JP2013026471A - P-type diffusion layer formation composition, manufacturing method of p-type diffusion layer, and manufacturing method of solar cell element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a p-type diffusion layer formation composition, a manufacturing method of a p-type diffusion layer, and a manufacturing method of a solar cell element capable of forming a p-type diffusion layer without causing an internal stress and a warpage in a silicon substrate in a manufacturing step of a solar cell element using the silicon element and obtaining a sufficient ohmic contact even if the step is simplified.SOLUTION: A p-type diffusion layer formation composition contains a glass powder including an acceptor element and a dispersion medium. A p-type diffusion layer and a solar cell element having this p-type diffusion layer are manufactured by coating this p-type diffusion layer formation composition on a semiconductor substrate and performing thermal diffusion treatment.

Description

  The present invention relates to a solar cell element p-type diffusion layer forming composition, a p-type diffusion layer manufacturing method, and a solar cell element manufacturing method. More specifically, the present invention relates to the internal stress of a silicon substrate as a semiconductor substrate. The present invention relates to a technique for forming a p-type diffusion layer that can be reduced to suppress damage at crystal grain boundaries, to suppress crystal defect growth, and to suppress warpage.

The manufacturing process of the conventional silicon solar cell element is demonstrated.
First, a p-type silicon substrate having a textured structure formed on the light receiving surface is prepared so as to promote the light confinement effect, and then a donor element-containing compound such as phosphorus oxychloride (POCl ₃ ), nitrogen, oxygen In this mixed gas atmosphere, several tens of minutes are performed at 800 ° C. to 900 ° C. to uniformly form the n-type diffusion layer on the substrate. In this conventional method, since phosphorus is diffused using a mixed gas, n-type diffusion layers are formed not only on the surface but also on the side surface and the back surface. Therefore, a side etching process for removing the side n-type diffusion layer is necessary. Further, the n-type diffusion layer on the back surface needs to be converted into a p ⁺ -type diffusion layer. An aluminum paste is applied on the n-type diffusion layer on the back surface, and this is baked, and the n-type diffusion layer is diffused by aluminum diffusion. To a p ⁺ type diffusion layer.

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

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

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

Japanese Patent Laid-Open No. 2003-223813

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

Means for solving the problems are as follows.
<1> A p-type diffusion layer forming composition containing a glass powder containing an acceptor element and silver oxide, and a dispersion medium.
<2> The p-type diffusion layer forming composition according to <1>, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium).
<3> The glass powder containing the acceptor element is at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , AgO, SiO ₂ , K ₂ O, At least one glass selected from Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, V ₂ O ₅ , SnO, ZrO ₂ , and MoO _3. The p-type diffusion layer forming composition according to the above <1> or <2>, comprising a constituent component.

<4> A p-type diffusion having a step of applying the p-type diffusion layer forming composition according to any one of <1> to <3> on a semiconductor substrate and a step of performing a thermal diffusion treatment. Layer manufacturing method.
<5> A step of applying the p-type diffusion layer forming composition according to any one of <1> to <3> on a semiconductor substrate and a thermal diffusion treatment to form a p-type diffusion layer. The manufacturing method of the solar cell element which has a process and the process of forming an electrode on the formed n type diffused layer.
<6> The glass layer formed on the n-type diffusion layer is not removed between the step of forming the n-type diffusion layer and the step of forming the electrode, or a part of the glass layer is removed. The method for producing a solar cell element according to <5>, wherein the solar cell element is removed.

  According to the present invention, in the manufacturing process of a solar cell element using a silicon substrate, it is possible to form a p-type diffusion layer without generating internal stress in the silicon substrate and warping of the substrate, thereby simplifying the process. However, sufficient ohmic contact can be obtained.

It is sectional drawing which shows notionally an example of the manufacturing process of the solar cell element of this invention. (A) is the top view which looked at the solar cell element from the surface, (B) is the perspective view which expands and shows a part of (A).

First, the p-type diffusion layer forming composition of the present invention will be described, and then a p-type diffusion layer using the p-type diffusion layer forming composition and a method for producing a solar cell element will be described.
In this specification, the term “process” is not limited to an independent process, and even if it cannot be clearly distinguished from other processes, the term “process” is used if the intended action of the process is achieved. included. In the present specification, “to” indicates a range including the numerical values described before and after the values as a minimum value and a maximum value, respectively.

