Polycrystalline thin film CuInS2-on-Cu-tape (CISCuT) solar cells were studied using deep level transient spectroscopy (DUS). Temperature scans between 5 and 320 K reveal a large positive peak and a smaller negative peak. The positive peak is analysed using isothermal DLTS measurements which indicates a deep level defect with a very high concentration, contributing significantly to the carrier concentration at room temperature. The negative peak can be related to an energy barrier, possibly located at the back contact. We find an estimated barrier height of 164 meV. Electrical injection DLTS and optical injection DLTS measurements were also carried out. (C) 2006 Elsevier B.V. All rights reserved.