Unraveling Transformation Pathways of Colloidal Semiconductor Perovskite Magic-Sized Clusters at Sub-Ambient Temperature.

Colloidal semiconductor magic-sized clusters (MSCs) with precise atomic compositions and unique optical properties, which are observed as intermediate species in the synthesis of quantum dots (QDs) have been widely explored. To deeply understand transformation pathways of MSCs and control their composition/stability are essential to form large-scale high quality QDs with mono-dispersity and enhanced optical properties. However, the transformation pathway of ionic compound semiconductor MSCs with weak bond binding energy have rarely been investigated. In this work, taking ionic CsPbBr₃ MSCs as a representative model system, we here report both thermally-induced direct (Pathway 3) and precursor compounds (PCs) assisted (Pathway 1) transformation between binary PbBr₂ MSCs (absorption centered at ∼390 nm) and ternary CsPbBr₃ MSCs (absorption centered at ∼415 nm) at sub-ambient temperature, which have been first illustrated in ionic perovskite MSCs systems. Moreover, when increasing reaction temperature to 80°C, MSC-415 dissociate into monomers/fragments (Pathway 2) to form larger sized nanocrystals (NCs). In addition, the compositions and structures of MSCs have been experimentally and theoretically studied. This work contributes to fundamental understandings of transformation mechanism of perovskite MSCs/NCs systems, which is beneficial to synthesize size- and composition-controlled colloidal semiconductor QDs and NCs with tailored optical properties.