Numerical Simulation Of Directional Solidification Of Polysilicon Under Multiple Physical Fields Coupling

Solar energy is a clean renewable energy, which is an ideal choice to solve the energy crisis. At present, with the features of simple productive process and the advantages of low cost etc, polysilicon solar cell has been used widely. However,polysilicon directional solidification is a complex crystal growth process under the action of multi-physical fields coupling. It is difficult to master the change regulation of various physical fields,when silicon melt in the actual industrial production process. With the development of computer numerical simulation technology,simulation method has became an effective means to observe the process of crystal growth intuitively. In this paper, the polysilicon crystal growth process is simulated by using simulation software named Comsol Multiphysics version 4.3a. The distribution of the silicon melt thermal field, flow field, magnetic field, stress field was obtained in the process of numerical simulation, which has provided a new way to explore polysilicon directional growth.At first, the influence of the composite structure of crucibles with the cooling platform and the distribution of heater in the polysilicon directional solidification furnace to the distribution regulation of thermal field and flow field was explored by coupling thermal field and flow field. Then, the crucible shapes, crucible chamfering radius and temperature gradient on the internal silicon crystal to the influence law of heat field and stress field was analyzed. The inverted-cone crucible is beneficial to reduce the thermal stress field distribution in the polysilicon. The values of thermal stress in the crystals goes down with the increase of radius chamfering in crucible gradually. With the increase of temperature gradient in the silicon crystal, the average thermal stress in the crystal increase but increase range reduced gradually. After that,The process of polysilicon crystal direction was studied under the coupling of thermal field, flow field and magnetic field. The change situation of parameters in the process of polysilicon directional solidification under the different magnetic structure,different magnetic field distribution and different magnetic field strength was analyzed with emphasis. With the distance reduced from 60 mm to-60 mm betweenthe magnetic field coil magnetic and center surface in the silicon melt, the largest velocity decrease from 70 μm/s to 41 μm/s in the silicon melt by more than 41.43%.When the magnetic field coil’s distance remain below 60 mm in the center surface of the silicon melt and magnetic field intensity increases from 0T to 0.8T gradually, the axial temperature gradient in the silicon melt drop largely for 15 k/cm. The changing rule of the flow field in the three periods(early, middle and late) of the polysilicon crystal phases was revealed under the action of multi physics fields through the establishment of two-dimensional axisymmetric transient model. When the magnetic field vary from 0T to 1T in polysilicon crystalline phase, the peak values of velocity decreased from 51.644 μm/s in the crystallization of the early to 21.074 μm/s in the crystallization of the late and average flow velocity is reduced 42.11%, 58.59% and42.11% in the three periods of polysilicon crystalline under multi field coupling respectively. The above simulation results show that the numerical simulation technology is very important theoretical guiding significance to the manufacturing of polysilicon in the future.