Improved performance and stability of perovskite solar cells by iodine-immobilizing with small and flexible bis(amide) molecule

The iodine loss in the perovskite layer is currently-one of the major limit for further boosting power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs). Iodine-poor interface dominates the generation of some deep level defects and the phase collapse in the perovskite layer. So how to adequately immobilize the iodine and passivate the existing undercoordinated lead cations is a critical challenge. Herein, the interaction between the bifunctional amide group and the perovskite layer was systematically investigated. The Malonamide (MAM) with bis(amide) group in structure can selectively hold iodine in place or interact with undercoordinated lead cations through adjusting the molecular conformation, resulting in more ideal I/Pb ratio, highly suppressed ion migration, harmonized surface potential and reduced defect density. Eventually, a significantly improved efficiency of 24.13% was demonstrated with the MAM-treating devices, and the device kept 96% of its initial efficiency after 900 h under continuous illumination.