JP2005251928A - Polycrystal silicon solar cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solar cell capable of enhancing photoelectric conversion efficiency. <P>SOLUTION: The polycrystal silicon solar cell comprises a first conductive type high concentration impurity region 7 formed in the vicinity of a crystal grain boundary 5 of a substrate from the surface side of a first conductive type polycrystal silicon substrate 1, and a second conductive type impurity layer 9 formed on the surface side of the substrate. Electric resistance is reduced in the vicinity of the crystal grain boundary 5 by the high concentration impurity region 7. As a dangling bond in the vicinity of the crystal grain boundary 5 is made inactive by high concentration impurities, the center of recoupling is decreased and the photoelectric conversion efficiency is enhanced. Further, since the dangling bond is made inactive by impurities of the same conductive type as the substrate 1, the high concentration impurity region 7 of the same conductive type as the substrate 1 is formed in the vicinity of the crystal grain boundary 5. For this reason, the electric resistance is decreased in the vicinity of the crystal grain boundary 5, thus leading to the enhancement of the photoelectric conversion efficiency. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polycrystalline silicon solar cell and a method for manufacturing the same.

In polycrystalline silicon solar cells, the presence of crystal grain boundaries greatly affects the quality. A large number of dangling bonds exist at the crystal grain boundaries of polycrystalline silicon. Since these dangling bonds serve as carrier recombination centers, the lifetime of the carriers is greatly shortened. In addition, the strain appearing at the grain boundary portion affects the energy band in the polycrystalline silicon semiconductor to form a depletion region, which hinders carrier movement. Thus, the existence of crystal grain boundaries greatly deteriorates the device characteristics using polycrystalline silicon. Conventionally, inactivation of grain boundaries using hydrogen passivation by methods such as hydrogen plasma treatment and hydrogen ion implantation has been performed. (For example, refer to Patent Document 1).
JP-A-7-183552

  However, although the photoelectric conversion efficiency is improved to some extent by the inactivation of the grain boundaries by hydrogen passivation or the like, it is not sufficient.

  This invention is made | formed in view of the situation which concerns, and provides the solar cell which can further improve a photoelectric conversion efficiency.

  The polycrystalline silicon solar cell according to the present invention is formed on the surface side of the first conductivity type polycrystalline silicon substrate from the surface side of the first conductivity type and is formed on the surface side of the substrate. The second conductivity type impurity layer is provided, and the electrical resistance of the substrate in the vicinity of the crystal grain boundary is reduced by the high concentration impurity region.

  According to the present invention, the dangling bonds in the vicinity of the crystal grain boundaries are inactivated by a high concentration of impurities, so that the number of recombination centers is reduced and the photoelectric conversion efficiency is improved.

  In addition, since the dangling bond is inactivated by the impurity having the same conductivity type as that of the substrate, a high concentration impurity region having the same conductivity type as that of the substrate is formed in the vicinity of the crystal grain boundary. Therefore, the electrical resistance of the substrate in the vicinity of the crystal grain boundary is reduced, leading to an improvement in photoelectric conversion efficiency.

  The polycrystalline silicon solar cell of the present invention is formed on the surface side of the first conductivity type polycrystalline silicon substrate from the surface side of the first conductivity type and is formed on the surface side of the substrate. The second conductivity type impurity layer is provided, and the electrical resistance of the substrate in the vicinity of the crystal grain boundary is reduced by the high concentration impurity region.

1. Polycrystalline Silicon Substrate As the first conductivity type polycrystalline silicon substrate, an n-type or p-type polycrystalline silicon substrate can be used. The impurity concentration of the polycrystalline silicon substrate is preferably about 1 × 10 ¹⁵ atoms / cm ³ .

2. High concentration impurity region 2-1. Configuration A first conductivity type high concentration impurity region is formed in the vicinity of a crystal grain boundary of the substrate from the surface side of the first conductivity type polycrystalline silicon substrate. The high concentration impurity region may be formed in the vicinity of the front surface of the substrate, for example, in the vicinity of the pn junction, or may reach the back surface of the substrate. In either case, the effect of reducing the recombination center and reducing the electrical resistance of the substrate in the vicinity of the crystal grain boundary can be obtained, and as a result, the photoelectric conversion efficiency can be improved.

