Greatly Enhanced Optical Absorption of a Defective MoS₂ Monolayer through Oxygen Passivation

Structural defects in the molybdenum disulfide (MoS2) monolayer are widely reported and greatly degrade the transport and photoluminescence. However, how they influence the optical absorption properties remains unclear. In this work, by employing many-body perturbation theory calculations, we investigate the influence of sulfur vacancies (SVs), the main type of intrinsic defects in the MoS2 monolayer, on the optical absorption and exciton effect. Our calculations reveal that the presence of SVs creates localized midgap states in the bandgap, which results in a dramatic red-shift of the absorption peak and stronger absorbance in the visible light and near-infrared region. Nevertheless, the SVs can be finely repaired by oxygen passivation and are beneficial to the formation of the stable localized excitons, which greatly enhance the optical absorption in the spectral range. The defect-mediated/-engineered absorption mechanism is well understood, which offers insightful guides for improving the performance of two-dimensional dichalcogenide-based optoelectronic devices.