Thermal tolerance of perovskite quantum dots dependent on A-site cation and surface ligand

A detailed picture of temperature dependent behavior of Cs_xFA_1-xPbI₃  perovskite quantum dots across the composition range is constructed by  performing in situ optical spectroscopic and structural measurements,  supported by theoretical calculations that focus on the relation between  A-site chemical composition and surface ligand binding. The thermal  degradation mechanism depends not only on the exact chemical  composition, but also on the ligand binding energy. The thermal  degradation of Cs-rich perovskite quantum dots is induced by a phase  transition from black γ-phase to yellow δ-phase, while FA-rich  perovskite quantum dots with higher ligand binding energy directly  decompose into PbI₂. Quantum dot growth to form large bulk size grain is observed for all Cs_xFA_1-xPbI₃  perovskite quantum dots at elevated temperatures. In addition, FA-rich  quantum dots possess stronger electron−longitudinal optical phonon  coupling, suggesting that photogenerated excitons in FA-rich quantum  dots have higher probability to be dissociated by phonon scattering  compared to Cs-rich quantum dots.