JP2012231012A - P-type diffusion layer forming composition, method for manufacturing p-type diffusion layer, and method for manufacturing solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a p-type diffusion layer forming composition capable of forming a p-type diffusion layer without causing an internal stress in a silicon substrate and a warpage of the substrate, in a manufacturing process of a solar cell element using the silicon substrate, a method for manufacturing the p-type diffusion layer, and a method for manufacturing the solar cell element.SOLUTION: The p-type diffusion layer forming composition contains glass powder including an acceptor element, and a dispersant containing a binder having a solubility parameter being equal to or less than 12(MJ/m). The p-type diffusion layer forming composition is applied to the substrate and is subjected to heat diffusion treatment, whereby a p-type diffusion layer and a solar cell element including the p-type diffusion layer are produced.

Description

  The present invention relates to a p-type diffusion layer forming composition for a solar cell element, a method for producing a p-type diffusion layer, and a method for producing a solar cell element. More specifically, the present invention reduces internal stress of silicon as a semiconductor substrate. In addition, the present invention relates to a p-type diffusion layer forming technique capable of suppressing damage at crystal grain boundaries, suppressing crystal defect growth, and suppressing warpage.

The manufacturing process of the conventional silicon solar cell element is demonstrated.
First, a p-type silicon substrate having a textured structure is prepared so as to promote the light confinement effect and achieve high efficiency, and then 800 to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen. The n-type diffusion layer is uniformly formed by performing several tens of minutes. In this conventional method, since phosphorus is diffused using a mixed gas, n-type diffusion layers are formed not only on the surface but also on the side surface and the back surface. Therefore, side etching is performed to remove the n-type diffusion layer on the side surface. Further, the back surface of the n-type diffusion layer must be converted into the p ⁺ -type diffusion layer, an aluminum paste is printed on the back, by firing this, the n-type diffusion layer at the same time as the p ⁺ -type diffusion layer , Got ohmic contact.

  However, since the aluminum paste has a low electrical conductivity, the sheet resistance must be lowered, and the aluminum layer formed on the entire back surface usually has a thickness of about 10 to 20 μm after firing. Furthermore, since the thermal expansion coefficients of silicon and aluminum differ greatly, a large internal stress is generated in the silicon substrate during the firing and cooling processes, causing damage to crystal boundaries, increasing crystal defects, and warping.

In order to solve this problem, there is a method of reducing the coating amount of the paste composition and thinning the back electrode layer. However, when the application amount of the paste composition is reduced, the amount of aluminum diffusing from the surface of the p-type silicon semiconductor substrate becomes insufficient. As a result, the desired BSF (Back Surface Field) effect (the effect of improving the collection efficiency of the generated carriers due to the presence of the p ⁺ -type diffusion layer) cannot be achieved, resulting in a problem that the characteristics of the solar cell deteriorate. .

  Therefore, for example, a paste composition comprising aluminum powder, an organic vehicle, and an inorganic compound powder having a thermal expansion coefficient smaller than that of aluminum and any one of a melting temperature, a softening temperature and a decomposition temperature higher than the melting point of aluminum. Has been proposed (see, for example, Patent Document 1).

JP-A-2003-223813

However, even when the paste composition described in Patent Document 1 is used, there is a case where warpage cannot be sufficiently suppressed.
The present invention has been made in view of the above-described conventional problems, and in the manufacturing process of a solar cell element using a silicon substrate, a p-type diffusion layer is produced without generating internal stress in the silicon substrate and warping of the substrate. It is an object of the present invention to provide a p-type diffusion layer forming composition capable of forming a p-type diffusion layer, a method for producing a p-type diffusion layer, and a method for producing a solar cell element.

Means for solving the problems are as follows.
<1> A p-type diffusion layer forming composition containing glass powder containing an acceptor element and a dispersion medium containing a binder having a solubility parameter of 12 (MJ / m ³ ) ^1/2 or less.
<2> The p-type diffusion layer forming composition according to <1>, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium).
<3> The glass powder containing the acceptor element is at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O ₃ , and SiO ₂ , K ₂ O, and Na ₂ O. And at least one glass component material selected from Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO _3. The p-type diffusion layer forming composition according to <1> or <2>.

