JP2011192804A - Method of manufacturing solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar cell having improved efficiency of power generation by reducing an electric resistance of electrodes. <P>SOLUTION: The method of manufacturing the solar cell includes the steps of forming a photoelectric conversion layer 13 made of either an amorphous silicon or a microcrystalline silicon or both of them on a surface electrode layer 12 of a transparent substrate 11 having the surface electrode layer formed thereon, and forming a backside transparent electrode layer on the photoelectric conversion layer. In the method, the backside transparent electrode layer is formed by applying a dispersion liquid containing conductive fine particles on the surface of a photoelectric conversion layer by wet coating to form a coating 24a of the conductive fine particles, then, irradiating the formed coating of conductive particles with an ultraviolet ray of output of 0.5-10 J/cm<SP>2</SP>, applying a dispersion liquid 24b containing a binder on the coating of conductive fine particles which is irradiated with the ultraviolet ray by using wet coating to impregnate the binder component, forming a transparent conductive coating 24, and baking the transparent conductive coating. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a silicon-based thin film type or multi-junction solar cell.

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

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

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

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

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)

  Moreover, in a thin film solar cell, in order to improve electric power generation efficiency, the electrical resistance of each electrode itself is reduced, and the favorable contact property or electroconductivity between a photoelectric converting layer and electrodes or between electrodes is calculated | required. However, the conventional thin-film solar cell has a problem in that the power generation efficiency is lowered due to an increase in the electrical resistance of the electrode itself due to mixing of substances that inhibit conductivity such as organic substances in the electrode during the electrode formation process. .

  An object of the present invention is to provide a method for manufacturing a solar cell with improved power generation efficiency by reducing the electrical resistance of an electrode.

As shown in FIG. 1 or FIG. 3, the first aspect of the present invention is that amorphous silicon or microcrystalline silicon is formed on the surface-side electrode layer 12 of the transparent substrate 11 having the surface-side electrode layer 12 formed on the surface. In the solar cell manufacturing method in which the photoelectric conversion layer 13 composed of either one or both is formed and the back surface side transparent electrode layer 14 is formed on the photoelectric conversion layer 13, the formation of the back surface side transparent electrode layer 14 is illustrated in FIG. As shown in FIG. 2 or FIG. 4, a dispersion liquid containing conductive fine particles is applied to the surface of the photoelectric conversion layer 13 by a wet coating method to form a conductive fine particle coating 24 a, and then the conductive fine particles formed By irradiating the coating film 24a with ultraviolet rays at an output of 0.5 to 10 J / cm ² and applying the dispersion liquid 24b containing the binder to the coating film 24a of the conductive fine particles irradiated with the ultraviolet rays using a wet coating method. Binder component Impregnated, forming a transparent conductive coating film 24, characterized in that it is carried out by firing the transparent conductive coating film 24.

  A second aspect of the present invention is the invention based on the first aspect, wherein the ultraviolet irradiation lamp used for ultraviolet irradiation is a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp or an excimer lamp. And

  The 3rd viewpoint of this invention is a solar cell obtained by the manufacturing method based on a 1st or 2nd viewpoint.

  In the manufacturing method according to the first aspect of the present invention, photoelectric conversion comprising either one or both of amorphous silicon and microcrystalline silicon on the surface-side electrode layer of the transparent substrate having the surface-side electrode layer formed on the surface. In the method for manufacturing a solar cell in which a back surface side transparent electrode layer is formed on the photoelectric conversion layer, the back side transparent electrode layer is formed on the surface of the photoelectric conversion layer with a dispersion containing conductive fine particles. After applying a wet coating method to form a coating film of conductive fine particles, the conductive fine particle coating film is irradiated with ultraviolet rays at a specific output, and the conductive fine particle coating film irradiated with ultraviolet rays contains a binder. The dispersion is applied by using a wet coating method to impregnate the binder component, form a transparent conductive coating film, and fire the transparent conductive coating film. Thereby, the electrical resistance of an electrode can be lowered | hung and power generation efficiency can be improved.

It is the figure which represented typically the cross section of the thin film solar cell of this invention. In FIG. 1, it is the figure which represented typically the cross section before baking a transparent conductive coating film. It is the figure which represented typically the cross section of the thin film solar cell of another form of this invention. In FIG. 3, it is the figure which represented typically the cross section before baking a transparent conductive coating film. It is the figure which represented typically the top view which shows the state which masked with the tape on the photoelectric converting layer surface in an Example. It is a figure which shows the state which measures the contact resistance of the multijunction type thin film silicon solar cell for evaluation in an Example.

  Next, an embodiment for carrying out the present invention will be described with reference to the drawings. As shown in FIG. 1 or FIG. 3, the method for manufacturing a solar cell of the present invention comprises amorphous silicon or microcrystalline silicon on the surface-side electrode layer 12 of the transparent substrate 11 having the surface-side electrode layer 12 formed on the surface. The photoelectric conversion layer 13 which consists of any one or both of these is formed, and the back side transparent electrode layer 14 is formed on this photoelectric conversion layer 13. And it has the structure which provided the back surface side reflective electrode layer 16 on this back surface side transparent electrode layer 14. FIG.

