An Innovative Technique of Preparing Solar Grade Silicon Wafers from Metallurgical Grade Silicon by In-Situ Purification

75655-The photovoltaics industry has found that traditional sources of secondary grade polysilicon are no longer readily available at inexpensive prices, and prices are getting significantly higher. Reducing the cost of the silicon wafers is the key to lowering the price of crystalline silicon solar cells to competitive levels. This project will develop a single-step wafer fabrication process in which metallurgical grade silicon (MGSi) is purified by dissolving it in a tin (Sn) melt. The solar silicon wafers then can be drawn directly from the Sn-dissolved MGSi melt by edge-defined film growth (EFG) or ribbon growth methods. Phase I will determine the feasibility of EFG growth of thin silicon wafers from tin-dissolved MGSi. The effect of such control parameters as concentration, temperature, and pulling speed will be studied. The resulting silicon wafers will be characterized and processed into solar cells. Commercial Applications and Other Benefits as described by the awardee: The proposed technology should be a cost effective way to fabricate solar cells. Instead of using more expensive solar grade silicon (at $20 per kg), it uses metallurgical grade silicon (at $2 per kg) as a direct feedstock.