The p-type diffusion layer forming composition of the present invention contains a glass powder containing at least an acceptor element and silver oxide (hereinafter may be simply referred to as “glass powder”) and a dispersion medium, and further has coating properties and the like. In consideration of the above, other additives may be contained as necessary.
Here, the p-type diffusion layer forming composition contains glass powder containing an acceptor element and silver oxide, and after applying to the silicon substrate, the acceptor element can be thermally diffused to form a p-type diffusion layer. Material. By using the p-type diffusion layer forming composition of the present invention, the p ⁺ -type diffusion layer forming step and the ohmic contact forming step can be separated, and the choice of electrode material for forming the ohmic contact is widened. The options also expand. For example, if a low resistance material such as silver is used for the electrode, a low resistance can be achieved with a thin film thickness. Further, the electrodes need not be formed on the entire surface, and may be partially formed like a comb shape. As described above, by forming a partial shape such as a thin film or a comb shape, it is possible to form a p-type diffusion layer while suppressing the occurrence of internal stress in the silicon substrate and warping of the substrate.

Therefore, when the p-type diffusion layer forming composition of the present invention is applied, a conventionally widely used method, that is, printing an aluminum paste and firing it to turn the n-type diffusion layer into a p ⁺ -type diffusion layer. At the same time, the internal stress in the substrate and the warpage of the substrate that are generated by the method of obtaining the ohmic contact are suppressed.
Moreover, since the acceptor component in glass powder is hard to volatilize also during baking, it is suppressed that a p-type diffused layer is formed except for a desired area | region by generation | occurrence | production of volatilization gas. The reason for this is considered that the acceptor component is bonded to an element in the glass powder or is taken into the glass, so that it is difficult to volatilize.

  Here, in the present invention, glass powder containing silver oxide is used. This silver oxide is deposited as silver particles in a glass layer formed on the p-type diffusion layer through a thermal diffusion treatment step. When the silver particles are distributed in the glass layer, the conductivity of the glass layer itself can be increased. As a result, a good ohmic contact can be formed between the electrode and the silicon substrate without removing the glass layer by an etching step before forming the electrode on the p-type diffusion layer. Therefore, according to the present invention, even when the glass layer etching step is omitted, the ohmic contact between the electrode and the p-type diffusion layer becomes sufficient, and it is possible to prevent the process from becoming complicated.

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

  The glass powder can control the melting temperature, softening temperature, glass transition temperature, chemical durability, and the like by adjusting the component ratio as necessary.

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

  The content ratio of the acceptor element-containing substance in the glass powder is preferably set in consideration of the melting temperature, the softening temperature, the acceptor element doping behavior, and the chemical durability, and is generally 1% by mass to 90% by mass. The content is preferably 3% by mass or more and more preferably 80% by mass or less.

The content ratio of silver oxide in the glass powder is preferably set in consideration of the precipitation amount of silver particles, the melting temperature, the softening temperature, and the chemical durability, and is generally 1% by mass to 75% by mass. It is preferably 3% by mass or more and 70% by mass or less.
Further, in the glass powder, the content of silver oxide with respect to the acceptor element-containing substance is preferably set appropriately in consideration of the precipitation amount of silver particles, the melting temperature, the softening temperature, and the chemical durability. % To 200% by mass, and more preferably 5% to 150% by mass.

Moreover, it is preferable that glass powder contains the glass component substance described below.
Examples of glass component materials include SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, V ₂ O ₅ , SnO, and ZrO _{2. , WO 3, MoO 3, MnO} , La 2 O 3, Nb 2 O 5, Ta 2 O 5, Y 2 O 3, TiO 2, GeO 2, TeO 2 , and _Lu 2 _{O 3} and the like, _SiO 2, At least selected from K ₂ O, Na ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, V ₂ O ₅ , SnO, ZrO ₂ , and MoO ₃ It is preferable to use one type.

