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

75655S The photovoltaics (PV) industry is having difficulty finding enough raw materials to match its rapid growth. In addition, traditional sources of secondary grade polysilicon are no longer readily available at inexpensive prices. Reducing the cost of solar silicon wafers is the key to lowering the price of crystalline silicon solar cells. 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. In Phase I, test runs were carried out with a broad range of tin concentrations. A significant amount of impurity reduction was observed when compared to the starting MGSi. It was also observed that the amount of tin incorporated into the growing wafer decreased along with the reduction in the solvent (tin) concentration, while the impurity reduction level remained more or less the same. Phase II will optimize the solution composition and processing conditions, construct a prototype system for solar wafer fabrication, characterize of the produced silicon materials, and evaluate of the photovoltaic properties of the fabricated wafers. Commercial Applications and Other Benefits as described by the awardee: Most commercial production in the photovoltaic industry is based on crystalline silicon, which is likely to be the preferred material for the near term. The proposed technology should be a cost effective way to fabricate these 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. In addition, energy costs would be greatly reduced.