Creation and relaxation of light- and bias-induced metastabilities in Cu(In,Ga)Se2

Metastabilities in Cu(In,Ga)Se2 based solar cells were investigated. Capacitance and conductance transients were measured in order to analyze carrier trapping and emission processes related to the creation and relaxation of metastable states. Our experimental findings support the theoretical predictions of Lany and Zunger [Lany and Zunger, J. Appl. Phys. 100, 113725 (2006)] for a (VSe-VCu) complex, a defect with negative-U energy that can exist in both the donor and acceptor configurations. We show that two different defect reactions induced by either voltage bias or illumination lead to the same acceptor configuration of the defect. The relaxation process is the same for light- and bias-induced metastabilities in devices and thin films. Time constants and activation energies for all investigated processes have been obtained. The results agree very well with the values calculated for (VSe-VCu) divacancy.