Light-induced increase of nonradiative recombination centers in hydrogenated nanocrystalline silicon solar cells under reverse electric bias

We studied photoluminescence (PL) of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells in the annealed and light-soaked states under various electric biases during light soaking. PL intensity from grain boundaries decreased after light soaking under a reverse bias, which implies a reduction in the radiative recombination rate as a consequence of an increase in nonradiative recombination centers in grain-boundary regions. However, such PL change was not observed after light soaking under open-circuit condition. The results suggest that the reverse bias during light soaking enhanced metastable defect generation in the grain-boundary regions, which is consistent with the explanation in our previous nc-Si:H cell stability studies.