Low-Temperature Absorption, Photoluminescence, and Lifetime of CsPbX₃ (X = Cl, Br, I) Nanocrystals

The absorption and photoluminescence, both steady-state and time-resolved, of CsPbX₃ (X = Cl, Br, I) nanocrystals are reported at temperatures ranging from 3 to 300 K. These measurements offer a unique window into the fundamental properties of this class of materials which is considered promising for light-emitting and detection devices. The bandgaps are shown to increase from low to high temperature, and none of the examined cesium-based perovskite nanocrystals exhibit a bandgap discontinuity in this temperature range suggesting constant crystal phase. Time-resolved measurements show that the radiative lifetime of the band-edge emission depends strongly on the halide ion and increases with heating. The increasing lifetime at higher temperatures is attributed primarily to free carriers produced from exciton fission, corroborated by the prevalence of excitonic character in absorption. The results particularly highlight many of the similarities in physical properties, such as low exciton binding energy and long lifetime, between CsPbI₃ and hybrid organic–inorganic plumbotrihalide perovskites.