Synergistic Interfacial Dangling‐Bond Passivation for Enhanced Moisture Resistance in Perovskite Photovoltaics

ABSTRACT Control of the crystallization process and post‐treatment are key to the fabrication of high‐performance perovskite photovoltaics. During the natural crystallization of perovskite thin films, uncapped dangling bonds readily form at interfaces, induce severe nonradiative recombination losses, and act as preferential sites for the ingress of moisture and oxygen, accelerating a continual phase transitions and structural decomposition. If this kind of continual degradation is not adequately addressed, it will be difficult to achieve good stability in perovskite solar cell devices. Here, a multifunctional small molecule, tetrahydrothiophene‐2‐carboxylic acid (TTA), is introduced as a single interfacial modifier for post‐treatment to simultaneously achieve effective defect passivation and enhance environmental stability. The carboxyl group of TTA strongly coordinates with dangling bonds, suppressing deep‐level defects, while sulfur in the tetrahydrothiophene ring interacts with free PbI 2 to restrain further perovskite decomposition. TTA can form a dense, hydrophobic interfacial layer that blocks water penetration. As a result, TTA‐modified perovskite solar cells achieve a high‐power conversion efficiency of 26.7%, with a fill factor of 85.5% and an open‐circuit voltage of 1.20 V. Notably, unencapsulated devices retain 92.1% of their initial efficiency after 200 h at 70% relative humidity, and 92% after 800 h of continuous illumination under AM 1.5G.