In the quest for photosensitive materials in the infrared spectral range that do not contain heavy metals, we investigated silver sulfide nanocrystals and found broadband detection from the visible to the infrared (IR) up to 2500 nm wavelength. The silver sulfide nanocrystals were synthesized by a facile method at room temperature, and integrated into a planar photodetector architecture. The device performance was studied in visible and near-infrared (NIR) regions. The photodetection studies showed that the Ag2S photodetector with high sulfur atom vacancy concentration detected 1550 nm and 2500 nm wavelength with relatively high responsivity and specific detectivity at room temperature and 78 K, respectively. The photophysical, structural, and DFT studies indicate that the origin of high-performance near-IR detection ability of the proposed photodetector up to 2500 nm wavelength was related to the formation of S vacancies. In particular, DFT studies demonstrated that bandgap narrowing occurs in silver sulfide crystals by the presence of S vacancies. Although many research works highlighted highly crystalline materials with low defects, the results in this study demonstrated the promising effects of sulfur vacancies in silver sulfide nanocrystals for low-energy photon detection.