Improved seeded directional solidification process for producing high-efficiency multi-crystalline silicon ingots for solar cells

We proposed an improved process design for the industrial mc-Si seeded directional solidification process to produce high-quality multi-crystalline silicon ingots for high-efficiency solar cells. A transient global model of heat transfer was employed to investigate the effects of the process design parameters on the melt-crystal interface shape, thermal field, and thermal stress distribution in the solidified silicon ingot during the solidification process. Ingot casting experiments were carried out and the solar cell performance was measured. The results show that the melt-crystal interface shape in the improved process design remains convex during almost the whole solidification process, and the thermal stress level at the bottom of the solidified ingots is significantly lower than in the original process design. Based on the experimental results, the quality of grown silicon ingots and the conversion efficiency of solar cells were analyzed. The shadow region present in the silicon ingot produced with the original process design disappears and the morphology of the ingot is improved with a more homogeneous distribution of grain orientation using the improved process design. The average yield rate of the solidified silicon ingot is 8.18% higher with the improved process design. The average conversion efficiency of solar cells is higher with the improved process design (17.59%) than with the original process design (17.48%). (C) 2014 Elsevier B.V. All rights reserved.