Nonmonotonic temperature-dependent bandgap change of CsPbCl3 films induced by optical phonon scattering

The CsPbCl3 perovskite films are successfully grown on quartz substrates by radio frequency (RF)-magnetron sputtering method and their detailed photoluminescence properties are studied over the temperatures from 10 K to 300 K. There exists one near bandgap emission peak (∼410 nm) in the violet region with typical lifetime of few nanoseconds at room temperature. To our surprise, with temperature increasing, this band shows nonmonotonic shift, which is different to the traditional semiconductor like silicon or the same group of perovskites like MAPbI3 or CsPbBr3. The origin of this band and its temperature-dependent shift can be well described with the Bose-Einstein two-oscillator model that takes into account the interaction between electrons and phonons including acoustic phonons and optical phonons. Due to the anisotropic optical properties of the perovskite crystal, the (001)-orientated films have stronger electron phonon coupling and weaker exciton binding energy.