Specific examples of the glass powder containing an acceptor element include a system containing the acceptor element-containing substance, silver oxide, and the glass component substance, and a B ₂ O ₃ —AgO—SiO ₂ system (acceptor element-containing substance—oxidation). silver - described in the order of the glass component material, hereinafter the _{same), B 2 O 3 -AgO-} ZnO _-based, B ₂ O 3 -AgO-PbO system, etc. of the acceptor element-containing material as a _B 2 _{O 3} system including, Al ₂ O ₃ -AgO-SiO ₂ system or the like of the acceptor element-containing material as a system containing _Al 2 _{O 3,} glass, such as systems containing _Ga 2 _{O 3} as the acceptor element-containing material of Ga ₂ O 3 -AgO-SiO ₂ system, etc. Is mentioned. It may also be a glass powder _B 2 _O 3 -AgO system or the like which does not contain a glass component material.

_{Incidentally, B 2 O 3 -AgO-Al} 2 O 3 _system, such as the _{Ga 2 O 3 -AgO-B 2} O 3 system or the like, may be a glass powder containing two or more acceptor element-containing material.
In the above, a two-component glass or a composite glass containing three components is exemplified, but glass powder containing four or more kinds of substances such as B ₂ O ₃ —AgO—SiO ₂ —Na ₂ O may be used as necessary.

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

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

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

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

  The content ratio of the glass powder containing the acceptor element and the silver oxide in the p-type diffusion layer forming composition is determined in consideration of applicability, diffusibility of the acceptor element, and the like. Generally, the content ratio of the glass powder in the p-type diffusion layer forming composition is preferably 0.1% by mass or more and 95% by mass or less, and more preferably 1% by mass or more and 90% by mass or less.

Next, the dispersion medium will be described.
The dispersion medium is a medium in which the glass powder is dispersed in the composition. Specifically, a binder, a solvent, or the like is employed as the dispersion medium.

  Examples of the binder include polyvinyl alcohol, polyacrylamides, polyvinyl amides, polyvinyl pyrrolidone, polyethylene oxides, polysulfonic acid, acrylamide alkyl sulfonic acid, cellulose ethers, cellulose derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch And starch derivatives, sodium alginates, xanthan, gua and gua derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, (meth) acrylic acid resins, (meth) acrylic acid ester resins (e.g. , Alkyl (meth) acrylate resins, dimethylaminoethyl (meth) acrylate resins, etc.), butadiene resin , Styrene resin, or copolymers thereof, Additional be appropriately selected siloxane resin. These are used singly or in combination of two or more.

  The molecular weight of the binder is not particularly limited, and it is desirable to adjust appropriately in view of the desired viscosity of the composition.

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

The content ratio of the dispersion medium in the p-type diffusion layer forming composition is determined in consideration of applicability and acceptor concentration.
The viscosity of the p-type diffusion layer forming composition is preferably 10 mPa · s or more and 1000000 mPa · s or less, more preferably 50 mPa · s or more and 500000 mPa · s or less in consideration of applicability.

  Next, the manufacturing method of the p-type diffusion layer and solar cell element of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view conceptually showing an example of the manufacturing process of the solar cell element of the present invention. In the subsequent drawings, common constituent elements are denoted by the same reference numerals.

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

Next, in FIG. 1B, the n-type diffusion layer 12 is uniformly formed by performing several tens of minutes at 800 ° C. to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen, and oxygen. To do. At this time, in the method using the phosphorus oxychloride atmosphere, the diffusion of phosphorus extends to the side surface and the back surface, and the n-type diffusion layer is formed not only on the surface but also on the side surface and the back surface. Therefore, side etching is performed to remove the n-type diffusion layer on the side surface.

1 (3), the p-type diffusion layer forming composition is applied on the n-type diffusion layer on the back surface of the p-type semiconductor substrate 10, that is, the surface that is not the light receiving surface. The physical layer 13 is formed. In the present invention, the coating method is not limited, and examples thereof include a printing method, a spin method, a brush coating, a spray method, a doctor blade method, a roll coater method, and an ink jet method.
Is not particularly limited as coated amount of the p-type diffusion layer forming composition, for example, be a 0.05g ^{/ m 2} ~1.05g ^/ m 2 as a glass powder content, 0.065 g / ^{m 2} It is preferable that it is -0.02 g / m < ² >.

