Reduced ion migration and enhanced photoresponse in cuboid crystals of methylammonium lead iodide perovskite

The optoelectronic and photocatalytic properties of a number of semiconductor materials, including halide perovskites, have recently been found to be facet-dependent. While methylammonium lead iodide (CH₃NH₃PbI₃) perovskite - an important material for energy applications - has shown facet-dependent electronic properties as well, most studies on CH₃NH₃PbI₃ perovskite were performed on rhombo-dodecahedral (or rhombic) single crystals with the (2 0 0) and (1 1 2) facets exposed. In contrast, less is known about the electronic properties, including mixed conductivity behavior and possible in-plane anisotropy, of the (0 0 2) facet. Thus, we report a facile method for the growth of cuboid crystals of CH₃NH₃PbI₃ perovskite with the (0 0 2) and (1 1 0) facets exposed. Two-terminal devices fabricated on the (0 0 2) facet demonstrate significantly improved charge transport and optoelectronic characteristics compared to those on the (2 0 0) facet of typical rhombic crystals, including: reduced ion migration, low dark current, and temporally-stable high photocurrents. These desirable characteristics of cuboid crystals are linked to their favorable growth conditions and preferred facet orientations. Our results provide a guidance for utilizing facets and crystal growth to achieve more efficient in-plane halide perovskite devices.