Analysis of TCO/p(a-Si:C:H) heterojunction and its influence on p-i-n a-Si:H solar cell performance

The ASPIN computer simulator, which enables analysis of transparent conducting oxide (TCO)/a-Si:C:H/a-Si:H/TCO heterostructures, was used to examine the influence of different front TCO/p(a-Si:C:H) heterojunctions on TCO/p-i-n/TCO/metal a-Si:H solar cell performance. Separate analysis of TCO/p(a-Si:C:H) structure for both SnO2 and ZnO indicates that the mismatch between the high contact potential and the measured potential barrier at the p-layer surface can be resolved by a large density of interface defect states, causing a steep potential decrease in the interface. Analysis of the detrimental effects of a-Si:C:H chemical oxidation in SnO2/p(a-Si:C:H), which were simulated by the increased surface state density in the a-Si:C:H, showed that the potential barrier in a p-layer with oxidized surface is increased. The impact of both TCO/p(a-Si:C:H) interface states and a-Si:C:H surface states on the photoelectric properties of p-i-n a-Si:H solar cells is discussed, and a possible improvement of Voc is envisaged.