We report temperature-dependent photoluminescence (PL) in polycrystalline ASnI3 perovskites (A = Cs+, CH3NH3 +, and HC(NH2)2 +), demonstrating extremely robust emission up to very high temperatures (523 K for CsSnI3). The PL peak energy (EPL) monotonically blueshifts with increasing temperature, indicating band gap widening. Variable temperature synchrotron powder X-ray diffraction analysis confirms that these changes are associated with progressive emphanitic off-centering and dynamic fluctuations of the perovskite lattice. In CsSnI3, three different temperature gradients of EPL are defined (0.29 meV K-1 below 200 K, 0.17 meV K-1 from 200 to 400 K, and 0.48 meV K-1 above 400 K), commensurate with the onset of dynamic structural disorder at 200 K and its saturation at 400 K as the Cs+ atoms rattle independently of the [SnI3]- perovskite lattice. These results explain how solution-processed perovskites with massive defect concentrations can yield high optoelectronic performance at elevated temperatures.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films