Optimized Cooling Process Simulation And Experimental Verification In Directional Solidification Of Multicrystalline Silicon

Multicrystalline silicon solar cells are the PV market mainstream and the directional solidification is the main technology for producing multicrystlline silicon ingots. The optimization of the directional solidification process can help to reduce energy consumption and improve the quality of multicrystalline silicon ingots in the cooling stage. Based on the normal cooling process, we investigate the influence of twelve different process curves on the temperature field, stress field and the dislocation density with FEM, consisting six different amplitude process curves based on the former heating up stage of Tc2and six different intersection process curves of Tc2and Te1. The analysis of dislocation density was performed using the CRSS dislocation model and HAS dislocation model separately. We found that average von Mises stress, maximum von Mises stress and dislocation density were the least value when Tc2linearly decreased and intersected with Tel in800K. The ultimate stress distribution showed the same trend with a bit difference of numerical value with the different process curves and so the dislocation density distribution was. The result in HAS dislocation model which considered the creep was more in line with the actual process than that in CRSS dislocation model. It had little different effect on the results when strain hardening factor was variant or constant in HAS or when we use CRSS model equivalent stress alternative to HAS model equivalent stress. While it had a great impact on the results if we considered the different geometry on the top surface of the multicrystalline silicon ingot, the results showed the stress and dislocation density with horizontal plane were the minimum in the ingot.Then we simulated the effects of different tapping temperature point on the stress and dislocation density in the multicrystalline silicon ingot. We found that the best tapping temperature was600K and the dislocation density and stress would increase when the temperature was higher than650K and700K.Finally, we made simulation and experimental comparative analysis of2K/min and5K/min cooling rate on the dislocation density with the small size of the silicon block, respectively. Simulation results show that the radiation, temperature, and average von Mises stress and dislocation density under5K/min cooling rate were all greater than those under2K/min cooling rate. Later through experiments, we found the overall dislocation density under5K/min cooling rate increased15.4%, greater than that under2K/min cooling rate (11.2%). The simulation and experimental results validate each other well.