Phase control in mixed halide methylammonium lead perovskites using silicon nanotube templates

Mixed halide perovskite nanostructures of composition CH₃NH₃PbI_3-xBr_x (x = 0, 0.25, 0.50, 0.75, and 3) and inner diameter (ID = 30, 70, and 200 nm) using silicon nanotube (SiNT) templates are described. For a given composition, the photoluminescence (PL) of these mixed halide perovskites is compared to that of bulk perovskite microwires/microcubes. Interestingly, for CH₃NH₃PbI_2.25Br_0.75 formed within these NTs, precise control of the cubic phase of this perovskite is maintained over time, as monitored by X-ray diffraction up to 21 days; this behavior is in stark contrast to the microwire, nontemplated structure of the same composition, which reverts to the tetragonal phase during this period. For the 70 and 200 nm ID templates, these NTs also provide some stabilization and effective packaging of the perovskite with regard to crystallinity and PL intensity over this time period.