  The transparent substrate 11 is made of a light transmissive substrate made of glass, ceramics or a polymer material, or two or more types 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-side electrode layer 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 this surface side electrode layer 12, for example, ITO (indium oxide-tin oxide composite oxide), ATO (antimony oxide-tin oxide composite oxide), SnO ₂ (tin oxide), ZnO (zinc oxide), Examples of the film include IZO (indium oxide-zinc oxide composite oxide) and AZO (aluminum oxide-zinc oxide composite oxide). The surface-side electrode layer 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 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 which doped any. The surface side electrode layer 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 forming the surface side electrode layer 12 by the wet coating method, it is performed similarly to the case where the below-mentioned back side transparent electrode layer 14 is formed by the wet coating method. The ZnO is suitable as a material for the surface-side electrode layer 12 because it has high light transmittance, low resistance, and plasticity and is inexpensive.

  On the surface-side electrode layer 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 sequentially stacked from the substrate 11 side. It is a pin 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. The intermediate layer is preferably made of a material used for the front-side electrode layer 12 and the back-side transparent electrode layer 14.

  On the photoelectric conversion layer 13, a back side transparent electrode layer 14 is formed. The back side transparent electrode layer 14 is provided to suppress mutual diffusion between the photoelectric conversion layer 13 and the back side reflective electrode layer 16 and to increase the reflection efficiency of the back side reflective electrode layer 16. The back side transparent electrode layer 14 is formed by a wet coating method. A sputtering method has been conventionally used to form the back surface side transparent electrode layer 14, but the refractive index of the film of the back surface side transparent electrode layer 14 formed by this sputtering method is determined by the material of the target material. It is difficult to obtain a desired refractive index. On the other hand, in the case of using the wet coating method, a film formed by using the wet coating method is formed by adjusting the components of the composition or the like because the composition formed by mixing conductive fine particles and other components is applied. Formation of a film having a low refractive index of about 1.5 to 2 is facilitated. The back surface side transparent electrode layer 14 having a low refractive index gives a back reflection effect on the optical design to the back surface side reflective electrode layer 16 to be joined. Therefore, the back surface side transparent electrode layer 14 formed using a wet coating method. The back-side reflective electrode layer 16 bonded to the surface has a higher reflectance than the back-side reflective electrode layer 16 bonded to the high-refractive-index back-side transparent electrode layer 14 formed by sputtering.

  In the formation of the back surface side transparent electrode layer 14 by the wet coating method, two dispersions of a dispersion containing no conductive fine particles and a dispersion containing no conductive fine particles and a dispersion containing conductive fine particles are included. Use. The conductive fine particle dispersion containing no binder component is a dispersion in which conductive fine particles are dispersed in a dispersion medium. As the conductive fine particles, ITO (Indium Tin Oxide: indium oxide-tin oxide composite oxide), ATO (Antimony Tin Oxide: antimony oxide-tin oxide composite oxide) tin oxide powder, Al, Co, Fe, Zinc oxide powder containing one or more metals selected from the group consisting of In, Sn, Ga and Ti is preferred. Of these, ITO, ATO, AZO (Aluminum Zinc Oxide), IZO (Indium Zinc Oxide), TZO (Tin Zinc Oxide: Tin-containing zinc oxide composite oxide) Is particularly preferred. The average particle diameter of the conductive fine particles is preferably in the range of 10 to 100 nm in order to maintain stability in the dispersion medium, and particularly preferably in the range of 20 to 60 nm.

  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.

  It is preferable to add a coupling agent to the conductive fine particle dispersion according to other components to be used. That is, the bonding between the conductive fine particles and the binder and the adhesion between the backside transparent electrode layer 14 formed of the conductive fine particle dispersion and the binder dispersion and the photoelectric conversion layer 13 or the backside reflective electrode layer 16 are improved. Because. Examples of the coupling agent used for preparing the conductive fine particle dispersion 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.

また、導電性微粒子を含まないバインダ分散液は、バインダ成分として、加熱により硬化するポリマー型バインダ又はノンポリマー型バインダのいずれか一方又は双方を含む。ポリマー型バインダとしては、アクリル樹脂、ポリカーボネート、ポリエステル、アルキッド樹脂、ポリウレタン、アクリルウレタン、ポリスチレン、ポリアセタール、ポリアミド、ポリビニルアルコール、ポリ酢酸ビニル、セルロース及びシロキサンポリマ等が挙げられる。またポリマー型バインダには、アルミニウム、シリコン、チタン、ジルコニウム、クロム、マンガン、鉄、コバルト、ニッケル、銀、銅、亜鉛、モリブデン又は錫の金属石鹸、金属錯体或いは金属アルコキシドの加水分解体が含まれることが好ましい。この金属アルコキシドの加水分解体にはゾルゲルを含む。ノンポリマー型バインダとしては、金属石鹸、金属錯体、金属アルコキシド、ハロシラン類、２−アルコキシエタノール、β−ジケトン及びアルキルアセテート等が挙げられる。また金属石鹸、金属錯体又は金属アルコキシドに含まれる金属は、アルミニウム、シリコン、チタン、ジルコニウム、クロム、マンガン、鉄、コバルト、ニッケル、銀、銅、亜鉛、モリブデン、錫、インジウム又はアンチモンである。これらポリマー型バインダ、ノンポリマー型バインダが、加熱により硬化することで、低温での低いヘイズ率及び体積抵抗率の裏面側透明電極層１４の形成を可能とする。バインダ分散液中のこれらバインダの含有割合は、０．０１〜５０質量％の範囲内が好ましく、０．５〜２０質量％の範囲内が特に好ましい。

Moreover, the binder dispersion liquid which does not contain electroconductive fine particles contains either one or both of the polymer type binder and the non-polymer type binder which harden | cure by heating as a binder component. 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 the back-side transparent electrode layer 14 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.

