Research On The Simulation Of Thermal Flow Field For Polycrystalline Silicon And The Improvement Of Experimental Equipment

As a kind of solar cell, Polycrystalline silicon solar cell takes the biggest market share at the present. In order to reduce the cost of power generation, the quality of polysilicon crystals must be improved while the cost of pruduction must be reduced, which is just the target of scientific research personnel. Compared to those chemical process, metallurgy process costs less and makes less pollution when produce polysilicon, thus becomes the hotspot of research. However, the conversion efficiency of the crystal battery produced through the metallurgy process still needs to be improved, and the impurity content is not entirely satisfactory. After improving the experimental facilities and investigating into the distribution of thermal flow field in the directional solidification process when producing the Polycrystalline silicon, we can indirectly change the shape of solid-liquid interface, the pattern of thermal flow field and the distribution of impurity content, so as to improve the crystal’s quality and reduce the production cost.Our research, first makes a discription of the multi-physics field system for the directional growth of the Polycrystalline silicon. Then theoretically analysis the characteristics of the directional solidification process when the Polycrystalline silicon grows. We also investigate the microstructure characteristic, growing conditions and the solidification interface shape of the crystals, and the influence brings by the technological parameters, so as to get the governing equation and the boundary conditions of the growth system. Lastly, we use COMSOL Multiphysics (the multi-field coupling software of finite element analysis) to imitate the thermal flow field in the directional solidification system. Combined with the mathematical theory, the result shows that the internal flow field of the silicon melt is created mainly by the buoyancy and changes as the process of growth proceeded.Moreover, this paper makes a research into the distribution of the thermal flow field during the directional solidification process under the influence of magnetic field. We add a set of magnetic equipment in the ingot furnace, providing homogeneous axial magnetic field by helmholtz coil, to inmitate the directional solidification process of the silicon melt in the axial magnetic field. The result shows that the temperature distribution is more homogeneous during the growing process of the Polycrystalline silicon under the influence of the magnetic field. Because of the lorentz force, the flow field has been restrained, especially the radial flow. At the same time, we devise to improve the Argon flow guiding device above the free surface of the silicon melt, and inmitate the distribution of the oxygen impurities in the silicon melt when the location parameter of the flow deflector changes. Through the comparasion of the experimental data, we get the optimal design parameters of the flow deflector. They are:the distance(h) between the exit of the flow deflector and the free surface of the silicon melt is5mm, the distance(d) between the exit of the flow deflector and the side walls of the crucible is2.5mm, the angle(θ) between the flow deflector and the Argon tube is95°。Under the circumstances of unchanged Argon flow, these can help to reduce the oxygen impurity content in the silicon melt to the minimum, and achieve the goal of controlling the oxygen as well as improving the quality of the crystal.