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

The semiconductor substrate coated with the p-type diffusion layer forming composition is heat-treated at 600 ° C. to 1200 ° C. By this heat treatment, the acceptor element diffuses into the semiconductor substrate, and a p ⁺ -type diffusion layer 14 is formed. A known continuous furnace, batch furnace, or the like can be applied to the heat treatment.
The thermal diffusion treatment time can be appropriately selected according to the content of the acceptor element contained in the p-type diffusion layer forming composition. For example, it may be 1 minute to 60 minutes, and more preferably 2 minutes to 30 minutes.

Since a glass layer (not shown) is formed on the surface of the formed p ⁺ -type diffusion layer 14, this glass is removed by etching in a normal method. As the etching, a known method such as a method of immersing in an acid such as hydrofluoric acid or a method of immersing in an alkali such as caustic soda can be applied.

Here, according to the present invention, silver particles are deposited on the glass phase on the surface of the p ⁺ -type diffusion layer 14, and the glass layer itself exhibits high conductivity. Therefore, it is possible to proceed to the next step (formation of an antireflection film) without performing the etching. Alternatively, without completely removing the glass layer, it is possible to leave a part and proceed to the next step. The presence or absence of the etching step and the degree of etching can be appropriately selected in consideration of the thickness of the formed glass layer, the amount of silver particles deposited, the conductivity of the glass layer, and the like. Therefore, according to the manufacturing method of the present invention, the etching process of the glass layer becomes unnecessary, or etching until the glass layer is completely removed is not required, and the process is simplified.

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

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

In FIG. 1 (4), an antireflection film 16 is formed on the n-type diffusion layer 12 formed above. The antireflection film 16 is formed by applying a known technique. For example, when the antireflection film 16 is a silicon nitride film, it is formed by a plasma CVD method using a mixed gas of SiH ₄ and NH ₃ as a raw material. At this time, hydrogen diffuses into the crystal, and orbits that do not contribute to the bonding of silicon atoms, that is, dangling bonds and hydrogen are combined to inactivate defects (hydrogen passivation).
More specifically, the mixed gas flow rate ratio NH ₃ / SiH ₄ is 0.05 to 1.0, the reaction chamber pressure is 13.3 Pa (0.1 Torr) to 266.6 Pa (2 Torr), It is formed under conditions where the temperature is 300 to 550 ° C. and the frequency for plasma discharge is 100 kHz or more.

  In FIG. 1 (5), a surface electrode metal paste is printed, applied and dried by screen printing on the antireflection film 16 on the surface (light receiving surface) to form the surface electrode 18. The metal paste for a surface electrode contains (1) metal particles and (2) glass particles as essential components, and includes (3) a resin binder and (4) other additives as necessary.

Next, the back electrode 20 is also formed on the p ⁺ -type diffusion layer 14 on the back surface. As described above, in the present invention, the material and forming method of the back electrode 20 are not particularly limited. For example, the back electrode 20 may be formed by applying and drying a back electrode paste containing a metal such as aluminum, silver, or copper. At this time, a silver paste for forming a silver electrode may be partially provided on the back surface for connection between elements in the module process.

  In FIG. 1 (6), the said electrode is baked and a solar cell element is completed. When firing for several seconds to several minutes in the range of 600 ° C. to 900 ° C., the antireflection film 16 that is an insulating film is melted by the glass particles contained in the electrode metal paste on the surface side, and the silicon surface is also partially melted, Metal particles (for example, silver particles) in the paste form a contact portion with the silicon substrate 10 and solidify. Thereby, the formed surface electrode 18 and the silicon substrate 10 are electrically connected. This is called fire-through.

  The shape of the surface electrode 18 will be described. The surface electrode 18 includes a bus bar electrode 30 and finger electrodes 32 intersecting with the bus bar electrode 30. FIG. 2A is a plan view of a solar cell element in which the surface electrode 18 includes a bus bar electrode 30 and a finger electrode 32 intersecting with the bus bar electrode 30 as viewed from the surface. FIG. 2B is an enlarged perspective view illustrating a part of FIG.

  Such a surface electrode 18 can be formed by means such as screen printing of the above-described metal paste, plating of an electrode material, or vapor deposition of an electrode material by electron beam heating in a high vacuum. The surface electrode 18 composed of the bus bar electrode 30 and the finger electrode 32 is generally used as an electrode on the light receiving surface side and is well known, and it is possible to apply known forming means for the bus bar electrode and finger electrode on the light receiving surface side. it can.