  In preparing the binder dispersion, it is preferable to use a dispersion medium of the same type as the dispersion medium used in the preparation of the conductive fine particle dispersion. 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. 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 0.1 to 10% by mass. Moreover, the transparency in the formed transparent electrode layer is also improved by the addition of the water-soluble cellulose derivative. 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 0.1 to 10% by mass.

  As shown in FIG. 1, the back side transparent electrode layer 14 is formed using the two dispersions described above, with the first layer 14a containing both conductive fine particles and a binder component as a lower layer, and mainly from the binder component. As shown in FIG. 3, the first layer 14b including both the conductive fine particles and the binder component as the lower layer, and the second layer 14c not including the binder component as shown in FIG. There is a method to make the upper layer. The back side transparent electrode layer formed by the first forming method is formed in a state where the entire surface of the conductive oxide fine particle layer is covered with the second layer 14b made of the binder component, and therefore it is said that the change with time is small. There are advantages. On the other hand, the back side transparent electrode layer formed by the second forming method is effective in increasing the fill factor, which is one of the factors that determine the conversion efficiency.

  First, as shown in FIG. 2 or FIG. 4, a conductive fine particle dispersion containing no binder component is applied on the photoelectric conversion layer 13 using a wet coating method, and the temperature is 20 to 120 ° C., preferably 25 to 60 ° C. Is dried for 1 to 30 minutes, preferably 2 to 10 minutes, to form the conductive fine particle coating 24a. In the case of the second forming method, the coating is performed so that the thickness of the back-side transparent electrode layer after firing is 0.01 to 0.5 μm, preferably 0.05 to 0.1 μm. . In addition, before forming the back surface side transparent electrode layer 14 on the photoelectric converting layer 13, you may irradiate the surface of the photoelectric converting layer 13 with an ultraviolet-ray on the same conditions as the conditions mentioned later. Thereby, a substance that hinders conductivity, such as an attached organic substance on the surface of the photoelectric conversion layer 13, which becomes a contact surface with the back surface side transparent electrode layer 14, is removed, and the contact between the photoelectric conversion layer 13 and the back surface side transparent electrode layer 14. As a result, the electric resistance during power generation can be lowered and the power generation efficiency of the solar cell can be improved.

Then, on the coating film 24a of the conductive fine particles described above it is formed, irradiated with ultraviolet rays at an output 0.5~10J / cm ^2. In this manufacturing method, in forming the back side transparent conductive layer, two dispersions are used and applied in separate steps. Therefore, after forming a coating film of conductive fine particles, the binder dispersion is impregnated. In addition, due to the organic matter or the like adhering to the coating film surface of the conductive fine particles, the organic matter may be mixed in the back side transparent electrode layer after the formation. When organic substances are mixed in the electrode, the electrical resistance of the electrode itself increases, and as a result, the power generation efficiency of the solar cell decreases. In order to prevent this, ultraviolet rays are irradiated on the conductive fine particle coating film with the output in the specific range.

  An ultraviolet lamp is used as an ultraviolet irradiation method. Although the kind of ultraviolet lamp which can be used in the present invention is not particularly limited, specifically, a low-pressure mercury lamp (main wavelength 254 nm), a high-pressure mercury lamp (main wavelengths 254 nm and 365 nm), a metal halide lamp (main wavelength 365 nm), an excimer lamp ( Main wavelength 120-310 nm) can be used.

As the output of the ultraviolet radiation (intensity and integration time), 1 cm ² per preferably ^{0.5~10J / cm 2, 1~9.5J / cm} 2 is more preferable.

  The reason why the output of the ultraviolet rays to be irradiated is within the above range is that if the output of the ultraviolet rays is less than the lower limit value, the adhering organic substances on the surface of the conductive fine particles cannot be sufficiently removed. This is because the coating film of the conductive fine particles and further the photoelectric conversion layer are damaged, and as a result, the electric resistance is increased, so that it is not possible to improve the power generation efficiency of the solar cell.

  Next, the binder dispersion liquid 24b containing the binder component is impregnated on the conductive fine particle coating film 24a irradiated with ultraviolet rays by a wet coating method. In the first forming method shown in FIG. 1 having the second layer 14b mainly composed of a binder component as an upper layer, the entire surface of the conductive fine particle coating 24a after ultraviolet irradiation is dispersed in the binder as shown in FIG. It coat | covers so that it may coat | cover completely with the liquid 24b. Moreover, the mass of the binder component in the binder dispersion to be applied is 0.5 to 10 mass ratio (the binder dispersion to be applied) 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 that the binder component mass / the conductive oxide fine particle mass). 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. In the first forming method, the conductive oxide fine particle dispersion and the binder dispersion are applied such that the thickness of the back-side transparent electrode layer after firing is 0.01 to 0.5 μm, preferably 0.03 to 0.03 μm. Apply to a thickness of 0.1 μm. After impregnating the binder dispersion, the back side transparent conductive coating film 24 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.

