Upgrading metallurgical grade (MG) silicon for use as solar grade feedstock

The most attractive approach to upgrade metallurgical-grade (MG) silicon is to chemically refine impurities, especially boron (B) and phosphorus (P), in the molten state followed by directional solidification. The most problematic impurity is B as it has the highest segregation coefficient. A simple refining process of blowing gas through the melt was developed to reduce B in MG silicon effectively, and the process has been scaled up to charge sizes up to 150 kg. The B reduction has been maintained with increase in charge sizes and confirmed by using it on B-doped silicon at ten times the concentration. The simplicity of the refining process when adapted to a commercial MG silicon plant is expected to produce solar grade (SoG) silicon at low cost.