Optical Properties of Binary Nanocrystal Superlattices Produced by Assemblies of Strongly and Weakly Confined CsPbBr₃ Perovskite Nanocrystals

Periodicity in long range-ordered nanocrystal superlattices (NC SLs) can be exploited to alter or even tailor the properties of the individual NC building blocks while generating new collective electronic and optical phenomena as a result of the enhanced interactions between NCs. Perovskite NCs have emerged as highly attractive building blocks for SLs, based on their facile fabrication as sharp, monodisperse cubes as well as due to the observation of superfluorescence from single and multi-component perovskite NC superstructures.<br/>Binary superlattices of the ABO₆ type, produced via self-assemblies of CsPbBr₃ NCs with sizes in the strong (~5 nm) and weak (~18 nm) confinement regime are being demonstrated for the first time. We discuss the optical properties of such binary SLs, focusing on the electronic interactions between the strongly and weakly-confined NC excitons. Transient photoluminescence and absorption measurements indicate efficient depletion of the small NC exciton population at the few to tens of ps scale; a concomitant delay of the transient absorption rise time signal of the large NC exciton bleaching is also observed. Such results are consistent with a highly efficient energy transfer process from the small to the large NCs within the binary superstructure. On-going experiments are investigating whether the fast energy funneling into the weakly confined NC excitons can compete and influence the characteristics and dynamics of the superfluorescence observed in such binary perovskite SLs.