  On the other hand, in the second forming method shown in FIG. 3 with the second layer 14c not containing the binder component as an upper layer, the second layer not containing the binder component among the back-side transparent electrode layers 14 formed after firing. The binder dispersion liquid 24b is completely impregnated to a predetermined depth of the coating film 24a of conductive fine particles after irradiation with ultraviolet rays so that 14c is exposed to 1 to 30% of the volume of the first layer 14a (FIG. 4). In addition, the coating here is such that the mass of the binder component in the binder dispersion to be coated is a mass ratio of 0.05 to 0.5 with respect to the total mass of the fine particles contained in the coating film of the applied conductive fine particles. It is preferable to apply so that it becomes (mass of binder component / mass of conductive fine particles in binder dispersion to be applied). 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 24b, the transparent conductive coating film 24 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.

  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.

  Finally, the substrate having a transparent conductive coating is placed in the air or in an inert gas atmosphere such as nitrogen or argon at a temperature of 130 to 400 ° C., preferably 150 to 350 ° C., for 5 to 60 minutes, preferably 15 to By holding and baking for 40 minutes, the back surface side transparent electrode layer 14 is formed as shown in FIG. 1 or FIG.

  On the back side transparent electrode layer 14, the back side reflective electrode layer 16 is formed. Since this back surface side reflective electrode layer 16 plays a role of improving the power generation 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 again, a high diffuse reflectance is required. The For this reason, the back side reflective electrode layer 16 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 backside reflective electrode layer 16 is not particularly limited, but 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. When the back side reflective electrode layer 16 is formed by a wet coating method, an electrode composition in which metal nanoparticles are dispersed in a dispersion medium is used. This electrode composition 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 reflectance of the back-side reflective electrode layer 16 formed using this electrode composition decreases. It is. 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 the protective agent is desorbed or decomposed (separated) by heating when the carbon number is 4 or more This is because it is difficult to burn), and a large amount of organic residue remains in the back side reflective electrode layer 16, which deteriorates or deteriorates, and the conductivity and reflectivity of the back side reflective electrode layer 16 decrease.

  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 that is easily desorbed or decomposed (separated / burned) by heating, a large proportion of the organic molecule occupies it, so that a large amount of organic residue remains in the back-side reflective electrode layer 16. This residue may be altered or deteriorated to reduce the conductivity and reflectance of the back-side reflective electrode layer 16, or the particle size distribution of the metal nanoparticles may be widened to reduce the density of the back-side reflective electrode layer 16. Moreover, it is because the electroconductivity and reflectance of the back surface side reflective electrode layer 16 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.

  The electrode composition containing the metal nanoparticles further includes one or more additives selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds, and silicone oils. It is preferable. As the additive, an organic polymer, metal oxide, metal hydroxide, organometallic compound, or silicone oil contained in the electrode composition 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. Moreover, when the back surface side reflective electrode layer 16 is formed using this composition for electrodes, the grain growth by sintering between metal nanoparticles can be adjusted. The formation of the back-side reflective electrode layer 16 using this electrode composition 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.

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. When the content of the additive exceeds 20%, the conductivity of the back-side reflective electrode layer 16 formed is adversely affected, and 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 (Indium Tin Oxide), ATO (Antimony Tin Oxide), IZO (Indium Zic Oxide). Indium-zinc oxide composite oxide), AZO (Aluminum Zinc Oxide: aluminum oxide-zinc oxide composite oxide) and the like.

  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 electrode composition, the metal nanoparticles other than silver nanoparticles are composed of gold, platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and manganese. It is preferable to further contain metal nanoparticles composed of one kind of particles selected from the group or two or more kinds of mixed compositions or alloy compositions. 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 back electrode layer 16 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 an electrode composition should contain 2.5-95.0 mass% with respect to 100 mass% of electrode compositions which consist of a metal nanoparticle and a dispersion medium. Is preferable, and it is further more preferable to contain 3.5-90 mass%. This is because if the content ratio with respect to 100% by mass of the electrode composition exceeds 95.0% by mass, the required fluidity as an ink or paste is lost during wet coating of the electrode composition.

