TWI488222B - 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 the 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 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 becomes a 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 such a thick aluminum layer is formed, since the thermal expansion coefficient of the crucible differs greatly from the thermal expansion coefficient of aluminum, the difference causes a large internal stress to be generated in the crucible substrate during the calcination and cooling. The reason is that the crystal grain boundary is damaged, the crystal defects are increased, and the warpage is caused.

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, when the paste composition described in Japanese Laid-Open Patent Publication No. 2003-223813 is used, there is 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 generation of internal stress and substrate warpage in the tantalum substrate, and forming A composition of a p-type diffusion layer for forming a p-type diffusion layer, a method for producing a p-type diffusion layer, and a method for producing a solar cell element.

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 having a softening temperature of 300 ° C to 950 ° C, and a dispersion medium.

<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, SnO, ZrO ₂ At least one glass component substance of CeO ₂ and MoO ₃ .

The composition for forming a p-type diffusion layer according to any one of the above aspects, wherein the glass powder has a crystallization temperature of 1050 ° C or higher.

<5> A method of 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 the above <1> to <4>, and a method of performing thermal diffusion treatment step.

<6> 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 <4> 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.

[Effects of the Invention]

According to the present invention, it is possible to provide a composition for forming a p-type diffusion layer by forming a p-type diffusion layer by suppressing generation of internal stress and substrate warpage in the ruthenium substrate in the manufacturing process of the solar cell element using the ruthenium substrate. A method for producing a p-type diffusion layer and a method for producing a solar cell element.

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 the present specification, "to" means a range including the numerical values described before and after the minimum value and the maximum value. 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 (hereinafter, simply referred to as "glass powder") having at least an acceptor element and having a softening temperature of 300 ° C to 950 ° C, and a dispersion medium, and further considering the coating. Cloth, etc., may also contain other additives as needed.

Here, the composition forming the p-type diffusion layer means that the acceptor element is contained, and the acceptor element can be thermally diffused to form a p by, for example, being applied to a germanium substrate and then subjected to thermal diffusion treatment (calcination). The material of the 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 the electrode into 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 to make the n-type diffusion layer into a p ⁺ -type diffusion layer while obtaining an ohmic contact.

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

Specific examples of the glass powder containing the acceptor element include both the above-mentioned acceptor element-containing substance and the above-mentioned glass component substance, and examples thereof include a B ₂ O ₃ —SiO ₂ system (a substance containing an acceptor element). The order of the glass component substances is the same as the above, and the B ₂ O ₃ -ZnO system, the B ₂ O ₃ -PbO system, the B ₂ O ₃ -CeO ₂ system, the B ₂ O ₃ individual system or the like contains B ₂ O ₃ as a content. A system of a substance of an acceptor element, an Al ₂ O ₃ -SiO ₂ system or the like containing Al ₂ O ₃ as a substance containing an acceptor element, and a Ga ₂ O ₃ -SiO ₂ system or the like containing Ga ₂ O ₃ as a receptor. A glass powder of a material system such as an element.

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 may be, for example, a B ₂ O ₃ —SiO ₂ —Na ₂ O system, a B ₂ O ₃ —SiO ₂ —CeO ₂ system, or the like. A glass powder containing three or more substances.

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, the crystallization temperature, and the chemical durability. In general, it is preferably 0.1% by mass or more and 95% by mass. % or less, more preferably 0.5% by mass or more and 90% by mass or less.

Specifically, when it is a B ₂ O ₃ -CeO ₂ system glass, the content ratio of CeO ₂ is preferably from 1% by mass to 50% by mass, more preferably from 3% by mass to 40% by mass. By the content ratio, the p-type diffusion layer can be formed more uniformly.

Further, the softening temperature of the glass powder is important from the viewpoint of obtaining a uniform p-type diffusion layer by diffusing the acceptor element more efficiently into the ruthenium substrate during the thermal diffusion treatment described later. In the present invention, the softening temperature of the glass powder is from 300 ° C to 950 ° C, preferably from 350 ° C to 900 ° C, more preferably from 370 ° C to 850 ° C, still more preferably from 400 ° C to 800 ° C.