<4> A p-type diffusion having a step of applying the p-type diffusion layer forming composition according to any one of <1> to <3> on a semiconductor substrate and a step of performing a thermal diffusion treatment. Layer manufacturing method.
<5> A step of applying the p-type diffusion layer forming composition according to any one of <1> to <3> on the semiconductor substrate and a thermal diffusion treatment to form a p-type diffusion layer And a step of forming an electrode on the formed p-type diffusion layer.

  According to the present invention, it is possible to form a p-type diffusion layer without generating internal stress in the silicon substrate and warping of the substrate in the manufacturing process of the solar cell element using the silicon substrate.

First, the p-type diffusion layer forming composition of the present invention will be described, and then a p-type diffusion layer using the p-type diffusion layer forming composition and a method for producing a solar cell element will be described.
In this specification, the term “process” is not limited to an independent process, and is included in the term if the intended action of the process is achieved even when it cannot be clearly distinguished from other processes. . In the present specification, numerical ranges indicated using “to” indicate ranges including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. Further, when referring to the amount of each component in the composition in the present specification, when there are a plurality of substances corresponding to each component in the composition, the plurality of the components present in the composition unless otherwise specified. It means the total amount of substance.

The p-type diffusion layer forming composition of the present invention comprises a glass powder containing at least an acceptor element (hereinafter sometimes simply referred to as “glass powder”) and a solubility parameter of 12 (MJ / m ³ ) ^1/2 or less. A dispersion medium containing a certain binder, and may further contain other additives as required in consideration of coating properties and the like.
Here, the p-type diffusion layer forming composition includes a glass powder containing an acceptor element, and a material capable of forming a p-type diffusion layer by thermally diffusing the acceptor element after being applied to a silicon substrate. Say. By using the p-type diffusion layer forming composition containing the acceptor element in the glass powder, the p ⁺ -type diffusion layer forming step and the ohmic contact forming step can be separated, and the choice of electrode materials for forming the ohmic contact is expanded. The choice of electrode structure is also widened. For example, if a low resistance material such as silver is used for the electrode, a low resistance can be achieved with a thin film thickness. Further, the electrodes need not be formed on the entire surface, and may be partially formed like a comb shape. As described above, by forming a partial shape such as a thin film or a comb shape, it is possible to form a p-type diffusion layer while suppressing the occurrence of internal stress in the silicon substrate and warping of the substrate.

Therefore, if the p-type diffusion layer forming composition of the present invention is applied, a conventionally widely employed method, that is, printing an aluminum paste and firing it to turn the n-type diffusion layer into a p ⁺ -type diffusion layer. At the same time, the internal stress in the substrate and the warpage of the substrate that are generated by the method of obtaining the ohmic contact are suppressed.
Furthermore, since the acceptor component in the glass powder is not easily volatilized even during firing, the formation of a p-type diffusion layer other than the desired region due to the generation of the volatilizing gas is suppressed.

The glass powder containing the acceptor element according to the present invention will be described in detail.
An acceptor element is an element that can form a p-type diffusion layer by doping into a silicon substrate. As the acceptor element, a Group 13 element can be used, and examples thereof include B (boron), Al (aluminum), and Ga (gallium).

Examples of the acceptor element-containing material used for introducing the acceptor element into the glass powder include B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O ₃ , and B ₂ O ₃ , Al ₂ O _3, and Ga ₂ O _3. It is preferable to use at least one selected from

Moreover, the glass powder containing an acceptor element can control a melting temperature, a softening point, a glass transition point, chemical durability, etc. by adjusting a component ratio as needed. Furthermore, it is preferable to contain the glass component substance described below.
Examples of glass component materials include SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ , WO ₃ , Examples include MoO ₃ , MnO, La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , GeO ₂ , TeO _2, and Lu ₂ O _3. SiO ₂ , K ₂ O, It is preferable to use at least one selected from Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO ₃ .

