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 (200) and (112) facets exposed. In contrast, less is known about the electronic properties, including mixed conductivity behavior and possible in-plane anisotropy, of the (002) facet. Thus, we report a facile method for the growth of cuboid crystals of CH3NH3PbI3 perovskite with the (002) and (110) facets exposed. Two-terminal devices fabricated on the (002) facet demonstrate significantly improved charge transport and optoelectronic characteristics compared to those on the (200) 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.