Intrinsic defects govern carrier trapping and recombination in two-dimensional semiconductors, yet the microscopic origin of defect-dependent capture dynamics remains unclear. Here, we compute carrier capture coefficients of vacancy defects, treating monolayer ${\mathrm{MoS}}_2$ as a prototype, from first principles. We find that the sulfur monovacancy is present 0.25 eV below the conduction band and has a capture coefficient of $\sim {10}^{-15}{\mathrm{cm}}^3/\mathrm{s}$. In contrast, the sulfur divacancy exhibits a seven-orders-of-magnitude higher capture coefficient ($\sim {10}^{-8}{\mathrm{cm}}^3/\mathrm{s}$), despite being only moderately deeper in energy. This enhancement originates from strong lattice relaxation enabling efficient multiphonon capture. Consequently, monovacancies contribute weakly to trapping, while sulfur divacancies dominate nonradiative recombination and reduce quantum yield. In contrast, molybdenum vacancies and sulfur antisites contribute to deep level states with smaller capture coefficients, indicating a limited role in carrier trapping in $n$-type devices.

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• Carrier generation & recombination
• Point defects
• Transition metal dichalcogenides