Towards a quantitative model for BO regeneration by means of charge state control of hydrogen

The bulk minority carrier lifetime of p-type Cz-silicon material decreases due to light induced degradation caused by the formation of recombination active BO related defects. Regeneration at elevated temperatures under carrier injection is an adequate method for transformation of these BO-related defects into a non-recombination active complex and thus for long term recovery of the minority carrier lifetime. Next to prolonged temperature treatments and carrier injection, the charge state of hydrogen is assumed to play a major role for regeneration. However, the incorporation of hydrogen and especially correctly charged hydrogen has not been proven. The physical mechanism of the regeneration process is not understood yet and still under discussion. So far no physical model explaining the regeneration process is present. For introducing a model explaining the regeneration process we investigate the influence of the concentration of charged hydrogen on the reaction kinetics on the regeneration process. By combining reaction kinetics with statistical mechanics we will show a quantitative model for BO-regeneration considering the charge state of hydrogen. Comparing experimental and simulated values a good agreement between the experiment and the model is observed. Based on the model we are able to simulate transient defect concentrations during degradation-regenerations cycles over a wide variety of process parameters: temperature and carrier injection, giving an insight into the sophisticated process control for passivating active BO-complexes. Simulation results confirm the incorporation of fast diffusing non-charged hydrogen in the passivation of BO-related defects in cz-silicon solar cells. We conclude that the dissociation of B-H pairs and subsequent diffusion of non-charged hydrogen is the limiting process for regeneration in the material system investigated within this contribution. (C) 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).