Research On The Effect Of Process Parameters On The Directional Solidification Rate Of Polysilicon

In the photovoltaic industry,the quality of solar grade polysilicon has an important impact on the photovoltaic conversion efficiency of photovoltaic systems.In addition to the quality of the material itself,production process of the polysilicon also plays an important role in the quality of the solar grade polysilicon.The detection and control of the rate of growth of the polysilicon ingot process is an important part of the process development.At present,there are many studies on the influence of the rate of ingot growth on the distribution of impurities in polycrystalline silicon and the quality of ingot,but there are few studies on the influence of ingot casting process on the rate of growth.Therefore,this paper is working on the ingot casting process of the solar grade polysilicon directional solidification process.Starting from the directional solidification process,the polysilicon ingot production is tested to obtain the growth rate curve.The heat flow balance in the polysilicon ingot is analyzed,and the influence of the ingot process parameters on the thermal field of the ingot furnace is obtained by using the simulation tool.A new method for detecting the rate of the solidification rate of the ingot is proposed.The main conclusions of this paper are as follows:(1)Based on the thermal equilibrium relationship in the directional solidification thermal field,the temperature gradient of the ingot solidification process is obtained.The results show that in the physical sense,the ratio of the temperature gradient in the liquid phase to the temperature gradient in the solid phase during solidification is ?=-ks/kl+?Lv/Tm-T2x.This ratio is not a simple linear relationship.As the directional solidification progresses,the liquid-solid phase temperature gradient ratio increases,and its rate of increase slows down.(2)Based on the thermal equilibrium relationship of directional solidification thermal field and the law of liquid-solid phase temperature gradient ratio,the calculation model of solidification rate v during directional solidification is established.The theoretical calculation value of solidification rate is vcal=1/?Llatent[(T1cal-Tm)kl/x-L-(T2-Tm)ks/x].By comparing the theoretical value with the experimental value,it is found that the degree of coincidence is good,which can provide a certain degree of support for the evaluation and regulation of the solidification rate during the directional solidification of polysilicon.(3)Through the modification of the geometry model of the polysilicon ingot furnace and the physical properties of the components,a simulation calculation model of the polysilicon ingot furnace which can be used in production practice is obtained.Using the solid model for numerical calculation,the distribution of the thermal field in the ingot furnace is obtained,and a higher degree of fitting is achieved compared with the actual polycrystalline silicon ingot furnace thermal field,which can provide strong support for the optimization of the production process.(4)This paper establishes the relationship between the production parameters of polysilicon ingot production,the internal thermal field of polysilicon ingot,and the growth rate of polysilicon ingot.The thermal field distribution inside the polysilicon ingot is obtained by numerical simulation to calculate the specific process parameters.Then,the solidification rate of the silicon ingot is calculated from the temperature distribution inside the ingot by the heat flow balance relationship in the polysilicon ingot.