JP2009170577A - Method of manufacturing solar cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a solar cell capable of obviating the need of desiccation after printing, and of providing an electrode pattern of a high aspect ratio. <P>SOLUTION: This manufacturing method of a solar cell includes a process of printing a pattern of conductive paste on a board, and exposing the printed pattern to light. The manufacturing method of a solar cell is characterized in that the conductive paste contains conductive inorganic powder, glass frit, and a photosensitive organic constituent; and the content of an organic solvent in the conductive paste is not larger than 1 mass%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a solar cell capable of forming an electrode pattern having a high aspect ratio with a small number of steps.

  In recent years, there has been a remarkable development in the solar cell industry, but the high cost of solar cell production has hindered the widespread use of solar cells. As a solar cell, for example, a p-type silicon substrate with a pn junction, an antireflection film, and a grid electrode formed on the light receiving surface side having a concavo-convex structure and a back electrode layer and a back electrode formed on the opposite side is there.

  For forming these electrodes, a method is known in which a conductive paste composed of conductive powder, glass frit, organic vehicle and organic solvent is subjected to pattern printing by screen printing, followed by drying and baking (for example, Patent Document 1). .

However, the conductive paste contains a large amount of organic solvent, and there are problems that a large amount of energy is required for drying after printing, and that the pattern after printing is sagging and a pattern with a high aspect ratio cannot be obtained. It was.
JP 2007-19106 (2nd page)

  Then, in view of the said prior art, this invention aims at providing the manufacturing method of the solar cell which makes the drying after printing unnecessary and can obtain the electrode pattern of a high aspect ratio.

  That is, the present invention is a method for manufacturing a solar cell including a step of pattern-printing a conductive paste on a substrate and exposing the conductive paste, wherein the conductive paste contains a conductive inorganic powder, a glass frit, and a photosensitive organic component. The content of the organic solvent in the paste is 1% by mass or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing process of the solar cell which abbreviate | omits a drying process and can obtain a high aspect-ratio electrode pattern can be provided.

  The conductive paste used in the present invention contains a conductive inorganic powder, glass frit and a photosensitive organic component.

  As the conductive inorganic powder, one selected from the group consisting of Ag, Au, Pd, Ni, Cu, Al, and Pt can be used. These may be in a single state or an alloy state. Since the light receiving surface electrode of a solar cell is required to have a small area and low resistance so as not to block light, in order to make a thin line width and a thick electrode, these conductive inorganic powders It is preferable that the particle diameter is not so small. As the particle diameter, the center diameter of the volume reference distribution is preferably in the range of 1 to 20 μm, and the maximum particle size is preferably 40 μm or less, and more preferably, the center diameter of the volume reference distribution is in the range of 1 to 10 μm. The particle size is 30 μm or less.

  The glass frit has a fire-through property (when the conductive paste printed on the antireflection layer is baked, the antireflective layer located below the conductive paste also melts at the same time. The material and the substrate are brought into contact with each other to obtain ohmic connection) and the adhesiveness to the substrate is selected, but there is no particular limitation, and a known one can be used. The softening point and glass transition temperature of the glass frit are appropriately selected depending on the firing temperature, and the components of the frit glass are adjusted according to the softening point and glass transition temperature.

  Further, elements such as P, Ti, Bi, Co, Zn, Zr, Fe, and Cr may be contained in the frit glass in order to stabilize the fire-through property. Further, it is also effective to add a metal such as V, Mo, W, or a compound thereof, or to add carbon powder or the like for darkening.

  The conductive paste used in the method for manufacturing a solar cell according to the present invention contains a photosensitive organic component. Since the conductive paste used in the present invention has an organic solvent content of 1% by mass or less as will be described later, pattern printing is performed using a conductive paste containing a photosensitive organic component, and exposure is performed without stickiness. A pattern can be formed. If a conductive paste that does not contain a photosensitive organic component and has an organic solvent content of 1% by mass or less is used, a paste that cannot be printed with a pattern due to its viscosity is too high. This causes a problem that the print pattern is easily disturbed.

