Numerical analysis of light elements transport in a unidirectional solidification furnace

Quantitative study of light elements such as carbon and oxygen in multi-crystalline silicon for solar cells is required to grow crystals with high quality. The transport of both carbon and oxygen is one of the critical issues to increase efficiency of solar cells made of silicon materials. Concentrations of carbon and oxygen in a furnace affect each others, therefore it is important to control mass transfer of carbon and oxygen in a furnace. Numerical calculation with a chemical reaction between carbon and oxygen was carried out to study how both light impurities are incorporated into crystals through the melt and gas during solidification process. The effects of flow rate and pressure on the impurities were examined. An increase in the flow rate can reduce both carbon and oxygen impurities in the crystal, though the reduction of carbon is more obvious. An increase in gas pressure can also obviously reduce the oxygen impurity but has only a small effect on the carbon impurity. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim