Photoexcited Carrier Dynamics of In2S3 Thin Films

Indium sulfide (In2S3) is a promising absorber base for substitutionally doped intermediate band photovoltaics (IBPV); however, the dynamics of charge carriers traversing the electronic density of states that determine the optical and electronic response of thin films under stimuli have yet to be explored. The kinetics of photophysical processes in In2S3 grown by oxygen-free atomic layer deposition are deduced from photoconductivity, photoluminescence (PL), and transient absorption spectroscopy. We develop a map of excited-state dynamics for polycrystalline thin films including a secondary conduction band similar to 2.1 eV above the first, plus sulfur vacancy and indium interstitial defect levels resulting in long-lived (similar to 100 ns) transients. Band-edge recombination produces PL and stimulated emission, which both intensify and red-shift as deposition temperature and grain size increase. The effect of rapid conduction band electron relaxation (<30 ps) and deep defect levels on IBPV employing In2S3-based absorbers is finally considered.