Suppression of dislocations and twins by inducing asymmetrical grain boundaries for casting high-quality monocrystalline silicon ingot

Abstract

Cast monocrystalline silicon (CMC-Si) is a promising photovoltaic substrate owing to the advantage of low cost of directional solidification. However, the high dislocation density and other crystal defects, such as twins, have limited its further application. We proposed a new seed pavement method, namely, the construction of asymmetrical large angle grain boundaries, to suppress the generation of dislocations and other crystal defects. Two CMC-Si ingots, Ingot-A for the traditional method of seed pavement and Ingot-B for the new method of seed pavement, have been casted. The results show that, the crystal quality of Ingot-A is remarkably lower than that of Ingot-B. For Ingot-A, a large number of dislocations are induced, such as small angle grain boundaries, which come from the seed junctions due to size error of the seeds. And some twins are brought out at the symmetric grain boundaries, which reduces the proportion of the (100) crystal plane. For Ingot-B, there are large angle orientation relationships between the adjacent seeds. This asymmetrical large angle grain boundaries have not formed small angle boundaries, and successfully prevented the generation of dislocations and twins. The average conversion efficiency of Ingot-B (21.81%) is significantly higher than that of Ingot-A (20.63%).