In the above-described method for manufacturing a p-type diffusion layer and a solar cell element, a mixed gas of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen is used to form an n-type diffusion layer on a silicon substrate which is a p-type semiconductor substrate. Although used, the n-type diffusion layer may be formed using the n-type diffusion layer forming composition. The n-type diffusion layer forming composition contains a Group 15 element such as P (phosphorus) or Sb (antimony) as a donor element.

In the method using the n-type diffusion layer forming composition for forming the n-type diffusion layer, first, the n-type diffusion layer forming composition is applied to the light-receiving surface which is the surface of the p-type semiconductor substrate, and the p-type of the present invention is applied to the back surface. The diffusion layer forming composition is applied and heat-treated at 600 ° C to 1200 ° C. By this heat treatment, the donor element diffuses into the p-type semiconductor substrate on the front surface to form an n-type diffusion layer, and the acceptor element diffuses on the back surface to form a p ⁺ -type diffusion layer. Except for this step, a solar cell element is produced by the same steps as those described above.

In the above description, the solar cell element in which the n-type diffusion layer is formed on the front surface, the p ⁺ -type diffusion layer is formed on the back surface, and the front surface electrode and the back surface electrode are provided on the respective layers has been described. If the composition for forming a diffusion layer is used, a back contact type solar cell element can be produced.
The back contact type solar cell element has all electrodes provided on the back surface to increase the area of the light receiving surface. That is, in the back contact type solar cell element, it is necessary to form both the n-type diffusion region and the p ⁺ -type diffusion region on the back surface to form a pn junction structure. The n-type diffusion layer forming composition of the present invention can form an n-type diffusion site at a specific site, and can therefore be suitably applied to the production of a back contact type solar cell element.

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

[Example 1]
On the p-type silicon substrate surface on which the texture was formed, an n-type diffusion layer was formed by the following general method. First, the silicon substrate was placed on a quartz boat and inserted into a quartz tube heated to 850 ° C. An n-type diffusion layer was formed by diffusing phosphorus over the entire surface of the substrate by a gas diffusion method using phosphorus oxychloride (POCl ₃ ) as a diffusion source. Specifically, nitrogen (N ₂ ) as a carrier gas is passed through the liquid POCl ₃ filled in the bubbler container, and POCl ₃ is introduced into the quartz tube. When POCl ₃ is mixed with oxygen (O ₂ ), P ₂ O ₅ is deposited on the surface of the silicon substrate, and this serves as a diffusion source to diffuse phosphorus into the silicon substrate. The heat treatment time was 30 minutes.

  Thereafter, hydrofluoric acid treatment was applied to the entire surface of the silicon substrate to remove the phosphate glass formed on the substrate surface. Specifically, the hydrofluoric acid treatment was immersed in a 10% aqueous hydrofluoric acid solution for 5 minutes. Then, running water washing and drying were performed. No glass layer remained on the substrate surface after the hydrofluoric acid treatment.

Subsequently, B ₂ O ₃ —AgO—ZnO—SiO ₂ glass powder (B ₂ O ₃ : 18.5%, AgO: 27.5%, ZnO: 24.5%, SiO ₂ : 23.8%, Al ₂ O ₃ : 5.7%) powder (hereinafter sometimes abbreviated as “G01”) was prepared. 20 g of the obtained glass powder (G01), 0.5 g of ethyl cellulose, and 10 g of 2- (2-butoxyethoxy) ethyl acetate are mixed and pasted using an automatic mortar kneader, and a p-type diffusion layer forming composition is formed. A product was prepared.

  Next, the prepared paste was applied to the entire surface of one side of a p-type silicon substrate having an n-type diffusion layer formed on the surface by screen printing, and dried on a hot plate at 150 ° C. for 5 minutes. Subsequently, thermal diffusion treatment was performed for 30 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in a 10% aqueous hydrofluoric acid solution for 5 minutes to remove the glass layer, washed with running water, and dried. No glass layer remained on the substrate surface after the hydrofluoric acid treatment.

