Taking into account the fact that the distribution of defect states at the interface does not have strictly symmetrical shape, we present a simulation study of a-Si: H(n)/c-Si(p) and a-Si: H(p)/c-Si(n) structures with regard to the defect states at the interface, band offsets and doping concentration of the emitter. The presented results suggest for a-Si: H(n)/c-Si(p) solar cells a strong influence of the introduced broken symmetry between acceptor and donor defect states on the open-circuit voltage, whereas the a-Si: H(p)/c-Si(n) structure benefits from inherent favorable band alignment and remains unaffected. (C) 2010 Elsevier B.V. All rights reserved.