  The photosensitive organic component includes a monomer, oligomer or polymer having a polymerizable unsaturated group in the molecule. As a photosensitive organic component constituting the conductive paste in the present invention, a monomer, oligomer or polymer having a polymerizable unsaturated group in the molecule is used as a component that plays a role in controlling the pattern shape after printing or adjusting the viscosity of the conductive paste. .

  As the monomer having a polymerizable unsaturated group in the molecule, a compound having an active carbon-carbon unsaturated double bond can be used. As the functional group, monofunctional and polyfunctional compounds having a vinyl group, an allyl group, an acrylate group, a methacrylate group, or an acrylamide group can be applied. Specific examples include allylated cyclohexyl diacrylate, polyethylene glycol diacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, ditrimethylolpropane tetraacrylate, glycerol diacrylate, methoxylated cyclohexyl diacrylate, neopentyl. Glycol diacrylate, propylene glycol diacrylate, polypropylene glycol diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate, bisphenol A diacrylate, diacrylate of bisphenol A-ethylene oxide adduct, diacrylate of bisphenol A-propylene oxide adduct Acrylates or the above compounds Compounds of Lil group part or all replaced with methacrylic groups.

  Moreover, it is preferable that the monomer which has a polymerizable unsaturated group in the molecule | numerator whose viscosity in 25 degreeC is in the range of 1-100 mPa * s is contained in the electrically conductive paste of this invention. More preferably, it includes a monomer having a polymerizable unsaturated group in the molecule whose viscosity at 25 ° C. is in the range of 1 to 50 mPa · s. By including the monomer, the viscosity of the conductive paste can be easily adjusted. Specific examples of the monomer include 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, 2- (2-ethoxyethoxy) ethyl acrylate, tetrahydrofurfuryl acrylate, lauryl acrylate, 2-phenoxyethyl acrylate, Isodecyl acrylate, isooctyl acrylate, tridecyl acrylate, 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, triethylene glycol diacrylate, or of the above compounds Examples thereof include compounds in which one part or all acryl groups are replaced with methacryl groups.

  In the present invention, one or more of these can be used. The monomer is added in the range of 2 to 20% by mass with respect to the conductive paste, and more preferably in the range of 5 to 15% by mass. If the amount of the monomer is too small, the fluidity of the conductive paste at room temperature is lost, and pattern printing may be poor. On the other hand, when the amount of the monomer is too large, the viscosity of the conductive paste decreases, and the desired film thickness may not be obtained.

  Furthermore, since the conductive paste used in the present invention is photocured after pattern printing, the polymerizable polyfunctional group having a number of polymerizable unsaturated groups in the range of 2 to 6 in order to shorten the photocuring time. It is preferable to include a monomer. If a monomer having a polymerizable unsaturated group number exceeding 6 is used, the compatibility may be poor and the printability of the conductive paste may be poor. In addition, when only the polymerizable polyfunctional monomer having the number of polymerizable unsaturated groups within the range of 2 to 6 is used, the pattern shape may be deteriorated due to polymerization shrinkage at the time of photocuring. It is also effective to use a polymerizable polyfunctional monomer having a number of groups in the range of 2 to 6 and a polymerizable monofunctional monomer having one polymerizable unsaturated group. In this case, the mass ratio of the polymerizable polyfunctional monomer having a polymerizable unsaturated group number in the range of 2 to 6 and the polymerizable monofunctional monomer having one polymerizable unsaturated group is 90:10 to 30:70. Preferably there is. When the mass ratio is within the above range, shortening of the photocuring time and polymerization shrinkage during photocuring can be suppressed, and the pattern shape can be controlled.

