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Halide perovskites have emerged as disruptive semiconductors for applicationsincluding photovoltaics and light emitting devices, with modular optoelectronicproperties realisable through composition and dimensionality tuning. LayeredRuddlesden-Popper perovskites of the form BA2MAn-1PbnI3n+1, where n is thenumber of lead-halide and methylammonium (MA) sheets spaced by longerbutylammonium (BA) cations, are particularly interesting due to their uniquetwo-dimensional character and charge carrier dynamics dominated by stronglybound excitons. However, long-range energy transport through exciton diffusionin these materials is not understood or realised. Here, we employ localtime-resolved luminescence mapping techniques to visualise exciton transport inhigh-quality exfoliated flakes of the BA2MAn-1PbnI3n+1 perovskite family. Weuncover two distinct transport regimes, depending on the temperature rangestudied. At temperatures above 100 K, diffusion is mediated by thermallyactivated hopping processes between localised states. At lower temperatures, anon-uniform energetic landscape emerges in which exciton transport is dominatedby energy funnelling processes to lower energy states, leading to long rangetransport over hundreds of nanometres even in the absence of exciton-phononcoupling and in the presence of local optoelectronic heterogeneity. Efficient,long-range and switchable excitonic funnelling offers exciting possibilities ofcontrolled directional long-range transport in these 2D materials for newdevice applications.

Local energy landscape drives long exciton diffusion in 2D halide perovskite semiconductors