When the softening temperature of the glass powder is less than 300° C., the glass component is easily crystallized during the thermal diffusion treatment at a high temperature, and the etching removal property of the glass component after the thermal diffusion treatment tends to be lowered. The acceptor element tends to be volatilized due to a decrease in melting point, and tends to form a p-type diffusion layer in an unnecessary portion during thermal diffusion treatment. Further, when the softening temperature of the glass powder exceeds 950 ° C, there is a tendency that the glass is hardly softened during the heat diffusion treatment, and the glass powder maintains a granular shape, so that the glass component is not uniformly covered on the ruthenium substrate under the microscopic state. When the acceptor element is diffused, the formability of the p-type diffusion layer becomes uneven, and the sheet resistance value increases.

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).

Further, in the present invention, the crystallization temperature of the glass powder is preferably 1050 ° C or higher, more preferably 1100 ° C or higher, and still more preferably 1200 ° C or higher. When the crystallization temperature is 1050 ° C or higher, crystallization of the glass component during thermal diffusion treatment is suppressed. Thereby, the residual of the crystallizing compound is suppressed in the glass component etching removal step after the thermal diffusion treatment, and the etching removal property of the glass component is improved.

Further, the crystallization temperature of the glass powder can be easily measured by a known differential thermal analyzer (DTA) based on the peak of heat generation.

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, molybdenum-niobium, tantalum, alumina, quartz, carbon, and the like, and are appropriately selected in consideration of the melting temperature, the environment, and the reactivity with the molten material.

Next, a molten metal is prepared by heating in an electric furnace at a temperature corresponding to the composition of the glass. 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, cellulose ethers, cellulose derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch and starch derivatives, sodium alginate, Sanxian Xanthan, guar and guar derivatives, scleroglucan, tragacanth or dextrin derivatives, (meth)acrylic resins, (meth) acrylate resins ( For example, a (meth)acrylic acid alkyl ester resin, a (meth)acrylic acid dimethylaminoethyl ester resin, etc., a butadiene resin, a styrene resin, these copolymers, a decane resin, etc. are mentioned. 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, three Propylene 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, tetrapropylene glycol methyl- An ether solvent such as 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, B 3-methoxybutyl ester, methyl amyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, 2-(2-butoxyethoxy)ethyl acetate, benzyl acetate, Cyclohexyl acetate, methylcyclohexyl acetate, decyl acetate, methyl acetate, ethyl acetate, diethylene glycol methyl ether, diethylene glycol monoethyl ether, diethylene glycol acetate - N-butyl ether, dipropylene glycol methyl ether acetate, dipropylene glycol ethyl acetate, ethylene glycol diacetate, ethoxy triethylene glycol acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, Diethyl oxalate, di-n-butyl oxalate, 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 glycol ethyl ether acetate, diethylene glycol methyl ether acetate, diethylene glycol diethyl ether acetate, diethylene glycol-n-butyl ether acetate, propylene glycol methyl ether acetate Ester, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, dipropylene glycol methyl ether acetate, dipropylene glycol diethyl ether acetate, γ-butyrolactone, γ-valerolactone and other ester solvents; acetonitrile, N -A Pyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone, N-butylpyrrolidone, N-hexylpyrrolidone, N-cyclohexylpyrrolidone, N,N-dimethylformamide, N , aprotic polar solvent such as N-dimethylacetamide, dimethyl hydrazine; methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, second butanol, third Alcohol, 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, second octanol, n-nonanol, n-nonanol, second-undecanol, trimethylnonanol, Di-tetradecanol, second-heptadecanol, phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethylene glycol, 1,2-propanediol, 1,3-butanediol, diethylene glycol Alcohol solvent such as dipropylene glycol, triethylene glycol or tripropylene glycol; ethylene glycol methyl ether, ethylene glycol ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, two Ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-hexyl ether, ethoxy triethylene glycol, tetraethylene glycol mono-n-butyl ether, C a glycol monoether solvent such as alcohol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether or tripropylene glycol monomethyl ether; α-terpinene, α-terpineol, laurylene, allo-olene (allo) -ocimene), a terpene solvent such as limonene, dipentene, α-pinene, β-pinene, terpineol, terpene ketone, basilene, and water celery; 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.

The viscosity of the composition forming the p-type diffusion layer is preferably from 10 mPa·S or more to 1,000,000 mPa·S or less, more preferably from 50 mPa·S or more to 500,000 mPa·s or less, in view of coatability.

Next, a method of manufacturing the p-type diffusion layer and the solar cell element of the present invention will be described.

