On the Role of Molecular Conformation of the Passivating Agents for High-performance Perovskite Solar Cells

Molecular structure engineering of passivating agents has proven to be a pivotal strategy for developing high-performance perovskite solar cells (PSCs). Although previous studies have focused on molecular configuration design, the influence of molecular conformations on device performance remains largely unexplored. Herein, we systematically investigate this critical factor by developing a series of diammonium iodide passivators with tunable conformational rigidity through aryl or alkyl group modifications. Notably, PSC performance exhibits a consistent enhancement with increasing rotational flexibility of the ammonium groups. Detailed carrier dynamics analysis reveals a direct correlation between molecular conformational freedom and defect passivation effectiveness. Theoretical calculations demonstrate that both static geometric matching and dynamic conformation adaptability to perovskite lattice defects govern the passivation quality. The optimized passivator with maximum conformational flexibility enables PSCs to achieve a champion power conversion efficiency of 26.6% (certified stabilized efficiency: 26.4%). This study establishes molecular conformation engineering as a crucial dimension in defect passivation strategies and provides fundamental insights for advancing perovskite photovoltaics.