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High efficiency low cost thin film silicon solar cell design and method for making

United States Patent

5,897,331
April 27, 1999
View the Complete Patent at the US Patent & Trademark Office
National Renewable Energy Laboratory - Visit the NREL Technology Transfer Website
Optical Furnace offers improved semiconductor device processing capabilities
A semiconductor device having a substrate, a conductive intermediate layer deposited onto said substrate, wherein the intermediate layer serves as a back electrode, an optical reflector, and an interface for impurity gettering, and a semiconductor layer deposited onto said intermediate layer, wherein the semiconductor layer has a grain size at least as large as the layer thickness, and preferably about ten times the layer thickness. The device is formed by depositing a metal layer on a substrate, depositing a semiconductive material on the metal-coated substrate to produce a composite structure, and then optically processing the composite structure by illuminating it with infrared electromagnetic radiation according to a unique time-energy profile that first produces pits in the backside surface of the semiconductor material, then produces a thin, highly reflective, low resistivity alloy layer over the entire area of the interface between the semiconductor material and the metal layer, and finally produces a grain-enhanced semiconductor layer. The time-energy profile includes increasing the energy to a first energy level to initiate pit formation and create the desired pit size and density, then ramping up to a second energy level in which the entire device is heated to produce an interfacial melt, and finally reducing the energy to a third energy level and holding for a period of time to allow enhancement in the grain size of the semiconductor layer.
Sopori; Bhushan L. (Denver, CO)
Midwest Research Institute (Kansas City, MO)
08/ 745,951
November 8, 1996
CONTRACTUAL ORIGIN OF THE INVENTION The United States Government has rights in this invention under Contract No. DE-AC0283CH10093 between the U.S. Department of Energy and the National Renewable Energy Laboratory, a Division of Midwest Research Institute.