Numerical and experimental investigation of sectional heater for improving multi-crystalline silicon ingot quality for solar cells

The sectional heater of industrial-scale directional solidification furnace was designed for improving the quality of the high performance multi-crystalline silicon ingots used for solar cell fabrication. A global numerical model was adopted to investigate the effect of the modified furnace on the thermal field distribution, the shape of the crystal-melt interface and the thermal stress distribution in the solidified silicon ingot during the directional solidification process. Simulation results indicate that the crystal-melt interface shape in the modified furnace with the sectional heater changes from convex at the earlier stage to slightly flat at the later stage, and the thermal stress level at the bottom corner of the solidified ingots is clearly lower than that in the conventional furnace. Furthermore, the designed furnace with the sectional heater was built and experiments corresponding to the numerical simulations were carried out. It was found that a more uniform minority carrier lifetime distribution, lower dislocation cluster density, and lower oxygen concentration were obtained for the silicon ingot grown using the modified furnace. Additionally, the average conversion efficiency of the solar cells fabricated using the grown ingots was evaluated, and it was found that a higher efficiency was obtained for the cells fabricated using the ingots obtained with the modified furnace (18.64%) compared to that for the cells fabricated using the ingots obtained with the conventional furnace (18.54%).