Real-Time In Situ Observation of CsPbBr₃ Perovskite Nanoplatelets Transforming into Nanosheets

The manipulation of nano-objects through heating is aneffectivestrategy for inducing structural modifications and therefore changingthe optoelectronic properties of semiconducting materials. Despiteits potential, the underlying mechanism of the structural transformationsremains elusive, largely due to the challenges associated with theirin situ observations. To address these issues, we synthesize temperature-sensitiveCsPbBr(3) perovskite nanoplatelets and investigate theirstructural evolution at the nanoscale using in situ heating transmissionelectron microscopy. We observe the morphological changes that startfrom the self-assembly of the nanoplatelets into ribbons on a substrate.We identify several paths of merging nanoplates within ribbons thatultimately lead to the formation of nanosheets dispersed randomlyon the substrate. These observations are supported by molecular dynamicssimulations. We correlate the various paths for merging to the randomorientation of the initial ribbons along with the ligand mobility(especially from the edges of the nanoplatelets). This leads to thepreferential growth of individual nanosheets and the merging of neighboringones. These processes enable the creation of structures with tunableemission, ranging from blue to green, all from a single material.Our real-time observations of the transformation of perovskite 2Dnanocrystals reveal a route to achieve large-area nanosheets by controllingthe initial orientation of the self-assembled objects with potentialfor large-scale applications.