Effects of pulsed laser annealing on deep level defects in electrochemically-deposited and furnace annealed CuInSe2 thin films

Abstract

CuInSe2 (CISe) is a prototype material for the I–III–VI chalcopyrites such as Cu(In,Ga)(S,Se)2 used as absorber layers in thin film photovoltaic cells. Carefully-controlled pulsed-laser annealing (PLA) is a unique annealing process that has been demonstrated to improve the device performance of chalcopyrite solar cells. Here, we investigate the changes in defect populations after PLA of electrochemically-deposited CISe thin films previously furnace annealed in selenium vapor. The films were irradiated in the sub-melting regime at fluences inducing temperatures up to 840±100K. Deep-level transient spectroscopy on Schottky diodes reveals that the activation energy of the dominant majority carrier trap changes non-monotonically from 215±10meV for the reference sample, to 330±10meV for samples irradiated at 20 and 30mJ/cm2, and then back to 215±10meV for samples irradiated at 40mJ/cm2. A hypothesis involving competing processes of diffusion of Cu and laser-induced generation of In vacancies may explain this behavior.