Elucidation of the excited-state dynamics in CuInS2 thin films

Transient absorption (TA) and photoluminescence spectroscopy have been performed on spray-deposited CuInS2 thin films. Sulfur and indium vacancies introduce electronic states in the bandgap located at 1.5 and 0.15 eV above the valence band, respectively. Deep donor and deep acceptor doublet states at 1.1 and 0.2 eV are assigned to copper/indium antisite defects. The excited-state dynamics, which are derived from TA experiments, show electronic coupling between indium antisite defects and indium vacancies. The Shockley, Read, and Hall recombination model has been modified to account for this coupling and to simulate the TA results. Furthermore, the lifetime of the 1.1 eV state is found to be 20-50 mu s, which is related to the low photovoltage of CuInS2 based solar cells.