Mechanistic studies of CsPbBr3 superstructure formation

Abstract

All-inorganic perovskite superstructures (SCs) were recently reported to have formed through the self-assembly of perovskite nanocrystals (NCs) in hot injection synthesis. The presence of SCs leads to miniband formation in both conduction and valence bands and a red-shifted emission. The formation process of SCs is highly attractive and has so far been attributed to the van der Waals attraction between hydrophobic ligands and perovskite NCs at higher concentrations. However, there was no study to confirm this. Herein, we propose a new mechanism for CsPbBr₃ SC formation via cooling method manipulation and varying the amount of PbBr₂. We found that the amount of PbBr₂ is crucial for SC formation although an excess of PbBr₂ prevents SC formation. We also proposed that excess PbBr₂ could occupy Br vacancies to form CsPbBr₃–PbBr₂ linkages which assemble into CsPbBr₃ SCs. To the best of our knowledge, this is the first study to explain the importance of the amount of PbBr₂ in CsPbBr₃ SC formation. We obtained a maximum 34 nm total shift of CsPbBr₃ emission, demonstrating the huge potential of SCs in emission tuning. Our mechanism to explain the SC formation would contribute to the rational design of CsPbX₃ light emitting diodes, lasers, and other optoelectronic devices.