Thermal, structural and electrical study of the effect of annealing on the passivation by amorphous silicon of n-type crystalline (100) silicon surfaces

Hydrogenated amorphous silicon (a-Si:H) layers deposited by chemical vapour deposition provide an attractive route to achieve high performance crystalline silicon (c-Si) solar cells due to their deposition at low temperatures and their superior passivation quality. A post-deposition annealing of such layers typically enables a further strong reduction in defect states at the a-Si:H/c-Si interface, due to the saturation of dangling bonds by atomic hydrogen. In this work, we present the evolution of the effective lifetime during annealing at different temperatures. We find that at lower deposition temperatures (150 degrees C) the high density of Si-H-2 bonds in as deposited layers results in higher defect density and worse passivation quality. In contrast, deposition at higher temperatures (200 degrees C) leads to a structural improvement of the short range order in the a-Si:H layer and a decrease of the disorder in the film network. The presence of a dense material mixed with a fraction of SiH2 at the interface favors further improvement of the passivation during a post-deposition anneal, resulting in the best case in an effective lifetime of 10ms. (C) 2014 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).