The journal of physical chemistry letters | 2019
PbI2-MoS2 Heterojunction: Van der Waals Epitaxial Growth and Energy Band Alignment.
Abstract
Van der Waals (vdW) epitaxy offers a promising strategy without lattice and processing constrains to prepare atomically clean and electronically sharp interfaces for fundamental studies and electronic device demonstrations. Herein, PbI2 was thermally deposited at high vacuum conditions onto CVD-grown monolayer MoS2 flakes in a vdW epitaxial manner to form 3D-2D heterojunctions, which is promising for vdW epitaxial growth of perovskite films. XRD, XPS, Raman, and AFM measurements reveal the structural properties of the high-quality heterojunctions. Photoluminescence (PL) measurements reveal that the PL emissions from the bottom MoS2 flakes are greatly quenched compared to their as-grown counterparts, which can be ascribed to the band alignment-induced distinct interfacial charge transfer behaviors. Strong interlayer excitons can be detected at PbI2/MoS2 interface, indicating an effective type-II band alignment, which can be further confirmed by UPS measurements. The results provide a new material platform for the application of the vdW heterojunctions in electronic and optoelectronic devices.