Method for producing solar cell-grade silicon from rice hulls
AssigneeExxon Research & Engineering Co.
InventorsJames A. Amick, John V. Milewski, Franklin J. Wright
Life of this patent
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Abstract
The present invention relates to the production of high purity solar grade silicon from common rice hulls. A unique process for material purification and reduction includes leaching the rice hulls in acid followed by treatment with high purity water, coking the acid-cleaned hulls in a non-oxidizing ambient, compensating the carbon or silica content of the coked hulls to obtain a desired carbon to silica ratio and reducing the silica to produce high purity silicon.
Claims31
A process for producing solar grade high purity silicon from common rice hulls comprising:
- leaching the rice hulls in acid and in water,
- coking the leached rice hulls to produce a composite of carbon and silica,
- adjusting the carbon to silica ratio of the coked rice hulls to less than about 2:1,
- thermally reducing the adjusted carbon and silica mixture to produce elemental silicon.
A process for producing a silicon single crystal solar cell comprising:
- (a) leaching rice hulls in acid and water;
- (b) coking the leached rice hulls in a non-oxidizing atmosphere;
- (c) adjusting the carbon to silica content ratio to below about 2.5 to 1;
- (d) reducing the adjusted rice hulls at a temperature of about 1900.degree. C. to form silicon and carbon monoxide;
- (e) growing a single crystal boule from said silicon;
- (f) sawing said single crystal boule into thin wafers;
- (g) providing a suitable junction in or on said wafers;
- (h) providing ohmic contacts to either side of said junction to form a solar cell.
A process for producing a high purity feedstock of carbon and silica from common rice hulls which feedstock is capable of being reduced to high purity elemental silicon, said process comprising the steps of leaching the rice hulls in acid and in water then coking the leached rice hulls to provide a composite of carbon and silica.
A process for producing a carbon and silica feedstock from common rice hulls capable of being reduced to high purity elemental silicon comprising steps of:
- leaching the rice hulls in acid solution containing from 10% to 50% by volume HCl followed by rinsing the hulls in distilled deionized water, coking the leached rice hulls at a temperature of about 920.degree. C. in an atmosphere of argon containing 1% anhydrous HCl to produce a composite of carbon and silica having an impurity content less than about 100 ppm.
Dependencies are inferred from the claim text.