The high concentration impurity region preferably has a concentration of 1 × 10 ¹⁸ to 1 × 10 ²⁰ atoms / cm ³ . This is because when the density is smaller than 1 × 10 ¹⁸ , the effect of providing the high-concentration impurity region is not sufficient, and when the density is larger than 1 × 10 ²⁰ , the distortion of the crystal structure of Si increases and the characteristics of the solar cell are deteriorated. is there. The high concentration impurity region is preferably formed by doping B or Al in the vicinity of the crystal grain boundary of the substrate.

2-2. Formation Method The high-concentration impurity region includes, for example, a process of (a) forming an impurity layer made of a first conductivity type impurity on the substrate surface, and (b) diffusing the impurity near the crystal grain boundary of the substrate by heat treatment. The method can be used to form.

  Since the diffusion rate of atoms is large in the vicinity of the crystal grain boundary, the first conductivity type impurity contained in the impurity layer is preferentially diffused in the vicinity of the crystal grain boundary to form a high concentration impurity region.

The impurity layer made of the first conductivity type impurity preferably has a thickness of 1 to 50 μm. This is because when the thickness is smaller than 1 μm, the first conductivity type impurity cannot be sufficiently diffused in the vicinity of the crystal grain boundary, and when it is larger than 50 μm, it takes time to remove the impurity layer in a subsequent process. This impurity layer can be formed by, for example, a screen printing method.
The first conductivity type impurity is preferably composed of lead borosilicate, B ₂ O ₃ , or Al.

  Moreover, it is preferable that heat processing is performed at 800 degreeC below. When the temperature is higher than 800 ° C., the impurity diffuses also in the portion other than the grain boundary of the p-type polycrystalline silicon substrate. As a result, the impurity concentration of the substrate deviates from the design value, and the device characteristics may be deteriorated. It is. The heat treatment is preferably performed at a temperature equal to or higher than the melting point of the impurity layer. This is because impurities are not sufficiently diffused at a temperature lower than the melting point.

2-3. Post-processing It is preferable to remove the impurity layer made of the first conductivity type impurity after forming the high-concentration impurity region. It is also preferable to remove the Si alloy layer formed in the step of forming the high concentration impurity region. These are preferably removed with an acid. Moreover, it is preferable to use hydrochloric acid or hydrofluoric acid as the acid. It is preferable to use these acids because they have a sufficient removal effect, and because these acids are frequently used in other cleaning steps of the solar cell, the steps can be simplified.

3. Second conductivity type impurity layer 3-1. Configuration An impurity layer of the second conductivity type is formed on the surface side of the substrate. “Substrate surface side” means on the surface of the substrate or in the vicinity of the surface of the substrate.

3-2. Manufacturing Method When the second conductivity type impurity layer is formed on the surface of the substrate, it can be formed by, for example, a CVD method. In addition, when the second conductivity type impurity layer is formed near the surface of the substrate, for example, an impurity layer made of the second conductivity type impurity is formed on the substrate surface, and the impurity is diffused by heat treatment. can do. The second conductivity type impurity layer may be formed by ion implantation of the second conductivity type impurity near the surface of the substrate. Regardless of which method is used, the second conductivity type impurity layer can be formed under known conditions.

4). Others 4-1. Antireflection Film The polycrystalline silicon solar cell of the present invention preferably further includes an antireflection film on the second conductivity type impurity layer. In this case, surface reflection of light incident on the solar cell can be reduced, and as a result, photoelectric conversion efficiency can be improved. The antireflection film is preferably made of a transparent film such as a silicon oxide film. The antireflection film can be formed by a CVD method or the like.

4-2. Back surface electric field layer The polycrystalline silicon solar cell of the present invention preferably includes a back surface electric field layer on the back surface side of the substrate. By forming the back surface electric field layer, carrier recombination loss can be reduced, and as a result, photoelectric conversion efficiency can be improved. The back surface electric field layer can be formed, for example, by printing an Al paste on the back surface of the substrate and heat-treating the substrate.

4-3. Front / Back Electrodes In addition to the above configuration, the front / back electrodes are formed on the front / back sides of the substrate to form the polycrystalline silicon solar cell of the present invention. The front and back electrodes can be formed using a silver paste, for example. The front and back electrodes can be formed by a vapor deposition method or the like.

  FIG. 1 is a cross-sectional view illustrating the manufacturing process of the polycrystalline silicon solar cell according to the first embodiment. Hereinafter, the manufacturing method of the polycrystalline silicon solar cell according to the present embodiment will be described with reference to FIG.

