Numerical Study of von Mises Stress During Continuous Casting of Multicrystalline Silicon With Large-Size Grains

Continuous casting is a promising technique for massive production of multicrystalline silicon (mc-Si). A theoretically advanced study is performed here to investigate the growth of mc-Si with large grain size, which has much higher photoelectric efficiency than normal mc-Si. However, the casting technique results in high thermal stresses due to its inherent features, and limits the photovoltaic applications of mc-Si because of the stress-induced dislocations. For the analysis and optimization of dislocation formation, a computer-aided method has been applied to investigate thermal stress distribution in the growing ingot of continuous casting. The regions of dislocation multiplication are evaluated by comparing von Mises stress to the critical resolved shear stress. It is found that the stress levels are especially high in the regions close to the solid and liquid (S/L) interface, and that the mold wall has a significant effect on the von Mises stress distribution if the billet were attached on the wall. The triple point is better to keep below the mould bottom to avoid its effect during the growth by certain techniques during the industrial production. Parametric studies were further performed to discuss the effects of growth conditions, such as sheath height, environment temperature, and pulling rate on the distribution of the maximum von Mises stress in the billet. The results imply theoretically that multicrystalline silicon with low stress-induced dislocation could be produced by continuous casting with strictly controlled growth parameters.