JP5691268B2 - P-type diffusion layer forming composition, method for producing p-type diffusion layer, and method for producing solar battery cell - Google Patents

Description

  The present invention relates to a solar cell p-type diffusion layer forming composition, a p-type diffusion layer manufacturing method, and a solar cell manufacturing method. More specifically, the present invention relates to the internal stress of crystalline silicon 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 crystalline silicon solar cell will be described.
First, a p-type silicon substrate having a textured structure is prepared so as to promote the light confinement effect and achieve high efficiency, and then 800 to 900 ° C. in a mixed gas atmosphere of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen. A few tens of minutes is performed to form an n-type diffusion layer uniformly 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, side etching is performed to remove the n-type diffusion layer on the side surface. In addition, the n-type diffusion layer on the back surface needs to be converted into a p ⁺ -type diffusion layer. At the same time as printing the aluminum paste on the back surface and baking it to make the n-type layer into a p ⁺ -type layer, ohmic Getting contact.

  However, 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 to 20 μm after firing. Furthermore, when such a thick aluminum layer is formed, the coefficient of thermal expansion differs greatly between silicon and aluminum, so that a large internal stress is generated in the silicon substrate during the firing and cooling processes, causing damage to crystal grain boundaries and crystal defects. In some cases, it could cause an increase in length and warpage.

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 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 battery cell using a crystalline silicon substrate, the p-type is suppressed while suppressing internal stress in the silicon substrate and warping of the substrate. A p-type diffusion layer-forming composition capable of forming a diffusion layer and having excellent dispersion stability, a method for producing a p-type diffusion layer, and a method for producing a solar battery cell Offering is an issue.

Means for solving the problems are as follows.
<1> A p-type diffusion layer forming composition containing a glass powder containing an acceptor element, a binder having a weight average molecular weight of 5,000 to 500,000, and a solvent ,
Applying the p-type diffusion layer forming composition onto a semiconductor substrate, heat-treating the semiconductor substrate applied with the p-type diffusion layer forming composition to form a p-type diffusion layer on the semiconductor substrate, removing the glass formed on the surface of the p-type diffusion layer, and a p-type diffusion layer forming composition used in a method for producing a p-type diffusion layer .

<2> The glass powder includes a glass component substance and an acceptor element-containing substance, and a content ratio of the acceptor element-containing substance in the glass powder is 1% by mass or more and 90% by mass or less. A p-type diffusion layer forming composition.

<3> The p-type diffusion layer forming composition according to <1> or <2>, wherein the pH (25 ° C.) is in the range of 2 to 13.

<4> The p-type according to any one of <1> to <3>, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). Diffusion layer forming composition.

<5> The glass powder is at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O. And at least one glass component material selected from BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, SnO, ZrO ₂ , and MoO _3. The p-type diffusion layer forming composition according to any one of <4>.

<6> A step of applying the p-type diffusion layer forming composition according to any one of <1> to <5> on a semiconductor substrate, and a semiconductor substrate coated with the p-type diffusion layer forming composition A method for producing a p-type diffusion layer , comprising: a step of forming a p-type diffusion layer on the semiconductor substrate by heat treatment; and a step of removing glass formed on a surface of the p-type diffusion layer.

<7> on the semiconductor substrate, wherein <1> a step of applying a p-type diffusion layer forming composition according to any one of to <5>, the semiconductor substrate coated with the p-type diffusion layer forming composition A method of manufacturing a solar cell , comprising: a step of heat-treating a p-type diffusion layer on the semiconductor substrate; and a step of removing glass formed on a surface of the p-type diffusion layer .

  According to the present invention, in a manufacturing process of a solar battery cell using a crystalline silicon substrate, a p-type diffusion layer capable of forming a p-type diffusion layer while suppressing the occurrence of internal stress and substrate warpage in the silicon substrate. A p-type diffusion layer-forming composition that is a layer-forming composition and excellent in dispersion stability, a method for producing a p-type diffusion layer, and a method for producing a solar battery cell can be provided.

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 will be described.
In the present 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 as long as 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 that as a minimum value and a maximum value, respectively.

The p-type diffusion layer forming composition of the present invention includes at least one kind of glass powder containing at least an acceptor element (hereinafter sometimes simply referred to as “glass powder”) and a binder having a weight average molecular weight of 5,000 to 500,000. And at least one solvent, and may further contain other additives as required in consideration of coating properties and the like.
Here, the p-type diffusion layer forming composition contains an acceptor element. For example, the p-type diffusion layer is formed by thermally diffusing the acceptor element by applying thermal diffusion treatment (baking) after being applied to a silicon substrate. A material that can be used. 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 more effectively suppressing internal stress in the silicon substrate and generation of warpage of the substrate. .

Therefore, when the p-type diffusion layer forming composition of the present invention is applied, a method widely used in the past, that is, printing an aluminum paste and firing it to convert the n-type layer into a p ⁺ -type layer simultaneously. In the method of obtaining the ohmic contact, the generation of internal stress in the substrate and the warpage of the substrate that are generated is suppressed.

  Furthermore, in the p-type diffusion layer forming crude composition of the present invention, the content ratio of the acceptor element-containing substance in the glass powder contained therein is preferably 1% by mass or more and 90% by mass or less. Thereby, a surface resistance value falls and the performance as a photovoltaic cell can be improved. Details of the acceptor element-containing material will be described later.

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

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

Further, the glass powder can control the melting temperature, softening point, glass transition point, chemical durability, and the like by adjusting the component ratio as necessary. Furthermore, it is preferable to contain the components 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. , MoO ₃ , 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, etc., SiO ₂ , K ₂ O, Na It is preferable to use at least one selected from ₂ O, Li ₂ O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, SnO, ZrO ₂ , and MoO ₃ .

Specific examples of the glass powder containing an acceptor element include B ₂ O ₃ —SiO ₂ , B ₂ O ₃ —ZnO, B ₂ O ₃ —PbO, Al ₂ O ₃ —SiO ₂ , and B ₂ O _3. -al ₂ O _{3 system,} Ga ₂ O 3 -SiO _{2 system, Ga 2 O 3 -B 2 O} 3 _system, and a glass such as B 2 _{O 3} alone system.
In the above, the single component glass or the composite glass containing two components is exemplified, but three or more types of composite glass such as B ₂ O ₃ —SiO ₂ —Na ₂ O may be used as necessary.

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

  The content ratio of the acceptor element-containing substance in the glass powder is 1% by mass or more in consideration of the doping concentration of the acceptor element in the silicon substrate, the melting temperature of the glass powder, the softening point, the glass transition point, and the chemical durability. It is preferable that it is 90 mass% or less.

  By setting the content ratio of the acceptor element-containing substance in the glass powder to 1% by mass or more, the doping concentration of the acceptor element into the silicon substrate is sufficiently obtained, and the p-type diffusion layer is sufficiently formed. Further, the content ratio of the acceptor element-containing substance is 90% by mass or less, so that the acceptor element-containing substance is prevented from being volatilized during the thermal diffusion treatment, and the acceptor element diffusion extends to the side surface and the back surface. There is a possibility that the p-type diffusion layer is formed not only on the surface coated with the mold diffusion layer forming composition but also on the side surface and the back surface other than the desired part.

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

  In particular, the surface sheet having a p-type diffusion layer formed even when a certain amount or more of the acceptor element is added to the p-type diffusion layer-forming composition while taking into account the amount of the acceptor element in which the p-type diffusion layer is sufficiently formed Considering that the resistance does not decrease beyond a certain value and that it is necessary to suppress the volatilization of the acceptor element-containing substance, the content ratio of the acceptor element-containing substance in the glass powder is 30% by mass or more and 70% by mass. It is even more preferable that:

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

Specifically, in the case of B ₂ O ₃ —SiO ₂ glass, the content ratio of B ₂ O ₃ is preferably 1% by mass to 90% by mass, and preferably 3% by mass to 80% by mass. It is more preferable that

  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.

