Exciton diffusion in two-dimensional metal-halide perovskites

There is an increasing interest in 2D perovskites for solar harvesting and light-emitting applications due to their superior chemical stability as compared to bulk perovskites. However, the reduced dimensionality in 2D perovskites results in excitonic excited states which dramatically modify their optoelectronic properties. While the carrier dynamics in bulk systems is increasingly well understood, a detailed understanding about the spatial dynamics of excitons in 2D perovskites is lacking. Here, we present the direct measurement of the diffusivities and diffusion lengths of excitons in 2D perovskites, revealing both the spatial and temporal exciton dynamics. We find that changing the organic spacer, cation or dimensionality of the perovskite yield dramatically different diffusivities, due to strong exciton-phonon interactions and potentially the formation of large exciton-polarons. Our results provide clear design parameters for more efficient 2D perovskite solar cells and LEDs.