Research and Preparation of High Quality Polysilicon Ingots and Multicrystalline Silicon (mc-Si) Cells

Abstract

Directional solidification is a main method of mc-Si production for solar cells. The main impurities in MS-Si are oxygen and carbon. In this paper, an improved furnace was designed to reduce the carbon and oxygen impurity in MS-Si at unidirectional solidification process. Simulation results showed that the flow pattern of impurity gas at the top of the silicon melt significantly improved under the small cover conditions and the impurity gas eddy currents was also avoided. Experimental results show that the carbon and oxygen content inside the ingot were both significantly reduced when the eddy currents inside the crucible was suppressed and the average minority carrier’s lifetime of silicon block was significantly increased under the conditions of small cover plate. Meantime, the average cell efficiency of ingot was more than 17% under small cover condition which is significantly higher than that of the ordinary ingot.