  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 glass powder containing an acceptor element is produced by the following procedure.
First, weigh the ingredients and fill the crucible. Examples of the material for the crucible include platinum, platinum-rhodium, iridium, alumina, quartz, carbon, and the like, 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 uniform melt. At this time, it is desirable to stir the melt uniformly.
Subsequently, the melt that has become uniform is poured onto a zirconia substrate, a carbon substrate, or the like to vitrify the melt.
Finally, the glass is crushed into powder. A known method such as a jet mill, a bead mill, or a ball mill can be applied to the pulverization.

  The content ratio of the glass powder containing the acceptor element in the p-type diffusion layer forming composition is determined in consideration of applicability, acceptor element diffusibility, and the like. 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.

  The p-type diffusion layer forming composition of the present invention contains at least one binder having a weight average molecular weight of 5000 to 500,000 and at least one solvent. These serve as a dispersion medium for the glass powder.

  Examples of the binder include dimethylaminoethyl (meth) acrylate polymer, polyvinyl alcohol, polyacrylamides, polyvinylamides, polyvinylpyrrolidone, poly (meth) acrylic acids, polyethylene oxides, polysulfonic acid, acrylamide alkyl sulfonic acid, and cellulose ether. , Cellulose derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, ethyl cellulose, gelatin, starch and starch derivatives, sodium alginate, xanthan, gua and gua derivatives, scleroglucan and scleroglucan derivatives, tragacanth and tragacanth derivatives, dextrin and dextrin derivatives, Acrylic resin, acrylic ester resin, butadiene resin, styrene resin, and their Coalescence, and can appropriately select such as silicon dioxide. These are used singly or in combination of two or more.

  In the p-type diffusion layer forming composition of the present invention, the binder contained therein has a weight average molecular weight of 5,000 to 500,000. Thereby, the viscosity which can apply | coat a p-type diffused layer formation composition on a silicon substrate uniformly can be adjusted. If the molecular weight of the binder is less than 5000, the viscosity of the p-type diffusion layer forming composition may increase. This can be considered, for example, because the three-dimensional repulsion when adsorbed on glass particles is insufficient and the particles aggregate.

On the other hand, when the weight average molecular weight of the binder is larger than 500,000, the binders aggregate in the solvent, and as a result, the viscosity of the p-type diffusion layer forming composition may increase.
In addition to this, when the weight average molecular weight of the binder is increased, the combustion temperature of the binder is increased, the binder is not completely combusted in the thermal diffusion process, and the diffusion of the acceptor element is difficult to proceed. There is a possibility of diffusing to the substrate.

Considering the above, the molecular weight of the binder is preferably 6000 or more and 450,000 or less, and more preferably 6500 or more and 400,000 or less.
In addition, the weight average molecular weight of a binder is measured by the normal method using GPC.

  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, γ-butyrolactone, γ-valerolactone , Diethyl ether, methyl ethyl ether, methyl-n-di-n-propyl ether, di-iso-propyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane, dimethyldioxane, 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, 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, Ethylene glycol di-n-butyl ether, triethylene 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, Propylene glycol methyl ethyl ether, dipropylene 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 Propylene 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, tetra Ether solvents such as propylene glycol methyl-n-butyl ether, dipropylene glycol di-n-butyl ether, tetrapropylene glycol methyl-n-hexyl ether, tetrapropylene glycol di-n-butyl ether, methyl acetate, ethyl acetate, n-acetate Propyl, i-propyl acetate, n-butyl acetate, i-butyl acetate, sec-butyl acetate, n-pentyl acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate, 2-ethylbutyl acetate, 2-ethyl acetate Ethylhexyl, 2- (2-butoxyethoxy) ethyl acetate, benzyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, nonyl acetate, methyl acetoacetate, ethyl acetoacetate, diethylene glycol monomethyl ether acetate, diethylene acetate Recall monoethyl ether, diethylene glycol acetate mono-n-butyl ether, dipropylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate, glycol diacetate, methoxytriglycol acetate, ethyl propionate, n-butyl propionate, i propionate i -Ester solvents such as amyl, diethyl oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl lactate, n-amyl lactate, ethylene glycol methyl ether propionate, ethylene glycol ethyl ether propio , Ethylene glycol methyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol methyl ether acetate, diethylene glycol ethyl ether Cetate, ether acetate solvents such as diethylene glycol-n-butyl ether acetate, propylene glycol methyl ether acetate, propylene glycol ethyl ether acetate, propylene glycol propyl ether acetate, dipropylene glycol methyl ether acetate, dipropylene glycol ethyl ether acetate, acetonitrile, N -Aprotic such as methylpyrrolidinone, N-ethylpyrrolidinone, N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone, N-cyclohexylpyrrolidinone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide 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, 1,2-propylene glycol, 1,3-butylene Coal, alcohol solvents such as diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, ethylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n -Glycols such as 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 mono Ether-based solvents, and water. These are used singly or in combination of two or more.

