Research On Process Optimization Of High-efficiency Polycrystalline Silicon Ingot Casting Process

Currently,the main production methods for monocrystalline and polycrystalline silicon products in the market are Czochralski method and polycrystalline silicon directional solidification method.With the development of polycrystalline silicon technology,high efficiency polycrystalline ingot casting technology based on directional solidification method occupies the photovoltaic(PV)market,due to its advantages of large-scale production,short production cycle,simple operational process and low energy consumption.There are some defects and impurities inside polycrystalline silicon ingot(PSI),which have been important factors influencing the conversion efficiency of polycrystalline silicon solar cells.High efficiency PSI casting technology is able to reduce internal defects and improve the quality of PSIs.But it needs stable and precise control parameters for different production equipment.Therefore,it is necessary to further optimize the PSI casting process,in order to find the optimal technological parameters and produce high quality PSIs.The aim of this research is to test the technology of high efficiency PSI casting process,and to study the heat insulating cage(HIC)parts of the DDL type PSI furnace.Current problem is that high efficiency PSI casting process fails due to excessive melting of seed crystals at the bottom of the crucible during the melting stage of PSI.To solve the problem,this study analyzes the influence of the HIC opening on the high efficiency PSI casting process.In this way,the bottom seed crystal layer can be wholly retained and the optimal PSI casting process can be achieved.The process of polycrystalline silicon crystal growth is also the process of defect,impurity redistribution.Through further analyzing the impact of HIC lifting speed on directional solidification process,it is possible to minimize the internal defects and move the internal impurities to the peripheral region of PSIs.As a result,it can further improve the quality of PSIs,increase the utilization of PSIs and reduce production costs.High quality PSIs have the advantages of homogeneous grain size,low dislocation density,and been widely used.Through the study of the problem of excessive melting of seed crystal layer in the process of high efficiency PSI casting process,the retention of bottom seed crystal can reach 98% by optimizing the opening of HIC.On the other hand,in the process of the polycrystalline silicon directional solidification,the internal defects and the distribution of impurities are closely related to the shape of the crystal growth interface.The results show that the overall yield of PSI is improved and the utilization of PSI is increased by 1.5%~2% compared with the process before optimization.It is worth mentioning that this study is based on existing equipment to optimize the process,without requiring additional equipment,which further improves the use of equipment.The results provide valuable guidance to actual industrial production processes.