JP5803080B2 - P-type diffusion layer forming composition, p-type diffusion layer forming composition manufacturing method, p-type diffusion layer manufacturing method, and solar cell manufacturing method - Google Patents

Description

  The present invention relates to a solar cell p-type diffusion layer forming composition, a p-type diffusion layer forming composition manufacturing method, a p-type diffusion layer manufacturing method, and a solar cell manufacturing method. The present invention relates to a p-type diffusion layer forming technique capable of reducing internal stress of crystalline silicon as a semiconductor substrate, suppressing crystal grain boundary damage, suppressing crystal defect growth, and suppressing 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, in-plane without generating internal stress in the silicon substrate and warping of the substrate. Providing a p-type diffusion layer forming composition capable of forming a p-type diffusion layer with small variations, a method for producing a p-type diffusion layer forming composition, a method for producing a p-type diffusion layer, and a method for producing a solar battery cell Is an issue.

Means for solving the problems are as follows.
<1> A p-type diffusion layer forming composition that is applied onto a semiconductor substrate and forms a p-type diffusion layer on the semiconductor substrate.
A glass powder containing acceptor element, and a dispersion medium, containing, the frequency distribution of volume-based glass powder has two maximum peaks, particle size of the maximum peak of the small diameter side, the large diameter side A p-type diffusion layer forming composition having a maximum peak particle size of 0.01 to 0.50 times.

<2> The p-type diffusion layer forming composition according to <1>, wherein a particle diameter of a maximum peak on the small diameter side is 0.01 μm or more and 5 μm or less.

<3> The p-type diffusion layer forming composition according to <1> or <2>, wherein the acceptor element is at least one selected from B (boron), Al (aluminum), and Ga (gallium). .

<4> 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 <3>.

<5> The method for producing a p-type diffusion layer forming composition according to any one of <1> to <4>,
A first glass powder containing an acceptor element; and a second glass powder containing an acceptor element and having a volume average particle size of 0.01 to 0.50 times the volume average particle size of the first glass powder. The manufacturing method of a p-type diffused layer formation composition including the process of mixing glass powder and a dispersion medium.

<6> A method for producing a p-type diffusion layer, comprising: a step of applying the p-type diffusion layer forming composition according to any one of <1> to <4>, and a step of performing a thermal diffusion treatment.

<7> A step of applying the p-type diffusion layer forming composition according to any one of <1> to <4> on the semiconductor substrate and a thermal diffusion treatment to form a p-type diffusion layer. And a method for producing a solar battery cell.

  According to the present invention, in a manufacturing process of a solar battery cell using a crystalline silicon substrate, a p-type diffusion layer with small in-plane variation is formed while suppressing generation of internal stress and substrate warpage in the silicon substrate. P-type diffusion layer forming composition, p-type diffusion layer forming composition manufacturing method, p-type diffusion layer manufacturing method, and solar cell manufacturing method 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 contains a glass powder containing at least an acceptor element (hereinafter sometimes simply referred to as “glass powder”) and a dispersion medium, and further considers coating properties and the like. Other additives may be contained as necessary. The frequency distribution of the glass powder on a volume basis has a plurality of maximum peaks, and in any two of the plurality of maximum peaks, the particle diameter of the maximum peak on the small diameter side is the maximum on the large diameter side. It is 0.01 times or more and 0.50 times or less of the peak particle diameter.

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.

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, SnO, ZrO ₂ , MoO ₃ , La ₂ O ₃ , Nb ₂ O ₅ , Ta ₂ O ₅ , Y ₂ O ₃ , TiO ₂ , GeO ₂ , TeO _2, and Lu ₂ O _{3, and the} like can be mentioned. SiO ₂ , K ₂ O, Na ₂ O, Li ₂ It is preferable to use at least one selected from 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.

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

Specifically, for example, in the case of B ₂ O ₃ —SiO ₂ glass, the content ratio of B ₂ O ₃ is preferably 1% by mass or more and 90% by mass or less, and preferably 3% by mass or more and 80% by mass. The following is more preferable.

  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.

