The changes of the electronic properties of the absorber layer in the ZnO/CdS/Cu(In,Ga)Se-2 photovoltaic devices induced by the 'damp heat' test have been investigated by use of junction capacitance techniques. Deep level transient spectroscopy and admittance spectroscopy have been employed for characterization of the bulk and interface levels in the absorber. Additional information on the transport mechanisms has been provided by the analysis of current-voltage characteristics. We conclude that the 'damp heat' treatment introduces deep electron traps, thus increasing the absorber compensation and decreasing V-infinity of the devices. The same states facilitate transport of carriers by means of trap-assisted tunneling, causing a decrease of the fill factor. O-Sc is a probable candidate for a defect introduced by the humidity test.