An alkaline solution is applied to the tantalum substrate as the p-type semiconductor substrate 10 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 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 on the surface opposite to the light-receiving surface, to form a composition layer for forming a p-type diffusion layer. 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 may 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 case, it is dried at a temperature of about 80 ° C to 300 ° C 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 p-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. Further, the furnace environment during the heat diffusion treatment may be appropriately adjusted to air, oxygen, nitrogen, or the like as needed.

The heat 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, or the softening temperature of the glass powder, and the like. For example, it can be set to 1 minute to 60 minutes, more preferably 5 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 make the n-type diffusion layer into the 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, when 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 it becomes the cause of 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) may be applied, and the thickness of the electrode on the back surface may be formed thinner than the previous thickness, and it is not necessary to form the entire portion. On the surface. 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 to discharge the plasma. It is formed under conditions of 100 kHz or more.

On the antireflection film of the surface (light-receiving surface), a metal paste for surface electrode coating was applied by screen printing 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 for 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 the 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 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.

Further, the entire contents disclosed in Japanese Patent Application No. 2010-100227 are incorporated herein 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. In addition, as long as there is no special description in advance, all reagents are used as chemicals. In addition, "%" means "% by mass" as long as there is no explanation in advance.

[Example 1]

B ₂ O ₃ -CeO ₂ system glass having an average particle diameter of 4.9 μm (B ₂ O ₃ : 39.6%, CeO ₂ : 10%, BaO: 10.4%, using an automatic mortar mixing device). MoO ₃ : 10%, ZnO: 30%) 20 g of powder and 0.3 g of ethyl cellulose and 7 g of 2-(2-butoxyethoxy)ethyl acetate were mixed and pasteified to form a p-type. The composition of the diffusion layer.

The B ₂ O ₃ -CeO ₂ system glass powder was heated by a thermal analysis device (TG-DTA, DTG60H type, measurement conditions: heating rate 20 ° C / min, air flow rate 100 ml / min) manufactured by Shimadzu Corporation (share) As a result of the analysis, the softening temperature was 600 °C.

Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

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.

Next, the prepared paste (the composition forming the p-type diffusion layer) is applied onto one surface of a p-type germanium substrate (hereinafter sometimes referred to as "back surface") by screen printing, and heated at 150 ° C. Dry on the plate for 5 minutes. Then, heat diffusion treatment was performed for 10 minutes in an electric furnace set to 1000 ° C, and then, in order to remove the glass layer, the substrate was immersed in 10% hydrofluoric acid for 5 minutes, and then washed with running water. Thereafter, drying is carried out.

The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 45 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate. The results are shown in Table 1.

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 15 minutes. The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 35 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 3]

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 30 minutes. The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 20 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 4]

The glass powder was set to a B ₂ O ₃ -ZnO system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 40%, ZnO: 40%, CeO ₂ : 10%, MgO: 5). A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1 except that %, CaO: 5%) was used, and the p-type diffusion layer was formed using the composition forming the p-type diffusion layer. Further, the softening temperature of the glass powder was 580 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 48 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 5]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 30%, SiO ₂ : 50%, CeO ₂ : 10%, ZnO). :10%), except that a composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and the composition for forming a p-type diffusion layer was used to form a p-type diffusion layer. Further, the glass powder had a softening temperature of 680 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 52 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 6]

A p-type diffusion layer was formed in the same manner as in Example 5 except that the thermal diffusion treatment time was set to 30 minutes. The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 33 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 7]

The glass powder was set to a B ₂ O ₃ -PbO system glass (B ₂ O ₃ : 30%, PbO: 50%, ZnO: 20%) having a substantially spherical particle shape and an average particle diameter of 3.2 μm. A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and the composition for forming a p-type diffusion layer was used to form a p-type diffusion layer. Further, the softening temperature of the glass powder was 340 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 17 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 8]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 30%, SiO ₂ : 10%, PbO: 40%, ZnO: A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1 except that 10%, CaO: 10%), and the p-type diffusion layer was formed using the composition forming the p-type diffusion layer. Further, the softening temperature of the glass powder was 370 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 25 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 9]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 30%, SiO ₂ : 10%, PbO: 30%, ZnO: A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1 except that 20%, NaO: 10%), and the composition for forming a p-type diffusion layer was used to form a p-type diffusion layer. Further, the softening temperature of the glass powder was 390 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 31 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 10]

