Silicon purification through metallurgical processes for PV silicon production

The photovoltaic (PV) industry is in rapid growth and a large supply of PV feedstock materials must be provided to maintain this growth. Since silicon is the dominant material for the fabrication of solar cells, low-cost solar-grade silicon (SoG-Si) feedstock is demanded. The most cost-effective and direct approach for producing SoG-Si is to purify and upgrade metallurgical-grade silicon (MG-Si). Many impurities in MG-Si can be effectively removed through directional solidification of molten silicon. However, the removal of boron (B) and phosphorus (P) by this method is difficult and expensive due to the relatively large distribution coefficients of these elements. Therefore, the elimination of B and P to the levels required for SoG-Si feedstock requires the development of new processes. In the present study, the effect of impurities on the solar cell efficiencies and the impurity contents in silicon materials are studied. The metallurgical processes that can be applied to purify metallurgical silicon to solar grade silicon are reviewed and evaluated. It is shown that under development metallurgical refining processes are applicable to produce solar grade silicon.

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