Intrinsic point defects in transition metal dichalcogenides (TMDs) significantly affect their crystal structure and optoelectronic properties. In this study, intrinsic point defects in the 2H and 1T phases of two-dimensional Janus WSSe were investigated in depth using first-principles methods, including vacancies, interstitials, antisites, and their effects on the atomic structure, thermodynamic stability, electronic, optical, and magnetic properties of the materials. The results show that the 1T phase of WSSe is more prone to lattice defects compared to the 2H phase, with vacancies (${\mathrm{V}}_{\mathrm{S}}, {\mathrm{V}}_{\mathrm{Se}}$) and interstitials (${\mathrm{S}}_{\mathrm{Se}}, {\mathrm{Se}}_{\mathrm{S}}$) between S and Se atoms being the most easily formed point defects. In the 2H phase, W atom vacancies (${\mathrm{V}}_{\mathrm{W}}$), interstitials (${\mathrm{W}}_{\mathrm{i}}$), and W atom substitutions for sulfur (${\mathrm{W}}_{\mathrm{S}}, {\mathrm{W}}_{\mathrm{Se}}$) are deep-level defects that easily form nonradiative recombination centers for carriers, affecting their lifetime. Additionally, ${\mathrm{W}}_{\mathrm{S}}$ and ${\mathrm{W}}_{\mathrm{Se}}$ defects in the 2H phase and ${\mathrm{W}}_{\mathrm{S}}$ defects in the 1T phase can induce local magnetic moments in the material, providing a feasible approach for generating magnetism in WSSe materials. Furthermore, the absorption characteristics of 2H WSSe with intrinsic defects exhibit stability within the visible light spectrum. These findings not only deepen the understanding of defect engineering in Janus-TMDs for tuning electronic and optical properties but also have important implications for the design and optimization of Janus MXY optoelectronic devices.

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• Optoelectronics
• Point defects
• Monolayer films
• Transition metal dichalcogenides
• Two-dimensional electron system
• Density functional calculations