Crystal facet engineering induced anisotropic transport of charge carriers in a perovskite

Precise control of crystal orientations and macroscopic morphology of a perovskite crystal is crucial for various optoelectronic applications relying on charge carrier transport tuning along exposed crystal facets. Here, taking methylammonium lead bromide (CH₃NH₃PbBr₃) as an example, and employing a novel crystal facet engineering method, we successfully construct two kinds of perovskite crystals with exposed {001} and {110} facets. We find that the free carriers' photoluminescence lifetime on the {001} facets can be 3 times longer than that on {110} facets. The related mechanisms are investigated via fluorescence lifetime imaging microscopy and in situ transmission electron microscopy. These indicate that the different trap state density of exposed facets and crystal structure changing of CH₃NH₃PbBr₃ under light and electron beam irradiation lead to the differences in carrier transport along different facets. By distinguishing the charge carrier transport on different CH₃NH₃PbBr₃ exposed facets, micro-photodetectors have been constructed. A device fabricated with the {001} exposed facets exhibited two orders of magnitude higher photocurrent and half as much dark current as a {110} facet-based device. Thus, the crystal facet engineering of perovskites can be widely adopted for understanding physical/chemical properties of perovskite crystals and provides great potential for novel perovskite optoelectronic device applications.