Influence of bound hydrogen states on BO-regeneration kinetics and consequences for high-speed regeneration processes

Abstract

Recombination active boron-oxygen related defects typically limit the efficiency of solar cells made from boron-doped, oxygen-rich silicon. This limitation can be overcome by applying a regeneration process that requires slightly elevated temperatures, carrier injection, and the presence of hydrogen in the silicon substrate in order to regenerate quickly and completely.<br />The influence of mid-temperature steps up to 400°C on the regeneration kinetics is investigated and the results can be explained with the efficacy of the regeneration process depending on the hydrogen bonding states prior to regeneration. Boron-hydrogen pairs are found to be good candidates to be the relevant hydrogen source during regeneration. The long-term stability of the regenerated state is tested under solar cell operating conditions, and the thermal activation energy of its destabilization is determined to be 1.25 ± 0.05 eV.<br />Limiting factors for high-speed regeneration processes are discussed, and a high temperature / high illumination procedure is presented, allowing complete regeneration in less than 10 s. This makes regeneration feasible as an in-line process in solar cell production.