    The oligomer or polymer having a polymerizable unsaturated group in the molecule can be obtained by polymerization or copolymerization of components selected from compounds having a carbon-carbon double bond. By adding a photoreactive group to the side chain or molecular end of such an oligomer or polymer, an oligomer or polymer having a polymerizable unsaturated group in the molecule can be obtained.

  Preferred polymerizable unsaturated groups are those having an ethylenically unsaturated group. Examples of the ethylenically unsaturated group include a vinyl group, an allyl group, an acrylic group, and a methacryl group.

  The method of adding such a side chain to an oligomer or polymer is an ethylenically unsaturated compound or acrylic acid chloride having a glycidyl group or an isocyanate group with respect to a mercapto group, amino group, hydroxyl group or carboxyl group in the oligomer or polymer. There is a method of making an addition reaction of methacrylic acid chloride or allyl chloride.

  Examples of the ethylenically unsaturated compound having a glycidyl group include glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, glycidyl ethyl acrylate, crotonyl glycidyl ether, glycidyl crotonic acid, and glycidyl ether of isocrotonic acid. Examples of the ethylenically unsaturated compound having an isocyanate group include (meth) acryloyl isocyanate and (meth) acryloylethyl isocyanate. Further, ethylenically unsaturated compounds having a glycidyl group or an isocyanate group, acrylic acid chloride, methacrylic acid chloride or allyl chloride are 0.05 to 1 with respect to a mercapto group, amino group, hydroxyl group or carboxyl group in the oligomer or polymer. It is preferable to add a molar equivalent.

  The oligomer or polymer having a polymerizable unsaturated group in the molecule preferably has a weight average molecular weight (Mw) in the range of 2000 to 200000 and a number average molecular weight (Mn) in the range of 1000 to 50000. More preferably, Mw is in the range of 5000 to 100,000, and Mn is in the range of 1000 to 30000. When Mw and Mn are within the above ranges, handleability is good and uniform curability can be obtained during photocuring.

  The conductive paste in the present invention contains a monomer, oligomer or polymer having a polymerizable unsaturated group in the molecule, but none of these components has the ability to absorb actinic rays, so that photocuring can be performed. It is necessary to use a photopolymerization initiator. The photopolymerization initiator is selected depending on the light source used for photocuring, and a radical photopolymerization initiator, a cationic photopolymerization initiator, or the like can be used.

