Recent progress in upgrading metallurgical-grade silicon to solar-grade silicon via pyrometallurgical routes

Abstract

Si-based photovoltaic solar power has been rapidly developed as a renewable and green energy source. The widespread use of Si-based solar cells requires large amounts of solar-grade Si (SoG−Si) to manufacture Si wafers. Chemical routes, mainly the modified Siemens process, have dominated the preparation of polycrystalline SoG−Si; however, traditional chemical techniques employ a series of complex chemical reactions involving various corrosive and hazardous reagents. In addition, large amounts of complex waste solar cells and Si kerf slurry waste gradually accumulate and are difficult to recycle using these approaches. New methods are required to meet the demand for SoG−Si preparation and Si waste recycling. The metallurgical route shows promise but is hindered by the problem of eliminating B and P from metallurgical-grade Si (MG−Si). Various pyrometallurgical treatments have been proposed to enhance the removal of B and P from MG−Si. This article reviews Si refining with slag treatment, chlorination, vacuum evaporation, and solvent refining, and summarizes and discusses the basic principles and recent representative studies of the four methods. Among these, solvent refining is the most promising and environmentally friendly approach for obtaining low-cost SoG−Si and is a popular research topic. Finally, a simple and green approach, i.e., a combination of solvent refining, slag treatment, or vacuum directional solidification, is proposed for low-cost SoG−Si preparation using MG−Si or Si wastes as raw materials.

Keywords

silicon refining / solar-grade silicon / solvent refining / vacuum evaporation / slag treatment / Si kerf slurry waste

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