The content ratio of the binder and the solvent in the p-type diffusion layer forming composition is appropriately selected in consideration of coating properties, acceptor element-containing substance concentration, and the like.
In the present invention, the content ratio of the binder may be, for example, 0.01 to 5% by mass with respect to the p-type diffusion layer forming composition, and is 0.1 to 3% by mass from the viewpoint of dispersion stability. It is preferable. Moreover, as a content rate of a solvent, it can be set to 1-60 mass% with respect to a p-type diffused layer formation composition, and it is preferable that it is 5-40 mass% from a viewpoint of dispersion stability.

  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.

  It is also possible to further increase the dispersibility of the glass particles in the solvent by adding a small amount of a pH adjusting agent to the p-type diffusion layer forming composition. Specifically, by adjusting the pH, the zeta potential (approximation of the particle surface potential) can be changed, and electrostatic repulsion can be imparted between the glass particles.

  Examples of the pH adjuster include dilute hydrochloric acid, dilute sulfuric acid, dilute nitric acid, tartaric acid, citric acid, fumaric acid, malic acid, phytic acid, succinic acid, gluconic acid, lactic acid, sodium hydroxide, potassium carbonate, sodium bicarbonate, carbonate Sodium etc. are mentioned. These are used singly or in combination of two or more.

In addition, the pH of the p-type diffusion layer forming composition is appropriately set in consideration of the equipotential point of the glass composition (the pH at which the zeta potential becomes 0 and the particles easily aggregate), acid resistance, and alkali resistance. In general, the pH (25 ° C.) is preferably 2.0 or more and 13.0 or less, and more preferably 3.0 or more and 12.0 or less.
The pH is measured at 25 ° C. using a normal pH measuring device.

Specifically, in the case of B ₂ O ₅ —SiO ₂ glass, the pH (25 ° C.) of the p-type diffusion layer forming composition is preferably 3.0 or more and 11.0 or less. More preferably, it is 0 or more and 10.0 or less.

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

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

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

Then, the p-type diffusion layer forming composition is applied onto the n-type diffusion layer on the back surface of the p-type semiconductor substrate, that is, the surface that is not the light receiving surface. In the present invention, the coating method is not limited, and examples thereof include a printing method, a spin method, a brush coating, a spray method, a doctor blade method, a roll coater method, and an ink jet method.
There is no particular restriction on the coating amount of the p-type diffusion layer forming composition, for ^example, be a ^{10g / m 2 ~250g / m 2} , it is preferably 20g / ^{m 2} ~150g / 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 to 300 ° C. for about 1 to 10 minutes when using a hot plate, and about 10 to 30 minutes when using a dryer or the like. The drying conditions depend on the solvent composition of the p-type diffusion layer forming composition and are not particularly limited to the above conditions in the present invention.

The semiconductor substrate coated with the p-type diffusion layer forming composition is subjected to thermal diffusion treatment at 600 to 1200 ° C. By this thermal diffusion treatment, the acceptor element diffuses into the semiconductor substrate, and a p ⁺ -type diffusion layer is formed. A known continuous furnace, batch furnace, or the like can be applied to the thermal diffusion treatment. Further, the furnace atmosphere during the thermal diffusion treatment can be appropriately adjusted to air, oxygen, nitrogen or the like.
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 can be 1 to 60 minutes, and more preferably 2 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. As the etching, a known method such as a method of immersing in an acid such as hydrofluoric acid or a method of immersing in an alkali such as caustic soda can be applied.

