Reverse Bias Induced Metastable Effects in Cu(In,Ga)Se2 Photovoltaic Devices

The effects of reverse bias stressing have been studied on CuInGaSe₂ thin-film solar cell devices. Finished cells were subjected to treatments of various levels of negative voltage bias at different temperatures and for different durations. Metastable changes in the defect profiles as measured by drive-level capacitance profiling (DLCP) were observed. Modeling of the effects suggests a mechanism in which a conversion of shallow acceptors to deep acceptors in the high field region near the barrier interface is largely responsible for the changes in the profiles. In addition, we observe a significant decrease in the open-circuit voltage after long exposure to bias, which may result from increased recombination through the larger number of deep defects near the interface. These effects are entirely reversible by annealing at zero bias at 370 K for one hour