TWI556289B - Composition for forming p-type diffusion layer, method for forming p-type diffusion layer, and method for producing photovoltaic cell element - Google Patents

Description

Composition for forming p-type diffusion layer, method for producing p-type diffusion layer, and method for producing solar cell element

The present invention relates to a composition for forming a p-type diffusion layer of a solar cell element, a method for producing a p-type diffusion layer, and a method for manufacturing a solar cell element. More specifically, the present invention relates to a semiconductor substrate which can be reduced as a semiconductor substrate. The internal stress of the ruthenium substrate, the damage of the crystal grain boundary, the growth of crystal defects, and the p-type diffusion layer formation technique for suppressing warpage.

The manufacturing steps of the prior 矽 solar cell element will be described.

First, in order to promote the optical confinement effect to achieve high efficiency, a p-type germanium substrate having a texture structure is prepared, and then in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen. The treatment was performed at 800 ° C to 900 ° C for several tens of minutes to form an n-type diffusion layer on the substrate in the same manner. In this prior method, since phosphorus is diffused by using a mixed gas, an n-type diffusion layer is formed not only on the surface but also on the side surface and the back surface. For these reasons, side etching is required to perform an n-type diffusion layer for removing the side. In addition, the n-type diffusion layer on the back side needs to be converted into a p ⁺ -type diffusion layer, so that the aluminum paste is printed on the back side and then calcined (sintered) so that the n-type diffusion layer is transformed into the p ⁺ type layer while obtaining ohmic contact. .

However, the aluminum layer formed of the aluminum paste has a low electrical conductivity, and in order to reduce the sheet resistance, the aluminum layer usually formed on the entire back surface must have a thickness of about 10 μm to 20 μm after firing. Further, if a thick aluminum layer is formed as described above, since the coefficient of thermal expansion of the crucible differs greatly from the coefficient of thermal expansion of aluminum, this difference causes a large internal stress in the crucible substrate during calcination and cooling. It promotes the damage of crystal grain boundaries, the growth of crystal defects, and the cause of warpage.

In order to solve this problem, there is a method of reducing the amount of coating of the paste composition and making the back electrode layer thin. However, when the coating amount of the paste composition is reduced, the amount of aluminum diffused from the surface of the p-type germanium semiconductor substrate to the inside becomes insufficient. As a result, the desired back surface field (BSF) effect (the effect of increasing the collection efficiency of the carrier due to the presence of the p ⁺ type layer) cannot be achieved, and thus the solar cell is generated. The problem of declining characteristics.

For example, a paste composition comprising aluminum powder, an organic vehicle, and a thermal expansion coefficient smaller than aluminum and having a melting temperature, a softening temperature, and a decomposition temperature is proposed in Japanese Patent Laid-Open Publication No. 2003-223813. An inorganic compound powder which is higher than the melting point of aluminum.

However, it is described in Japanese Patent Laid-Open Publication No. 2003-223813. In the case of the paste composition, there is also a case where warpage cannot be sufficiently suppressed.

The present invention has been made in view of the above problems, and an object of the invention is to provide a method for manufacturing a solar cell element using a tantalum substrate, thereby suppressing occurrence of internal stress in the tantalum substrate and warpage of the substrate. A p-type diffusion layer is formed, and a composition for forming a p-type diffusion layer of a solar cell element having a low surface resistance value, a method for producing a p-type diffusion layer, and a method for producing a solar cell element can be produced.

The method for solving the above problems is as follows.

<1> A composition for forming a p-type diffusion layer, comprising: a glass powder containing an acceptor element, and a dispersion medium, wherein the glass powder includes a substance containing an acceptor element, and a glass component substance, the glass powder The content ratio of the above-mentioned receptor element-containing substance is from 1% by mass to 90% by mass.

<2> The composition for forming a p-type diffusion layer according to the above <1>, wherein the acceptor element is at least one selected from the group consisting of B (boron), Al (aluminum), and Ga (gallium).

<3> The composition for forming a p-type diffusion layer according to the above <1> or <2>, wherein the glass powder containing the above-mentioned acceptor element comprises: selected from the group consisting of B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O At least one of ₃ containing an acceptor element; and selected from the group consisting of SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, At least one glass component substance of SnO, ZrO ₂ and MoO ₃ .