  Subsequently, an antireflection film (silicon nitride film) having a thickness of 90 nm was formed by plasma CVD on the surface on which the n-type diffusion layer was formed, on which the p-type diffusion layer forming composition was not applied. A commercially available silver electrode paste (manufactured by DuPont, trade name: PV159) was printed on the light receiving surface so as to have an electrode pattern as shown in FIG. The electrode pattern was composed of a finger line with a width of 150 μm and a bus bar with a width of 1.5 mm, and the printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so that the film thickness after firing was 20 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

  Subsequently, an aluminum electrode paste (manufactured by PVG Solutions, trade name: Hyper BSF Al Paste) was used in the same manner as described above, using a screen printing method on the back surface (the surface on which the p-type diffusion layer forming composition was applied, and so on) Printed on the entire surface. Moreover, the printing conditions of the aluminum electrode paste were appropriately adjusted so that the film thickness of the aluminum electrode was 15 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

  Subsequently, using a tunnel furnace (manufactured by Noritake Co., Ltd., single-row transport W / B tunnel furnace), a heat treatment (firing) is performed in an air atmosphere at a firing maximum temperature of 800 ° C. and a holding time of 10 seconds. The formed solar cell element 1 was produced. In the solar cell element 1, no warpage of the substrate occurred.

[Example 2]
A solar cell element 2 was produced in the same manner as in Example 1 except that the electrode was formed without performing hydrofluoric acid treatment after the thermal diffusion treatment of the p-type diffusion layer forming composition. In the solar cell element 2, no warpage of the substrate occurred.

[Example 3]
A solar cell element 3 was produced in the same manner as in Example 1 except that the thermal diffusion treatment time for the p-type diffusion layer forming composition was 35 minutes. No glass layer remained on the substrate surface after the hydrofluoric acid treatment. Further, in the solar cell element 3, no warping of the substrate occurred.

[Example 4]
A solar cell element 4 was produced in the same manner as in Example 2 except that the thermal diffusion treatment time for the p-type diffusion layer forming composition was 35 minutes. In the solar cell element 4, no warpage of the substrate occurred.

[Example 5]
A solar cell element 5 was produced in the same manner as in Example 1 except that the temperature of the thermal diffusion treatment of the p-type diffusion layer forming composition was set to 900 ° C. No glass layer remained on the substrate surface after the hydrofluoric acid treatment. Further, in the solar cell element 5, no substrate warpage occurred.

[Example 6]
A solar cell element 6 was produced in the same manner as in Example 2 except that the temperature of the thermal diffusion treatment of the p-type diffusion layer forming composition was set to 900 ° C. In the solar cell element 6, no warpage of the substrate occurred.

[Example 7]
The glass powder composition was changed to B ₂ O ₃ —AgO—Bi ₂ O ₃ —SiO ₂ glass (B ₂ O ₃ : 14.1%, AgO: 13.9%, Bi ₂ O ₃ : 66.7%, SiO ₂ N-type diffusion layer was formed in the same manner as in Example 1 except that: 5.3% (hereinafter sometimes abbreviated as “G02”), and a solar cell element 7 was produced. No glass layer remained on the substrate surface after the hydrofluoric acid treatment. Further, in the solar cell element 7, no warpage of the substrate occurred.

[Example 8]
A solar cell element 8 was produced in the same manner as in Example 7 except that the electrode was formed without performing hydrofluoric acid treatment after the thermal diffusion treatment of the p-type diffusion layer forming composition. Further, in the solar cell element 8, no warping of the substrate occurred.

[Example 9]
A solar cell element 9 was produced in the same manner as in Example 7 except that the temperature of the thermal diffusion treatment of the p-type diffusion layer was 950 ° C. and the time was 35 minutes. No glass layer remained on the substrate surface after the hydrofluoric acid treatment. Further, in the solar cell element 9, no warping of the substrate occurred.

[Example 10]
A solar cell element 10 was produced in the same manner as in Example 8 except that the temperature of the thermal diffusion treatment of the p-type diffusion layer was 950 ° C. and the time was 35 minutes. In the solar cell element 10, no warpage of the substrate occurred.

[Example 11]
A solar cell element 11 was produced in the same manner as in Example 7 except that the temperature of the thermal diffusion treatment of the p-type diffusion layer was 900 ° C. and the time was 40 minutes. The glass layer did not remain on the surface of the p-type silicon substrate after the hydrofluoric acid treatment. Further, in the solar cell element 11, no warping of the substrate occurred.

