Metastabilities in the electrical characteristics of CIGS devices: Experimental results vs theoretical predictions

Recent theoretical calculations have traced an origin of light- and voltage bias-induced metastabilities in Cu(In,Ga)Se2-based solar cells to negative-U properties of the VSe–VCu complex. In this paper we compare experimental findings with theoretically predicted properties of these defects and calculated values of parameters characteristic for transitions between their different states. Profiles of net acceptor concentrations in the relaxed and metastable states obtained by capacitance profiling have been studied, as well as annealing kinetics of the persistent defect distributions by thermally stimulated capacitance and conductivity. Good qualitative and quantitative agreement are found between theory of VSe-related defects and experimental results. The consequences from the point of view of photovoltaic efficiency of the Cu(In,Ga)Se2-based solar cells are discussed.