Specific examples of the glass powder containing the acceptor element include both the acceptor element-containing substance and the glass component substance, and B ₂ O ₃ —SiO ₂ system (in the order of acceptor element-containing substance−glass component substance). Description, the same applies hereinafter), B ₂ O ₃ —ZnO system, B ₂ O ₃ —PbO system, B ₂ O ₃ single system, etc., a system containing B ₂ O ₃ as an acceptor element-containing substance, Al ₂ O ₃ —SiO ₂ Examples thereof include glass powders such as a system containing Al ₂ O ₃ as an acceptor element-containing material such as a system, a Ga ₂ O ₃ —SiO ₂ system, and a system containing Ga ₂ O ₃ as an acceptor element-containing material such as a system.
_Further, Al ₂ O 3 _-B 2 _{O 3 system,} Ga ₂ O 3 _-B as 2 _{O 3} system or the like, may be a glass powder containing two or more acceptor element-containing material.
In the above, a single component glass or a composite glass containing two components is exemplified, but a glass powder containing three or more components such as B ₂ O ₃ —SiO ₂ —Na ₂ O may be used.

  The content ratio of the glass component substance in the glass powder is preferably set as appropriate in consideration of the melting temperature, the softening point, the glass transition point, and the chemical durability, and is generally 0.1% by mass to 95% by mass. It is preferable that it is 0.5 mass% or more and 90 mass% or less.

  The softening point of the glass powder is preferably 200 ° C. to 1000 ° C., more preferably 300 ° C. to 900 ° C., from the viewpoints of diffusibility during the diffusion treatment and dripping.

Examples of the shape of the glass powder include a substantially spherical shape, a flat shape, a block shape, a plate shape, a scale shape, and the like. From the viewpoint of application property to a substrate and uniform diffusibility when an n-type diffusion layer forming composition is used. It is desirable to have a substantially spherical shape, flat shape, or plate shape. The particle size of the glass powder is desirably 50 μm or less. When glass powder having a particle size of 50 μm or less is used, a smooth coating film is easily obtained. Further, the particle size of the glass powder is more preferably 10 μm or less. The lower limit is not particularly limited, but is preferably 0.01 μm or more.
Here, the particle diameter of glass represents a volume average particle diameter, and can be measured by a laser scattering diffraction method particle size distribution measuring apparatus or the like.

The glass powder containing an acceptor element is produced by the following procedure.
First, weigh the ingredients and fill the crucible. Examples of the material for the crucible include platinum, platinum-rhodium, iridium, alumina, quartz, carbon, and the like, and are appropriately selected in consideration of the melting temperature, atmosphere, reactivity with the molten material, and the like.
Next, it heats with the temperature according to a glass composition with an electric furnace, and is set as a melt. At this time, it is desirable to stir the melt uniformly.
Subsequently, the obtained melt is poured onto a zirconia substrate, a carbon substrate or the like to vitrify the melt.
Finally, the glass is crushed into powder. A known method such as a jet mill, a bead mill, or a ball mill can be applied to the pulverization.

  The content ratio of the glass powder containing the acceptor element in the p-type diffusion layer forming composition is determined in consideration of applicability, acceptor element diffusibility, and the like. In general, the content ratio of the glass powder in the p-type diffusion layer forming composition is preferably 0.1% by mass or more and 95% by mass or less, more preferably 1% by mass or more and 90% by mass or less, The content is more preferably 1.5% by mass or more and 85% by mass or less, and particularly preferably 2% by mass or more and 80% by mass or less.

Next, the dispersion medium will be described.
The dispersion medium is a medium in which the glass powder is dispersed in the composition. The dispersion medium contains at least one binder (hereinafter also referred to as “specific binder”) having a solubility parameter (SP value) of 12 (MJ / m ³ ) ^1/2 or less, and at least one solvent as necessary. Further includes species.
Since the dispersion medium contains a specific binder, for example, a p-type diffusion layer forming composition is applied to a semiconductor substrate and dried to form a coating layer, followed by a post-process for applying an alcohol solvent such as ethanol. Even if it is a case, since the formed coating layer is excellent in solvent resistance, its shape can be maintained, and a p-type diffusion layer can be formed in a desired shape.

