BO-Related Defects: Overcoming Bulk Lifetime Degradation in Crystalline Si by Regeneration

Abstract

Boron-oxygen related defects formed under working conditions of a c-Si solar cell can be a showstopper for new cell concepts enabling higher conversion efficiencies. The recombination activity of these defects can be reduced to negligible values by a regeneration process under elevated temperatures and in the presence of excess charge carriers in the Si bulk. It is shown that this process also relies on the presence of H in the c-Si bulk. Regeneration kinetics can be sped up by higher temperatures, higher concentrations of excess charge carriers and higher H concentration in the c-Si bulk. But care has to be taken to avoid a destabilization reaction taking place at higher temperature, resulting in the BO-related defects being again present in the recombination-active state. A 3-state model with the corresponding reaction rates between the different defects states describes the experimental findings and can be used for predictions of an optimized regeneration process.