<4> A method for producing a p-type diffusion layer, comprising: a step of forming a composition for forming a p-type diffusion layer according to any one of <1> to <3> above And the step of performing thermal diffusion treatment.

<5> A method for producing a solar cell element, comprising the step of applying a composition for forming a p-type diffusion layer according to any one of the above <1> to <3> on a semiconductor substrate, and performing thermal diffusion a step of forming a p-type diffusion layer and a step of forming an electrode on the formed p-type diffusion layer.

According to the present invention, in the manufacturing step of the solar cell element using the tantalum substrate, the internal stress in the tantalum substrate and the warpage of the substrate can be suppressed, and the p-type diffusion layer can be formed. Further, by setting the range of the content ratio of the substance containing the acceptor element of the invention, the surface resistance value is lowered, and the performance as a solar cell element can be improved.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

First, the composition for forming a p-type diffusion layer of the present invention will be described. Next, a method for producing a p-type diffusion layer and a solar cell element using a composition for forming a p-type diffusion layer will be described.

Furthermore, in the present specification, the term "process" means not only an independent step but also a case where it cannot be clearly distinguished from other steps, and if the step can achieve the intended effect, then Also included in this term. In addition, In the present specification, "~" means a range including the numerical values described before and after the minimum value and the maximum value, respectively. Further, in the present specification, when the amount of each component in the composition is referred to, when a plurality of substances corresponding to the respective components are present in the composition, unless otherwise specified, the presence of the composition is indicated. The total amount of the plurality of substances.

The composition for forming a p-type diffusion layer of the present invention includes a glass powder containing at least an acceptor element (hereinafter sometimes referred to simply as "glass powder"), and a dispersion medium, and may further contain other properties as needed. additive.

Here, the composition forming the p-type diffusion layer means that the acceptor element is contained, and the acceptor element can be thermally diffused by, for example, being applied to a tantalum substrate and then subjected to thermal diffusion treatment (calcination/sintering). A material that forms a p-type diffusion layer. By using the composition for forming a p-type diffusion layer of the present invention, the formation step of the p ⁺ -type diffusion layer and the step of forming the ohmic contact can be separated, thereby expanding the selection of the electrode material for forming the ohmic contact, and also Expanded options for electrode construction. For example, when 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 electrode does not need to be formed on the entire surface, and the comb-shaped electrode may be partially formed in a shape such as a comb shape. By forming a partial shape such as a film or a comb shape as described above, it is possible to form a p-type diffusion layer while suppressing internal stress in the ruthenium substrate and occurrence of warpage of the substrate.

Therefore, when the composition for forming a p-type diffusion layer of the present invention is applied, the generation of internal stress generated in the substrate and the warpage of the substrate in the previously widely used method are suppressed, and the previously widely used method is: printing The aluminum paste is then calcined, and a method of obtaining an ohmic contact while making the n-type diffusion layer into a p ⁺ -type diffusion layer.

Further, since the acceptor component in the glass powder is hardly sublimated during calcination, it is suppressed that the p-type diffusion layer is formed outside the desired region due to the generation of the volatilized gas. The reason for this is considered to be that, for example, the acceptor component is bonded to an element in the glass powder or introduced into the glass, so that it is difficult to volatilize.

Furthermore, the content ratio of the receptor element-containing substance in the glass powder contained in the composition for forming a p-type diffusion layer of the present invention is 1% by mass or more and 90% by mass or less. Thereby, the surface resistance value is lowered, and the performance as a solar cell element can be improved. The details of the substance containing the acceptor element will be described later.

The glass powder containing the acceptor element of the present invention will be described in detail. The term "receptor element" means an element which can form a p-type diffusion layer by being doped into a germanium 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 substance for introducing an acceptor element into the glass powder include B ₂ O ₃ , Al ₂ O ₃ , and Ga ₂ O ₃ , preferably selected from B ₂ O ₃ , Al. At least one of ₂ O ₃ and Ga ₂ O ₃ .

