Halide perovskites have shown great potential for light emission and photovoltaicVisualising buried local carrier diffusion in halide perovskite crystals via two-photon microscopy applications due to their remarkable electronic properties and their compatibility with cost-effective fabrication techniques. Although the device performances are promising, they are still limited by microscale heterogeneities in their photophysical properties. In particular, the relation between local heterogeneities and the diffusion of charge carriers at the surface and in the bulk, crucial for an efficient collection of charges in a light harvesting device, is not well understood. Here, we develop a photoluminescence tomography technique in a confocal microscope using one- and two-photon excitation to distinguish between local surface and bulk diffusion of charge carriers in methylammonium lead bromide single crystals. This method allows us to probe the local temporal diffusion at various excitation depths, and we use it to construct statistics of local electronic diffusion coefficients. We find that these values range between 0.3 to 2 cm2 per second depending on the local trap density and the morphological environment - a distribution that would be missed from analogous macroscopic or surface-measurements. We reconstruct tomographic images of carrier diffusion to reveal barriers to carrier transport likely due to buried crystal defects. Our work unveils a new framework to understand and homogenise diffusion pathways, which are extremely sensitive to local properties and buried defects. The technique will be broadly applicable to a range of semiconductor materials. 

Visualising buried local carrier diffusion in halide perovskite crystals via two-photon microscopy

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.