Research On Improving Methods Of The Yield Of Solar Grade Polysilicon

As an important renewable energy,solar energy has attracted worldwide attention for its development and utilization.The solar cells with polysilicon as substrate material are rapidly growing due to their high conversion efficiency,small ecological impact and long-term non-degradation.One of the core issues of solar energy industry is the development of polysilicon materials with high quality product rate.Polycrystalline silicon produced by physical metallurgy has become the main mode of production for realizing large-scale solar-grade silicon.In the physical metallurgical process,the directional solidification,impurity content and cutting process of polysilicon have great influence on the properties of solar cells.In this paper,the methods on improving the yield of polysilicon by Ningxia Ning Electric Photovoltaic Materials Co.,Ltd.is studied.By analyzing the process flow of polysilicon production,the reasonable selection of directional solidification parameters,improving the pull-down method of insulation plate and controlling the cutting range of silicon ingot is proposed to improve the yield of polysilicon.The main contents of this paper are as follows:(1)Combining with the actual conditions in the production process of the ingot factory,the effect of solidification rate on the effective segregation coefficient of different metal impurities and the effect of solidification rate on the removal of various metal impurities are discussed based on analyzing the principle,method and equipment of directional solidification.In order to improve the purification effect of polysilicon in ingot furnace,the methods and measures of improving the yield of polysilicon by directional solidification are proposed from the aspect of the selection of solidification rate.(2)The effect of the heat insulation pull-down rate on the yield of polysilicon by directional solidification was studied.Two different solutions are given and compared to improve the purification effect of polysilicon in ingot furnace.(3)In view of the process flow of silicon ingots for cutting silicon wafers,,the relationship between the concentration of metal impurity and the purification height of silicon ingot is analyzed based on working principle of the slicing and the cutting equipment.The control scheme of cutting range of polysilicon ingot is proposed to improving the yield,and the height of sawing silicon ingots is decreased as much as possible to reduce the loss of silicon material under the premise of the impurity concentration satisfying the standard.