Recent Progress on 2D Group II-VI Binary Chalcogenides ZnX and CdX (X = S, Se, Te): From a Theoretical Perspective

2D nanomaterials of ZnX and CdX (X = S, Se, and Te) usually produced by colloidal synthesis are coated with various organic ligands; however, recent experimental work on ZnS and ZnSe demonstrates that the organic ligands can be removed with heating, and the freestanding 2D sheets of ZnS and ZnSe are then fabricated. The freestanding zinc chalcogenide single layers demonstrate superior solar water splitting efficiency and photostability, and hold great promise for numerous optoelectronic applications. Here, recent advances in 2D group II-VI binary chalcogenides ZnX and CdX are presented from a theoretical perspective. Specifically, the article starts with 2D-layered organic-inorganic hybrid materials of group II-VI binary chalcogenides ZnX and CdX, and then focuses on the freestanding 2D nanosheets of pristine inorganic ZnX and CdX. Various possible structures of 2D ZnX and CdX proposed by first-principles calculations, and their unique electronic and optical structures are discussed. It is envisioned that the freestanding 2D-layered sheets of ZnX and CdX, as well as their derivatives, are potential synthesis targets for a great wealth of applications in energy storage and conversion.