First-principles study on stability, electronic and optical properties of Janus-functionalized ZnO monolayer and bilayer for optoelectronic device

Two-dimensional materials have aroused enormous interests due to the novel physical properties and wide potential applications in optoelectronic devices. Monolayer or bilayer ZnO, as a typical two-dimensional metal-oxide, also exhibits astonishing properties. Motivated by the recent successful synthesis of Janus metal-oxide monolayer and bilayer, we have investigated the stability, electronic and optical properties of pristine and Janus F–ZnO–Cl monolayer and bilayer by the first-principles calculations. The results show that Janus F–ZnO–Cl monolayer and bilayer exhibit mechanical and dynamical stability without any imaginary modes of phonon spectra. Furthermore, the Janus functionalized will break the planar structure and form the buckled atomic layer in the monolayer and bilayer ZnO. Moreover, based on the HSE06 functional, Janus F–ZnO–Cl monolayer and bilayer exhibit the direct semiconductor characteristic, and the band gaps are narrowed from 3.374 eV to 2.563 eV, and from 3.185 eV to 1.022 eV, respectively. Upon Janus-functionalized, there are a large amount of charge (0.54 e) transfers from the ZnO layer to the functionalized species. In addition, Janus F–ZnO–Cl monolayer and bilayer could strongly absorb light in a wide range from the visible light to the infrared light at different level. The current findings open the possibilities for the application of ZnO-based material in optoelectronic devices.