  First, the p-type impurity layer 3 made of Al paste is screen-printed with a thickness of about 50 μm on the surface of the p-type polycrystalline silicon substrate 1 to obtain the structure shown in FIG.

  Next, the p-type impurity layer 3 is dried at 200 ° C. for 1 minute and baked at 700 ° C. for 1 minute. By this step, Al diffuses in the vicinity of the crystal grain boundary 5, and a p-type high concentration impurity region 7 is formed in the vicinity of the crystal grain boundary 5 of the substrate 1 to obtain the structure shown in FIG. The high-concentration impurity region 7 is formed because the diffusion rate of atoms is high in the vicinity of the crystal grain boundary 5, so that the p-type impurity contained in the impurity layer 3 is preferentially diffused in the vicinity of the crystal grain boundary 5. is there. By forming the high-concentration impurity region 7, dangling bonds in the vicinity of the crystal grain boundaries 5 are inactivated by the high-concentration impurities, so that the number of recombination centers is reduced and the photoelectric conversion efficiency is improved. Further, since the dangling bond is inactivated by the impurity having the same conductivity type as that of the substrate 1, a high concentration impurity region 7 having the same conductivity type as that of the substrate 1 is formed in the vicinity of the crystal grain boundary 5. Therefore, the electrical resistance in the vicinity of the crystal grain boundary 5 is reduced, which leads to further improvement in photoelectric conversion efficiency.

  Next, the obtained substrate 1 is immersed in hydrochloric acid for 10 minutes, and the Al paste layer 3 and the AlSi alloy layer generated in the firing / diffusion process are removed to obtain the structure shown in FIG.

Next, the p ⁺ layer 8 is formed on the back side of the substrate 1 and the n ⁺ layer 9 is formed on the light receiving side to obtain the structure shown in FIG. The p ⁺ layer 8 is formed by printing an Al paste on the back surface of the substrate 1 and heat-treating the substrate 1. The n ⁺ layer 9 is formed by applying POCl ₃ to the surface of the substrate 1 and thermally diffusing it at 850 ° C. for 20 minutes.

  Next, the antireflection film 10 is formed on the surface of the substrate 1, and the front and back electrodes 11 and 12 are formed on the front and back sides of the substrate 1 to obtain the structure shown in FIG. The manufacture of the solar cell of the example is completed. The front and back electrodes are formed by vapor deposition using silver paste.

  A method for manufacturing a polycrystalline silicon solar cell according to Example 2 will be described with reference to FIG.

First, the p-type impurity layer 3 made of B ₂ O ₃ is applied on the surface of the p-type polycrystalline silicon substrate 1 to a thickness of about 50 μm, thereby obtaining the structure shown in FIG.

  Next, the p-type impurity layer 3 is heat-treated at 500 ° C. for 10 minutes. By this step, B diffuses in the vicinity of the crystal grain boundary 5, and a p-type high concentration impurity region 7 is formed in the vicinity of the crystal grain boundary 5 of the substrate 1, thereby obtaining the structure shown in FIG. The principle of forming the high concentration impurity region 7 and the effect thereof are the same as those in the first embodiment.

Next, the obtained substrate 1 is immersed in hydrofluoric acid for 10 minutes, and the B ₂ O ₃ layer 3 and the alloy layer generated in the firing / diffusion process are removed to obtain the structure shown in FIG.

Next, the p ⁺ layer 8 is formed on the back side of the substrate 1 and the n ⁺ layer 9 is formed on the light receiving side to obtain the structure shown in FIG. The p ⁺ layer 8 is formed by printing an Al paste on the back surface of the substrate 1 and heat-treating the substrate 1. The n ⁺ layer 9 is formed by applying POCl ₃ to the surface of the substrate 1 and thermally diffusing it at 850 ° C. for 20 minutes.

  Next, the antireflection film 10 is formed on the surface of the substrate 1, and the front and back electrodes 11 and 12 are formed on the front and back sides of the substrate 1 to obtain the structure shown in FIG. The manufacture of the solar cell of the example is completed. The front and back electrodes are formed by vapor deposition using silver paste.

  A method for manufacturing a polycrystalline silicon solar cell according to Example 3 will be described with reference to FIG.