As described above, the frequency distribution of the glass powder has a plurality of maximum peaks, and in any two of the plurality of maximum peaks, the particle diameter of the maximum peak on the small diameter side is the maximum on the large diameter side. It is 0.01 times or more and 0.50 times or less of the peak particle diameter. The plurality of maximum peaks may have at least two maximum peaks satisfying the above relationship, and may have maximum peaks other than the two maximum peaks satisfying the above relationship.
The particle diameter of the maximum peak on the small diameter side is desirably 0.04 to 0.50 times the particle diameter of the maximum peak on the large diameter side, and is 0.08 to 0.50 times. Is more desirable.

  By having two maximum peaks in which the frequency distribution of the glass powder satisfies the above relationship, in the p-type diffusion layer forming composition applied on the substrate, a small glass powder is filled in a gap between relatively large glass powders, The contact area between the glass powder and the substrate increases. Therefore, it is considered that the acceptor element in the glass powder is easily diffused to the substrate uniformly throughout the region where the p-type diffusion layer is formed, and a p-type diffusion layer with small in-plane variation is obtained. In addition to having a maximum peak on both the large-diameter side and the small-diameter side, the packing density of the glass powder is increased as described above as compared with the case where there is no maximum peak on the small-diameter side. The viscosity of the p-type diffusion layer forming composition can be kept low compared with the case where there is no maximum peak on the diameter side, and the dispersibility reduction of the glass powder can be suppressed.

The particle diameter of the maximum peak on the small diameter side is desirably 0.01 μm or more and 5 μm or less. When the particle diameter of the maximum peak on the small diameter side is within the above range, for example, even if unevenness (texture) exists on the surface of the substrate, glass powder having a particle diameter within the above range is in the uneven valley portion. Get in. That is, as will be described later, on the surface of the substrate, for example, the depth is 0.1 μm or more and 10 μm or less, and the interval is 0. After forming irregularities (textures) of infinite number of pyramids of 1 μm or more and 10 μm or less, both the p-type diffusion layer and the n-type diffusion layer are partially formed (for example, in a comb shape). There is a case. Even when the p-type diffusion layer forming composition is applied to the substrate having such irregularities, the glass powder having the particle diameter in the above range enters the valley portion as described above, and further, the glass powder and the substrate The contact area increases. Therefore, it is considered that the acceptor element in the glass powder is more easily diffused into the substrate, and a p-type diffusion layer with small in-plane variation is obtained.
The particle diameter of the maximum peak on the small diameter side is more preferably 0.01 μm or more and 4 μm or less.

  The particle diameter of the maximum peak on the large diameter side is not particularly limited as long as the above relationship is satisfied, but the viewpoint of improving the contact area between the glass powder and the substrate and the viscosity of the p-type diffusion layer forming composition are kept low. From the viewpoint of improving the dispersibility of the glass powder, it is preferably from 0.5 μm to 30 μm, and more preferably from 1 μm to 25 μm.

As a method for obtaining glass powder having two maximum peaks whose frequency distribution satisfies the above relationship, for example, control of pulverization conditions (for example, type of dispersion medium, shear strength during pulverization, pulverization time, etc.) (for example, weakening of shear strength) In addition to a method of obtaining a glass powder having two maximum peaks, a method of preparing two types of glass powders having different volume average particle diameters by controlling the grinding conditions.
As a method for producing a p-type diffusion layer forming composition using two types of glass powders having different volume average particle diameters, specifically, for example, the first glass powder and the volume average particle diameter are The manufacturing method including the process of mixing the 2nd glass powder which is 0.01 to 0.50 times the volume average particle diameter in 1 glass powder, and a dispersion medium is mentioned. In the mixing step, for example, the first glass powder and the second glass powder may be added to the dispersion medium and mixed, or the dispersion medium added with the first glass powder and the second glass powder may be mixed. The dispersion medium to which the glass powder is added may be mixed, or the first glass powder and the second glass powder may be mixed and then the mixture may be added to the dispersion medium.