The solubility parameter of the specific binder is 12 (MJ / m ³ ) ^1/2 or less, preferably 11.5 (MJ / m ³ ) ^1/2 or less, 9.0 (MJ / m ³ ) More preferably, it is ^1/2 or more and 11.5 (MJ / m ³ ) ^1/2 or less.
When the solubility parameter of the binder exceeds 12 (MJ / m ³ ) ^1/2 , the shape of the coating layer cannot be sufficiently maintained when an alcohol solvent or the like is applied to the coating layer made of the p-type diffusion layer forming composition. There is a case.

Here, the solubility parameter (hereinafter also referred to as “SP value”) is a value represented by the square root of the molecular aggregation energy. The SP values of various binders are described in Kodansha Scientific edition “Practical Polymer for Engineers” (by Koji Mukai) and the like, and this value is the SP value in this specification. The SP value is a value at 25 ° C.
The SP value can be calculated by the method described in the Maruzen edited by “Solution and Solubility” (by Kozo Shinoda). The SP value of the binder not described in “Practical Polymer for Engineers” It is calculated by the method described in “Solubility”.

Specific examples of binders having an SP value of 12 (MJ / m ³ ) ^1/2 or less include, for example, polyisobutylene, ethylene propylene resin, polyethylene, natural rubber, butadiene resin, polymethyl methacrylate, polyethylene terephthalate, epoxy resin, phenol Examples thereof include resins and siloxane resins.
These are used singly or in combination of two or more.

The molecular weight of the specific binder is not particularly limited, and it is desirable to adjust appropriately in view of the desired viscosity as the composition. 5000 to 500000 are preferable, 10000 to 200000 are more preferable, and 20000 to 100000 are most preferable.
The weight average molecular weight can be measured by a conventional method using, for example, the GPC method.

  The content of the specific binder in the p-type diffusion layer forming composition is not particularly limited. For example, in the p-type diffusion layer forming composition, it is 0.02% by mass to 40% by mass, preferably 0.1% by mass to 20% by mass, and more preferably 0.5% by mass to 10% by mass. It is.

  The p-type diffusion layer forming composition of the present invention is selected from poly (meth) acrylate alkyl, polyethylene terephthalate, epoxy resin and phenol resin from the viewpoint of solvent resistance, and a specific binder having a weight average molecular weight of 10,000 to 200,000. Is preferably 0.1 to 20% by mass, selected from poly (meth) acrylate alkyl, polyethylene terephthalate, epoxy resin and phenol resin, and 0.5 to 0.5 specific binder having a weight average molecular weight of 20,000 to 100,000. More preferably, the content is 10% by mass to 10% by mass.

p-type diffusion layer-forming composition, SP value in addition to the 12 ^(MJ / ^{m 3) 1/2} or less of the binder, SP value within a range not to impair the effects of the present invention ^{12 (MJ / m 3) 1} / ^It may further contain more than ^two binders.
Examples of binders having an SP value exceeding 12 (MJ / m ³ ) ^1/2 include, for example, cellulose derivatives such as polyvinyl alcohol, cellulose, carboxymethyl cellulose, and hydroxyethyl cellulose, gelatin, starch and starch derivatives, sodium alginates, xanthan, guar, and the like. Examples include guar derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives.
When the p-type diffusion layer forming composition contains a binder having an SP value exceeding 12 (MJ / m ³ ) ^1/2 , the content can be 5% by mass or less, and 2% by mass or less. Is preferred.

