Solar-grade silicon: the next decade

We survey the current silicon feedstock situation and its implications for silicon solar cell production. Prospects for Siemens-type processes (i.e., distillation and pyrolysis of chlorosilanes/silane) are considered. We argue that some new silicon solar cell technologies, such as AstroPower's Silicon-Film/spl trade/ product, can tolerate levels of impurities previously considered prohibitive for photovoltaic applications. This development will permit the use of low-cost metallurgical refining processes, such as directional solidification, slagging, sparging and other gas treatments, for purifying silicon. Such approaches have a realistic potential for producing virtually unlimited supplies of solar-grade silicon at prices in the neighborhood of $10/kg. Some of the more promising metallurgical routes for making solar-grade silicon will be overviewed and compared, especially from the perspective of Silicon-Film/spl trade/ sheet production.