Using Time-Resolved Microscopy to Probe Exciton Diffusion in CsPbBr₃ Superlattices

Exciton transport is critical to the performance of semiconductor nanocrystals in optoelectronic devices. Within most nanocrystal assemblies, exciton transport is a diffusive process mediated by Förster resonant energy transfer (FRET). Both structural and dynamic disorder can affect FRET-mediated exciton diffusion through their impact on factors such as nanocrystal spacing, transition dipole alignment, exciton radiative lifetimes, and excitonic coherence. The combined impact of these factors on exciton transport is complex and not well-understood in emerging semiconductor materials like lead halide perovskites. Here, we use time-resolved photoluminescence microscopy to investigate the effects of different types of disorder on exciton transport in CsPbBr₃ nanocube assemblies. This technique allows us to directly visualize the movement of excitons within the nanocrystal assembly. We determine the effect of structural disorder across different nanocrystal sizes by comparing exciton transport in highly ordered superlattices and in disordered assemblies, and we determine the effect of dynamic disorder by varying the temperature from 5K to room temperature. These investigations shed light on exciton transport mechanisms and could inform future design strategies for nanocrystals in optoelectronic devices.