Numerical simulation approach to investigate the effect of side heaters lifting on the carbon impurity and thermal stress of multi-crystalline ingot
摘要
In this study, we adopted simulation approach to investigate the effect of side heater block movement on the temperature distribution and melt-crystal interface of multi-crystalline silicon grown by directional solidification (DS) process. Few non-metallic impurities such as nitrogen, carbon, and oxygen are generated from the DS furnace, and each impurity atom is segregated into the ingot based on their solubility in the crystal. We concentrated primarily on lowering the carbon content because it directly affects the conversion efficiency of the solar cell. The movement of the side heater during the solidification process allowed us to achieve the convex melt-crystal interface. The maximum carbon concentration for a conventional system is 4.9 × 1017 atoms cm−3, and under the influence of a modified heating system maximum carbon concentration is reduced to 2.4 × 1017 atoms cm−3. The thermal stress is reduced from 1.2 × 105 Pa to 1.3 × 104 Pa and dislocations reduced from 4.5 × 102 1 m−2 to 1.2 × 101 1 m−2 in the multi-crystalline silicon (mc-Si) ingot during the crystallization process. Based on the modeling results, the design of the furnace has a significant impact on the shape of the melt-crystal interface, temperature distribution, thermal stress, dislocations, power consumption and the tendency of impurities for segregation throughout the growth process.