The p-type diffusion layer forming composition preferably contains at least one solvent as a dispersion medium.
Examples of the solvent include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-iso-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone, methyl-n-pentyl ketone, methyl-n-hexyl ketone, Ketone solvents such as diethyl ketone, dipropyl ketone, di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2,4-pentanedione, acetonylacetone; diethyl ether, methyl ethyl ether, methyl -N-propyl ether, di-iso-propyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether Ter, ethylene glycol di-n-propyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol methyl n-propyl ether, diethylene glycol methyl n-butyl ether, diethylene glycol di-n-propyl ether , Diethylene glycol di-n-butyl ether, diethylene glycol methyl-n-hexyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, triethylene glycol methyl n-butyl ether, triethylene glycol di-n- Butyl ether, G Ethylene glycol methyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetradiethylene glycol methyl ethyl ether, tetraethylene glycol methyl n-butyl ether, diethylene glycol di-n-butyl ether, tetraethylene glycol methyl n-hexyl Ether, tetraethylene glycol di-n-butyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol dibutyl ether, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol methyl ethyl Ether, zip Lopylene glycol methyl-n-butyl ether, dipropylene glycol di-n-propyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol methyl-n-hexyl ether, tripropylene glycol dimethyl ether, tripropylene glycol diethyl ether, tripropylene Glycol methyl ethyl ether, tripropylene glycol methyl-n-butyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether, tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl ether, tetradipropylene glycol methyl ethyl Ether, tetrapropylene glycol methyl-n-butyl ether Ether solvents such as dipropylene glycol di-n-butyl ether, tetrapropylene glycol methyl-n-hexyl ether, tetrapropylene glycol di-n-butyl ether; methyl acetate, ethyl acetate, n-propyl acetate, i-propyl acetate, acetic acid n-butyl, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2- (2- Butoxyethoxy) ethyl, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether acetate, diethylene glycol monoethyl ether acetate, dipropylene glycol acetate Methyl ether, dipropylene glycol ethyl ether, glycol diacetate, methoxytriglycol acetate, ethyl propionate, n-butyl propionate, i-amyl propionate, diethyl oxalate, di-n-butyl oxalate, lactic acid Methyl, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propionate, ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate, propylene Ester solvents such as glycol ethyl ether acetate, propylene glycol propyl ether acetate, γ-butyrolactone, γ-valerolactone; N-methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, etc. Aprotic polar solvent: methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, sec-butanol, t-butanol, n-pentanol, i-pentanol, 2-methylbutanol, sec -Pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol, sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol, trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, Alcohol solvents such as 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monophenyl ether, Diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol Mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, ethoxytriglycol, tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether Glycol monoether solvents such as α-terpinene, α-terpineol, myrcene, alloocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, carvone, ocimene, and ferrandrene; water . These are used singly or in combination of two or more.
In the case of an n-type diffusion layer forming composition, α-terpineol, diethylene glycol mono-n-butyl ether, and 2- (2-butoxyethoxy) ethyl acetate are preferred from the viewpoint of applicability to the substrate.

The constitution and content ratio of the dispersion medium in the p-type diffusion layer forming composition are determined in consideration of applicability and acceptor concentration.
The viscosity of the p-type diffusion layer forming composition is preferably 10 mPa · s or more and 1000000 mPa · s or less, and more preferably 50 mPa · s or more and 500000 mPa · s or less in consideration of applicability. The viscosity of the p-type diffusion layer forming composition is measured at 25 ° C. and 5 rpm using an E-type viscometer.

  Next, the manufacturing method of the p-type diffused layer and solar cell element of this invention is demonstrated.

First, an alkaline solution is applied to a silicon substrate which is a p-type semiconductor substrate to remove a damaged layer, and a texture structure is obtained by etching.
Specifically, the damaged layer on the silicon surface generated when slicing from the ingot is removed with 20% by mass caustic soda. Next, etching is performed with a mixed solution of 1% by mass caustic soda and 10% by mass isopropyl alcohol to form a texture structure. In the solar cell element, by forming a texture structure on the light receiving surface (surface) side, a light confinement effect is promoted, and high efficiency is achieved.

Next, several tens of minutes are performed at 800 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen to uniformly form an n-type diffusion layer. At this time, in the method using the phosphorus oxychloride atmosphere, the diffusion of phosphorus extends to the side surface and the back surface, and the n-type diffusion layer is formed not only on the surface but also on the side surface and the back surface. Therefore, side etching is performed to remove the side n-type diffusion layer.

Then, the p-type diffusion layer forming composition is applied onto the n-type diffusion layer on the back surface of the p-type semiconductor substrate, that is, the surface that is not the light receiving surface. In the present invention, the coating method is not limited, and examples thereof include a printing method, a spin method, a brush coating, a spray method, a doctor blade method, a roll coater method, and an ink jet method.
Is not particularly limited as coated amount of the p-type diffusion layer forming composition, for example, be a 0.01g ^{/ m 2} ~100g ^/ m 2 as a glass powder content, 0.1 g ^/ m 2 to 10 g / M ² is preferable.

