Control of extended defects in cast and seed cast Si ingots for photovoltaic application

We discuss the defect evolution in conventional cast and seed cast Si ingot growths for photovoltaic application. Three different cast Si ingots were grown in one directional solidification furnace. The two extremes are the seed cast ingots (mono-Si), where growth starts from monocrystalline silicon seeds, and the multicrystalline silicon grown from small randomly oriented grains. The conventional multicrystalline (mc-) cast Si ingots are grown without any seeds and have grain structures in between the two extremes. It was found that in mc-Si the evolution of grain boundaries take place in several steps. On the other hand, the major defects in mono-Si are dislocations and are generated by stress due to thermal gradient in the ingot.