Modeling of the impact of Se-vacancies on the electrical properties of Cu(In,Ga) Se2 films and junctions

In this contribution we aim at a better understanding the influence of metastable V-Se defects on electrical characteristics of Cu(In,Ga) Se-2-based solar cells. In order to achieve this goal we calculate the distribution of V-Se charge states by solving numerically the equations involving transition rates between the metastable donor and acceptor configuration. By varying systematically the set of three parameters in a broad range (net shallow acceptor doping level, V-Se defect density and temperature) we analyze quantitatively in which conditions and how the metastable defects influence/control the Fermi level position and hence the free carrier concentration. Using these results, we calculate time constants for conversion processes between donor and acceptor configurations. In the second part of the paper we model the influence of V-Se-related defects on capacitance-voltage (CV) space charge profiles in different metastable states (reverse bias and light soaking). We propose a method allowing the evaluation of the lower bound for the metastable V-Se defect concentration from CV profiles. (C) 2013 Elsevier B.V. All rights reserved.