We report a novel quaternary solid solution (Ag–Cu–Sb–S or ACSS) serving as a photo-absorber material in the photoelectrochemical field for the first time, and ZnO/ACSS nanoarrays exhibited a photocurrent density of 4.45 mA cm⁻². The research indicates that ZnO/ACSS composite structures have enormous potential in PEC hydrogen generation systems.