Study Of Solar Polycrystalline Silicon Directional Growth Ingot Technology

At present,the photovoltaic industry is developing more and more rapidly,and ciystalline silicon solar cells account for the largest proportion in the entire photovoltaic industry.Among them,monocrystalline silicon solar cells have low impurity content,high conversion efficiency,and the production cost of single crystals is gradually reduced,resulting in a decrease in the proportion of polycrystalline silicon solar cells.Therefore,research on the quality of poiyciystalline silicon is needed to increase the market share of polycrystalline silicon.In this paper,the 800kg directional solidification polycrystalline furnace used in the current industrialization is used as a model.The mathematical physics model is established according to the polysilicon mass transfer heat transfer,fluid mechanics,and other theoretical and basic governing equations.In addition,the professional crystal growth software CGsim is used to numerical analyze the industrialized directional solidification furnace,which provides a theoretical basis for industrial production.The main work of this paper is as follows:(1)Simulated the effect of solid-liquid interface shape,oxygen content,SiC,Si deposits on the cover plate and heater consumption of different thermal insulation blocks at different crystal growth period.The results indicate that the shape of solid-liquid interface and the average concentration of oxygen at the solid-liquid interface is the lowest under the top insulation structure.Due to the SiO content in the atmosphere under the top insulation structure is lower than other structure,the SiC particles formed are least,moreover,the maximum deposition rate of SiC is reduced by 16.8%in contrast the original structure;in addition,the total consumption of carbon on the heater is also reduced with the increase of the insulation block,and tlie top insulation structure has the lowest carbon consumption on the heater,which can maximize the service life of the heater.Under the optimal themal field structure,different thickness seed crystals were laid in the melt stage.The comparison found that the seed layer thickness is 30mm,which is the best parameter for crystal growth.(2)Under the optimal thermal field structure and seed thickness,research the effect of SiC particles at different furnace pressure.The results show that the maximum deposition rate of SiC on the top of crucible increases gradually with the increase of pressure,however,the maximum SiC content in the melt increases and then decreases with the pressure increases gradually.Considering the SiC deposition particles on the concrete cover and the SiC content in the melt,the pressure of the furnace is about 3000pa(22.5tor),which is the best process parameter for crystal growth.(3)Under the optimal thermal field structure,seed thickness and pressure,the influence of argon flow rate on melt convection shape,melt temperature and solid-liquid interface stress was studied.The results show that when the argon flow rate at 20slm to 25slm,there are two large convection in the melt,which is beneficial to the volatilization of impurities;the temperature gradient distribution in the melt is the most uniform at 20slm,which is most favorable for crystal growth.In addition,the solid-liquid interface stress and shape increase with the increase of argon flow rate.The smaller the gas flow rate,the smaller the fluctuation at the solid-liquid interface,which is more conducive to improving the crystal quality.(4)Under the optimal themial field structure and crystal pulling process parameters,the effects of the pulling rate on the solid-liquid interface in different crystal growth stages were studied.The results show that the polycrystalline silicon ingot adopts low pulling speed in the initial stage and the late stage,and the high pulling speed in the middle stage.The total time of the ingot changes little and the crystal quality can be improved.Finally,the co-manufacturer uses optimized process parameters and thermal field structure to cast polycrystalline silicon ingots to verify the rationality of numerical simulation.The results show that the quality of polysilicon is well,the life of the top and bottom minority is higher,and the yield rate is also improved.