Study on the passivation mechanism of short-chain ammonium salt OAI at the bottom of perovskite films

Abstract The stability and efficiency of perovskite solar cells (PSCs) are core bottlenecks for their commercialization. Especially in inverted structures, the bottom interface is prone to carrier loss and phase decomposition due to defects. Passivation is one of the effective methods to solve these problems. In terms of passivation agent selection, traditional long-chain ammonium salt passivation has issues such as hindered carrier transport. Therefore, this study adopts short-chain ammonium salt octylammonium iodide (OAI) to passivate the bottom interface of perovskite films, aiming to balance the compatibility between defect repair and carrier transport. A bottom passivation layer was formed by spin-coating OAI isopropanol solutions with different concentrations (0.5–1.0 mg ml −1 ) on the surface of mesoporous alumina, and the passivation effect was explored. The results demonstrate that OAI forms an ftted passivation layer by coordinating -NH 3 + with uncoordinated Pb 2+ and filling iodine vacancies with hydrophobic chains, which improves the bottom morphology and crystallization quality of the film, reduces defect density, prolongs carrier lifetime, and balances defect repair and carrier transport. The results show that the treatment with 0.75 mg ml −1 OAI achieves the best effect: the power conversion efficiency (PCE) of the device is increased from 18.6% to 21.2%; the open-circuit voltage, short-circuit current density, and fill factor are all significantly optimized; the hysteresis index is reduced from 4.77% to 1.42%. The unencapsulated device retains 86% of its initial efficiency after 600 h in a nitrogen environment at 60 °C, indicating significantly improved stability. This study provides an effective strategy for interface optimization of perovskite devices.