Synthesis and separation of Si-Fe alloy to produce high-purity silicon

The metallurgical route is a prospective method to replace the Siemens process to produce silicon for solar cells. However, the imperfect removal efficiencies of boron (B) and phosphorus (P) from silicon are the major issue. Herein, we report a novel approach to produce high-purity silicon for solar cells by the reaction of SiC with SiO2 and pure FeO (with low B and P) in vacuum, which first forms Si-Fe alloy and is followed by milling and acid leaching. Pure FeO can not only reduce the silicon formation temperature but also provide an abundance of pure iron elements that serve as an impurities getter to capture B and P during the formation of silicon. Compared with the traditional metallurgical methods, this work could remove B and P from silicon directly during the formation of silicon. The refining ratios of B and P from the raw materials to the Fe-Si alloy were about 71.05% and 93.49%. Characterizations of the Si-Fe alloy indicate that many defects exist in the FeSi2 phase of the milled Si-Fe alloy, which is convenient for the elimination of Fe, B and P by acid leaching. Final silicon had a purity of 99.99 wt.% with 0.04 ppmw B and 0.07 ppmw P, which had met the requirement of B and P for solar cells (B ≤ 0.15 ppmw, P ≤ 0.35 ppmw). This strategy significantly decreased energy consumption and shortened production process of high-purity silicon and is thus an effective and scalable approach for the production of silicon for solar cells.