Dynamic Observations on Formation of Coffee-Ring Structures from the Degradation of Cesium Lead Halide Perovskite Nanocrystals.

Nanomaterials of halide perovskites have attracted increasing attention for their remarkable potential in optoelectronic devices, but their instability to environmental factors is the core issue impeding their applications. In this context, the microscopic understanding of their structural degradation mechanisms upon external stimuli remains incomplete. Herein, we took an emerging member of this material family, Cs 4 PbBr 6 nanocrystals (NCs), as an example and investigated the degradation pathways as well as underlying mechanisms under an electron beam by using in situ transmission electron microscopy. Our atomic-scale study identified the distinct degradation stages for the NCs toward interesting coffee-ring PbBr 2 structures, which are caused by the organic surface capping agents as well as surface energy of NCs. Our findings present a fundamental insight for the degradation of halide perovskite NCs and may provide indispensable guidance for their structural design and stability improvement.