  As a method for controlling the volume average particle size of the first glass powder and the volume average particle size of the second glass powder to satisfy the above relationship, for example, the volume average particle size of the first glass powder is Examples include a method of controlling the particle diameter of the maximum peak on the large diameter side and controlling the volume average particle diameter of the second glass powder to the particle diameter of the maximum peak on the small diameter side. However, depending on the mixing ratio of the first glass powder and the second glass powder, the particle size distribution, etc., the volume average particle diameter of the controlled first glass powder and the second glass powder, the large diameter side and The particle diameter of the maximum peak on the small diameter side may not match. In such a case, the volume average particle diameters of the first glass powder and the second glass powder may be controlled so that the target maximum peak is obtained.

Here, the frequency distribution of the glass powder is measured, for example, by using a particle size distribution measuring device (manufactured by Beckman Coulter, Inc., model number: LS13320) as a measuring device, and measuring a dispersion in which the glass powder is dispersed in a solvent (for example, water). The particle size obtained in this way is obtained, for example, by dividing it by 0.01 μm to 50 μm (depending on the particle size range to be measured), and drawing the frequency distribution on the volume basis from the small diameter side.
The volume average particle diameter is obtained by drawing a cumulative distribution of the particle diameter obtained by the above method from the small diameter side with respect to the volume, and the particle diameter at 50% accumulation is defined as the volume average particle diameter.

The ratio of the peak height at the maximum peak on the large diameter side to the peak height at the maximum peak on the small diameter side is preferably in the range of 1: 5 to 100: 1, and more preferably in the range of 1: 3 to 50: 1. .
The ratio of the peak height corresponds to the blending ratio of the first glass powder and the second glass powder, and the blending ratio of the first glass powder and the second glass powder ( The mass ratio is preferably in the range of 20: 1 to 1:20, more preferably in the range of 10: 1 to 1:10.

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.

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 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.

  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, 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 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 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 n-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 make the n-type diffusion layer 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.

[Example 1]
B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) glass powder (trade name: TMX-404, manufactured by Toago Material Technology Co., Ltd.) 10 g (volume average by grinding with a bead mill) B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) glass powder (trade name: TMX-404, manufactured by Toago Material Technology Co., Ltd.) 10 g (pulverized with a bead mill to a volume average particle size of 1 μm), 0.5 g of ethyl cellulose, and 10 g of 2- (2-butoxyethoxy) ethyl acetate were mixed to form a paste, and a p-type diffusion layer forming composition was obtained. Prepared.

  When the volume frequency particle size distribution of the obtained p-type diffusion layer forming composition was determined, there were two maximum peaks, the particle diameter of the maximum peak on the large diameter side was 10 μm, and the particle diameter of the maximum peak on the small diameter side was 1 μm. Met.

Next, the prepared p-type diffusion layer forming composition was applied to the surface of a p-type silicon substrate having an n-type layer formed on the surface so as to have an application amount of 70 g / m ² by screen printing. Dry on plate 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 hydrofluoric acid for 5 minutes to remove the glass layer, washed with running water, and dried.

The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 195 to 207Ω / □, and B (boron) was diffused to form a p-type diffusion layer. Further, the substrate was not warped.
In addition, the value of the sheet resistance on the above surface was obtained by measuring 5 points × 5 points at an equal interval in a region of 156 cm × 156 cm and showing the minimum value and the maximum value (the same applies to the following examples and comparative examples). ).

[Example 2]
Example 1 except that B ₂ O ₃ —SiO ₂ —RO (R: Mg, Ca, Sr, Ba) glass powder (trade name: TMX-603, manufactured by Toago Material Technology Co., Ltd.) was used. A p-type diffusion layer was formed in the same manner as described above. The sheet resistance on the surface on which the p-type diffusion layer forming composition was applied was 40 to 49Ω / □, and B (boron) was diffused to form a p-type diffusion layer. Further, the substrate was not warped.

