Computational investigations of an a-Si:H solar cell have indicated that interface states at the SnO2/p-a-Si:H interface enhance device performance by about 5%. A detailed analysis has revealed that the interface states enhance the drift field by capturing electrons from the valence band. This enhances the effective electric field acting on the electrons, resulting in electrons being swept out of the p-layer. This, in turn, decreases the electron concentration in the p-layer, relative to the case where interface states are absent. It was found that dangling-bond states are the dominant recombination mechanism in the p-layer, and that their location very near to midgap ensures that Shockley-Read-Hall recombination through them is proportional to the electron concentration only. Since the introduction of interface states reduces the electron concentration, dangling-bond recombination in the p-layer is reduced, resulting in an increase in the short-circuit current and maximum power output, relative to the cell in which interface states are absent. (C) 2002 Elsevier Science B.V. All rights reserved.