A multilayer nucleation model for twinning during directional solidification of multi-crystalline silicon

Abstract

Twin nucleation is an important phenomenon in the directional solidification of photovoltaic multi-crystalline silicon. Unfortunately, the models proposed so far were not sufficient to explain the small undercooling (<1K) for twinning observed in the experiments. In this paper, we propose a multilayer nucleation mechanism for twinning during silicon directional solidification. When the nucleus contains more than one layer, the free energy of formation for the nucleus can be reduced. Asa result, the critical radius decreases and the twinning probability increases. The required undercooling for twinning based on the present model could be reduced to around 0.4–0.6K, which is much more consistent with the experimental observations.