Temperature-dependent nonmonotonous evolution of excitonic blue luminescence and Stokes shift in chlorine-based organometallic halide perovskite film

The chlorine-based organometallic halide perovskite (Cl-OHP) film with a (001)-preferred orientation and good crystallization has been synthesized by a hybrid sequential deposition process. The photoluminescence and absorption spectra of the Cl-OHP film in the blue light region have been investigated at operating temperatures ranging from 10 to 350 K. The Cl-OHP film shows a strong exciton-related emission of which the exciton binding energies at low temperature and high temperature are 136 meV and 41 meV, respectively. It is found that the blueshift from excitonic luminescence is initially observed at temperature below 175 K, and then, the redshift occurs from 175 to 350 K. Meanwhile, the bandgap of the Cl-OHP film widens with the increase in operating temperature. The nonmonotonous shifts on the emission peak energy are attributed to the competition between the Stokes effect and bandgap widening. This should contribute to the understanding of photophysical processes in Cl-OHP materials and devices.