Atomically unraveling the structural evolution of surfaces and interfaces in metal halide perovskite quantum dots.

Revealing the local structural change of metal halide perovskites (MHPs) induced by external conditions is important to understand their performance and stability in optoelectronic applications. However, previous studies on the properties and structures of MHPs were usually limited by the spatial resolution of the probe, and it is still challenging to obtain their atomic structural information in real space. In this work, we apply the integrated differential phase contrast scanning transmission electron microscopy to the low-dose imaging of CsPbI 3 quantum dots (QDs). In particular, the local structures in QDs, such as surfaces and interfaces, can be atomically resolved. Then, the structural evolution of CsPbI 3 QDs under various external conditions can be unraveled during in-situ heating or ex-situ treatments, where they will lose cubic shapes and fuse to larger particles. The changes in surfaces and interfaces with missing Cs ions and PbI 6 octahedrons can be semi-quantitatively studied by profile analysis and bond-length measurement in images. Finally, the density functional theory calculations are performed to illustrate the properties and stabilities of the different structures that we observed. These results provide atomic-scale insights into the structural evolution of QDs, which is of great importance to modify the performance of perovskite materials and devices. This article is protected by copyright. All rights reserved.