Temperature-Dependent Transient Microscopy of Excitons and Free Carriers in Perovskites

Recent studies have revealed that exciton transport in low-dimensional perovskite materials deviates significantly from anticipated trends, exhibiting much higher diffusivities, excitation memory effect, and the potential roles of excitonic fine structure and superradiance. These findings raise critical questions about whether such phenomena are inherent to all perovskites, including their bulk (3D) counterparts, or are specific to lower dimensionality. While <i>charge transport</i> mechanisms in bulk perovskites are well understood, <i>exciton transport</i> remains largely unexplored. In this work, we use temperature-dependent transient photoluminescence microscopy (TPLM) to access distinct transport regimes dominated by excitons and free charges, benchmarking behavior in high-quality epitaxially-grown perovskite single crystals. We compare our results with the predictions from the Saha equation describing the thermal equilibrium between the two species. Anomalous and fast transport behavior of excitons is revealed at cryogenic temperatures, providing insights into the excited state landscape in perovskite materials.