Fundamental Aspects of Silicon Refining

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Silicon is the primary material for manufacture of solar cells, accounting for over 90 percent of today's market for photovoltaic (PV) materials. Nevertheless, the limited supply and high price of Si have created a major obstacle to realizing the technology's potential for becoming a major electricity producer. This is chiefly because currently there is no dedicated process for production of solar grade silicon (SoG-Si) at acceptable cost and high production rate. In the past several years, our Sustainable Materials Processing Research Group, along with several other groups have been striving for developing technologies that would produce SoG-Si at a lower cost compared to today's processes. Most of the emphasis in such research works has been development of process(es) through experimental work followed by optimization, that will reach commercial scale in the shortest time possible. Similar to any other development, often the fundamental aspects that are essential to optimizing the technology have not been looked into, in details in several cases. Though this discovery grant, the fundamental aspects of several silicon purification techniques will be investigated. In particular, four topics related to the thermodynamics of Si refining are of interest and will be studied (a) distribution of impurities (P and B) between solid silicon and binary silicon alloys with Fe, Cu, and Zn, (b) thermodynamics of impurity distribution between slag and metal for slags containing various oxides and under a range of oxygen potentials, (c) thermodynamics of P and B distribution between alloys of Si (with Cu, Al) and molten salt, and (d) solubility of silica in cryolite based molten salts. This kind of research is essential in supporting the previous activities related to developing a technology for generation of SoG-Si. In addition, such fundamental studies are critical in creating a knowledge base in the relatively young field of high purity Si processing by pyrometalllurgical techniques. The long term benefits are generation of clean energy through advancing solar energy field, and training several graduate and undergraduate students with expertise in the fields of materials processing, energy materials, and characterization.