Optoelectronic properties of monolayer and bilayer AgI: role of many-body interactions

Abstract

In an outstanding experimental advance in the field of two-dimensional materials, monolayer AgI was synthesized using a graphene encapsulation approach (Mustonen et al. in Adv Mater 34(9):2106922, 2022). Herein, inspired by this experimental achievement, the intrinsic electronic and optical properties of monolayer and bilayer AgI are investigated using the density functional theory and many-body perturbation theory. For the bilayer, two different stackings are considered namely AA and AB. The results indicate that monolayer and bilayer AgI are direct band gap semiconductors. The G₀W₀ band gap is predicted to be 3.66, 1.45, and 1.58 eV for monolayer, bilayer AA, and bilayer AB, respectively. The optical spectra achieved from solving the Bethe–Salpeter equation show the first bright exciton to be located at 2.78, 0.65, and 0.75 eV for monolayer, bilayer AA, and bilayer AB, respectively. The obtained optical gaps for the bilayers are found to be much smaller than that of the monolayer, very suitable for optoelectronic applications in the visible light region. The exciton binding energy is calculated to be 0.88, 0.80, and 0.83 eV for monolayer, bilayer AA, and bilayer AB, respectively. Also, the average value of light absorption in the visible area is estimated to be 0.12, 1.16, and 1.09 × 10⁷ m⁻¹ for monolayer, bilayer AA, and bilayer AB, respectively. The effects of many-body interactions on the optical responses of the structures are evaluated. Overall, it is found that the optoelectronic performance of AgI is improved from monolayer to bilayer. This study provides a fantastic vision concerning the intrinsic physical properties of monolayer and bilayer AgI and highlights their characteristics for optoelectronics applications.