  Moreover, the dispersion medium which comprises the composition for electrodes for forming the back surface side reflective electrode layer 16 is 1 mass% or more with respect to 100 mass% of all the dispersion media, Preferably it is 2 mass% or more of water, 2 It is preferable to contain a solvent that is compatible with water in an amount of not less than mass%, preferably not less than 3 mass%, such as 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 if the water content is less than 2% by mass, it becomes difficult to sinter the film obtained by applying the electrode composition by a wet coating method at a low temperature. Furthermore, the conductivity and reflectance of the back-side reflective electrode layer 16 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, it is excellent in dispersion stability of the electrode composition and effective for low-temperature sintering of the coating film. There is an effect. 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 electrode composition as described above, and the coating film has a low temperature. Sintering also has an effective action. 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 an electrode composition containing metal nanoparticles for forming the back side reflective electrode layer 16 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. In addition, when an additive is further included in the electrode composition, the dispersion is one or more selected from the group consisting of organic polymers, metal oxides, metal hydroxides, organometallic compounds, and silicone oils. It is carried out by adding two or more additives in a desired ratio. Content of an additive is adjusted so that it may become in the range of 0.1-20 mass% with respect to 100 mass% of composition for electrodes obtained. As a result, an electrode composition in which silver nanoparticles chemically modified with a protective agent for an organic molecular main chain having 3 carbon skeletons is dispersed in a dispersion medium is obtained.
(b) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent that chemically modifies the silver nanoparticles is 2, except that the sodium citrate used when preparing the reducing agent aqueous solution is replaced with sodium malate A dispersion is prepared in the same manner as in the above (a). As a result, a dispersion having 2 carbon atoms in the carbon skeleton of the organic molecular main chain that chemically modifies the silver nanoparticles can be obtained.
(c) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent for chemically modifying the silver nanoparticles is 1, except that sodium citrate used when preparing the reducing agent aqueous solution is replaced with sodium glycolate A dispersion is prepared in the same manner as in the above (a). Thereby, a dispersion in which the carbon skeleton of the carbon skeleton of the organic molecular main chain for chemically modifying the silver nanoparticles is 1 is obtained.
(d) When the carbon number of the carbon skeleton of the organic molecular main chain of the protective agent for chemically modifying metal nanoparticles other than silver nanoparticles is 3, the metal constituting the metal nanoparticles other than silver nanoparticles is gold, Examples include platinum, palladium, ruthenium, nickel, copper, tin, indium, zinc, iron, chromium and manganese. The silver nitrate used to prepare the aqueous metal salt solution is chloroauric acid, chloroplatinic acid, palladium nitrate, ruthenium trichloride, nickel chloride, cuprous nitrate, tin dichloride, indium nitrate, zinc chloride, iron sulfate, sulfuric acid A dispersion is prepared in the same manner as in the above (a) except that it is replaced with chromium or manganese sulfate. Thereby, the dispersion whose carbon number of the carbon skeleton of the organic molecular principal chain of the protective agent which chemically modifies metal nanoparticles other than silver nanoparticles is 3 is obtained.

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

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

  In order to form the back-side reflective electrode layer 16 using the electrode composition, first, the electrode composition is applied onto the back-side transparent electrode layer 14 by a wet coating method, and the thickness after baking by heating is applied. Is formed to have a thickness of 0.05 to 2.0 μm, preferably 0.1 to 1.5 μm. Next, this electrode coating layer is kept in the atmosphere or in an inert gas atmosphere such as nitrogen or argon at a temperature of 130 to 400 ° C., preferably 150 to 350 ° C. for 5 minutes to 1 hour, preferably 15 to 40 minutes. And fired. Here, the thickness of the back-side reflective electrode layer 16 after firing was limited to a range of 0.05 to 2.0 μm. This is because if it is less than 0.05 μm, the surface resistance value of the electrode necessary for the solar cell becomes insufficient. Moreover, the heating temperature of the coating layer for electrodes was made into the range of 130-400 degreeC. This is because if the temperature is lower than 130 ° C., 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 back-side reflective electrode layer 16 after firing, and the residue is altered or deteriorated, so that the conductivity and reflectance of the back-side reflective electrode layer 16 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. Further, the heating time of the electrode coating layer was set in the range of 5 minutes to 1 hour. This is because the sintering between the metal nanoparticles becomes insufficient for less than 5 minutes, and it is difficult to desorb or decompose (separate / burn) by heating the protective agent. This is because a large amount of residue remains, and the residue is altered or deteriorated, so that the conductivity and reflectance of the back-side reflective electrode layer 16 are lowered.

When the back-side reflective electrode layer 16 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. It can be greatly reduced. The back-side reflective electrode layer 16 obtained by this method has an average diameter of pores appearing on the contact surface on the photoelectric conversion layer 13 side of the layer of 100 nm or less, an average depth at which pores are located is 100 nm or less, and the number density of pores 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. Moreover, the said back surface side reflective electrode layer 16 has the specific resistance close | similar to the specific resistance which the metal itself which comprises the metal nanoparticle contained in the composition for electrodes has. That is, it shows a specific resistance as low as a bulk that can be used as an electrode for a solar cell module. Moreover, the back surface side reflective electrode layer 16 of this invention is excellent in long-term stability, such as a reflectance of a film | membrane, adhesiveness, and a specific resistance compared with the film | membrane formed into a film by vacuum processes, such as a sputtering method. The reason for this is that the back-side reflective electrode layer 16 of the present invention formed in the atmosphere is less susceptible to moisture intrusion and oxidation than a film formed in vacuum.

  A barrier film may be formed on the back-side reflective electrode layer 16 via a back electrode reinforcing film (not shown) or without a back electrode reinforcing film.

  As described above, according to the manufacturing method of the present invention, it is possible to manufacture a solar cell in which electric resistance during power generation is reduced and power generation efficiency is improved.

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

<Example 1>
First, as shown in FIG. 2, a glass plate having 10 cm square and 4 mm thickness was prepared for the transparent substrate 11, and SnO ₂ was used as the surface side electrode layer 12. The film thickness of the surface side electrode layer 12 at this time was 800 nm, the sheet resistance was 10Ω / □, and the haze ratio was 15 to 20%.

  Next, as shown in Table 1 and Table 2 below, an amorphous silicon layer is formed with a thickness of 300 nm on the surface-side electrode layer 12 by using a plasma CVD method. A photoelectric conversion layer 13 was formed by forming a microcrystalline silicon layer with a thickness of 1.7 μm on the top using a plasma CVD method.

