Study On Optimization Of Thermal-Field Structure And Growth Process For High Efficiency Multi-crystalline Silicon Prepared By Induction Heating

High-efficiency multi-crystalline Si is one of the products of solar cells,which is produced by the directional solidification system.Reducing cost and improving quality is the key to improve the competitiveness for this kind of cells.Due to the high heating efficiency and feasible equipment,the induction melting is a potential method to produce solar-grade multi-crystalline Si.However,the research is not enough in this field.In this paper,the optimized design for the growing system of induction melting and the processing parameter for crystal growth has been carried on,and the obtained results have been verified by experiments.Following results have been summarized.Firstly,the growing system has been optimized.One composite insulation layer comprising of graphite and felt layers has been proposed,which could form two heating resource to improve the heating efficiency,thereby decreasing the power consumption.The distribution of Lorentz force was changed by the induced graphite layer,leading to form a single vortex in the melt.A insulation structure with 30mm graphite layer in thickness and one felt layer has been determined.The relationship between graphite crucible and Si melt has been constructed,ensuring one vortex formation in melt.A gap between graphite crucible and quartz crucible could weaken the melt convection and suppress the heat loss from the sidewall of crucible,which is beneficial to obtain desired solid-liquid interface.The optimized value of gap is 5mm.Secondly,the processing parameters of crystal growth has been analyzed.The results show that the distribution of Lorentz force could be influenced by the crucible position.One vortex in melt could be obtained when the crucible position is 0 or minor values.The melt convection was not changed in the whole growth process.And the shape of solid-liquid interface changed from concave to W-like to convex.In the initial and middle stage of crystal growth,the fluctuation of interface decreases with decreasing the crucible drawing speed.A higher drawing speed should be adopted for the final stage of crystal growth.The cooling capacity of cooling device was enhanced with decreasing the gap between graphite support and cooling device,which could compensate the velocity loss in the initial stage of crystal growth.Lastly,the obtained results from numerical simulation has been verified by experiments.A directional microstructure has been obtained in the ingot,indicating the simulated results with a high accuracy.In conclusion,this paper is focusing on preparation of multi-crystalline Si by induction melting solidification route.The processing technique has been optimized and verified.The heating efficiency of heater has been improved by inducing a graphite layer in insulation structure,thus the power consumption decreased.A relationship between graphite crucible and Si melt has been elaborated.Moreover,the growing velocity could be increasing by enhancing the cooling capacity of cooling device.Based on the research background of high-efficiency multi-crystalline silicon prepared by induction melting,the obtained results in this work are innovative and practical,which would facilitate the application of this technique.