Annealing CsPbX3 (X = Cl and Br) Perovskite Nanocrystals at High Reaction Temperatures: Phase Change and Its Prevention

Annealing perovskite nanocrystals at high reaction temperature changes their crystal phase, shape, and optical properties. Carrying out reactions between 180 and 250 degrees C, the impact of thermal annealing for CsPbCl3 and CsPbBr3 nanocrystals in a reaction flask was investigated here. At higher temperature, a phase change was observed instantly, which could not be trapped even with ice-bath cooling. Interestingly, using a calculated amount of preformed alkylammonium halides as dual passivating agents, the nanocrystals of both CsPbCl3 and CsPbBr3 could even be stabilized for hours of annealing at 250 degrees C. CsPbCl3, which was reported to be a poor emissive nanocrystal in comparison to CsPbBr3, could sustain even more than 5 h of annealing at 250 degrees C and recorded similar to 51% absolutely quantum yield. Details of the interface chemistry and the role of the used dual passivating agent for providing thermal stability are studied and reported in this Letter.