  Next, as shown in FIG. 5, it masked with the tape 17 so that the center part of the surface of the photoelectric converting layer 13 might be crossed.

  Next, as shown in Table 1 and Table 3 below, as conductive fine particles, 1.0 part by mass of ITO powder having an atomic ratio of Sn / (Sn + In) = 0.1 and a particle diameter of 0.03 μm, a coupling agent As a result, 0.01 parts by mass of the organic titanium coupling agent represented by the above formula (3) was added, and ethanol was added as a dispersion medium to make 100 parts by mass as a whole. This mixture was operated for 2 hours with a dyno mill (horizontal bead mill) using zirconia beads having a diameter of 0.3 mm to disperse the fine particles in the mixture, thereby obtaining a conductive fine particle dispersion. In addition, about the measuring method of the average particle diameter of the said electroconductive fine particles, it computed from the number average as follows. First, an electron micrograph of the target fine particles was taken. Regarding the electron microscope used for photographing, SEM or TEM was appropriately used depending on the size of the particle diameter and the type of powder. Next, from the obtained electron micrograph, the diameter of about 1000 particles was measured to obtain frequency distribution data. A numerical value with an accumulated frequency of 50% (D50) was taken as the average particle size.

  Further, 1.0 part by mass of a siloxane polymer obtained by hydrolyzing ethyl silicate as a binder was prepared, and ethanol was added as a dispersion medium to make the whole 100 parts by mass to obtain a binder dispersion.

  Next, as shown in FIG. 2, the conductive fine particle dispersion prepared above is applied onto the formed photoelectric conversion layer 13 by spin coating so that the film thickness of the conductive fine particle coating film 24a is 80 nm. Then, it was dried at a temperature of 50 ° C. for 5 minutes to form a conductive fine particle coating 24a.

Subsequently, a metal halide lamp (manufactured by USHIO INC.) Having a dominant wavelength of 365 nm is used.
The surface of the conductive fine particle coating 24a was irradiated with ultraviolet rays at an output of ³ J / cm ² . The ultraviolet illuminance meter made by USHIO was used for the measurement of ultraviolet energy.

  Next, on the conductive fine particle coating film 24a irradiated with ultraviolet rays, the entire surface of the conductive fine particle coating film is completely covered with the binder dispersion as shown in FIG. The transparent conductive coating film 24 was formed by impregnating the prepared binder dispersion liquid 24b so that the film thickness of the back-side transparent electrode layer 14 was 90 nm and drying at a temperature of 50 ° C. for 5 minutes. The binder dispersion was applied such that the mass of the binder component in the binder dispersion was 1/1 with respect to the total mass of the fine particles contained in the conductive fine particle coating film.

  Furthermore, as shown in FIG. 1, the back surface side transparent electrode layer 14 was formed by baking the transparent conductive coating film 24 at 200 degreeC for 30 minutes.

  After the formation of the back surface side reflective electrode layer 16, the tape 17 masked on the surface of the photoelectric conversion layer 13 was peeled off to obtain a multijunction thin film silicon solar cell for evaluation.

  Thereafter, as shown in FIG. 6, for the multi-junction thin film silicon solar cell for evaluation, a source meter 21 (manufactured by Keithley: Model 2400) was connected to the back-side reflective electrode layers 16 and 16 separated by masking. Resistance was measured from the current value when voltage was applied in this state, and the resistance value was defined as contact resistance. The results are shown in Table 1 below.

<Example 2>
As shown in Table 1 below, a low-pressure mercury lamp (manufactured by Ushio Inc.) having a dominant wavelength of 254 nm is used as the ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 0.5 J / cm ² , and the back surface A multi-junction thin film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that the fine particle / binder ratio of the side transparent electrode layer 14 was changed to 4/3, and the contact resistance was measured. The results are shown in Table 1.

<Example 3>
As shown in the following Table 1, a high-pressure mercury lamp (manufactured by Ushio Inc.) having principal wavelengths of 254 nm and 365 nm is used as an ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 10 J / cm ² , and the back surface The conductive fine particles forming the side transparent electrode layer 14 are Sn / (Sn + In) = 0.05 in terms of atomic ratio, ITO powder having a particle diameter of 0.02 μm, epoxy resin as the binder, and the fine particle / binder ratio is 2. A multi-junction thin-film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that it was set to / 1, and the contact resistance was measured. The results are shown in Table 1.

<Example 4>
As shown in the following Table 1, the photoelectric conversion layer 13 is composed of only an amorphous silicon layer having a thickness of 2.0 μm, and an excimer lamp having a main wavelength of 126 nm (USHIO Inc.) as an ultraviolet irradiation lamp used for ultraviolet irradiation. ITO with a UV irradiation output of 5 J / cm ² and conductive fine particles forming the back-side transparent electrode layer 14 in terms of atomic ratio of Sn / (Sn + In) = 0.02 and a particle diameter of 0.03 μm A multi-junction thin film silicon solar cell for evaluation was prepared in the same manner as in Example 1 except that an acrylic urethane resin was used as a binder, and the contact resistance was measured. The results are shown in Table 1.

