Thermoresponsive Emission Switching via Lower Critical Solution Temperature Behavior of Organic-Inorganic Perovskite...

Lead halide perovskites have shown much promise for high-performing solar cells due to their inherent electronic nature, and though the color of bright-light emitters based on perovskite nanoparticles can be tuned by halide mixing and/or size control, dynamic switching using external stimuli remains a challenge. This article reports an unprecedented lower critical solution temperature (LCST) for toluene solutions containing methylammonium lead bromide (MAPbBr₃ ), oleic acid, alkylamines, and dimethylformamide. The delicate interplay of these molecules and ions allows for the reversible formation and decomposition of MAPbBr₃ nanoparticles upon heating and cooling, which is accompanied by green and blue photoemissions at each state. An intermediate 1D crystal with PbBr₂ -amine coordination is found to play pivotal role in this, and a mechanistic insight is provided based on a three-state model. In addition to a high quantum yield (up to 85%), this system allows for control over the cloud point (30-80 °C) through compositional engineering and the luminescent color (blue to red) via halogen exchange, thus making it a versatile solution for developing functional molecular organic-inorganic LCST quantum dots.