  First, a p-type impurity layer 3 made of lead borosilicate is screen-printed with a thickness of about 50 μm on the surface of the p-type polycrystalline silicon substrate 1 to obtain the structure shown in FIG.

  Next, the p-type impurity layer 3 is dried at 200 ° C. for 1 minute, and further baked at 700 ° C. for 1 minute. By this step, B diffuses in the vicinity of the crystal grain boundary 5, and a p-type high concentration impurity region 7 is formed in the vicinity of the crystal grain boundary 5 of the substrate 1, thereby obtaining the structure shown in FIG. The principle of forming the high concentration impurity region 7 and the effect thereof are the same as those in the first embodiment.

  Next, the obtained substrate 1 is immersed in hydrofluoric acid for 10 minutes, and the lead borosilicate layer 3 and the alloy layer generated in the firing / diffusion process are removed to obtain the structure shown in FIG.

Next, the p ⁺ layer 8 is formed on the back side of the substrate 1 and the n ⁺ layer 9 is formed on the light receiving side to obtain the structure shown in FIG. The p ⁺ layer 8 is formed by printing an Al paste on the back surface of the substrate 1 and heat-treating the substrate 1. The n ⁺ layer 9 is formed by applying POCl ₃ to the surface of the substrate 1 and thermally diffusing it at 850 ° C. for 20 minutes.

  Next, the antireflection film 10 is formed on the surface of the substrate 1, and the front and back electrodes 11 and 12 are formed on the front and back sides of the substrate 1 to obtain the structure shown in FIG. The manufacture of the solar cell of the example is completed. The front and back electrodes are formed by vapor deposition using silver paste.

It is sectional drawing which shows the manufacturing process of the polycrystalline silicon solar cell which concerns on Example 1 of this invention.

Explanation of symbols

1 p-type polycrystalline silicon substrate 3 p-type impurity layer 5 crystal grain boundary 7 high-concentration impurity region 8 p ⁺ layer 9 n ⁺ layer 10 antireflection film 11 surface electrode 12 back electrode

Claims (11)

  A first conductivity type high concentration impurity region formed in the vicinity of a grain boundary of the substrate from the surface side of the first conductivity type polycrystalline silicon substrate; a second conductivity type impurity layer formed on the surface side of the substrate; A polycrystalline silicon solar cell characterized in that the electrical resistance of the substrate in the vicinity of the crystal grain boundary is reduced by the high concentration impurity region. The solar cell according to claim 1, wherein the high concentration impurity region has a concentration of 1 × 10 ¹⁸ to 1 × 10 ²⁰ atoms / cm ³ .   The solar cell according to claim 1, wherein the high concentration impurity region is formed by doping B or Al in the vicinity of a crystal grain boundary of the substrate.   The high concentration impurity region is formed by (a) forming an impurity layer made of an impurity of the first conductivity type on the substrate surface, and (b) diffusing the impurity near the crystal grain boundary of the substrate by heat treatment. The solar cell according to claim 1.   The solar cell according to claim 4, wherein the impurity layer made of the first conductivity type impurity has a thickness of 1 to 50 μm. The solar cell according to claim 4, wherein the first conductivity type impurity is composed of lead borosilicate, B ₂ O ₃ , or Al.   The solar cell according to claim 4, wherein the heat treatment is performed at 800 ° C. or less.   (1) A first conductivity type high-concentration impurity region is formed in the vicinity of a grain boundary of the substrate from the surface side of the first conductivity type polycrystalline silicon substrate, and (2) a second conductivity type impurity is formed on the surface side of the substrate. A method for manufacturing a polycrystalline silicon solar cell, comprising a step of forming a layer, wherein the electrical resistance of the substrate in the vicinity of the crystal grain boundary is reduced by the high concentration impurity region.   In step (1), (a) an impurity layer made of an impurity of the first conductivity type is formed on the substrate surface, and (b) the impurities are diffused in the vicinity of the crystal grain boundary of the substrate by heat treatment. 9. The manufacturing method according to claim 8, which is a step of forming a high-concentration impurity region of the first conductivity type in the vicinity of the boundary.   The manufacturing method according to claim 9, further comprising a step of removing the impurity layer made of the first conductivity type impurity and the Si alloy layer formed in the step (1) with an acid after the step (1).   The production method according to claim 10, wherein the acid is hydrochloric acid or hydrofluoric acid.

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