•An ammonium-pseudohalide ion pair provides both chemical and physical passivation •This ion pair converts defects in FAPbI3 to two water-resistant isolation layers •The passivated FAPbI3 PSC achieves 23.21% efficiency with excellent stability Either cationic ammonium or anionic pseudohalide compounds can passivate partial defects in perovskite solar cells (PSCs); however, their ion-pairing combination has rarely been studied because of its rarity. We present an ion-pairing passivating agent, diethylammonium diethyldithiocarbamate, synchronously providing both cationic and anionic ions, which can convert the surfaces of lead halide perovskite into two types of water-resistant compositions by forming strong chemical bonds. These synergistic capping compositions also reduce the defect density in the surface and bulk domains by passivating defect-nucleating sites, which can modify the surface energy level toward boosted photovoltage to 1.122 V and efficiency to 23.21% for pure-phase FAPbI3 PSCs. In addition, their water-resistant features can effectively prevent moisture damage into the perovskite layer and significantly elongate device stabilities. Either cationic ammonium or anionic pseudohalide compounds can passivate partial defects in perovskite solar cells (PSCs); however, their ion-pairing combination has rarely been studied because of its rarity. We present an ion-pairing passivating agent, diethylammonium diethyldithiocarbamate, synchronously providing both cationic and anionic ions, which can convert the surfaces of lead halide perovskite into two types of water-resistant compositions by forming strong chemical bonds. These synergistic capping compositions also reduce the defect density in the surface and bulk domains by passivating defect-nucleating sites, which can modify the surface energy level toward boosted photovoltage to 1.122 V and efficiency to 23.21% for pure-phase FAPbI3 PSCs. In addition, their water-resistant features can effectively prevent moisture damage into the perovskite layer and significantly elongate device stabilities.