Predict the influence of different defects on the electronic structure and optical properties of two-dimensional Bi ₂ S ₃ semiconductor materials based on first-principles calculations

Abstract Two-dimensional (2D) Bi 2 S 3 exhibits excellent light absorption potential, yet studies on the effects of point defects on its structural, optical and electronic properties remain scarce. Herein, first-principles calculations are employed to investigate six defects (Se-substituted S (Se S ), Te-substituted S (Te S ), As-substituted Bi (As Bi ), Sb-substituted Bi (Sb Bi ), S vacancy (V S ), and Bi vacancy (V Bi )) in monolayer 2D Bi 2 S 3 . The results show all six defects are structurally stable, with V Bi possessing the highest stability. All defects respond to ultraviolet light: Te S and V S enhance the intrinsic light absorption of 2D Bi 2 S 3 , induce absorption edge red-shift and extend the visible-near-infrared response; V Bi causes absorption edge blue-shift in the near-ultraviolet region (peak from 220 nm to 210 nm). The static dielectric constants of Te S , V S , V Bi , and Se S are improved, with Te S and V S showing a 2.5% increase. V Bi significantly narrows the band gap ( E g reduced to 0.539 eV). The bandgap narrowing induced by doping defects originates from the Se-4s, Te-5s, As-4s, Sb-5s, and S-3p orbitals. Notably, Te S and V S defects synergistically optimize light absorption and electrical conductivity.