  As radical photopolymerization initiator, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, benzyldimethyl ketal, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropane -1-one, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl-phenylketone, 1-phenyl-1,2-propanedione-2- (o- Ethoxycarbonyl) oxime, 2-methyl- [4- (methylthio) phenyl] -2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1 , Benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin iso Lopyl ether, benzoin isobutyl ether, benzophenone, methyl o-benzoylbenzoate, 4-phenylbenzophenone, 4,4-dichlorobenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyl-diphenyl sulfide, alkylated benzophenone, 3,3 ' , 4,4′-tetra (t-butylperoxycarbonyl) benzophenone, 4-benzoyl-N, N-dimethyl-N- [2- (1-oxo-2-propenyloxy) ethyl] benzenemethananium bromide, (4-Benzoylbenzyl) trimethylammonium chloride, 2-hydroxy-3- (4-benzoylphenoxy) -N, N, N-trimethyl-1-propenaminium chloride monohydrate, 2-isopropylthioxanthone, 2,4- Methylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, 2-hydroxy-3- (3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy) -N, N, N-trimethyl -1-propanaminium chloride, 2,4,6-trimethylbenzoylphenylphosphine oxide, 2,2′-bis (o-chlorophenyl) -4,5,4 ′, 5′-tetraphenyl-1,2- Biimidazole, 10-butyl-2-chloroacridone, 2-ethylanthraquinone, benzyl, 9,10-phenanthrenequinone, camphorquinone, methylphenylglyoxyester, η5-cyclopentadienyl-η6-cumenyl- Iron (1 +)-hexafluorophosphate (1-), diphenyl sulfide derivative Bis (η5-2,4-cyclopentadien-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) -phenyl) titanium, 4,4-bis (dimethylamino) Benzophenone, 4,4-bis (diethylamino) benzophenone, thioxanthone, 2-methylthioxanthone, 2-chlorothioxanthone, 4-benzoyl-4-methylphenylketone, dibenzylketone, fluorenone, 2,3-diethoxyacetophenone, 2, 2-dimethoxy-2-phenyl-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone, pt-butyldichloroacetophenone, benzylmethoxyethyl acetal, anthraquinone, 2-t-butylanthraquinone, 2-aminoanthraquinone , Β-chlorane Laquinone, anthrone, benzanthrone, dibenzsuberone, methyleneanthrone, 4-azidobenzalacetophenone, 2,6-bis (p-azidobenzylidene) cyclohexane, 2,6-bis (p-azidobenzylidene) -4-methylcyclohexanone, 2 -Phenyl-1,2-butadion-2- (o-methoxycarbonyl) oxime, 1,3-diphenylpropanetrione-2- (o-ethoxycarbonyl) oxime, N-phenylglycine, tetrabutylammonium (+1) n- Butyltriphenylborate (1-), naphthalenesulfonyl chloride, quinolinesulfonyl chloride, N-phenylthioacridone, 4,4-azobisisobutyronitrile, benzthiazole disulfide, triphenylphosphine, tetrabromine Cation dyes and borate anions that absorb near-ultraviolet light, such as combinations of photoreducing pigments such as carbon fluoride, tribromophenylsulfone, benzoyl peroxide and eosin, methylene blue, and reducing agents such as ascorbic acid and triethanolamine , Silver halide sensitized with near-infrared sensitizing dye and combination of reducing agent, titanocene, iron arene complex, organic peroxide, hexaaryl, biimidazole, N-phenylglycine, diaryliodonium At least one radical generator such as a salt and, if necessary, sensitizing dyes such as 3-substituted coumarins, cyanine dyes, merocyanine dyes, thiazole dyes, pyrylium dyes, and the like can be mentioned.

  Examples of the cationic photopolymerization initiator include iodonium salts, sulfonium salts, phosphate salts, and antimonate salts.

  In the present invention, one or more of these can be used. A photoinitiator is added in 0.05-10 mass% with respect to an electrically conductive paste, More preferably, it is 0.1-10 mass%. If the amount of the photopolymerization initiator is too small, photocuring is insufficient, and if the amount of the photopolymerization initiator is too large, the compatibility may be poor.

  By using a sensitizer together with the photopolymerization initiator, the sensitivity can be improved or the wavelength range effective for the reaction can be expanded.

  Specific examples of the sensitizer include 2,3-bis (4-diethylaminobenzal) cyclopentanone, 2,6-bis (4-dimethylaminobenzal) cyclohexanone, and 2,6-bis (4-dimethylamino). Benzal) -4-methylcyclohexanone, 4,4-bis (dimethylamino) chalcone, 4,4-bis (diethylamino) chalcone, p-dimethylaminocinnamylidene indanone, p-dimethylaminobenzylidene indanone, 2- (P-dimethylaminophenylvinylene) isonaphthothiazole, 1,3-bis (4-dimethylaminophenylvinylene) isonaphthothiazole, 1,3-bis (4-dimethylaminobenzal) acetone, 1,3-carbonylbis (4-Diethylaminobenzal) acetone, 3,3-carbonylbis (7-diethyl) Aminocoumarin), triethanolamine, methyldiethanolamine, triisopropanolamine, N-phenyl-N-ethylethanolamine, N-phenylethanolamine, N-tolyldiethanolamine, methyl 4-dimethylaminobenzoate, 4-dimethylaminobenzoic acid Ethyl, dimethylaminobenzoate isoamyl, diethylaminobenzoate isoamyl, benzoate (2-dimethylamino) ethyl, 4-dimethylaminobenzoate (n-butoxy) ethyl, 4-dimethylaminobenzoate 2-ethylhexyl, 3-phenyl- Examples include 5-benzoylthiotetrazole and 1-phenyl-5-ethoxycarbonylthiotetrazole.

