Persistent phenomena in the electrical characteristics of solar cells based on Cu(In,Ga)S2

Abstract

AbstractCurrent‐voltage and capacitance‐voltage characteristics of ZnO/CdS/CuInGaS2 solar cells have been measured in order to investigate persistent changes induced by the reverse bias stress or light soaking. Significant metastable fill factor loss after red illumination under reverse bias condition has been observed. We show a correspondence between relaxation times of the capacitance and photovoltaic parameters after all treatments proving that defects in the absorber are responsible for the changes. Similar phenomena have been observed in Cu(In,Ga)Se2 based devices, therefore we propose similar explanation – negative‐U defects in Cu(In,Ga)S2 which create a highly negatively charged layer close to the interface. They are responsible also for a difference between current transport in the dark and under illumination. Moreover, these defects seem to be a source of an limitation of the open circuit voltage in these devices. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)