[Example 3]
Example 1 except that B ₂ O ₃ —SiO ₂ —RO (R: Mg, Ca, Sr, Ba) -based glass powder (trade name: TMX-403, manufactured by Toago Material Technology Co., Ltd.) was used. A p-type diffusion layer was formed in the same manner as described above. The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 40 to 42 Ω / □, and B (boron) was diffused to form a p-type diffusion layer. Further, the substrate was not warped.

[Example 4]
As glass powder, B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) -based glass powder (trade name: TMX-404, manufactured by Toago Material Technology Co., Ltd.) 10 g (bead mill) ground to have a volume average particle diameter _{5μm), B 2 O 3 -SiO} 2 -R 2 O (R: Na, K, Li) based glass powder (trade name: TMX-404, manufactured by Tokan material technology (Co. P) Diffusion layer forming composition was prepared in the same manner as in Example 1 except that 10 g (made by a company) and pulverized with a bead mill to have a volume average particle size of 2.5 μm were used.

  When the frequency distribution of the obtained p-type diffusion layer forming composition was determined, there were two maximum peaks, the particle diameter of the maximum peak on the large diameter side was 5 μm, and the particle diameter of the maximum peak on the small diameter side was 2.5 μm. Met.

Moreover, p-type diffusion layer formation was performed like Example 1 using the obtained p-type diffusion layer forming composition.
The sheet resistance on the surface on which the p-type diffusion layer forming composition was applied was 114 to 128 Ω / □, and B (boron) was diffused to form a p-type diffusion layer. Further, the substrate was not warped.

[Comparative Example 1]
As glass powder, 20 g of B ₂ O ₃ —SiO ₂ —R ₂ O (R: Na, K, Li) glass powder (trade name: TMX-404, manufactured by Toago Material Technology Co., Ltd.) A p-type diffusion layer forming composition was prepared in the same manner as in Example 1 except that only the pulverized and volume average particle size of 10 μm was used.

  When the volume frequency particle size distribution of the obtained p-type diffusion layer forming composition was determined, the maximum peak was present only at 10 μm.

Moreover, p-type diffusion layer formation was performed like Example 1 using the obtained p-type diffusion layer forming composition.
The sheet resistance of the surface on which the p-type diffusion layer forming composition was applied was 198 to 253Ω / □, and the in-plane variation in sheet resistance was large.

  From the above results, it can be seen that the p-type diffusion layer can be formed without causing warpage of the substrate by using the p-type diffusion layer forming composition prepared in the example. Moreover, in an Example, it turns out that the in-plane variation of the sheet resistance of the surface at the side which apply | coated the p-type diffused layer formation composition is small.

Claims (7)

A p-type diffusion layer forming composition that is applied onto a semiconductor substrate and forms a p-type diffusion layer on the semiconductor substrate,
Containing glass powder containing an acceptor element, and a dispersion medium,
The frequency distribution of volume-based glass powder has two maximum peaks, particle size of the maximum peak of the small diameter side, 0.50 times 0.01 times of the particle diameter of the maximum peak of the large diameter side A p-type diffusion layer forming composition.   2. The p-type diffusion layer forming composition according to claim 1, wherein the particle diameter of the maximum peak on the small diameter side is 0.01 μm or more and 5 μm or less.   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 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, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, Tl 2 O, SnO, ZrO 2, and of claims 1 to 3 containing at least one glass component material selected from MoO ₃ The p-type diffusion layer forming composition according to any one of the above. It is a manufacturing method of the p-type diffused layer formation composition of any one of Claims 1-4,
A first glass powder containing an acceptor element; and a second glass powder containing an acceptor element and having a volume average particle size of 0.01 to 0.50 times the volume average particle size of the first glass powder. The manufacturing method of a p-type diffused layer formation composition including the process of mixing glass powder and a dispersion medium.   The manufacturing method of the p-type diffused layer which has the process of apply | coating the p-type diffused layer formation composition of any one of Claims 1-4, and the process of performing a thermal-diffusion process. Applying a p-type diffusion layer forming composition according to any one of claims 1 to 4 on a semiconductor substrate;
Applying a thermal diffusion treatment to form a p-type diffusion layer;
The manufacturing method of the photovoltaic cell which has this.