  One or two or more of these can be used in the conductive paste used in the present invention. When adding a sensitizer to the photosensitive paste of this invention, the addition amount is 0.05-10 mass% normally with respect to the photosensitive organic component, More preferably, it is 0.1-10 mass%. If the amount of the sensitizer is too small, the effect of improving photocuring is not exhibited, and if the amount of the sensitizer is too large, the compatibility may be poor.

  The conductive paste used in the present invention is characterized in that the content of the organic solvent is 1% by mass or less. When the amount of the organic solvent is large, a drying step is required after printing. Therefore, in the conductive paste used in the present invention, the amount of the organic solvent needs to be within the above range. Further, by including an organic solvent within the above range, the solubility of the photopolymerization initiator and the sensitizer can be improved, and a homogeneous conductive paste can be produced. In the present invention, an organic solvent is used for the purpose of dissolving other substances, refers to an organic substance that is liquid at normal temperature and has volatility in a temperature range of 10 to 200 ° C., and has no reactivity in the molecule. Excluding those having a saturated bond. The organic solvent is not particularly limited, but for example, methyl ethyl ketone, dioxane, acetone, cyclohexanone, cyclopentanone, isobutyl alcohol, isopropyl alcohol, tetrahydrofuran, dimethyl sulfoxide, γ-butyrolactone, bromobenzene, chlorobenzene, Dibromobenzene, dichlorobenzene, bromobenzoic acid, chlorobenzoic acid, etc., diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentane Diol, 2-ethyl-1,3-hexanediol, terpineol, 3-methyl-3-methoxybutanol, texanol, Down benzyl alcohol, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether, propylene glycol monomethyl ether acetate. You may use these in mixture of 2 or more types.

  In the conductive paste used in the present invention, it is also effective to add a polymerization inhibitor for the storage stability of the conductive paste. Specific polymerization inhibitors include hydroquinone, phenothiazine, pt-butylcatechol, 2,5-dibutylhydroquinone, mono-t-butylhydroquinone, 2,5-di-t-amylhydroquinone, N-phenylnaphthylamine, The addition amount of the polymerization inhibitor such as 2,6-di-t-butyl-p-methylphenol, chloranil, hydroquinone monomethyl ether, pyrogallol, etc. is added in the range of 0.01 to 1% by mass in the conductive paste. can do.

  Since the photosensitive paste of the present invention contains a large amount of inorganic powder, it is also effective to use a dispersant in order to disperse these uniformly. As the dispersant, known anionic dispersants, cationic dispersants, nonionic dispersants and the like can be used. However, in the present invention, since the dispersant contains a large amount of inorganic powder, the dispersant is an imidazole. It is particularly effective that the organic acid salt contains a cation as a constituent. Specifically, 1-methyl-1-taro-ylamidoethyl-2-taro-ylimidazolinium methosulfate, 1-ethylbis (1-methyl-2-heptadecylimidazolinium methosulfate), 1-octa Examples include decanoylaminoethyl-2-heptadecylimidazoline hydrochloride, 1-docosanoylaminoethyl-2-heneicosylimidazoline hydrochloride, and the like.

In the conductive paste used in the present invention, an ultraviolet absorber such as a thixotropic agent, a plasticizer, and a dye can be appropriately used depending on the purpose as other additive components. The conductive paste used in the present invention is prepared by blending various components so as to have a predetermined composition, preliminarily dispersed by a mixer such as a planetary mixer, and then homogeneously dispersed and kneaded by a disperser such as a three-roller. Next, a method for manufacturing a solar cell using the conductive paste will be described.

