Transient Numerical Simulation On Directional Solidification Of Multi-crystalline Silicon Under Multiphysics Coupling

Solar energy is an ideal renewable energy,which has been widely used because it is clean,pollution-free and can be widely used in different environments.Multi-crystalline silicon is widely used in solar photovoltaic industry.It is an important basic material of photovoltaic industry.The quality of silicon ingot has a great impact on the photovoltaic conversion efficiency of solar cells.Directional solidification is a common production method of high quality polysilicon,and it can reduce production cost.Based on the principle of directional solidification system,the numerical simulation model of directional solidification process of polysilicon was built by the finite element modeling software.Based on the theory of heat and mass transfer,theory of fluid dynamics and other theories,this model is coupled with multiple physical fields such as heat field,flow field,concentration field and magnetic field.In this paper,the effect of external magnetic field on the growth process of multi-crystalline silicon is investigated.It is found that when the applied magnetic field is vertical magnetic field,the magnetic field strength has a great influence on the crystallization process of multi-crystalline silicon.Increasing the magnetic field strength of vertical magnetic field can enhance the inhibition of melt convection,which is conducive to reducing the size of the lower circulation in the melt,thus reducing the oxygen impurity content in the silicon ingot.However,the increase of magnetic field strength can increase the deflection of the crystal-melt interface between the melt and the crystal after 100 minutes of crystallization.When the external magnetic field is the cusp magnetic field,the magnetic field distribution has a great influence on the crystallization process of silicon ingot.The intensity of magnetic field is smaller at the intersection position of upper and lower magnetic fields.When the intersection position of the magnetic field is located in the lower part of the silicon domain,the magnetic field strength in the upper part of the silicon domain is larger and the convection of the upper melt in silicon melt is strongly suppressed.When the intersection position of the magnetic field is located in the upper part of the silicon domain,the magnetic field strength in the lower part of the silicon domain is larger and the convection of the lower melt in silicon melt is strongly suppressed,and the size of the circulation in the lower part of the melt is reduced,so as to obtain the silicon ingot with less oxygen impurity content.