Atomic-Scale Polarization and Strain at the Surface of Lead Halide Perovskite Nanocrystals

Inorganic halide perovskite nanocrystals (NCs) are beingwidelyexplored as next-generation optoelectronic materials. Critical tounderstanding the optoelectronic properties and stability behaviorof perovskite NCs is the material's surface structure, wherethe local atomic configuration deviates from that of the bulk. Throughlow-dose aberration-corrected scanning transmission electron microscopyand quantitative imaging analysis techniques, we directly observedthe atomic structure at the surface of the CsPbBr3 NCs.CsPbBr3 NCs are terminated by a Cs-Br plane, andthe surface Cs-Cs bond length decreases significantly (& SIM;5.6%)relative to the bulk, imposing compressive strain and inducing polarization,which we also observed in CsPbI3 NCs. Density functionaltheory calculations suggest such a reconstructed surface contributesto the separation of holes and electrons. These findings enhance ourfundamental understanding of the atomic-scale structure, strain, andpolarity at the surface of inorganic halide perovskites and providevaluable insights into designing stable and efficient optoelectronicdevices.