Further, the glass powder containing the acceptor element may be adjusted in composition ratio as needed, thereby controlling the melting temperature, the softening temperature, the glass transition temperature, the chemical durability, and the like. It is preferable to further contain the glass component substance described below.

Examples of the glass constituent component include SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, V ₂ O ₅ , and SnO. ZrO ₂ , MoO ₃ , La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , GeO ₂ , TeO ₂ , Lu ₂ O _{3 ,} etc., preferably selected from SiO ₂ , At least one of K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, SnO, ZrO ₂ , and MoO ₃ .

Specific examples of the glass powder containing the acceptor element include a system including both the above-described acceptor element-containing substance and the above-described glass component substance, and examples thereof include a B ₂ O ₃ —SiO ₂ system (containing an acceptor element). The system-glass component substance is described in the following order, the B ₂ O ₃ -ZnO system, the B ₂ O ₃ -PbO system, the B ₂ O ₃ individual system, and the like, including B ₂ O ₃ as a substance containing an acceptor element. , Al ₂ O ₃ -SiO ₂ system contains Al ₂ O ₃ and the like as a material system containing the receptor element, Ga ₂ O ₃ -SiO ₂ system, and comprises Ga ₂ O ₃ as the acceptor element-containing material systems like Glass powder.

Further, it may be a glass powder containing two or more kinds of substances containing an acceptor element, such as an Al ₂ O ₃ -B ₂ O ₃ system or a Ga ₂ O ₃ -B ₂ O ₃ system.

In the above, a glass containing one component or a composite glass containing two components is exemplified, but a glass powder containing three or more components such as a B ₂ O ₃ —SiO ₂ —Na ₂ O system may be used.

Further, the glass powder may be adjusted in composition ratio as needed, thereby controlling the melting temperature, the softening temperature, the glass transition temperature, the chemical durability, and the like.

In consideration of the doping concentration of the acceptor element in the ruthenium substrate, the melting temperature, the softening temperature, the glass transition temperature, and the chemical durability of the glass powder, the content ratio of the substance containing the acceptor element in the glass powder is 1% by mass or more. 90% by mass or less.

When the content ratio of the substance containing the acceptor element in the glass powder is less than 1 In the mass%, the doping concentration of the acceptor element in the tantalum substrate is too low, and the p-type diffusion layer is not sufficiently formed. In addition, when the content ratio of the substance containing the acceptor element is more than 90% by mass, the substance containing the acceptor element is volatilized in the thermal diffusion treatment, so that the diffusion of the acceptor element also reaches the side surface and the back surface, and not only the surface is formed into a p-type. The diffusion layer may have a p-type diffusion layer formed on the side surface and the back surface other than the desired portion.

Furthermore, the content ratio of the substance containing an acceptor element in the glass powder is preferably 2% by mass or more and 80% by mass or less, and more preferably 10% by mass or more and 70% by mass or less.

In particular, when the following two aspects are considered, the content ratio of the substance containing the acceptor element in the glass powder is more preferably 30% by mass or more and 70% by mass or less, and the above two aspects mean that the p-type is sufficiently formed even if one side is considered. The amount of the acceptor element of the diffusion layer is such that a certain amount or more of the acceptor element is added to the composition forming the p-type diffusion layer, and the sheet resistance of the surface of the formed p-type diffusion layer does not fall below a certain value. And the necessity to inhibit the volatilization of substances containing acceptor elements.

In addition, the content ratio of the glass component in the glass powder is preferably set in consideration of the melting temperature, the softening temperature, the glass transition temperature, and the chemical durability, and is generally preferably 10% by mass or more and 99% by mass or less. It is more preferably 20% by mass or more and 98% by mass or less, and still more preferably 30% by mass or more and 90% by mass or less.

Specifically, when it is a B ₂ O ₃ -SiO ₂ system glass, the content ratio of B ₂ O ₃ is preferably from 1% by mass to 90% by mass, more preferably from 2% by mass to 80% by mass.

The softening temperature of the glass powder is preferably from 200 ° C to 1000 ° C, more preferably from 300 ° C to 900 ° C from the viewpoint of diffusibility at the time of diffusion treatment and dripping.

