Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
1999-05-05
2001-03-06
Picardat, Kevin M. (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S753000, C438S964000, C136S256000, C136S258000
Reexamination Certificate
active
06197611
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a crystalline silicon solar cell, and in more detail relates to a method for producing a high performance solar cell with a low production cost.
2. Description of the Related Art
Concave and convex patterns with a minute pyramidal (square pyramidal) shape called as a texture are formed on the surface of the crystalline silicon solar cell. The light reflected from one spot impinges again to the other spot of the surface of the crystalline solar cell by virtue of the texture structure composed of these inclined pyramidal surfaces, penetrating into the solar cell to be effectively absorbed in the solar cell. Although a portion of the impinging light that has not been fully absorbed but arrives at the back face of the solar cell is reflected back to the surface again, it can be reflected again at the surface comprising steeply inclined pyramidal surfaces, thereby confining the light in the solar cell to improve absorption of light and to enhance power generation.
The texture structure was formed in the conventional art by immersing the silicon wafer exposing (100) face into a mixed solution prepared by adding 5 to 30% by volume of isopropyl alcohol into an aqueous solution of sodium hydroxide (NaOH) or potassium hydroxide (KOH), warmed at a temperature of 60 to 95° C. with a concentration of several to more than ten percent. The etching speed with an alkali solution is the fastest on the (100) face of silicon and the slowest on the (111) face. Accordingly, when the (111) face accidentally appears during etching process of the (100) face as an initial face, the (111) face with slow etching speed is advantageously left on the surface. Since this (111) face is inclined by about 54 degree against the (100) face, pyramidal projections constituted of the (111) face and its equivalent faces are formed.
However, it was a problem that the method as described above requires a high process cost because the process uses isopropyl alcohol (IPA) as well as a high disposal cost of its drainage containing alcohol.
A method for forming textures with an aqueous solution of potassium carbonate (K
2
CO
3
) was presented at the 14th EUROPEAN PHOTOVOLTAIC SOLAR ENERGY CONFERENCE (BARCELONA, 1997) for solving the foregoing problem. In this method, silicon is etched in an aqueous solution of potassium carbonate (K
2
CO
3
) with a concentration of 1 to 30% by weight heated at 90 to 100° C. According to the report, the lowest reflectance (a mean reflectance of 12.3% at 400 to 1100 nm) was obtained by an etching using 30% by weight of an etching solution under the condition of 100° C. for 30 minutes.
The conventional art involves a problem that the method as described above requires a high process cost because the process uses isopropyl alcohol (IPA) as well as a high disposal cost of its drainage containing an alcohol. The method for forming textures using potassium carbonate (K
2
CO
3
) was presented for solving the foregoing problems. However, an examination for confirming the above result revealed that, although good textures are formed, uniformity of the pyramidal projections on the surface was poor.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for producing a silicon solar cell capable of producing the solar cell having a high luminous energy efficiency with a low production cost without using isopropyl alcohol (IPA) while forming highly uniform textures on the crystal face.
The present invention provides a method for producing a solar cell comprising the step of immersing a silicon substrate into an etching solution to form minute concave and convex patterns on the surface of the silicon substrate, wherein the etching solution is an aqueous solution containing sodium carbonate (Na
2
CO
3
).
The present invention also provides the above method wherein a concentration of sodium carbonate (Na
2
CO
3
) is preferably 8 to 23% by weight (a saturated solution).
The present invention also provides the above method wherein a temperature of the aqueous sodium carbonate (Na
2
CO
3
) solution is 80 to 100° C.
The present invention also provides a method for producing a silicon solar cell comprising the step of immersing a silicon substrate into a mixed etching solution to form minute concave and convex patterns on the surface of the silicon substrate, wherein the etching solution is a mixed solution of the aqueous sodium carbonate (Na
2
CO
3
) solution and an aqueous sodium hydroxide (NaOH) solution.
The present invention also provides a method for producing a silicon solar cell comprising the step of immersing a silicon substrate into a mixed etching solution to form minute concave and convex patterns on the surface of the silicon substrate, wherein the etching solution is a mixed solution of the aqueous sodium carbonate (Na
2
CO
3
) solution and an aqueous sodium bicarbonate (NaHCO
3
) solution.
The present invention also provides a method for producing a silicon solar cell comprising the step of immersing a silicon substrate into a mixed etching solution to form minute concave and convex patterns on the surface of the silicon substrate, wherein the etching solution is a mixed solution of the aqueous sodium carbonate (Na
2
CO
3
) solution, aqueous sodium bicarbonate (NaHCO
3
) solution and aqueous sodium hydroxide (NaOH).
The present invention also provides the above method further comprising the step of immersing the silicon substrate in an acid after forming minute concave and convex patterns on the surface of the silicon substrate.
In accordance with the method of the present invention, minute concave and convex patterns with high uniformity can be formed on the crystal face with a low production cost to provide a solar cell with high luminous energy efficiency, along with lowering the production cost including the cost of drainage disposal.
REFERENCES:
patent: 5759292 (1998-06-01), Arimoto et al.
patent: 6072117 (2000-06-01), Matsuyama et al.
Zaidi et al., “Si Texturing with Sub-Wavelength Structures,” IEEE 26th PVSC, pp. 171-174, Oct. 1997.
Einhaus et al., “Isotropic Texturing of Multicrystalline Silicon Wafers with Acipic Texturing Solutions,” IEEE 26thPVSC, pp. 167-170, Oct. 1997.
Hylton et al., “Determination of Fact Orientations of Alkaline Etched Multicrystalline Wafers,” IEEE 25th PVSC, pp. 725-732, May 1996.
Stocks et al. “Texturing of Polycrystalline Silicon,” IEEE First WCPEC, pp. 1551-1554, Dec. 1994.
Photovoltaic Solar Energy Conference, Proceedings of the International Conference, Jun. 30, 1997-Jul. 4, 1997, vol. 1, pp. 812-815.
Mitsubishi Denki & Kabushiki Kaisha
Picardat Kevin M.
LandOfFree
Method for producing silicon solar cell does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing silicon solar cell, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing silicon solar cell will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2511623