Detailed study of metastable effects in the Cu(InGa)Se2 alloys: Test of defect creation models

Abstract

AbstractWe have investigated metastable changes to Cu(InGa)Se2 solar cells in response to infrared optical exposure and forward injection current. Using the drive level capacitance profiling and admittance spectroscopy techniques, we are able to distinguish changes in the free hole carrier concentration from those of a deeper bulk trap. For both types of treatment, changes in these concentrations clearly follow a 1:1 ratio, in agreement with recent predictions of a microscopic model proposed by Lany and Zunger. The creation kinetics follow a strongly sub-linear power law at 250K, and we demonstrate that we can account for this using rate equations in which the metastable effect is initiated by electron capture into an empty defect state. The dependence on time and light intensity is (time) 0.22± 0.03 and (intensity) 0.53± 0.06, except at high light intensities where saturation is observed.