Novel Janus diamane CFCl: a stable and moderate bandgap semiconductor with a huge excitonic effect.

Semiconducting two-dimensional Janus materials have drawn increasing attention due to their novel optoelectronic properties. Here, employing first-principles calculations, we systematically explore the stability and electronic and optical properties of Janus diamane CFCl. The energetic and dynamical stabilities of CFCl have been verified using the cohesive energy and phonon dispersion calculations. It is predicted to possess a direct bandgap of ∼3 eV at the Γ point using the GW method. Also, the optical absorption spectrum of CFCl is dominated by the enhanced excitonic effects, in which a bright bound exciton with a large binding energy beyond 1 eV can be observed. The light absorption coefficient of CFCl for sunlight can be as large as 8 × 10 cm in the range of visible and near-ultraviolet light, suggesting its potential for optoelectronic applications. These findings enable a deep understanding of the physical properties of novel CFCl.