  First, phosphorus or the like is thermally diffused on the surface of a single crystal or polycrystalline p-type silicon substrate to form an n-type diffusion layer. Subsequently, an antireflection layer is formed on the n-type diffusion layer. Examples of the material for the antireflection layer include titanium oxide, silicon dioxide, and silicon nitride. These can be formed by, for example, a thermal CVD method or a plasma CVD method.

Next, the conductive paste is pattern printed on the surface of the antireflection layer. Examples of the pattern printing method include screen printing, coating by a blade coater, a table coater, and the like. After coating, exposure is performed using an exposure apparatus. Examples of the active light source used at this time include visible light, near ultraviolet light, ultraviolet light, electron beam, X-ray, and laser light. Among these, ultraviolet rays are most preferable, and as the light source, for example, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, a halogen lamp, or a germicidal lamp can be used. Among these, an ultrahigh pressure mercury lamp is suitable. Exposure conditions vary depending on the coating thickness, but exposure is performed for 0.1 to 10 minutes using an ultrahigh pressure mercury lamp with an output of 1 to 100 mW / cm ² . In the present invention, exposure after coating eliminates the need for drying after printing and prevents sagging of the pattern, so that a conductive pattern having a high aspect ratio can be formed.

  After exposure, baking is performed. The firing atmosphere and temperature vary depending on the type of paste and substrate, but firing is performed in an atmosphere of air, nitrogen, hydrogen, or the like. As the firing furnace, a batch-type firing furnace or a roller hearth-type continuous firing furnace can be used. A calcination temperature can be performed at 500-1000 degreeC.

  Further, a back electrode is formed on the back surface of the silicon substrate provided with the antireflection layer, and the conductive paste can also be used for the back electrode. At this time, the front electrode and the back electrode can be formed simultaneously by applying and exposing the front electrode and the back electrode, followed by baking.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited by these Examples.

(Conductive paste A)
80% by mass of Ag powder having a center particle size (D50) of 3.2 μm, a specific surface area of 0.35 m ² / g, a tap density of 5.1 g / cm ³ , 26% by mass of bismuth oxide, and silicon oxide 13 manufactured by a wet reduction method 2% by mass of glass powder with a center particle diameter (D50) of 1 μm, urethane acrylate Resin (UA-510H, manufactured by Kyoeisha Chemical Co., Ltd.) 6% by mass, monomer 10% by mass having a polymerizable unsaturated group added in the ratio shown in Table 1, photopolymerization initiator (2-methyl-1 [4 -(Methylthio) phenyl] -2-morpholino-1-propanone) 1% by mass, sensitizer (2,4-diethylthioxanthone) 0.5% by mass, dispersant (1-methyl-1-taro) Iriamidoethyl-2-taro-ylimidazolinium methosulfate) 0.45% by mass, polymerization inhibitor (pt-butylcatechol) 0.05% by mass was weighed and stirred and dispersed with 3 rollers. What was obtained.

(Conductive paste B)
80% by mass of Ag powder having a center particle size (D50) of 3.2 μm, a specific surface area of 0.35 m ² / g, a tap density of 5.1 g / cm ³ , 26% by mass of bismuth oxide, and silicon oxide 13 manufactured by a wet reduction method 2% by mass of glass powder having a center particle diameter (D50) of 1 μm, urethane acrylate, and pulverized glass having a composition of 10% by mass, 18% by mass of boron oxide, 14% by mass of barium oxide, 4% by mass of aluminum oxide, and 21% by mass of zinc oxide. Resin (UAE-510H manufactured by Kyoeisha Chemical Co., Ltd.) 6% by mass, 9.6% by mass of a monomer having a polymerizable unsaturated group in the molecule added at the ratio shown in Table 1, organic solvent (diethylene glycol monobutyl ether acetate) 4% by mass, photopolymerization initiator (2-methyl-1 [4- (methylthio) phenyl] -2-morpholino-1-propanone) 1% by mass, sensitizer 2,4-diethylthioxanthone) 0.5% by mass, dispersant (1-methyl-1-taro-ylamidoethyl-2-taro-ylimidazolinium methosulfate) 0.45% by mass, polymerization inhibitor (p -T-Butylcatechol) obtained by measuring 0.05% by mass and dispersing with three rollers after stirring.

