Application of impedance spectroscopy to investigate the electrical properties around the pn interface of Cu(In,Ga)Se2 solar cells

The application of impedance spectroscopy (IS) analytical theory to the characterization of Cu(In,Ga)Se-2 (CIGS)-based solar cells was investigated. The equivalent circuit of the CIGS solar cell consisting of series and parallel resistances and a capacitance-like element labeled as constant phase element (CPE) around the CdS/CIGS interface was developed. The CPE reflects the depletion layer thickness and the pn interface uniformity and quality. In particular, the CPE-p value, which is an index of impedance of CPE, affects the quality around the CdS/CIGS interface in terms of defect existence and inhomogeneity of the heterojunction. These results show possible candidate for the practical application of IS as a simple method for characterizing the heterogeneity of a pn interface. (C) 2012 Elsevier B.V. All rights reserved.