Further, the softening temperature of the glass powder can be easily measured based on the endothermic peak by a well-known differential thermal analyzer (DTA).

The shape of the glass powder includes a substantially spherical shape, a flat shape, a block shape, a plate shape, a scale shape, and the like, and the coating property or uniform diffusion property to the substrate when the composition for forming the n-type diffusion layer is formed. From the viewpoint, it is preferable to be substantially spherical, flat, or plate-shaped. The particle diameter of the glass powder is not particularly limited, and is preferably 100 μm or less. When a glass powder having a particle diameter of 100 μm or less is used, a smoother coating film is easily obtained. Further, the particle diameter of the glass powder is more preferably 50 μm or less. Further, the particle diameter of the glass powder is more preferably 10 μm or less. Further, the lower limit is not particularly limited, but is preferably 0.01 μm or more.

Here, the particle diameter of the glass means an 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 the acceptor element was produced by the following procedure.

First, the raw material is weighed and filled into the crucible. Examples of the material of the crucible include platinum, platinum-rhodium, iridium, aluminum oxide, quartz, carbon, and the like, and are appropriately selected in consideration of the melting temperature, the environment, and the reactivity with the molten material.

Secondly, it is made into a melting by heating in an electric furnace at a temperature corresponding to the composition of the glass. liquid. At this time, it is preferable to stir so that the melt becomes uniform.

Then, the obtained melt flows out onto a graphite plate, a platinum plate, a platinum-ruthenium alloy plate, a zirconia plate or the like to vitrify the melt.

Finally, the glass is pulverized to form a 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 composition forming the p-type diffusion layer is determined in consideration of coatability, diffusibility of the acceptor element, and the like. In general, the content ratio of the glass powder in the composition forming the p-type diffusion layer 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, and still more preferably 1.5% by mass or less. The mass% or more is 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 refers to a medium in which the glass powder is dispersed in the composition. Specifically, a binder, a solvent, or the like is used as a dispersion medium.

As the binder, for example, polyvinyl alcohol, polypropylene decylamine, polyvinyl decylamine, polyvinylpyrrolidone, polyethylene oxide, polysulfonic acid, acrylamide sulfonic acid, fiber can be suitably selected. Ethers, cellulose derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch and starch derivatives, sodium alginate, xanthan, Guar gum and guar gum derivatives, scleroglucan and scleroglucan derivatives, tragacanth and xanthan gum derivatives, dextrin and dextrin derivatives, (meth)acrylic resin, (methyl Acrylate resin (for example, alkyl (meth)acrylate resin, dimethylaminoethyl (meth)acrylate resin, etc.) In addition to the olefin resin, the styrene resin, or the copolymers thereof, a decane resin may be appropriately selected. These may be used alone or in combination of two or more.

The molecular weight of the binder is not particularly limited, and is preferably adjusted in view of the desired viscosity as a composition.