  Depending on the composition of the p-type diffusion layer forming composition, a drying step for volatilizing the solvent contained in the composition may be necessary after coating. In this case, drying is performed at a temperature of about 80 ° C. to 300 ° C. for 1 minute to 10 minutes when a hot plate is used, and about 10 minutes to 30 minutes when a dryer or the like is used. The drying conditions depend on the solvent composition of the p-type diffusion layer forming composition and are not particularly limited to the above conditions in the present invention.

The semiconductor substrate coated with the p-type diffusion layer forming composition is heat-treated at 600 ° C. to 1200 ° C. By this heat treatment, the acceptor element diffuses into the semiconductor substrate, and a p ⁺ -type diffusion layer is formed. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.
Since a glass layer is formed on the surface of the p ⁺ type diffusion layer, the glass is removed by etching. As the etching, a known method such as a method of immersing in an acid such as hydrofluoric acid or a method of immersing in an alkali such as caustic soda can be applied.

Further, in the conventional manufacturing method, an aluminum paste is printed on the back surface, and this is baked to change the n-type diffusion layer into a p ⁺ -type diffusion layer, and at the same time, an ohmic contact is obtained. However, since the electrical conductivity of the aluminum paste is low, the sheet resistance must be lowered, and the aluminum layer usually formed on the entire back surface must have a thickness of about 10 μm to 20 μm after firing. Furthermore, since the thermal expansion coefficients of silicon and aluminum differ greatly, a large internal stress is generated in the silicon substrate during the firing and cooling process, causing warpage.
This internal stress has a problem that the crystal grain boundary is damaged and the power loss increases. Further, the warpage easily damages the solar cell element in the transportation of the solar cell element in the module process and the connection with a copper wire called a tab wire. In recent years, the thickness of the silicon substrate has been reduced due to the improvement of the slice processing technique, and the solar cell element tends to be easily broken.

However, according to the manufacturing method of the present invention, after the n-type diffusion layer is converted into the p ⁺ -type diffusion layer by the p-type diffusion layer forming composition of the present invention, an electrode is separately provided on the p ⁺ -type diffusion layer. . Therefore, the material used for the back electrode is not limited to aluminum. For example, Ag (silver) or Cu (copper) can be applied, and the thickness of the back electrode can be made thinner than the conventional one. Further, it is not necessary to form the entire surface. Therefore, it is possible to reduce internal stress and warpage in the silicon substrate that occur during the firing and cooling processes.

An antireflection film is formed on the n-type diffusion layer formed as described above. The antireflection film is formed by applying a known technique. For example, when the antireflection film is a silicon nitride film, it is formed by a plasma CVD method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and orbits that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are combined to inactivate defects (hydrogen passivation).
More specifically, the mixed gas flow ratio NH ₃ / SiH ₄ is 0.05 to 1.0, the pressure in the reaction chamber is 0.1 Torr to 2 Torr, the temperature during film formation is 300 ° C. to 550 ° C., It is formed under the condition that the frequency for discharge is 100 kHz or more.

  On the antireflection film on the surface (light receiving surface), the surface electrode metal paste is printed, applied and dried by a screen printing method to form a surface electrode. The metal paste for a surface electrode contains metal particles and glass particles as essential components, and includes a resin binder and other additives as necessary.

Next, a back electrode is also formed on the p ⁺ -type diffusion layer on the back surface. As described above, in the present invention, the material and forming method of the back electrode are not particularly limited. For example, a back electrode paste containing a metal such as aluminum, silver, or copper may be applied and dried to form the back electrode. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between solar cell elements in the module process.

  The electrode is fired to complete the solar cell element. When fired in the range of 600 ° C. to 900 ° C. for several seconds to several minutes, the antireflective film, which is an insulating film, is melted by the glass particles contained in the electrode metal paste on the surface side, and the silicon surface is also partially melted. The metal particles (for example, silver particles) inside form a contact portion with the silicon substrate and solidify. Thereby, the formed surface electrode and the silicon substrate are electrically connected. This is called fire-through.