[Example 12]
A solar cell element 12 was produced in the same manner as in Example 8 except that the temperature of the thermal diffusion treatment of the p-type diffusion layer was 900 ° C. and the time was 40 minutes. In the solar cell element 12, no warping of the substrate occurred.

[Example 13]
Similarly to Example 1, a p-type silicon substrate having a texture formed thereon is formed with an n-type formation layer using POCl ₃ , a p-type diffusion layer formation using glass particles (G01), and an antireflection film by plasma CVD. Formed. No glass layer remained on the substrate surface after the hydrofluoric acid treatment.

  Thereafter, a commercially available silver electrode paste (manufactured by DuPont, trade name: PV159) was printed on the light-receiving surface so as to have an electrode pattern as shown in FIG. The electrode pattern was composed of a finger line with a width of 150 μm and a bus bar with a width of 1.5 mm, and the printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so that the film thickness after firing was 20 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation. Also, a commercially available silver electrode paste (manufactured by PVG Solutions, trade name: Hyper BSF Al Paste) is printed on the same pattern as the light receiving surface on the back surface, heated at a temperature of 150 ° C. for 15 minutes, and the solvent is evaporated. Removed.

  Subsequently, in the same manner as in Example 1, a solar cell element in which a desired electrode was formed by performing a heat treatment (firing) for 10 seconds at a maximum firing temperature of 800 ° C. in an air atmosphere using a tunnel furnace. 13 was produced. There was no warping of the substrate.

[Example 14]
A solar cell element 14 was produced in the same manner as in Example 13 except that the electrode was formed without performing hydrofluoric acid treatment after the thermal diffusion treatment of the p-type diffusion layer forming composition. There was no warping of the substrate.

[Example 15]
A solar cell element 15 was produced in the same manner as in Example 13 except that the composition of the glass powder was changed to G02. No glass layer remained on the substrate surface after the hydrofluoric acid treatment. Further, the substrate was not warped.

[Comparative Example 1]
First, an n-type diffusion layer was formed on a p-type silicon substrate in the same manner as in Example 1, 10% hydrofluoric acid aqueous solution treatment was applied to the entire surface of the silicon substrate, and phosphate glass formed on the substrate surface was removed. . No glass layer remained on the substrate surface after the hydrofluoric acid treatment.

  Next, an antireflection film (silicon nitride film) with a thickness of 90 nm was formed on the surface to be the light receiving surface by plasma CVD. A commercially available silver electrode paste (manufactured by DuPont, trade name: PV159) was printed on the light receiving surface so as to have an electrode pattern as shown in FIG. The electrode pattern was composed of a finger line with a width of 150 μm and a bus bar with a width of 1.5 mm, and the printing conditions (screen plate mesh, printing speed, printing pressure) were appropriately adjusted so that the film thickness after firing was 20 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

  Subsequently, an aluminum electrode paste (manufactured by PVG Solutions, trade name: Hyper BSF Al Paste) was printed on the entire back surface using the screen printing method as described above. Moreover, the printing conditions of the aluminum electrode paste were appropriately adjusted so that the film thickness of the aluminum electrode was 30 μm. This was placed in an oven heated to 150 ° C. for 15 minutes, and the solvent was removed by evaporation.

  Subsequently, using a tunnel furnace (manufactured by Noritake Co., Ltd., single-row transport W / B tunnel furnace), a heat treatment (firing) is performed in an air atmosphere at a firing maximum temperature of 800 ° C. and a holding time of 10 seconds. The formed solar cell element C1 was produced. In the solar cell element C1, the substrate warpage of about 1.5 mm occurred.

[Comparative Example 2]
The glass composition was changed to B ₂ O ₃ —ZnO—SiO ₂ glass (B ₂ O ₃ : 36.0%, ZnO: 29.5%, SiO ₂ : 28.8%, Al ₂ O ₃ : 5.7%). ) (Hereinafter, it may be abbreviated as “G03”.) A solar cell element C2 was produced in the same manner as in Example 2 except that it was changed.

[Comparative Example 3]
The glass composition was changed to B ₂ O ₃ —Bi ₂ O ₃ —SiO ₂ glass (B ₂ O ₃ : 18.0%, Bi ₂ O ₃ : 76.7%, SiO ₂ : 5.3%) (hereinafter, A solar cell element C3 was produced in the same manner as in Example 2 except that it was sometimes changed to “G04”.

