High-Temperature Refining of Metallurgical-Grade Silicon: A Review

Among currently known alternatives for renewable energy sources, solar power is generally regarded as having the most potential to satisfy the ever-growing demand. While solar photovoltaic power is a well-established technology, its widespread uptake has been hindered by prohibitively high price of units and, thusly, the price of electricity. This is due mainly to the high cost of the silicon used to fabricate the devices. This article presents a review of the development of established pyrometallurgical techniques as applied to refining metallurgical silicon to solar grade for the purposes of reducing the reliance on expensive traditional silicon feedstock. Four basic high temperature methods: solvent refining, slag treatment, vaporization, and electrorefining are described and the limitation and advantages of each method are presented. It is apparent that these techniques are very useful for removing impurities from silicon, but are often selective and not able to remove all problematic elements. Therefore, refining may need to be as a sequence of steps, targeting specific elements each time, or as novel methods combining multiple techniques simultaneously. Ultimately, the successful approach will have to achieve large-scale production by cost-effective means to replace current methods