Interactions of twin boundaries with intrinsic point defects and carbon in silicon

Abstract

Although multicrystalline silicon (mc-Si) is currently the most widely used material for fabricating photovoltaic cells, its electrical properties remain limited by several types of defects, which interact in complex ways that are not yet fully understood. A particularly important phenomenon is the interaction between grain boundaries and intrinsic point defects or impurity atoms, such as carbon, oxygen, nitrogen, and various types of metals. Here, we use empirical molecular dynamics to study the interactions of Σ3{111}, Σ9{221}, and Σ27{552} twin boundaries, which account for over 50% of all grain boundaries in mc-Si, with self-interstitials, vacancies, and substitutional carbon atoms. It is shown that twin boundary-point defect interaction energies increase with twinning order and that they are predominantly attractive. We also find that twin boundary interactions with substitutional carbon are highly spatially heterogeneous, exhibiting alternating repulsive-attractive regions that correlate strongly with the local bonding network. A robust picture is obtained by comparing predictions across a total of five different empirical potentials.