Synergistic redox-coordination molecular stabilizer counters iodine-related degradation for advanced perovskite solar cells

As one photovoltaic supernova, perovskite solar cells (PSCs) have exhibited certified power conversion efficiencies exceeding 27 %. Yet, the presence of enormous defects, mainly for the dominant iodine vacancy (V_I), always induces nonradiative recombination, ion migration, and triggers autocatalytic iodine oxidation into volatile I₂ and charge-localization-mediated metallic Pb⁰ clusters, which accelerate device failure and therefore hamper commercialization. However, popularly reported strategies that simultaneously enable vacancy passivation and iodine scavenging remain insufficient, highlighting the need for new additives. Herein, we employ 4-cyanophenylhydrazine hydrochloride (CPHCl) as an iodine-related synergistic redox-coordination stabilizer to address intrinsic instability and interface chemistry issues. After systematically characterizations, we demonstrate that CPHCl not only specifically eliminates I₂ intermediates by leveraging the redox-active hydrazine group (NH–NH₂) (I₂ + NH–NH₂ → 2HI + N=NH), but also passivates Pb²⁺/FA⁺ related defects via π-backdonation and hydrogen bonding by the electron-donating cyano (CtbndN) group, synergistically modulating the crystallization kinetics and improving the final quality of the perovskite film. As a result, vacancy-mediated I-ion migration and degradation are significantly relieved, enabling an enhanced efficiency of 25.56 % for the p-i-n inverted PSC with exceptional operational stability. This work provides a deep insight into screening perovskite stabilizers for advancing toward commercial longevity.