1. Field of the Invention
The present invention relates to a method of manufacturing a silicon solar cell, and, more particularly to a method of electrically insulating electrodes of the solar cell.
2. Description of the Related Art
In a silicon solar cell, light is converted into electricity by separating and collecting carriers (electrons and holes) with the aid of diffusion potential of a pn junction of the solar cell. Carriers are generated when light is irradiated to the pn junction.
Silicon solar cells can be of two types: front-surface-junction solar cells and back-surface-junction solar cell. In a front-surface-junction solar cell, as shown in
In a back-surface-junction solar cell, as shown in
The solar cells can be formed by various methods. Diffusion layer formation method, for example, is commonly used. Gas is used as a diffusion source in the diffusion layer formation method which makes this method cost effective and suitable for mass production. In the diffusion layer formation method, although a diffusion layer can be advantageously formed on the entire surface of the substrate, a short circuit is disadvantageously formed between the first electrode and the second electrode via the diffusion layer.
Parallel resistance of the solar cell decreases due to formation of the short circuit, thereby reducing Fill Factor (FF) that directly contributes to conversion efficiency of the solar cell. Therefore, as described in Japanese Patent Laid-Open Publication No. H5-326990 (see Page 3, FIG. 1), a part of the diffusion layer needs to be removed to electrically insulate the first electrode and the second electrode from each other. In a method employed for a front-surface-junction crystalline silicon solar cell, silicon wafers are stacked and the diffusion layer on the edges is removed by means of plasma.
Thin silicon wafers are generally used to reduce cost. However, thin wafers are fragile and they can break easily. Moreover, when a structure is employed in which a plurality of silicon wafers are stacked, each silicon wafer needs to be handled separately.
Solar cells can be formed using etching methods (mask etching method). The etching methods include wet etching and dry etching. Wet etching includes etching using an acid or an alkali. Dry etching includes etching using Reactive Ion Etching (RIE). However, the etching methods include a lot of steps such as application of etching resist, drying, removal of etching resist, washing, etc. so that the etching methods are costlier.
It is an object of the present invention to at least solve the problems in the conventional technology.
According to an aspect of the present invention, a method of manufacturing a solar cell includes forming a diffusion layer on a crystal-type silicon substrate, wherein the diffusion layer has a conductivity opposite to that of the substrate, etching and removing a part of the diffusion layer by using sodium silicate, and forming a first electrode that makes an electric contact with the diffusion layer and forming a second electrode that makes an electric contact with the substrate.
The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.
Exemplary embodiments of the present invention will be described below with reference to accompanying drawings. The present invention is not limited to these embodiments.
The method of manufacturing is explained in detail next. A wafer of multicrystalline silicon is prepared as the p-type silicon substrate 1 shown in
The p-type silicon substrate 1 is then inserted in a diffusion furnace, and phosphorus oxychloride (POCl3) is passed in the diffusion furnace to form the n-type diffusion layer 2 as shown in
After removing phosphorus glass on the outside of the diffusion layer by etching, sodium silicate 10 is applied, as shown in
Once the sodium silicate 10 dries, silicon is etched from the part of the p-type silicon substrate 1 where the sodium silicate 10 is applied, including the n-type diffusion layer 2. Heat is generated during the etching process and the heat further accelerates the etching process. Water evaporates during the etching and the etching stops when water is completely evaporated. Next, the sodium silicate 10 is removed by washing with water, and the anti-reflection coating 4 including a silicon nitride film is deposited on the front surface of the p-type silicon substrate 1 by using plasma Chemical Vapor Deposition (CVD) method.
Then, as shown in
It is not necessary to apply the sodium silicate 10 before depositing the anti-reflection coating 4. In other words, sodium silicate 10 can also be applied after depositing the anti-reflection coating 4 or after formation of the electrodes.
In the first embodiment, a part of the n-type diffusion layer is etched and removed by means of sodium silicate. Thus, the need to stack silicon wafers is eliminated, thereby reducing the load on the silicon wafers, preventing cracking and enabling reliable solar cell manufacturing. Further, sodium silicate of controlled viscosity is applied by means of the dispenser, and therefore, a mask for etching resist and screen printing is not needed.
Moreover, because the n-type diffusion layer only in the periphery of the back surface of the p-type silicon substrate is etched, the n-type diffusion layer on the edges of the p-type silicon substrate can continue contributing to generation of electricity, thereby enabling to increase the output current.
The method of manufacturing is explained in detail next. A wafer of multicrystalline silicon similar to the wafer used in the first embodiment is prepared as the p-type silicon substrate 1 shown in
The p-type silicon substrate 1 is then inserted in the diffusion furnace, and phosphorus oxychloride (POCl3) is passed in the diffusion furnace to form the n-type diffusion layer 2 as shown in
After removing the phosphorus glass on the outside of the diffusion layer by etching, the sodium silicate 10 is applied, as shown in
Once the sodium silicate 10 dries, it is removed by washing with water in a sequence similar to that in the first embodiment. The anti-reflection coating 4 including a silicon nitride film is deposited on the front surface of the p-type silicon substrate 1 by using the plasma CVD method in a sequence similar to that in the first embodiment.
Then, as shown in
It is not necessary to apply the sodium silicate 10 before depositing the anti-reflection coating 4. In other words, the sodium silicate 10 can also be applied after depositing the anti-reflection coating 4.
In the second embodiment, a part of the n-type diffusion layer is etched and removed by means of sodium silicate. Thus, a reliable solar cell manufacturing method that reduces the load on the silicon wafers can be applied to the back-surface-junction solar cell. Moreover, the etching resist is not needed during etching and removing a part of the n-type diffusion layer, thereby simplifying the etching process.
According to the present invention, a part of a diffusion layer that has conductivity opposite to a substrate is etched and removed by means of sodium silicate, thereby removing the need to stack silicon wafers, reducing the load on the silicon wafers, preventing occurrence of cracking, and enabling reliable solar cell manufacturing. Moreover, etching resist during removal of the diffusion layer is unnecessary. As a result, an increase in the number of processes during the etching process is prevented, so that manufacturing costs can be suppressed.
Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.
Number | Date | Country | Kind |
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2005-226865 | Aug 2005 | JP | national |
Number | Name | Date | Kind |
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4137123 | Bailey et al. | Jan 1979 | A |
4322571 | Stanbery | Mar 1982 | A |
20020098700 | Alwan et al. | Jul 2002 | A1 |
20040063326 | Szlufcik et al. | Apr 2004 | A1 |
20050126627 | Hayashida | Jun 2005 | A1 |
Number | Date | Country |
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100 32 279 | Jan 2002 | DE |
05-326990 | Dec 1993 | JP |
11-214722 | Aug 1999 | JP |
Number | Date | Country | |
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20070031986 A1 | Feb 2007 | US |