Further, in the conventional manufacturing method, an aluminum paste is printed on the back surface, and this is baked to change the n-type diffusion layer into a p ⁺ -type diffusion layer, and at the same time, an ohmic contact is obtained. However, 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 to 20 μm after firing. Further, when such a thick aluminum layer is formed, the thermal expansion coefficient differs greatly between silicon and aluminum, so that 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. In addition, the warp easily causes the cell to be damaged in the transportation of the solar battery cell in the module process and the connection with the copper wire called a tab wire. In recent years, due to the improvement of slicing technology, the thickness of the crystalline silicon substrate is being reduced, and the cells 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.

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

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

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

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

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

In the above-described method for manufacturing a p-type diffusion layer and solar battery cell, a mixed gas of phosphorus oxychloride (POCl ₃ ), nitrogen and oxygen is used to form an n-type diffusion layer in crystalline silicon that 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 subjected to thermal diffusion treatment at 600 to 1200 ° C. By this thermal diffusion 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, solar cells are produced by the same steps as the above method.

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.
Further, the weight average molecular weight of the binder was measured as a weight average molecular weight in terms of polyethylene using GPC for a commercially available product and catalog data for unknown ones.

[Example 1]
20 g of B ₂ O ₃ —SiO ₂ glass (B ₂ O ₃ : 10%) powder, ₃ g of ethyl cellulose (weight average molecular weight 140000) and 77 g of 2- (2-butoxyethoxy) ethyl acetate were mixed to make a paste, and p-type Diffusion layer forming composition 1 was prepared.
When the pH of the obtained p-type diffusion layer forming composition was measured at 25 ° C. using a pH meter, the pH (25 ° C.) was 5.6.

[Example 2]
In Example 1, p-type diffusion layer forming composition 2 was prepared in the same manner as in Example 1 except that the binder was changed to ethyl cellulose having a weight average molecular weight of 300,000. The pH (25 ° C.) was 5.6.

[Example 3]
In Example 1, a p-type diffusion layer forming composition 3 was prepared in the same manner as in Example 1 except that the glass powder was replaced with a B ₂ O ₃ —ZnO system (B ₂ O ₃ content: 60%). . The pH (25 ° C.) was 5.6.

[Example 4]
In Example 1, p-type diffusion layer forming composition 4 was prepared in the same manner as in Example 1 except that the binder was changed to polyvinyl alcohol (molecular weight: 250,000). The pH (25 ° C.) was 5.6.

[Example 5]
A p-type diffusion layer forming composition 5 was prepared in the same manner as in Example 1 except that in Example 1, the pH was adjusted to 3.8 using citric acid.

[Example 6]
In Example 1, p-type diffusion layer forming composition 6 was prepared in the same manner as in Example 1 except that the pH was adjusted to 10.6 using sodium hydrogen carbonate.

[Example 7]
In Example 1, p-type diffusion layer forming composition 7 was prepared in the same manner as in Example 1 except that the binder was changed to ethyl cellulose having a weight average molecular weight of 8000. The pH (25 ° C.) was 5.6.

[Example 8]
In Example 1, p-type diffusion layer forming composition 8 was prepared in the same manner as in Example 1 except that the binder was changed to ethyl cellulose having a weight average molecular weight of 450,000. The pH (25 ° C.) was 5.6.

[Comparative Example 1]
A p-type diffusion layer forming composition C1 was prepared in the same manner as in Example 1 except that in Example 1, the binder was changed to ethyl cellulose having a weight average molecular weight of 4500. The pH (25 ° C.) was 5.6.

[Comparative Example 2]
A p-type diffusion layer forming composition C2 was prepared in the same manner as in Example 1 except that in Example 1, the binder was changed to ethyl cellulose having a weight average molecular weight of 750,000. The pH (25 ° C.) was 5.6.