Examples of the solvent include acetone, methyl ethyl ketone, methyl-n-propyl ketone, methyl-isopropyl ketone, methyl-n-butyl ketone, methyl-isobutyl ketone, and methyl group. N-pentyl ketone, methyl-n-hexyl ketone, diethyl ketone, dipropyl ketone, di-isobutyl ketone, trimethyl fluorenone, cyclohexanone, cyclopentanone, methylcyclohexanone, 2 a ketone solvent such as 4-pentanedione or acetonylacetone; diethyl ether, methyl ethyl ether, methyl-n-propyl ether, di-isopropyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyl Dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol di-n-propyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethyl 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, triethylene glycol methyl-n-hexyl ether, tetraethylene glycol dimethyl ether, tetraethylene Alcohol diethyl ether, tetra-diethylene glycol methyl ethyl ether, tetraethylene glycol methyl-n-butyl ether, diethylene glycol di-n-butyl ether, tetraethylene glycol methyl-n-hexyl ether, tetraethylene Alcohol 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, dipropylene glycol Base-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, tetra-dipropylene glycol methyl ethyl ether, An ether solvent such as tetrapropylene glycol methyl-n-butyl ether, dipropylene glycol di-n-butyl ether, tetrapropylene glycol methyl-n-hexyl ether or tetrapropylene glycol di-n-butyl ether; methyl acetate, ethyl acetate, n-propyl acetate, Isopropyl acetate, n-butyl acetate, isobutyl acetate, second butyl acetate, n-amyl acetate, second amyl acetate, 3-methoxybutyl acetate, methyl amyl acetate, acetic acid 2- Ethyl butyl acrylate, 2-ethylhexyl acetate, 2-(2-butoxyethoxy)ethyl acetate, benzyl acetate, cyclohexyl acetate, methylcyclohexyl acetate, decyl acetate, B Methyl acetate, ethyl acetate, diethylene glycol methyl ether, diethylene glycol monoethyl acetate, diethylene glycol-n-butyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, ethylene Alcohol diacetate, ethoxy triethylene glycol acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, diethyl oxalate, oxalic acid di- N-butyl ester, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ether propionate, ethylene glycol methyl ether acetate, ethylene Alcohol ether acetate, diethylene glycol methyl ether acetate, diethylene glycol diethyl ether acetate, diethylene glycol-n-butyl ether acetate, propylene glycol methyl ether acetate, propylene glycol diethyl ether acetate, An ester solvent such as propylene glycol propyl ether acetate, dipropylene glycol methyl ether acetate, dipropylene glycol diethyl ether acetate, γ-butyrolactone or γ-valerolactone; acetonitrile, N-methylpyrrolidone, N- Ethylpyrrolidone, N-propylpyrrolidone, N-butylpyrrolidone, N-hexylpyrrolidone, N-cyclohexylpyrrolidone, N,N-dimethylformamide, N,N-dimethyl An aprotic polar solvent such as acetamide or dimethyl hydrazine; methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, second butanol, tert-butanol, n-pentanol, Isoamyl alcohol, 2-methylbutanol, second pentanol, third Pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol, second hexanol, 2-ethylbutanol, second heptanol, n-octanol, 2-ethylhexanol, Dioctanol, n-nonanol, n-nonanol, second-undecanol, trimethylnonanol, second-tetradecanol, second heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol , an alcohol solvent such as benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol or tripropylene glycol; ethylene glycol methyl ether, ethylene glycol Alcohol 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, ethoxy triethylene glycol , glycol monoether ether such as tetraethylene glycol mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether; α-terpinene, α-product Alcohol, lauryl olefin, allo-ocimene, limonene, dipentene, α-pinene, β-pinene, terpineol, erysone, basilene, parsyl, etc. Alkene solvent; water. These may be used alone or in combination of two or more.

When the composition for forming the n-type diffusion layer is formed, from the viewpoint of coatability of the substrate, α-terpineol, diethylene glycol mono-n-butyl ether, and acetic acid 2-(2- are preferable. Butoxyethoxy)ethyl ester.

The content ratio of the dispersion medium in the composition forming the p-type diffusion layer is determined in consideration of coatability and receptor concentration.

Considering the coating property, the viscosity of the composition forming the p-type diffusion layer is preferably 10 mPa. S above to 1000000mPa. Below S, more preferably 50mPa. S above to 500000mPa. S below.

Next, the manufacturer of the p-type diffusion layer and the solar cell element of the present invention The law is explained.

First, an alkaline solution is applied to a tantalum substrate as a p-type semiconductor substrate to remove the damaged layer, and a texture structure is obtained by etching.

Specifically, the damaged layer of the crucible surface generated when slicing from the ingot was removed using 20% by mass of caustic soda. Then, etching was carried out by using a mixed solution of 1% by mass of caustic soda and 10% by mass of isopropyl alcohol to form a texture structure. By forming a texture structure on the light-receiving surface (surface) side, the solar cell element can promote an optical confinement effect and achieve high efficiency.

Next, the treatment is performed at 800 ° C to 900 ° C for several tens of minutes in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen to form an n-type diffusion layer in the same manner. At this time, in the method using the phosphorus oxychloride environment, the diffusion of phosphorus also reaches 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 in order to remove the n-type diffusion layer on the side.

Then, the composition for forming the p-type diffusion layer is applied onto the back surface of the p-type semiconductor substrate, that is, the n-type diffusion layer which is not the surface of the light-receiving surface. In the present invention, the coating method is not limited, and examples thereof include a printing method, a spin coating method, a brush coating method, a spray method, a doctor blade method, a roll coater method, an inkjet method, and the like.

