Atomic Models for Surface Stabilization of Cesium Lead Halide Perovskite Nanocrystals within Chemical Effect of Metal Halides

Colloidal cesium lead halide perovskite nanocrystals (NCs) have been emerged as promising optoelectronic materials due to their unique optical properties and low-temperature solution processability. Despite the advantages, structural instability of the perovskite NCs leads to size and shape changes as well as phase transition, resulting in uncontrollable their physicochemical properties. Recent synthetic approach using metal halides made great progress on enhancing structural stability of the NCs. However, the influence of the additional metal halides on the perovskite NCs, especially on their surfaces, is not fully understood.
In this study, we formulate atomic models of perovskite surfaces for microscopic understandings on surface chemistry of the perovskite NCs in the presence of the metal halides. Based on electron counting models and first-principles DFT calculations, we found various ligand-passivated surfaces of the NCs strongly affected by chemical reactions that depend on the additional metal halides. From thermodynamic comparisons of our atomic models, we deduced that all surfaces could be greatly stabilized with the presence of the metal halides. Our results also account for the recent experimental observations on improving structural stability of the perovskite NCs.