  Table 1 collectively shows the conditions for forming the n-type diffusion layer and the conditions for producing the solar cell in the examples and comparative examples.

<Evaluation>
Evaluation of the produced solar cell element is as follows: WXS-155S-10 manufactured by Wacom Denso Co., Ltd. as pseudo-sunlight, and I-V CURVE TRACER MP-160 (manufactured by EKO INSTRUMENT Co., Ltd.) as a current-voltage (IV) evaluation measuring instrument. ) Was combined with the measuring device. Jsc (short-circuit current), Voc (open circuit voltage), FF (fill factor), and Eff (conversion efficiency) indicating power generation performance as a solar cell are JIS-C-8912, JIS-C-8913, and JIS-C-, respectively. It is obtained by performing measurement according to 8914. In the solar cell element having a double-sided electrode structure, the obtained measured values are converted into relative values with the measured value of Comparative Example 1 (solar cell element C1) as 100.0, and are shown in Table 2.

  From Table 2, it can be seen that in Comparative Example 2 and Comparative Example 3, the power generation performance was degraded as compared with Comparative Example 1. This can be considered as follows. That is, in Comparative Example 2 and Comparative Example 3, since the glass powder does not contain silver oxide, the resistance of the molten glass phase formed during the thermal diffusion treatment is increased, and the p-type diffusion layer on the electrode and the silicon substrate is increased. It is considered that the ohmic contact was insufficient.

  On the other hand, the power generation performance of the solar cell elements produced in Examples 1 to 15 was substantially equal to the measured value of the solar cell element of Comparative Example 1. In particular, when hydrofluoric acid treatment is performed after the thermal diffusion treatment of the p-type diffusion layer formation, aluminum is also diffused in the subsequent electrode formation, so that a higher concentration of aluminum has diffused, resulting in excellent ohmic contact. It is thought that it was formed. As a result, in the Example which performed the hydrofluoric acid process, the solar cell element excellent in the electric power generation performance was obtained compared with the comparative example 1. FIG. Moreover, since the example in which the hydrofluoric acid treatment was not performed also showed good power generation performance, it is considered that the silver particles were precipitated in the glass during the thermal diffusion treatment and the conductivity was improved.

  Furthermore, in Example 13 to Example 15, even in the solar cell element having a structure in which the aluminum electrode is not formed on the entire surface, a measured value equivalent to that of the solar cell element of Comparative Example 1 could be obtained. This is presumably because a good p-type diffusion layer was formed by the thermal diffusion treatment of the p-type diffusion layer forming composition. It was confirmed that excellent power generation performance can be obtained even when the electrode material on the back surface is a silver electrode and a thin electrode pattern is applied.

10 p-type semiconductor substrate 12 n-type diffusion layer 13 p-type diffusion layer forming composition layer 14 p ⁺ -type diffusion layer 16 antireflection film 18 surface electrode 20 back electrode (electrode layer)
30 Busbar electrode 32 Finger electrode

Claims (6)

  A p-type diffusion layer forming composition comprising a glass powder containing an acceptor element and silver oxide, and a dispersion medium.   The p-type diffusion layer forming composition according to claim 1, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). The glass powder containing the acceptor element is at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , AgO, SiO ₂ , K ₂ O, Na ₂ O. At least one glass component substance selected from Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, V ₂ O ₅ , SnO, ZrO ₂ , and MoO ₃ The p-type diffusion layer forming composition according to claim 1 or 2, comprising:   A method for producing a p-type diffusion layer, comprising: applying a p-type diffusion layer forming composition according to any one of claims 1 to 3 on a semiconductor substrate; and applying a thermal diffusion treatment. .   A step of applying the p-type diffusion layer forming composition according to any one of claims 1 to 3 on a semiconductor substrate, a step of forming a p-type diffusion layer by performing a thermal diffusion treatment, and formation Forming an electrode on the formed n-type diffusion layer, and a method for manufacturing a solar cell element.   The glass layer formed on the n-type diffusion layer is not removed or a part of the glass layer is removed between the step of forming the n-type diffusion layer and the step of forming the electrode. Item 6. A method for producing a solar cell element according to Item 5.