The goal of this work is to classify and systematically investigate the N-1 Deep Level Transient Spectroscopy (DLTS) response characteristic for Cu(In,Ga)Se-2-based heterojunctions. Up to four different peaks giving rise to the N-1 signal are observed. It is shown that the contribution of the components strongly depends on the metastable state of the sample (different kind of light soaking and reverse bias treatment) and measurement conditions. In the second part of the paper the unusual features of the N-1 response, such as an enormously high signal level, are discussed. It is argued, basing on the correlations between capacitance-voltage curves and DLTS spectra, that some of the properties might be due to intrinsic In-Cu DX centers. (C) 2010 Elsevier B.V. All rights reserved.