Quantifying Structural Heterogeneity in Individual CsPbBr₃ Quantum Dot Superlattices

A thorough understanding of the structural heterogeneity in CsPbBr3 quantum dot superlattices (SLs) is necessary for the realization of exciton coherence in these systems. Scanning transmission electron microscopy (STEM) coupled to fast-Fourier transform (FFT) analysis is utilized to characterize the structural properties of individual SLs. For each SL, the average constituent quantum dot size, size dispersity, and number of crystalline domains are quantified. Analysis of 40 individual SLs across eight growth experiments reveals that SLs are structurally heterogeneous but tend to have a narrower size distribution than the precursor solution due to size selection that occurs during evaporative self-assembly. We directly correlate STEM-FFT structural properties to low-temperature photoluminescence spectra for individual SLs, demonstrating that the substructure in the photoluminescence peak arises from multiple, locally ordered domains within the SL. In addition, we show that long-range structural disorder in an SL does not necessarily impact short-range phenomena such as exciton delocalization.