We investigated the influence of different Cu and Na contents on the electrical properties of Cu(In,Ga)(S,Se)(2) solar cells. The devices were characterized applying admittance spectroscopy and deep-level transient spectroscopy (DLTS). We observed four kinds of deep defect states in differing concentrations in the stoichiometry-varied samples: two acceptor-like deep-level states, one donor-like trap, and a midgap center. In order to characterize the properties of these defect states, we recorded the DLTS capacitance transients of a Na poor sample with different pulse widths (ranging from 100 mus to 1 s duration) at selected fixed temperatures. We discuss the properties of the defect states. (C) 2003 Elsevier Science B.V. All rights reserved.