In this work, we employed time resolved microwave conductivity (TRMC) and photoluminescence (PL) spectroscopy to gain fundamental understanding of the defect passivation mechanism in Sb2Se3 by sulfur treatment. We investigated the charge carrier dynamics of Sb2Se3 before and after sulfur treatment using TRMC and observed the passivation of deep defects in Sb2Se3 as evidenced by longer carrier lifetimes. We also show that the passivation of deep defects reduces not only surface recombination, but also bulk recombination using a wavelength dependent TRMC study. Furthermore, we demonstrate increased radiative recombination efficiency by suppression of nonradiative recombination pathways in sulfur-treated Sb2Se3 using PL spectroscopy. In addition to this, low frequency Raman spectroscopy (LFRS) showed increased long-range order in the Sb2Se3 semiconductor thin films upon sulfur treatment. These results explain the improved photovoltage of Sb2Se3 upon sulfur treatment, which presents a simple and efficient defect passivation strategy.