S Vacancy Engineered Electronic and Optoelectronic Properties of Ni-Doped MoS₂ Monolayer: A Hybrid Functional Study

The interaction between the substitutional Ni atom and the native S vacancy (V_S) in the monolayer MoS₂ has been systematically investigated using the Heyd–Scuseria–Ernzerhof hybrid functional method, aiming to elaborate how the V_S engineers the electronic and optoelectronic properties of Ni-doped monolayer MoS₂. The results show that V_S tends to stay next to Ni substitution to form a cluster in the monolayer MoS₂, which is found to be attributed to the strong attraction between them. With respect to Ni substitution alone, such a cluster induces more dispersive or delocalized intermediate bands within the band gap. These intermediate bands not only effectively act as stepping stones to relay valence electrons to the conduction band but also permit the multi-wavelength absorption of solar light, thus significantly enhancing the optical absorption of monolayer MoS₂. Thermodynamic and kinetic investigations have been conducted to elaborate the favorability for the formation of the Ni-V_S cluster in monolayer MoS₂. The outcome of this work is beneficial for offering guidance for modulating the electronic and optoelectronic properties of monolayer MoS₂ through defect engineering.