Diffusion of hydrogen and thus passivation of defects in silicon that can facilitate the fabrication of high-efficiency solar cells using low-cost silicon material mostly rely on the thermal treatment. In this contribution, we aim to investigate the effect of diode laser-induced thermal treatment on the hydrogen diffusion as well as the passivation of crystallographic defects in silicon and eventually open-up the window to employ lasers in achieving the high effectiveness in passivation. To do so, we employed a robust numerical model, which is developed in an open-source based computational fluid dynamics (CFD) platform, to explain the coupled thermal and diffusion-reaction phenomena initiated as well as controlled by the lasers. The results reveal some interesting insights into the considerable concentrations of hydrogen and the effective passivation of defects throughout the silicon substrate that will help in achieving the desired outcome in fabricating high-efficiency solar cells. Such as, with prolonged exposure times during the laser annealing, the bulk of the silicon substrate becomes recombination-active and eventually enables the possibility of conducting defect passivation, however meanwhile, enables the dissociation of hydrogen from the defect sites. While the dissociation of hydrogen can be controlled by employing short exposure times during laser annealing, the penetration length of hydrogen inside the substrate has to be considered as short exposure times result in a passivation-active region remain confined at the surface vicinity. The findings from this study will help as a valuable resource in further optimising the operating parameters during laser-induced thermal treatment.