The coating amount of the composition forming the p-type diffusion layer is not particularly limited. For example, the amount of the glass powder can be set to 0.01 g/m ² to 100 g/m ² , preferably 0.1 g/m ² to 10 g/m ² .

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

The semiconductor substrate coated with the composition for forming the p-type diffusion layer described above is subjected to thermal diffusion treatment at 600 ° C to 1200 ° C. By this thermal diffusion treatment, the acceptor element diffuses into the semiconductor substrate to form a p ⁺ -type diffusion layer. As the heat diffusion treatment, a known continuous furnace, a batch furnace, or the like can be applied. In addition, the furnace environment during the thermal diffusion treatment may be appropriately adjusted to air, oxygen, nitrogen, or the like.

The thermal diffusion treatment time can be appropriately selected in accordance with the content ratio of the acceptor element contained in the composition forming the p-type diffusion layer. For example, it can be set to 1 minute to 60 minutes, more preferably 2 minutes to 30 minutes.

Since a glass layer is formed on the surface of the formed p ⁺ -type diffusion layer, the glass layer is removed by etching. The etching can be carried out by 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.

Further, in the prior manufacturing method, the aluminum paste was printed on the back side and then calcined to convert the n-type diffusion layer into a p ⁺ -type diffusion layer while obtaining an ohmic contact. However, the aluminum layer formed of the aluminum paste has a low electrical conductivity, and in order to reduce the sheet resistance, the aluminum layer usually formed on the entire back surface must have a thickness of about 10 μm to 20 μm after firing. Further, if a thick aluminum layer is formed as described above, since the coefficient of thermal expansion of the crucible differs greatly from the coefficient of thermal expansion of aluminum, a large internal stress is generated in the crucible substrate during the calcination and cooling, and becomes The reason for warping.

This internal stress causes a problem that the crystal grain boundary of the crystal is damaged and the power loss is increased. Further, in the process of transferring the solar cell element in the module process or the connection with a copper wire called a tab wire, the solar cell element is easily broken. In recent years, as the slicing technology has been improved, the thickness of the tantalum substrate is being thinned, and the solar cell element tends to be more 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 composition for forming a p-type diffusion layer of the present invention described above, an electrode is additionally provided on the p ⁺ -type diffusion layer. Therefore, the material of the electrode for the back surface is not limited to aluminum, and for example, Ag (silver) or Cu (copper) or the like can be applied, and the thickness of the electrode on the back surface can be formed thinner than the previous thickness, and it is not necessary to form the entire surface. on. Therefore, internal stress and warpage in the tantalum substrate generated during the calcination and cooling can be reduced.

An anti-reflection film is formed on the n-type diffusion layer formed as described above. The antireflection film is formed using a well-known technique. For example, when the antireflection film is a tantalum nitride film, it is formed by a plasma chemical vapor deposition (CVD) method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses in the crystal, does not participate in the orbital of the bond of the helium atom, that is, the dangling bond and the hydrogen bond, and passivate the defect (hydrogen passivation).

More specifically, the mixed gas flow rate ratio NH ₃ /SiH ₄ is 0.05 to 1.0, the reaction chamber pressure is 0.1 Torr to 2 Torr, and the film formation temperature is 300 ° C to 550 ° C, so that the frequency of the plasma discharge is Formed under conditions of 100 kHz or more.

Printing on the anti-reflection film on the surface (light-receiving surface) by screen printing A surface electrode is coated with a metal paste and dried to form a surface electrode. The metal paste for surface electrodes contains metal particles and glass particles as essential components, and if necessary, a resin binder, other additives, and the like are contained.

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

The above electrode was calcined to prepare a solar cell element. When calcined in the range of 600 ° C to 900 ° C for several seconds to several minutes, the antireflection film as an insulating film is melted on the surface side by the glass particles contained in the metal paste for the electrode, and a part of the surface of the crucible is also melted. The metal particles (for example, silver particles) in the paste form a contact portion with the tantalum substrate and solidify. Thereby, the formed surface electrode and the germanium substrate are electrically connected. This is called fire through.