The shape of the surface electrode will be described. The surface electrode includes a bus bar electrode and a finger electrode that intersects the bus bar electrode.
Such a surface electrode can be formed by means such as screen printing of the above-described metal paste, plating of the electrode material, or vapor deposition of the electrode material by electron beam heating in a high vacuum. A surface electrode composed of a bus bar electrode and a finger electrode is generally used as an electrode on the light receiving surface side and is well known, and known forming means for the bus bar electrode and the finger electrode on the light receiving surface side can be applied.

In the above-described method for manufacturing a p-type diffusion layer and a solar cell element, a mixed gas of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen is used to form an n-type diffusion layer on a silicon substrate which is a p-type semiconductor substrate. Although used, the n-type diffusion layer may be formed using the n-type diffusion layer forming composition. The n-type diffusion layer forming composition contains a Group 15 element such as P (phosphorus) or Sb (antimony) as a donor element.
In the method using the n-type diffusion layer forming composition for forming the n-type diffusion layer, first, the n-type diffusion layer forming composition is applied to the light-receiving surface which is the surface of the p-type semiconductor substrate, and the p-type of the present invention is applied to the back surface. The diffusion layer forming composition is applied and heat-treated at 600 ° C to 1200 ° C. By this heat treatment, the donor element diffuses into the p-type semiconductor substrate on the front surface to form an n-type diffusion layer, and the acceptor element diffuses on the back surface to form a p ⁺ -type diffusion layer. Except for this step, a solar cell element is produced by the same steps as those described above.

  Examples of the present invention will be described more specifically below, but the present invention is not limited to these examples. Unless otherwise stated, all chemicals used reagents. “%” Means “% by mass” unless otherwise specified.

[Example 1]
B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) glass powder (trade name: TMX-404) having a substantially spherical particle shape, an average particle diameter of 4.9 μm, and a softening point of 561 ° C. 20 g of Toago Material Technology Co., Ltd.), 0.3 g of polymethyl methacrylate (weight average molecular weight 50,000, SP value 9.5), and 10 g of 2- (2-butoxyethoxy) ethyl acetate. Then, using an automatic mortar kneader, the mixture was made into a paste to prepare a p-type diffusion layer forming composition.

  The glass particle shape was determined by observing with a TM-1000 scanning electron microscope manufactured by Hitachi High-Technologies Corporation. The average particle size of the glass was calculated using a LS 13 320 type laser scattering diffraction particle size distribution analyzer (measurement wavelength: 632 nm) manufactured by Beckman Coulter, Inc. The softening point of the glass was determined from a differential heat (DTA) curve using a DTG-60H type differential heat / thermogravimetric simultaneous measuring device manufactured by Shimadzu Corporation.

Next, the prepared paste is applied on a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing and dried on a hot plate at 150 ° C. for 5 minutes to form an application layer having a thickness of about 18 μm. Formed.
The surface of the silicon substrate on which the coating layer was formed was washed with ethanol and dried in the air. When the surface of the dried silicon substrate was observed, the shape of the coating layer was maintained, and no deformation or expansion of the coating layer was observed.

  Subsequently, thermal diffusion treatment was performed for 30 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes to remove the glass layer, washed with running water, and dried.

  The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 190Ω / □, and B (boron) diffused to form a p-type diffusion layer. Further, no warpage occurred on the substrate.

  The sheet resistance was measured by a four-probe method using a Loresta-EP MCP-T360 type low resistivity meter manufactured by Mitsubishi Chemical Corporation.

[Example 2]
In Example 1, a p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that polyethylene terephthalate (weight average molecular weight 50,000, SP value 10.7) was used instead of polymethyl methacrylate. .
Next, the prepared paste is applied on a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing and dried on a hot plate at 150 ° C. for 5 minutes to form an application layer having a thickness of about 18 μm. Formed.
The surface of the silicon substrate on which the coating layer was formed was washed with ethanol and dried in the air. When the surface of the dried silicon substrate was observed, the shape of the coating layer was maintained, and no deformation or expansion of the coating layer was observed.

  Subsequently, thermal diffusion treatment was performed for 30 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes to remove the glass layer, washed with running water, and dried.

  The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 190Ω / □, and B (boron) diffused to form a p-type diffusion layer. Further, no warpage occurred on the substrate.

