Numerical Study and Experiment of Unbalanced Heat Dissipation Method in Directional Solidification of Photovoltaic Polysilicon
Directional solidification(DS)was an important process for physical purification of photovoltaic polysilicon.In order to improve the defect of large thermal stress and strain caused by one-dimensional heat dissipation in directional solidification,a innovative unbalanced heat dissipation structure and process were proposed,which used specific thermal resistance designs and heat dissipation channels to reduce thermal stress and strain.Using ProCAST software,three-dimensional numerical modeling of one-dimensional heat dissipation and unbalanced heat dissipation was carried out.The comparison results shows that compared with one-dimensional heat dissipation,the unbalanced heat dissipation scheme can reduce the average thermal stress by 52.56％,increase the average solidification rate by 20.67％,reduce the solidification time by 17.10％,and maintain the stability of the phase change interface in the non-one-dimensional temperature field.Using the YITIPV type vacuum ingot furnace and 3303 industrial silicon raw materials,a large-size ingot(1 mxl mx0.3 m)control experiment was carried out.The experiment proved that the unbalanced heat dissipation scheme can improve the solidification rate and product quality,the top of the prepared silicon ingot is flatter,the actual total solidification time is reduced by 15.75％,the energy consumption per unit weight of silicon is reduced by 17.86％,the ingot cracks are less,and the effective volume is larger.The sample analysis also shows that the average resistivity of the silicon wafer increase by 7.86％,and the impurity content of the three elements B,P,and Al decrease by 28.6％,15.2％,and 83.3％,respectively.The experiment not only confirm the effectiveness of the unbalanced heat dissipation structure and process but also verify the adaptability of the numerical model.This new structure and process improve the quality and production efficiency of ingots,reduce the risk and cost of ingot cracking,and have promotion and application value.
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