Ligand‐Optimized Inorganic Passivation with Alkylammonium Sulfates for Perovskite Photovoltaic

Comprehensive Summary Perovskite solar cells (PSCs) have reached power conversion efficiencies (PCEs) over 27%, yet further improvements in stability remain critical. Surface passivation is an effective strategy to reduce defects and enhance device durability. Inorganic passivation, in particular, offers stronger chemical bonding and denser protection against moisture and oxygen compared to organic small molecules. Recent studies have employed mild organic ligands to introduce inorganic anions, creating an inorganic passivation layer on the perovskite surface. Here, we report a solution‐based passivation approach using sulfate salts coordinated with butylamine, hexylamine, and octylamine, spin‐coated onto perovskite surfaces. By tuning the alkylamine chain length, we modulate the passivation effect. With hexylamine sulfate treatment, we achieve a champion PCE of 26.3% for small‐area devices and 23.4% for mini solar modules with an active area of 20.8 cm 2 . Moreover, under continuous illumination at 60 °C during maximum power point (MPP) tracking, the devices retain 97.2% of their initial efficiency after 600 h. Our results demonstrate that ligand‐optimized inorganic passivation using alkylammonium sulfates enables both high efficiency and excellent operational stability.