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

► A unique method is presented to determine the exciton binding energy in a polycrystalline CsSnI3 compound. ► A large exciton binding energy of 18 meV was deduced for the natural two-dimensional excitons in CsSnI3. ► CsSnI3 is important semiconductor since it has a direct band gap of 1.32 eV at 300 K. ► Exciton lifetime increases monotonically with temperature up to near room temperature.