Chemical vapor deposition growth of single-crystalline cesium lead halide microplatelets and heterostructures for optoelectronic applications

Organic–inorganic hybrid halide perovskites, such as CH₃NH₃PbI₃, have emerged as an exciting class of materials for solar photovoltaic applications; however, they are currently plagued by insufficient environmental stability. To solve this issue, all-inorganic halide perovskites have been developed and shown to exhibit significantly improved stability. Here, we report a single-step chemical vapor deposition growth of cesium lead halide (CsPbX₃) microcrystals. Optical microscopy studies show that the resulting perovskite crystals predominantly adopt a square-platelet morphology. Powder X-ray diffraction (PXRD) studies of the resulting crystals demonstrate a highly crystalline nature, with CsPbCl₃, CsPbBr₃, and CsPbI₃ showing tetragonal, monoclinic, and orthorhombic phases, respectively. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies show that the resulting platelets exhibit well-faceted structures with lateral dimensions of the order of 10–50 µm, thickness around 1 µm, and ultra-smooth surface, suggesting the absence of obvious grain boundaries and the single-crystalline nature of the individual microplatelets. Photoluminescence (PL) images and spectroscopic studies show a uniform and intense emission consistent with the expected band edge transition. Additionally, PL images show brighter emission around the edge of the platelets, demonstrating a wave-guiding effect in high-quality crystals. With a well-defined geometry and ultra-smooth surface, the square platelet structure can function as a whispering gallery mode cavity with a quality factor up to 2, 863 to support laser emission at room temperature. Finally, we demonstrate that such microplatelets can be readily grown on a variety of substrates, including silicon, graphene, and other two-dimensional materials such as molybdenum disulfide, which can readily allow the construction of heterostructure optoelectronic devices, including a graphene/perovskite/ graphene vertically-stacked photodetector with photoresponsivity > 10⁵ A/W. The extraordinary optical properties of CsPbX₃ platelets, combined with their ability to be grown on diverse materials to form functional heterostructures, can lead to exciting opportunities for broad optoelectronic applications.