Temperature-dependent photoluminescence of lead-free cesium tin halide perovskite microplates

Tin halide perovskites recently have attracted extensive research attention due to their similar electronic and band structures but non-toxicity compared with their lead analogues. In this work, we prepare high-quality CsSnX3 (X = Br, I) microplates with lateral sizes of around 1-4 mu m by chemical vapor deposition and investigate their low-temperature photoluminescence (PL) properties. A remarkable splitting of PL peaks of the CsSnBr3 microplate is observed at low temperatures. Besides the possible structural phase transition at below 70 K, the multi-peak fittings using Gauss functions and the power-dependent saturation phenomenon suggest that the PL could also be influenced by the conversion from the emission of bound excitons into free excitons. With the increase of temperature, the peak position shows a blueshift tendency for CsSnI3, which is governed by thermal expansion. However, the peak position of the CsSnBr3 microplate exhibits a transition from redshift to blueshift at similar to 160 K. The full width at half maximum of CsSnX3 broadens with increasing temperature, and the fitting results imply that longitudinal optical phonons dominate the electron-phonon coupling and the coupling strength is much more robust in CsSnBr3 than in CsSnI3. The PL intensity of CsSnX3 microplates is suppressed due to the enhanced non-radiative relaxation and exciton dissociation competing with radiative recombination. According to the Arrhenius law, the exciton binding energy of CsSnBr3 is similar to 38.4 meV, slightly smaller than that of CsSnI3.