Van der Waals epitaxy of type-II band alignment CsPbI3/TMDC heterostructure for optoelectronic applications

Abstract

Van der Waals epitaxy allows heterostructure formation without considering the lattice match requirement, thus is a promising method to form 2D/2D and 2D/3D heterojunction. Considering the unique optical properties of CsPbI₃ and transition metal dichalcogenides (TMDCs), their heterostructure presents potential applications in both photonics and optoelectronics fields. Here, we demonstrate selective growth of cubic phase CsPbI₃ nanofilm with thickness as thin as 4.0 nm and zigzag/armchair oriented nanowires (NWs) on monolayer WSe₂. Furthermore, we show growth of CsPbI₃ on both transferred WSe₂ on copper grid and WSe₂–based optoelectrical devices, providing a platform for structure analysis and device performance modification. Transmission electron microscopy (TEM) results reveal the epitaxial nature of cubic CsPbI₃ phase. The revealed growth fundamental of CsPbI₃ is universal valid for other two-dimensional substrates, offering a great advantage to fabricate CsPbI₃ based van der Waals heterostructures (vdWHs). X-ray photoelectron spectroscopy (XPS) and optical characterization confirm the type-II band alignment, resulting in a fast charge transfer process and the occurrence of a broad emission peak at lower energy. The formation of WSe₂/CsPbI₃ heterostructure largely enhances the photocurrent from 2.38 nA to 38.59 nA. These findings are vital for bottom-up epitaxy of inorganic semiconductor on atomic thin 2D substrates for optoelectronic applications.