Low-cost ultrapure (>99.9999%) solar-grade Si by electrorefining

The current SiHCl₃-based processes to produce ultrapure Si are one of the major bottlenecks to lower-cost wafer-Si solar cells. Molten-salt electrorefining of Si is an alternative process to ultrapure Si, with a significantly lower energy input of ∼15 kWh/kg. It is demonstrated that controlling the potential applied to the working electrode is critical in reducing impurity concentrations. A more positive potential on the working results in purer Si deposited on the counter electrode. With margin of error, the amount of Si deposited on the cathode is almost the same as the amount dissolved from the anode. A nonequilibrium factor which affects impurity concentrations is identified, i.e. contamination.