Current voltage characteristics of ZnO/CdS/CuGaSe2 single crystal solar cells which have gone through repetitive annealing treatment were analysed using the two-diode equation. The fitting analysis revealed that current transport in these cells is governed by two competing transport mechanisms relating strongly to interface states and that both mechanisms are thermally and light-activated. The activation energy values for both mechanisms were calculated from the temperature dependence of the parameters describing each of them. Furthermore, it was found that the calculated activation energy values depend on temperature and illumination intensity. A qualitative explanation for this dependence is given. (c) 2007 Elsevier Ltd. All rights reserved.