Mechanistic Studies of CsPbBr3 Superstructure Formation

All-inorganic perovskite superstructures (SCs) were recently reported to be 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 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 SCs 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 over-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. This is the first study to explain the importance of the amount of PbBr2 in CsPbBr3 SCs formation to the best of our knowledge. We obtained a maximum 34 nm total shift of CsPbBr3 emission, demonstrating the huge potential of SCs in emission tuning. Our mechanism to explain SC formation would contribute to the rational design of CsPbX3 light emitting diodes, lasers, and other optoelectronic devices.