[Example 3]
In Example 1, a p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that an epoxy resin (weight average molecular weight 50,000, SP value 10.9) was used instead of polymethyl methacrylate. .
Next, the prepared paste is applied on a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing and dried on a hot plate at 150 ° C. for 5 minutes to form an application layer having a thickness of about 18 μm. Formed.
The surface of the silicon substrate on which the coating layer was formed was washed with ethanol and dried in the air. When the surface of the dried silicon substrate was observed, the shape of the coating layer was maintained, and no deformation or expansion of the coating layer was observed.

  Subsequently, thermal diffusion treatment was performed for 30 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes to remove the glass layer, washed with running water, and dried.

  The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 190Ω / □, and B (boron) diffused to form a p-type diffusion layer. Further, no warpage occurred on the substrate.

[Example 4]
In Example 1, a p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that a phenol resin (weight average molecular weight 50,000, SP value 11.3) was used instead of polymethyl methacrylate. .
Next, the prepared paste is applied on a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing and dried on a hot plate at 150 ° C. for 5 minutes to form an application layer having a thickness of about 18 μm. Formed.
The surface of the silicon substrate on which the coating layer was formed was washed with ethanol and dried in the air. When the surface of the dried silicon substrate was observed, the shape of the coating layer was maintained, and no deformation or expansion of the coating layer was observed.

  Subsequently, thermal diffusion treatment was performed for 30 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes to remove the glass layer, washed with running water, and dried.

  The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 190Ω / □, and B (boron) diffused to form a p-type diffusion layer. Further, no warpage occurred on the substrate.

[Comparative Example 1]
A p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that cellulose (weight average molecular weight 50,000, SP value 15.7) was used instead of polymethyl methacrylate in Example 1.
Next, the prepared paste is applied on a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing, and dried on a hot plate at 150 ° C. for 5 minutes to form a coating layer having a thickness of about 18 μm. did.
The surface of the p-type silicon substrate on which the coating layer was formed was washed with ethanol and dried in the air. When the surface of the p-type silicon substrate after drying was observed, the surface of the coating layer was white and rough, and the shape of the coating layer was deformed, and the coating layer expanded to the uncoated region on the silicon substrate.

  Subsequently, thermal diffusion treatment was performed for 10 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes in order to remove the glass layer, and washed with running water. When the sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was measured, the p-type diffusion layer was formed even in the region where the coating layer was enlarged.

[Comparative Example 2]
In Example 1, a p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that polyvinyl alcohol (weight average molecular weight 50,000, SP value 12.6) was used instead of polymethyl methacrylate. .

Next, the prepared paste is applied on a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing, and dried on a hot plate at 150 ° C. for 5 minutes to form a coating layer having a thickness of about 18 μm. did.
The surface of the p-type silicon substrate on which the coating layer was formed was washed with ethanol and dried in the air. When the surface of the p-type silicon substrate after drying was observed, the surface of the coating layer was white and rough, and the shape of the coating layer was deformed, and the coating layer expanded to the uncoated region on the silicon substrate.

  Subsequently, thermal diffusion treatment was performed for 10 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes in order to remove the glass layer, and washed with running water. When the sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was measured, the p-type diffusion layer was formed even in the region where the coating layer was enlarged.

Claims (5)

Glass powder containing an acceptor element;
A dispersion medium containing a binder having a solubility parameter of 12 (MJ / m ³ ) ^1/2 or less;
A p-type diffusion layer forming composition comprising:   The p-type diffusion layer forming composition according to claim 1, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). The glass powder containing the acceptor element is at least one acceptor element-containing substance selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , and SiO ₂ , K ₂ O, Na ₂ O, Li _2. Or at least one glass component material selected from O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V ₂ O ₅ , SnO, ZrO ₂ and MoO _3. The p-type diffusion layer forming composition according to claim 2.   A method for producing a p-type diffusion layer, comprising: applying a p-type diffusion layer forming composition according to any one of claims 1 to 3 on a semiconductor substrate; and applying a thermal diffusion treatment. . Applying a p-type diffusion layer forming composition according to any one of claims 1 to 3 on a semiconductor substrate;
Applying a thermal diffusion treatment to form a p-type diffusion layer;
Forming an electrode on the formed p-type diffusion layer;
The manufacturing method of the solar cell element which has this.