(Conductive paste C)
80% by mass of Ag powder having a center particle size (D50) of 3.2 μm, a specific surface area of 0.35 m ² / g, a tap density of 5.1 g / cm ³ , 26% by mass of bismuth oxide, and silicon oxide 13 manufactured by a wet reduction method 2% by mass of glass powder with a center particle diameter (D50) of 1 μm, urethane acrylate Resin (UA-510H manufactured by Kyoeisha Chemical Co., Ltd.) 6% by mass, 9.2% by mass of a monomer having a polymerizable unsaturated group in the molecule added at the ratio shown in Table 1, organic solvent (diethylene glycol monobutyl ether acetate) 8% by mass, photopolymerization initiator (2-methyl-1 [4- (methylthio) phenyl] -2-morpholino-1-propanone) 1% by mass, sensitizer 2,4-diethylthioxanthone) 0.5% by mass, dispersant (1-methyl-1-talo-ylamidoethyl-2-taro-ylimidazolinium methosulfate) 0.45% by mass, polymerization inhibitor (p -T-Butyl catechol) obtained by measuring 0.05% by mass and dispersing with three rollers after stirring.

(Conductive paste D)
80% by mass of Ag powder having a center particle size (D50) of 3.2 μm, a specific surface area of 0.35 m ² / g, a tap density of 5.1 g / cm ³ , 26% by mass of bismuth oxide, and silicon oxide 13 manufactured by a wet reduction method 2% by mass of glass powder having a center particle diameter (D50) of 1 μm, urethane acrylate, and pulverized glass having a composition of 10% by mass, 18% by mass of boron oxide, 14% by mass of barium oxide, 4% by mass of aluminum oxide, and 21% by mass of zinc oxide. 6% by mass of resin (UA-510H manufactured by Kyoeisha Chemical Co., Ltd.), 5% by mass of a monomer having a polymerizable unsaturated group in the molecule added at the ratio shown in Table 1, 5% by mass of an organic solvent (diethylene glycol monobutyl ether acetate), 1% by mass of photopolymerization initiator (2-methyl-1 [4- (methylthio) phenyl] -2-morpholino-1-propanone), sensitizer (2,4 Diethylthioxanthone) 0.5% by mass, dispersant (1-methyl-1-taro-ylamidoethyl-2-taro-ylimidazolinium methosulfate) 0.45% by mass, polymerization inhibitor (pt-butyl) Catechol) obtained by measuring 0.05% by mass and dispersing with three rollers after stirring.

(Conductive paste E)
The center particle diameter (D50) produced by the wet reduction method is 3.2 μm, the specific surface area is 0.35 m ² / g, the tap density is 5.1 g / cm ³ , 85% by mass of Ag powder, bismuth oxide is 26% by mass, silicon oxide 13 2% by mass of a glass powder having a center particle diameter (D50) of 1 μm obtained by pulverizing a glass having a composition of 10% by mass, 18% by mass of boron oxide, 14% by mass of barium oxide, 4% by mass of aluminum oxide and 21% by mass of zinc oxide, ethyl cellulose resin (Dow Chemical Co., Ltd.) 3% by mass, organic solvent (terpineol) 11.5% by mass, dispersant (1-methyl-1-taro-ylamidoethyl-2-taro-ylimidazolinium methosulfate) 0.5 What was obtained by weighing and stirring with a three-roller after mass%.

