Influence of helium gas flow under the retort bottom to control the impurities in grown mc-Si ingot by DS process for photovoltaic application: Numerical simulation

The quality improvement of the mc-Si ingot is achieved by numerical simulation using the finite volume method. We have done the numerical simulation on a 2D symmetric Directional solidification furnace with helium gas flow at the bottom of the retort. In this process, the first nucleation starts at the bottom centre of the crucible due to spot cooling. The spot cooling process achieves the convex melt crystal interface during the growth process. It will push the impurity from the centre to the peripheral region of the ingot. This spot cooling method results show the acceptable range of the dislocation density and stress of the grown ingot. The melt-crystal interface, thermal stress, dislocation density and impurity formation of spot cooling system grown mc-Si have been ana-lysed and compared with the conventional DS system of the grown mc-Si ingot. It is seen from the results that the LID effect, SiC formation and dislocation density are reduced in the spot cooling system grown mc-Si ingot.