The shape of the surface electrode will be described. The surface electrode is composed of a bus bar electrode and a finger electrode that intersects the bus bar electrode.

Such a surface electrode can be formed by, for example, screen printing of the above-described metal paste, plating of an electrode material, vapor deposition of an electrode material by electron beam heating in a high vacuum, or the like. It is known that a surface electrode including a bus bar electrode and a finger electrode is generally used as an electrode on the light-receiving surface side, and a known method of forming a bus bar electrode and a finger electrode on the light-receiving surface side can be applied.

Further, in the above-described p-type diffusion layer and method for producing a solar cell element, in order to form an n-type diffusion layer on a germanium substrate as a p-type semiconductor substrate, phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen are used. The mixed gas, but a composition forming an n-type diffusion layer may also be used to form the n-type layer. In the composition for forming the n-type diffusion layer, an element of Group 15 such as P (phosphorus) or Sb (antimony) is contained as a donor element.

In the method of forming a composition for forming an n-type diffusion layer for the formation of an n-type diffusion layer, first, a composition for forming an n-type diffusion layer is applied to a light-receiving surface of a surface of a p-type semiconductor substrate, and is coated on the back surface. The composition for forming a p-type diffusion layer of the present invention is then subjected to thermal diffusion treatment at 600 ° C to 1200 ° C. By this thermal diffusion treatment, the donor element diffuses into the p-type semiconductor substrate to form an n-type diffusion layer, and the acceptor element diffuses on the back surface to form a p ⁺ -type diffusion layer. In addition to this step, the solar cell element was fabricated by the same steps as the above method.

In addition, the entire contents disclosed in Japanese Patent Application No. 2010-100225 are hereby incorporated by reference.

All of the documents, patent applications, and technical specifications described in the specification are the same as those which are specifically and individually described by reference to the respective documents, patent applications, and technical specifications, and are cited by reference. In this manual.

[Example]

Hereinafter, examples of the invention will be more specifically described, but the invention is not limited by the examples. Further, as long as there is no special description in advance, the reagents are all used in the chemicals. In addition, "%" means "% by mass" as long as there is no explanation in advance.

[Example 1]

B ₂ O ₃ -SiO ₂ system glass (B ₂ O ₃ : 10%) powder 20 g and ethyl group having a particle shape of a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 491 ° C using an automatic mortar mixing device 3 g of cellulose and 77 g of 2-(2-butoxyethoxy)ethyl acetate were mixed and pasteified to prepare a composition for forming a p-type diffusion layer.

Further, the glass particle shape was observed and judged using a TM-1000 scanning electron microscope manufactured by Hitachi High-Technologies Co., Ltd. The average particle diameter of the glass was calculated using a LS 13 320 laser scattering diffraction particle size distribution measuring apparatus (measuring wavelength: 632 nm) manufactured by Beckman Coulter Co., Ltd. The softening point of the glass is DTG-60H type differential heat manufactured by Shimadzu Corporation. The thermal weight synchronization measuring device was obtained from the differential heat (DTA) curve.

Then, the prepared paste was applied to the surface of the p-type ruthenium substrate by screen printing, and dried on a hot plate at 150 ° C for 5 minutes. Then, the film was subjected to thermal diffusion treatment 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 then washed with running water, followed by drying.

The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 90 Ω/□, and B (boron) was diffused to form a p-type diffusion layer. The sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

Further, 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]

A p-type diffusion layer was formed in the same manner as in Example 1 except that the thermal diffusion treatment time was set to 20 minutes. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 87 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

The sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 3]

A p-type diffusion layer was formed in the same manner as in Example 1 except that the time of the thermal diffusion treatment was set to 30 minutes. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 79 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 4]

The glass powder was replaced with a B ₂ O ₃ -SiO ₂ system glass powder (B ₂ O ₃ content: 30%) having a particle shape of a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 515 ° C. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 77 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 5]

The glass powder was replaced with a B ₂ O ₃ -SiO ₂ system glass powder (B ₂ O ₃ content: 50%) having a particle shape of a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 605 ° C. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 74 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 6]

