In-plane optical anisotropy in PbI2 nanosheets induced by CrOCl

Abstract

Interface symmetry breaking in heterojunctions can introduce enhanced performance in optoelectronic devices, tunnel transistors, and catalytic applications. Herein, we report a solution recrystallization method for fabricating high-quality two-dimensional PbI2 nanosheets on mechanically exfoliated thin CrOCl flakes. The high crystalline quality of the synthesized heterojunctions is confirmed by a suite of characterization techniques, including atomic force microscopy and high-resolution transmission electron microscopy. Density functional theory calculations reveal the formation of a type-II band alignment at the interface, accompanied by charge transfer from the upper PbI2 layer to the underlying CrOCl. Photoluminescence (PL) and Kelvin probe force microscopy measurements confirm the interfacial charge transfer. Especially, angle-resolved polarized Raman and PL spectroscopy reveal that CrOCl induces in-plane anisotropy (IPA) in PbI2 with anisotropy ratios of 1.64 (Raman) and 1.65 (PL), which is primarily attributed to the anisotropic interfacial charge interactions. Our findings provide a platform for expanding the application prospects of isotropic PbI2 in polarization-related fields through interface induced IPA.