<Example 5>
As shown in the following Table 1, the photoelectric conversion layer 13 is composed of only a microcrystalline silicon layer having a thickness of 2.0 μm, the output of ultraviolet irradiation is ² J / cm ² , and the back-side transparent electrode layer 14 is formed. For evaluation in the same manner as in Example 1 except that AZO powder having an atomic ratio of Al / (Al + Zn) = 0.1 and a particle diameter of 0.05 μm was used as the conductive fine particles, and the fine particle / binder ratio was 1/3. A multi-junction thin film silicon solar cell was prepared and contact resistance was measured. The results are shown in Table 1.

<Example 6>
As shown in the following Table 1, the photoelectric conversion layer 13 is composed of only an amorphous silicon layer having a thickness of 2.0 μm, and a low-pressure mercury lamp (USHIO) having a main wavelength of 254 nm as an ultraviolet irradiation lamp used for ultraviolet irradiation. Multi-junction thin film silicon for evaluation in the same manner as in Example 1 except that the output of ultraviolet irradiation was 8 J / cm ² and the fine particle / binder ratio of the back side transparent electrode layer 14 was 1/3. Solar cells were prepared and contact resistance was measured. The results are shown in Table 1.

<Example 7>
As shown in the following Table 1, a high-pressure mercury lamp (manufactured by Ushio Inc.) having dominant wavelengths of 254 nm and 365 nm is used as the ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 1 J / cm ² , and the back surface Implementation was performed except that ATO powder having an atomic ratio of Sb / (Sb + Sn) = 0.05 and a particle diameter of 0.03 μm was used as the conductive fine particles forming the side transparent electrode layer 14 and the fine particle / binder ratio was 4/1. In the same manner as in Example 1, a multijunction thin film silicon solar cell for evaluation was produced, and the contact resistance was measured. The results are shown in Table 1.

<Example 8>
As shown in the following Table 1, the photoelectric conversion layer 13 is composed of only a microcrystalline silicon layer having a thickness of 2.0 μm, and an excimer lamp (USHIO) having a main wavelength of 126 nm as an ultraviolet irradiation lamp used for ultraviolet irradiation. The output of ultraviolet irradiation is 6 J / cm ^2, and the conductive fine particles forming the back side transparent electrode layer 14 have an atomic ratio of Al / (Al + Zn) = 0.1 and a particle diameter of 0.08 μm. A multi-junction thin film silicon solar cell for evaluation was prepared in the same manner as in Example 1 except that the epoxy resin was used as the binder and the fine particle / binder ratio was 1/3, and the contact resistance was measured. The results are shown in Table 1.

<Example 9>
As shown in Table 1 below, a high-pressure mercury lamp (manufactured by Ushio Inc.) having principal wavelengths of 254 nm and 365 nm is used as an ultraviolet irradiation lamp used for ultraviolet irradiation, and the output of ultraviolet irradiation is 9.5 J / cm ^2. The PTO powder having an atomic ratio of P / (P + Sn) = 0.05 and a particle diameter of 0.03 μm was used as the conductive fine particles forming the back-side transparent electrode layer 14, and the fine particle / binder ratio was 1/3. Produced a multijunction thin film silicon solar cell for evaluation in the same manner as in Example 1, and measured the contact resistance. The results are shown in Table 1.

<Example 10>
As shown in the following Table 1, as the conductive fine particles forming the back side transparent electrode layer 14, ITO powder having an atomic ratio of Sn / (Sn + In) = 0.05 and a particle diameter of 0.03 μm was used. The coating film thickness is set to 90 nm, and the binder dispersion liquid is formed so that the second layer 14 c not containing the binder component is exposed as shown in FIG. 3 and the thickness of the first layer 14 a after baking is 80 nm. A multi-junction thin film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that the fine particle / binder ratio was 8/1, and the contact resistance was measured. The results are shown in Table 1.

<Example 11>
As shown in the following Table 1, a high-pressure mercury lamp (manufactured by Ushio Inc.) having principal wavelengths of 254 nm and 365 nm is used as an ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 4 J / cm ² , and the back surface As the conductive fine particles forming the side transparent electrode layer 14, ITO powder having an atomic ratio of Sn / (Sn + In) = 0.05 and a particle diameter of 0.03 μm was used, and the thickness of the conductive fine particle coating film was set to 90 nm. As shown in FIG. 3, the binder dispersion is impregnated so that the second layer 14c containing no binder component is exposed and the thickness of the first layer 14a after baking is 80 nm, and the fine particle / binder ratio is 10 A multi-junction thin-film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that it was set to / 1, and the contact resistance was measured. The results are shown in Table 1.

<Example 12>
As shown in Table 1 below, a low-pressure mercury lamp (manufactured by Ushio Inc.) having a dominant wavelength of 254 nm is used as the ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 5 J / cm ² , and the back side is transparent. As the conductive fine particles forming the electrode layer 14, ITO powder having an atomic ratio of Sn / (Sn + In) = 0.05 and a particle diameter of 0.03 μm was used, and the film thickness of the conductive fine particle coating film was set to 90 nm. As shown, the binder dispersion is impregnated so that the second layer 14c containing no binder component is exposed and the thickness of the first layer 14a after baking is 80 nm, and the fine particle / binder ratio is 8/1. A multi-junction thin film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that the contact resistance was measured. The results are shown in Table 1.

