AbstractThe perovskite‐inspired Cu2AgBiI6 (CABI) material has been gaining increasing momentum as photovoltaic (PV) absorber due to its low toxicity, intrinsic air stability, direct bandgap, and a high absorption coefficient in the range of 105 cm−1. However, the power conversion efficiency (PCE) of existing CABI‐based PVs is still seriously constrained by the presence of both intrinsic and surface defects. Herein, antimony (III) (Sb3+) is introduced into the octahedral lattice sites of the CABI structure, leading to CABI‐Sb with larger crystalline domains than CABI. The alloying of Sb3+ with bismuth (III) (Bi3+) induces changes in the local structural symmetry that dramatically increase the formation energy of intrinsic defects. Light‐intensity dependence and electron impedance spectroscopic studies show reduced trap‐assisted recombination in the CABI‐Sb PV devices. CABI‐Sb solar cells feature a nearly 40% PCE enhancement (from 1.31% to 1.82%) with respect to the CABI devices mainly due to improvement in short‐circuit current density. This work will promote future compositional design studies to enhance the intrinsic defect tolerance of next‐generation wide‐bandgap absorbers for high‐performance and stable PVs.