Photoluminescence study of polycrystalline CsSnI3 thin films: Determination of exciton binding energy

We report on the determination of exciton binding energy in perovskite semiconductor CsSnI3 through a series of steady state and time-resolved photoluminescence measurements in a temperature range of 10–300 K. A large binding energy of 18 meV was deduced for this compound having a direct band gap of 1.32 eV at room temperature. We argue that the observed large binding energy is attributable to the exciton motion in the natural two-dimensional layers of SnI4 tetragons in this material.