  In this work, we have systematically studied the role of point defects in the
recombination time of monolayer MoS$_2$ using time-dependent ab initio
non-adiabatic molecular dynamics simulations. Various types of point defects,
such as S vacancy, S interstitial, Mo vacancy and Mo interstitial have been
considered. We show that defects strongly accelerate the electron-hole
recombination, especially interstitial S atoms do that by 3 orders of magnitude
higher compared to pristine MoS$_2$. Mo defects (both vacancy and interstitial)
introduce a multitude of de-excitation pathways via various defect levels in
the energy gap. The results of this study provide some fundamental
understanding of photoinduced de-excitation dynamics in presence of defects in
highly technologically relevant 2D MoS$_2$.
