(Invited) Defects in Cast-Mono Crystalline Silicon

Abstract

Crystalline silicon, including Czochralski silicon (Cz-Si) and multicrystalline silicon (mc-Si),is main material for photovoltaic (PV) industry. How to produce more productive and less expensive crystalline silicon materials is still a big challenge. As we know, the seed-assisted growth method can be used to fabricate cast-mono (CM-Si) silicon by directional solidification, which should combine the both advantages of Cz-Si and mc-Si. However, there remain some problems to be resolved in growing CM-Si silicon ingots, particularly the control of dislocations which are the major and most detrimental defects in CM-Si. They can act as precipitation sites for impurities and thus reduce the carrier lifetime in ingots. Unlike mc-Si ingots, once dislocations are generated in the bottom of CM-Si ingots, they will glide and propagate along the growth direction without hindrance due to the lack of grain boundaries.In this presentation, we review our recent work of how to control defects, specially dislocations, in CM-Si. We induce a grain boundary by adjusting the orientation of seeds which can suppress the generation of dislocations originated from the junction of seeds. We have investigated the effect of Σ5, Σ13a grain boundary relationship at seed junctions of <100>-oriented CM-Si on dislocations and solar cell performance. We also use <110>-oriented seeds to grow new orientation CM-Si ingots to control the generation and propagation of dislocations. The results show that by designing the orientation of seeds, the dislocation density can be decreased and the solar cell efficiency can be improved obviously.