Slow intraband relaxation and localization of photogenerated carriers in CuIn{1−x}Ga{x}Se{2} thin films: Evidence for the existence of long-lived high-energy carriers

Abstract

The dynamics of free carriers in polycrystalline CuIn{1−x}Ga{x}Se{2} (CIGS) thin films were studied using picosecond time-resolved photoluminescence (PL) and femtosecond transient-absorption (TA) measurements. The PL spectrum and the TA decay component due to the band-to-band recombination of free carriers were observed in the picosecond time region. From excitation-photon-energy-dependent TA measurements, we identified a slow intraband relaxation of free carriers in the CIGS thin films. Collectively, the combination of PL and TA experiments reveal a global feature of energy relaxation and recombination processes of free carriers in the femtosecond to nanosecond time regions.