(495d) Semiconducting Halide Perovskite Nanomaterials and Heterojunctions

Recently, there is a renaissance of halide perovskite ABX₃ (A = organic ammonium cation, Cs; B = Pb²⁺; X = Cl^-, Br^-, I^-) as a promising class of semiconductor materials for a variety of optoelectronic device applications. Remarkable features have been discovered in the halide perovskite system, such as long charge carrier lifetime/diffusion length, large absorption coefficient, high photoluminescence quantum efficiency, etc. So far, most of work focuses on bulk crystals and polycrystalline thin films. Achieving new nanoscale morphologies (0D, 1D, or 2D) is of great interest because it offers a unique avenue to depart from the properties of the bulk materials and to study nanomaterials on a fundamental level in order to enable the incorporation of these materials into next-generation devices.

In this presentation, we demonstrate a novel substrate mediated crystallization method to growth high quality one dimensional nanowires with diameters ranging from 200 to 800 nm and lengths over 10 μm, and two dimensional sheets with lateral dimensional up to 20 μm and thickness down to one atomic layer (Science 2015, PNAS 2016). Such ionic semiconducting nanomaterials with excellent optical and electronic properties provide a versatile platform for understanding alloy and heterostructure formation. By combining with nanofabrication techniques, we further demonstrate spatially resolved anion exchange chemistry to achieve single crystalline halide perovskite heterojunctions (CsPbBr₃-CsPbCl₃ and CsPbBr₃-CsPbI₃) with sharp interfaces and multiple colour emissions (PNAS 2017). Such heterojunctions are useful in high performance nanoscale optoelectronics, including highly stable solar cells and colour tunable LEDs/Lasers.