 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 film formation, 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. The composite film 14 formed by this method further includes, in the transparent conductive film 14a, the above-mentioned additive element of a type different from the constituent elements, in addition to the constituent elements of the conductive oxide fine particles. Thereby, the work function on the surface of the transparent conductive film 14a becomes low, and the difference between the work function on the surface of the photoelectric conversion layer 13 or the work function on the surface of the conductive reflective film 14b becomes small. 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 the conversion 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 21 and Comparative Examples 1 to 6>
The composition shown in Table 1 and Table 2 below, conductive oxide fine particles having an average particle size of 0.025 μm, a dispersion medium, a binder, a coupling agent, and other components depending on the components used And the ratio shown in Table 1 and Table 2, with a total amount of 60 g, put this in a 100 cc glass bottle, and with a paint shaker using 100 g of zirconia beads (Microhaika, Showa Shell Sekiyu KK) with a diameter of 0.3 mm. By dispersing for 6 hours, a composition for forming a transparent conductive film was obtained. 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, In the same manner as the above-mentioned method for producing silver nanoparticles, metal nanoparticles other than silver nanoparticles are used 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. The dispersion of this metal nanoparticle is used as the second dispersion, and before adding the additives, the first dispersion and the second dispersion are made to have the ratios shown in the following Tables 3 and 4. 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. Next, after applying the composition for forming a transparent conductive film prepared as described above by various film forming methods so that the thickness after firing becomes 0.01 to 0.5 μm, it is dried at a temperature of 25 ° C. for 5 minutes. A transparent conductive coating was formed. Next, the composition for conductive reflective film prepared above was applied on the formed transparent conductive coating film by various film forming methods so that the thickness after firing was 0.05 to 2.0 μm, and then the temperature was changed. The conductive reflective coating film was formed by drying at 25 ° C. for 5 minutes. Subsequently, the composite film 14 was formed on the photoelectric conversion 13 layer by baking on the heat processing conditions shown in the following Table 3, Table 4, and the solar cell substrate was obtained. 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１〜２１及び比較例１〜６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，表６に示す。

<Comparison test and evaluation>
About the photovoltaic cell board | substrate which formed the composite film on the photoelectric converting layer of Examples 1-21 and Comparative Examples 1-6, the thickness of the transparent conductive film and conductive reflection film in a composite film, pore distribution in a conductive reflection film The series resistance was evaluated. These results are shown in Tables 5 and 6 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 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 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. Here, the diameter of the evaluated opening was determined by regarding the length of the opening in the cross-sectional view as the diameter.

(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１〜表６から明らかなように、比較例１〜６では、発電の際の直列抵抗が２０〜３０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１〜２１では、いずれも、発電の際の直列抵抗が１３以下という非常に低い値を示した。

As is apparent from Tables 1 to 6, in Comparative Examples 1 to 6, the series resistance during power generation showed a relatively high value of 20 to 30, whereas the composite film formed according to the present invention was provided. In each of Examples 1 to 21, the series resistance during power generation showed a very low value of 13 or less.

  INDUSTRIAL APPLICABILITY The present invention is extremely suitable as a technique for manufacturing a composite film for a solar cell that increases conversion 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 (8)

In the composition for forming a transparent conductive film used for forming the transparent conductive film of a composite film for a solar cell composed of a transparent conductive film and a conductive reflective film,
The composition for forming a transparent conductive film contains both conductive oxide fine particles and a binder component,
The conductive oxide fine particles are Sn or Zn-doped indium oxide containing In and Sn or Zn as constituent elements, or In, Sn, Al, Zn and In, Sn, Al, Ga or Ge as constituent elements. Ga or Ge-doped zinc oxide, or In, Ga, Al, or Sb-doped tin oxide containing Sn and In, Ga, Al, or Sb as constituent elements,
The conductive oxide fine particles further include a different type of additive element from the constituent elements,
The content ratio of the additive element is 0.01 to 20 mol% with respect to 100 mol% in total of the constituent element and the additive element in the conductive oxide fine particles. .   The additive elements are Na, K, Cs, Mg, Ca, Sr, Al, Cu, Ti, Nb, Si, P, Ga, Sn, In, Ge, Sb, La, Ce, Pr, Sm, Eu, Gd and The composition for forming a transparent conductive film according to claim 1, wherein the composition is one or more selected from the group consisting of Yb. 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 a composition for forming a transparent conductive film are applied by a wet coating method. Apply to form a transparent conductive 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 particles are Sn or Zn-doped indium oxide containing In and Sn or Zn as constituent elements, or In, Sn, Al, Zn and In, Sn, Al, Ga or Ge as constituent elements. Ga or Ge-doped zinc oxide, or In, Ga, Al, or Sb-doped tin oxide containing Sn and In, Ga, Al, or Sb as constituent elements,
The conductive oxide fine particles further include a different type of additive element from the constituent elements,
The content ratio of the additive element is 0.01 to 20 mol% with respect to a total of 100 mol% of the constituent element and the additive element in the conductive oxide fine particles. Forming method.   The additive elements are Na, K, Cs, Mg, Ca, Sr, Al, Cu, Ti, Nb, Si, P, Ga, Sn, In, Ge, Sb, La, Ce, Pr, Sm, Eu, Gd and The method for producing a composite film for a solar cell according to claim 3, which is one or more selected from the group consisting of Yb.   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 as described.   The composite film for solar cells which consists of the said transparent conductive film formed by the method of any one of Claim 3 thru | or 5, and the said electroconductive reflection film. From the contact surface with the transparent conductive film or the surface facing the contact surface in the conductive reflective film, the average diameter of pores appearing in a region having an average depth of 100 nm or less is 100 nm or less, and the number density of the pores is The composite film for a solar cell according to claim 6, wherein the number is 30 pieces / μm ² or less.   The solar cell provided with the composite film for solar cells of Claim 6 or 7.

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