The glass powder was replaced with a B ₂ O ₃ -SiO ₂ system glass powder (B ₂ O ₃ content: 60%) having a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 644 ° C. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 76 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 7]

The glass powder was replaced with a B ₂ O ₃ -SiO ₂ system glass powder (B ₂ O ₃ content: 70%) having a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 702 ° C. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 72 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 8]

The glass powder was replaced with a B ₂ O ₃ -SiO ₂ system glass powder (B ₂ O ₃ content: 85%) having a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 775 ° C. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 75 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 9]

The glass powder was replaced with a B ₂ O ₃ -ZnO system glass powder (B ₂ O ₃ content: 10%) having a particle shape of a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 505 ° C, in addition to A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 88 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 10]

The glass powder was replaced with a B ₂ O ₃ -PbO system glass powder (B ₂ O ₃ content: 40%) having a particle shape of a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 559 ° C, in addition to A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and a p-type diffusion layer was formed using the composition forming the p-type diffusion layer. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 68 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

On the other hand, the sheet resistance of the back surface was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed. In addition, warpage of the substrate did not occur.

[Example 11]

B ₂ O ₃ -SiO ₂ system glass (B ₂ O ₃ content: 10%) powder 19.7 g and Ag 0.3 g, ethyl cellulose 0.3 g, 2-(2-butoxyl acetate) using an automatic mortar mixing device 7 g of ethoxy)ethyl ester was mixed and pasteified to prepare a composition for forming a p-type diffusion layer. Thereafter, the same operation as in Example 1 was carried out.

As a result, there is no deposit of glass on the cleaned substrate, and the deposit has been easily removed. Further, the sheet resistance of the surface was 85 Ω/□, and it was judged that the p-type diffusion layer was not substantially formed on the back surface. In addition, warpage of the substrate did not occur.

[Comparative Example 1]

The glass powder was replaced with a B ₂ O ₃ -SiO ₂ system glass powder (B ₂ O ₃ content: 0.5%) having a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 466 ° C. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and the composition for forming the p-type diffusion layer was subjected to thermal diffusion treatment. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 1,000,000 Ω/□ or more and could not be measured, and it was judged that the p-type diffusion layer was not substantially formed.

[Comparative Example 2]

The glass powder was replaced with a B ₂ O ₃ —SiO ₂ system glass powder (B ₂ O ₃ content: 95%) having a particle shape of a substantially spherical shape, an average particle diameter of 3.1 μm, and a softening temperature of 805° C., A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and the composition for forming the p-type diffusion layer was subjected to thermal diffusion treatment. The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 70 Ω/□, and B (boron) was diffused to form a p-type diffusion layer.

However, the sheet resistance of the back surface was 123 Ω/□, and a p-type diffusion layer was also formed on the back surface.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

Claims (5)

A composition for forming a p-type diffusion layer, comprising: a glass powder containing an acceptor element; and a dispersion medium, wherein the composition forming the p-type diffusion layer does not contain a material for forming an electrode, wherein the glass powder includes an acceptor element The content of the glass component in the glass powder is 10% by mass or more and 99% by mass or less, and the content ratio of the element containing the acceptor element in the glass powder is 1% by mass or more. 90% by mass or less. The composition for forming a p-type diffusion layer according to claim 1, wherein the acceptor element is at least one selected from the group consisting of B (boron), Al (aluminum), and Ga (gallium). The composition for forming a p-type diffusion layer according to claim 1, wherein the glass powder containing the above-mentioned acceptor element comprises at least one selected from the group consisting of B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ . a substance containing an acceptor element; and selected from the group consisting of SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, SnO, ZrO ₂ , And at least one glass component substance in MoO ₃ . A method of producing a p-type diffusion layer, comprising: a step of coating a composition for forming a p-type diffusion layer according to any one of claims 1 to 3; The step of performing thermal diffusion treatment. A method for producing a solar cell element, comprising: coating a semiconductor substrate with a composition for forming a p-type diffusion layer according to any one of claims 1 to 3; performing thermal diffusion treatment a step of forming a p-type diffusion layer; and a step of forming an electrode on the formed p-type diffusion layer.