Spectral characteristics of a-Si:H/c-Si heterostructures

We have examined the current-voltage characteristic of i-a-Si:H/n-c-Si heterojunction Schottky solar cells in the dark and under different illumination (spectrum AM 1.5) intensities as well as the voltage- and temperature-dependent spectral response of these devices. The photocurrent from the crystalline silicon depends on both voltage and temperature due to their influence on the impact of the band offsets. From our measurements of the spectral response we conclude that there is a small conduction band offset Delta E sub(c) and a large valence band offset Delta E sub(v) at the i-a-Si:H/n-c-Si heterojunction. The large valence band offset inhibits the collection of photogenerated holes from the crystalline silicon under normal photovoltaic conditions. Thus, the current-voltage characteristic under illumination between V identical with 0 V and V identical with V sub(oc) is caused only by the photocurrent from the a-Si:H layer.