Thermodynamics of solar-grade-silicon refining

Solar energy will shortly be in great demand since it is inexhaustible and cleaner than any conventional energy resources. At present, an expensive grade of silicon for semiconductor (SEG-Si) is used for a solar cell to convert solar energy into electricity. However, the amount of supply is limited and we have to develop an innovative process for silicon production with low energy cost in order to spread the solar cell system widely. Using relatively inexpensive metallurgical grade silicon (MG-Si) as a starting material for making solar grade silicon (SOG-Si) is believed to be one of the ways to make solar cells less expensive. Impurities in MG-Si will shorten the lifetime of excited carriers in silicon solar cell and disturb electric generation. Hence, the removal of impurities from silicon is a significant issue in silicon solar cell fabrication. To discuss the possibility and efficiency of the impurity elimination process, evaluation of thermodynamic properties of impurities in molten silicon such as the activity coefficients and the interaction parameters of harmful impurities has been performed.