<Example 13>
As shown in Table 1 below, an excimer lamp (manufactured by Ushio Inc.) having a dominant wavelength of 126 nm is used as the ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 6 J / cm ² , and the back side transparent electrode As the conductive fine particles forming the layer 14, ITO powder having an atomic ratio of Sn / (Sn + In) = 0.05 and a particle diameter of 0.03 μm was used, and the thickness of the conductive fine particle coating film was set to 90 nm. In this way, the binder dispersion is impregnated so that the second layer 14c containing no binder component is exposed and the thickness of the first layer 14a after baking is 80 nm, and the fine particle / binder ratio is 10/1. A multi-junction thin film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that the contact resistance was measured. The results are shown in Table 1.

<Comparative Example 1>
As shown in the following Table 1, a multijunction thin film silicon solar cell for evaluation was produced in the same manner as in Example 1 except that the surface of the conductive fine particle coating film 24a was not irradiated with ultraviolet rays, and the contact resistance was measured. The results are shown in Table 1.

<Comparative example 2>
As shown in the following Table 1, a low-pressure mercury lamp (manufactured by Ushio Inc.) having a dominant wavelength of 254 nm is used as the ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 0.4 J / cm ² , and the back surface Implementation was performed except that ATO powder having an atomic ratio of Sb / (Sb + Sn) = 0.05 and a particle diameter of 0.03 μm was used as the conductive fine particles forming the side transparent electrode layer 14 and the fine particle / binder ratio was 4/1. In the same manner as in Example 1, a multijunction thin film silicon solar cell for evaluation was produced, and the contact resistance was measured. The results are shown in Table 1.

<Comparative Example 3>
As shown in Table 1 below, an excimer lamp (manufactured by Ushio Inc.) having a dominant wavelength of 126 nm is used as the ultraviolet irradiation lamp used for ultraviolet irradiation, the output of ultraviolet irradiation is 10.5 J / cm ² , and the back side Example except that AZO powder having an atomic ratio of Al / (Al + Zn) = 0.1 and a particle diameter of 0.05 μm was used as the conductive fine particles forming the transparent electrode layer 14 and the fine particle / binder ratio was 1/3. In the same manner as in Example 1, a multi-junction thin film silicon solar cell for evaluation was produced and the contact resistance was measured. The results are shown in Table 1.

<Comparative example 4>
As shown in the following Table 1, a multi-junction thin film silicon solar cell for evaluation was produced in the same manner as in Example 10 except that the surface of the conductive fine particle coating film 24a was not irradiated with ultraviolet rays, and the contact resistance was measured. The results are shown in Table 1.

表１から明らかなように、紫外線を照射しない比較例１では接触抵抗が８９Ω程度、比較例４では８０Ω程度と高い抵抗値になる傾向がみられた。また、紫外線照射の出力が小さい比較例２では接触抵抗が６２Ω程度と、比較例１や比較例４のそれよりは低くなるが、依然として高い抵抗値になる傾向がみられた。また、紫外線照射の出力が大きい比較例３では接触抵抗が１２０Ω程度と高い抵抗値になる傾向がみられた。

As can be seen from Table 1, there was a tendency that the contact resistance was about 89Ω in Comparative Example 1 where no ultraviolet light was irradiated and that the resistance value was about 80Ω in Comparative Example 4. Further, in Comparative Example 2 in which the output of ultraviolet irradiation was small, the contact resistance was about 62Ω, which was lower than those in Comparative Example 1 and Comparative Example 4, but a tendency to still have a high resistance value was observed. Further, in Comparative Example 3 in which the output of ultraviolet irradiation was large, there was a tendency that the contact resistance was as high as about 120Ω.

  On the other hand, in Examples 1-13, the result in which the contact resistance was suppressed to a low resistance value of about 16-24Ω was obtained.

  From this result, in the manufacture of solar cells, after irradiating the conductive fine-particle coating film with ultraviolet rays with a specific output, impregnating the binder component and forming a backside transparent electrode layer, the electrical resistance during power generation is reduced. It was confirmed that a solar cell with reduced power generation efficiency could be manufactured.

DESCRIPTION OF SYMBOLS 10 Solar cell 11 Transparent substrate 12 Front side electrode layer 13 Photoelectric conversion layer 14 Back side transparent electrode layer 16 Back side reflective electrode layer 24a Coating film of conductive fine particles 24b Binder dispersion liquid 24 Transparent conductive coating film

Claims (3)

A photoelectric conversion layer made of one or both of amorphous silicon and microcrystalline silicon is formed on the surface-side electrode layer of the transparent substrate having the surface-side electrode layer formed on the surface, and the back surface is formed on the photoelectric conversion layer. In the method of manufacturing a solar cell for forming the side transparent electrode layer,
The backside transparent electrode layer is formed by coating the surface of the photoelectric conversion layer with a dispersion containing conductive fine particles by a wet coating method to form a coating film of conductive fine particles, and then forming the conductive fine particles. By irradiating ultraviolet rays with an output of 0.5 to 10 J / cm < ² > onto the coating film, and applying a dispersion containing the binder to the coating film of the conductive fine particles irradiated with the ultraviolet rays using a wet coating method. A method for producing a solar cell, which is carried out by impregnating components, forming a transparent conductive coating film, and firing the transparent conductive coating film.   The method for manufacturing a solar cell according to claim 1, wherein the ultraviolet irradiation lamp used for the irradiation of ultraviolet rays is a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp or an excimer lamp.   The solar cell obtained by the manufacturing method of Claim 1 or 2.

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