[Evaluation]
-Dispersion stability-
About the p-type diffusion layer forming composition prepared by the above method, the initial viscosity measured within 1 hour after preparation and the time-lapse viscosity measured after standing at 20 ° C. for 6 hours The rate of change in viscosity was determined as the ratio of the difference between the initial viscosity and the initial viscosity ((viscosity with time−initial viscosity) / initial viscosity). The viscosity was measured at 20 ° C. using a rotary viscometer.
In addition, the state of the p-type diffusion layer forming composition after aging was visually observed.
The viscosity change and visual observation results were evaluated according to the following evaluation criteria. The results are shown in Table 1.

~Evaluation criteria~
A: Viscosity change rate was less than 0.05, and neither gelation nor aggregation of glass particles was observed.
B: Viscosity change rate was 0.05 or more and less than 0.10, and neither gelation nor aggregation of glass particles was observed.
C: Viscosity change rate was 0.10 or more and less than 0.15, and neither gelation nor aggregation of glass particles was observed.
D: Viscosity change rate was less than 0.15, but glass particles were gelled or aggregated.
E: Viscosity change rate was 0.15 or more, and glass particles were gelled or aggregated.

Next, the p-type diffusion layer forming composition prepared in Examples 1 to 8 was applied to the surface of the p-type silicon substrate by screen printing so that the coating amount was 70 g / m ^2, and a hot plate at 150 ° C. Dry for 5 minutes above. Subsequently, a thermal diffusion treatment was performed for 10 minutes in an electric furnace set at 1000 ° C., and then the substrate was immersed in hydrofluoric acid for 5 minutes to remove the glass layer, washed with running water, and then dried.

  The sheet resistance of the surface on the side where the p-type diffusion layer forming composition was applied and the sheet resistance of the back surface were measured. The results are shown in Table 1.

  As a result of applying the p-type diffusion layer forming composition of the present invention and performing thermal diffusion treatment, the surface sheet resistance is 100Ω / □ or less, and B (boron) is diffused to form a p-type diffusion layer. It was. The sheet resistance on the back surface was 1000000 Ω / □ or more and could not be measured, and no p-type diffusion layer was formed. Further, the substrate was not warped.

Claims (7)

A p-type diffusion layer forming composition containing a glass powder containing an acceptor element, a binder having a weight average molecular weight of 5,000 to 500,000, and a solvent ,
Applying the p-type diffusion layer forming composition onto a semiconductor substrate, heat-treating the semiconductor substrate applied with the p-type diffusion layer forming composition to form a p-type diffusion layer on the semiconductor substrate, removing the glass formed on the surface of the p-type diffusion layer, and a p-type diffusion layer forming composition used in a method for producing a p-type diffusion layer .   The p-type diffusion according to claim 1, wherein the glass powder includes a glass component substance and an acceptor element-containing substance, and a content ratio of the acceptor element-containing substance in the glass powder is 1% by mass or more and 90% by mass or less. Layer forming composition.   The p-type diffusion layer forming composition according to claim 1 or 2, wherein the pH (25 ° C) is in the range of 2 to 13. The p-type diffusion layer forming composition according to any one of claims 1 to 3, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). object. The glass powder includes at least one acceptor element-containing material selected from B ₂ O ₃ , Al ₂ O ₃ and Ga ₂ O ₃ , SiO ₂ , K ₂ O, Na ₂ O, Li ₂ O, BaO, And at least one glass component material selected from SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl ₂ O, SnO, ZrO ₂ , and MoO ₃ . The p-type diffusion layer forming composition according to any one of the above. The process of apply | coating the p-type diffused layer formation composition of any one of Claims 1-5 on a semiconductor substrate, and heat-processing the semiconductor substrate which apply | coated the said p-type diffused layer formation composition, A method for producing a p-type diffusion layer, comprising: forming a p-type diffusion layer on a semiconductor substrate; and removing a glass formed on a surface of the p-type diffusion layer. On a semiconductor substrate, and a heat treatment and applying a p-type diffusion layer forming composition according to any one of claims 1 to 5, the semiconductor substrate coated with the p-type diffusion layer forming composition The manufacturing method of the photovoltaic cell which has the process of forming a p-type diffused layer in the said semiconductor substrate, and the process of removing the glass formed in the surface of the said p-type diffused layer .