(Electrode pattern formation evaluation)
The conductive paste was screen-printed on a 4-inch silicon wafer (manufactured by E & M Co.) on which a nitride film of about 1000 mm was formed. As the screen plate, SUS200 mesh (wire diameter 30 μm, cocoon thickness 60 μm) was used. After screen printing, exposure was performed. As the exposure machine, a Dainippon Screen exposure machine (light source: 2 kW super high pressure mercury lamp) was used. The exposure amount is shown in Table 1. Then, it baked using the roller hearth baking furnace by Koyo Thermotech company for 10 minutes at 800 degreeC. After firing, the pattern cross section was observed using an electron microscope (manufactured by Keyence Corporation, VE-7800). The pattern shape was determined as follows.
○: No one can be seen, and the cross-sectional shape of the pattern is rectangular to trapezoidal ×: Whose is seen, and the cross-sectional shape of the pattern is rounded (evaluation of stickiness)
It was confirmed by touch that there was no tackiness after exposure or after drying.

(Evaluation of clogging)
After printing on 20 substrates, clogging occurred when the film was not printed uniformly on the substrate surface and the film thickness was uneven and the printed pattern was chipped.

(Examples 1-3)
In Examples 1 to 3 using the conductive paste containing silver powder, glass frit, and a photosensitive organic component as the conductive inorganic powder, and the content of the organic solvent in the conductive paste is 1% by mass or less, the drying step However, the pattern shape has a high aspect ratio pattern shape. However, some screen plates were clogged.

Example 4
Example 4 using a conductive paste containing a monomer having a polymerizable unsaturated group in a molecule having a viscosity in the range of 1 to 100 mPa · s (25 ° C.) in a range of 2 to 20% by mass in the conductive paste. Then, it has a pattern shape with a high aspect ratio that does not require any drying process and almost no pattern shape is observed. Also, the screen plate was not clogged.

(Example 5)
Conductive paste having a mass ratio of 90:10 to 30:70 of a polymerizable polyfunctional monomer having a polymerizable unsaturated group number in the range of 2 to 6 and a polymerizable monofunctional monomer having one polymerizable unsaturated group number In Example 5 using No. 1, a pattern shape having a high aspect ratio in which no dripping was observed without requiring a drying step. Also, the screen plate was not clogged. Furthermore, pattern formation was possible with low exposure amount (short-time exposure).

(Comparative Example 1)
When a conductive paste having an organic solvent amount of 5% by mass was used, a sticky surface could not be formed even after exposure.

(Comparative Example 2)
When a conductive paste containing no photosensitive organic component was used, a sticky surface could not be formed even after exposure.

(Comparative Example 3)
After printing the conductive paste containing no photosensitive organic component, it was dried at 100 ° C. for 60 minutes using a hot air dryer manufactured by Tabai. There was no stickiness and pattern formation was possible, but there was some sag in the pattern, and a high aspect ratio pattern shape could not be obtained.

Claims (3)

  A method of manufacturing a solar cell comprising a step of pattern-printing a conductive paste on a substrate and exposing the conductive paste, wherein the conductive paste contains a conductive inorganic powder, a glass frit and a photosensitive organic component, and the organic solvent in the conductive paste Content is 1 mass% or less, The manufacturing method of the solar cell characterized by the above-mentioned.   The conductive paste has a viscosity at 25 ° C. of 1 to 100 mPa · s as a photosensitive organic component, and a monomer having a polymerizable unsaturated group in the molecule is in the range of 2 to 20% by mass in the conductive paste. The method for producing a solar cell according to claim 1, comprising:   The conductive paste contains, as a photosensitive organic component, a polymerizable polyfunctional monomer having a polymerizable unsaturated group number in the range of 2 to 6 and a polymerizable monofunctional monomer having one polymerizable unsaturated group, the polymerization The method for producing a solar cell according to claim 1 or 2, wherein the mass ratio of the polymerizable polyfunctional monomer and the polymerizable monofunctional monomer is in the range of 90:10 to 30:70.