A model is presented for p-n hetero-junction solar cells in which interface recombination is the dominant diode current transport mechanism. The model explains the large diode ideality factor (n > 2) and the increased saturation current density in terms of increased density of interface states N-ir. Furthermore, the model allows us to explain the non-translation between illuminated and dark J-V characteristics. The explanation is based on the assumption that, for high interface state density values, both the depletion layer width and the diffusion voltage in the p- and n-side of the junction are functions of N-ir. The interface recombination leads to lower values of the open-circuit voltage, short-circuit current density, and fill factor. These results are illustrated by numerical calculations of solar cell parameters and compared with experimental data achieved for ZnO/CdS/CuGaSe2 single-crystal solar cells. (C) 2003 Elsevier B.V. All rights reserved.