Thickness-Controlled Wafer-Scale Single-Crystalline MAPbBr3 Films Epitaxially Grown on CsPbBr3 Substrates by the Droplet-Evaporated Crystallization Method.

The perovskite single-crystalline thin films, which are free of grain boundaries, would be highly desirable in boosting device performance due to their high carrier mobility, low trap density, and large carrier diffusion length. Herein, a facile room-temperature approach to epitaxially grow MAPbBr3 single-crystalline films on CsPbBr3 substrates by the droplet-evaporated crystallization method is reported. A large-area continuous MAPbBr3 single-crystal film about 15 × 15 mm2 in size has been heteroepitaxially grown on CsPbBr3 substrates. The surface morphology, composition, and single crystallinity were characterized by a scanning electron microscope, an energy-dispersive spectrometer, an electron probe microanalyzer, and high-resolution X-ray diffractions, respectively. The thickness of the films could be adjusted from 1 to 18 μm by varying the concentration of the solution from 10 to 50 wt %. The epitaxial relationship of MAPbBr3 (010)∥CsPbBr3 (010), MAPbBr3 [101]∥CsPbBr3 [200] was authenticated using XRD, pole figure, and TEM. The low defect density of 4.6 × 1011 cm-3 and high carrier mobility of 261.94 cm2 V-1 s-1 of the MAPbBr3 film measured by the SCLC method are comparable to those of bulk single crystals. An on/off ratio of ∼113 was achieved according to current-voltage curves. Our research demonstrates the first large-area single-crystal heterojunction of a hybrid perovskite with an all-inorganic perovskite, which may show unique properties in optoelectronic applications.