The glass powder was set to a B ₂ O ₃ -ZnO system glass having a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 30%, ZnO: 40%, CaO: 20%, Al ₂ O _{3 )} :10%), except that a composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1, and the composition for forming a p-type diffusion layer was used to form a p-type diffusion layer. Further, the softening temperature of the glass powder was 505 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 43 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 11]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 50%, SiO ₂ : 10%, ZnO: 30%, CaO: 10), and the composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1 except that the thermal diffusion treatment time was set to 20 minutes, and the p-type diffusion layer was used to form a p-type. Diffusion layer. Further, the softening temperature of the glass powder was 690 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 56 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 12]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass (B ₂ O ₃ : 22%, SiO ₂ : 58%, CaO: 20%) having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm. Except that the composition for forming the 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 used to form a p-type diffusion layer. Further, the softening temperature of the glass powder was 850 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 78 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 13]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass (B ₂ O ₃ : 25%, SiO ₂ : 60%, CaO: 15%) having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm. Except that the composition for forming the 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 used to form a p-type diffusion layer. Further, the softening temperature of the glass powder was 880 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface coated with the side on which the p-type diffusion layer was formed was 82 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Example 14]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 20%, SiO ₂ : 65%, CaO: 10%, Al _{2 )} A composition for forming a p-type diffusion layer was prepared in the same manner as in Example 1 except that O ₃ : 5%), and the composition for forming a p-type diffusion layer was used to form a p-type diffusion layer. Further, the softening temperature of the glass powder was 940 °C. Further, the crystallization temperature is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was 96 Ω/□, and B (boron) was diffused to form a p ⁺ -type diffusion layer. On the other hand, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was too large to 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 on the substrate.

[Comparative Example 1]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm (B ₂ O ₃ : 10%, SiO ₂ : 20%, pbO: 40%, NaO: 30%), except that 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. Further, the softening temperature of the glass powder was 240 °C.

B (boron) is diffused on the surface coated with the side on which the composition forming the p-type diffusion layer is applied to form a p ⁺ -type diffusion layer. In addition, the sheet resistance of this surface was 63 Ω/□. However, the sheet resistance of the portion where the composition for forming the p-type diffusion layer was not applied was 70 Ω/□, and the p ⁺ -type diffusion layer was formed to an unnecessary portion. Furthermore, warpage of the substrate does not occur on the substrate.

[Comparative Example 2]

The glass powder was set to a B ₂ O ₃ -SiO ₂ system glass (B ₂ O ₃ : 5%, SiO ₂ : 93%, NaO: 2%) having a particle shape of a substantially spherical shape and an average particle diameter of 3.2 μm. Except that the composition for forming the 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. Further, the softening temperature of the glass powder is 1100 ° C or more, which exceeds the measurement range of the thermal analysis apparatus.

The sheet resistance of the surface on the side on which the composition on which the p-type diffusion layer was formed was too large to be measured, and it was judged that the p ⁺ -type diffusion layer was not substantially formed. Furthermore, warpage of the substrate does not occur on the substrate.

As described above, by using the composition for forming a p-type diffusion layer of the present invention, the p-type diffusion layer can be uniformly formed without causing warpage of the ruthenium substrate.

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 (6)

A composition for forming a p-type diffusion layer, which is a composition for forming a p-type diffusion layer, the method for forming the p-type diffusion layer comprising: applying the composition for forming the p-type diffusion layer described above to a step of forming a composition layer forming a p-type diffusion layer on the semiconductor substrate; a step of heat-treating the semiconductor substrate on which the composition layer forming the p-type diffusion layer is formed, and forming a p-type diffusion layer on the semiconductor substrate; a step of removing the glass formed on the surface of the p-type diffusion layer, the composition forming the p-type diffusion layer comprising: a glass powder containing an acceptor element and having a softening temperature of 300 ° C to 950 ° C; and a dispersion medium. 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, SnO, ZrO ₂ , CeO ₂ and MoO ₃ at least one glass component material. The composition for forming a p-type diffusion layer according to claim 1, wherein the glass powder has a crystallization temperature of 1050 ° C or higher. 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 4; and a step of performing a thermal diffusion treatment. A method of manufacturing 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 4; 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.