Efficient and Durable Tin‐Lead Narrow‐Bandgap Perovskite Solar Cells via Synergistic (100) Crystallization Control and Interfacial Modification

ABSTRACT The performance of tin‐lead perovskite solar cells (PSCs) is limited by perovskite crystallographic inhomogeneity and interfacial defect‐induced non‐radiative recombination. Besides, the grain growth orientation is more difficult to control compared to pure lead perovskite. We developed 6‐hydroxypyridazine‐3‐carboxylic acid (HCA) as an additive, whose diazine ring nitrogen and carboxyl C═O can prefer coordinating with Sn 2+ ions, thereby synchronizing the crystallization kinetics of tin and lead components. This molecule can also induce the crystallization of perovskite along the (100) plane, promoting the formation of vertical‐through‐grain morphology to reduce defect density and enhance charge transport. Furthermore, the PEDOT:PSS substrate was modified with a SAM molecule, (4‐(6‐methoxy‐9H‐thieno[2′,3′:4,5]thieno[3,2‐b]indol‐9‐yl)butyl)phosphonic acid (MeOK), which forms close π‐π stacking with PEDOT. This interaction reduces the PSS content on the PEDOT:PSS surface, thereby mitigating acidic corrosion for prolonged stability. Concurrently, the molecular dipole of MeOK optimizes the energy level alignment and suppresses non‐radiative recombination of the buried interface. The devices fabricated based on this synergistic strategy achieved a power conversion efficiency (PCE) of 24.08%. The corresponding all‐perovskite tandem solar cells reached a PCE of 28.81%, and after 1000 h of maximum power point tracking, they maintained 90% of their initial efficiency.