An ammonium-pseudohalide ion pair for synergistic passivating surfaces in FAPbI₃ perovskite solar cells

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.