Results are presented showing the effects on amorphous silicon (a-Si) photovoltaic performance of the interfaces associated with a silicon carbide (a-Si:C) p+ layer. Carbon grading into the intrinsic layer from the p+ layer increases open circuit voltage (Voc) from O.7V to 0.88V. This effect is very similar to the boron profile effect reported earlier and supports the contention that Voc is being limited by an electron current at the p-i interface. The interface between the p+ a-Si:C layer and the transparent conductive oxide (TCO) is shown to be a potential source of high series resistance, with an abrupt interface showing the most serious problem. The effect is explained by electron injection from the TCO into the p+ layer being inhibited as a result of band mismatch.