2D materials have shown great promise in various applications including solar cells, but their use as light-harvesting active layers in photovoltaic (PV) devices is limited. Herein, surface-oxidized antimonene sheets are prepared using a liquid-phase exfoliation method and employed as an active light absorber material after functionalization. It is shown that 2D antimonene possesses unique surface chemistry that allows it to form photoactive Sb2S3 light absorbers for solar cells under ambient conditions. Under the standard PV testing conditions (AM1.5G), devices fabricated with 2D antimonene-based light-harvesting materials deliver a power conversion efficiency (PCE) of up to 4.28%. This novel type of solar cell exhibits outstanding operational stabilities, preserving >90% of the initial PCE after aging for 60 min at a temperature of 85 °C, retaining >95% of the initial efficiency after exposure to continuous light illumination under 1 sun for 180 min, and maintaining its functionality after being underwater for 25 min. This work opens new avenues for research in 2D materials and photovoltaics.