A unified ligand-dimensional design to halt cation migration in perovskite photovoltaics

Organic cation migration, particularly that of formamidinium (FA ⁺ ), remains a major factor limiting the long-term stability of perovskite solar cells (PSCs). Low-dimensional/three-dimensional (LD/3D) heterojunctions have shown promise for mitigating this migration, yet systematic comparisons under a unified processing and scaffold framework are lacking. Here, we develop a family of pyridine-based ligands that enable the formation of structurally well-defined LD/3D heterojunctions spanning perovskite-related 2D, 1D, 1D intercalated, and 0D metal-halide motif architectures under identical processing. This platform reveals that the 2D/3D configuration uniquely couples geometric confinement with multidirectional hydrogen bonding to immobilize FA ⁺ and enhance carrier performance. Consequently, PSCs achieve a champion efficiency of 26.88% (certified 26.52%) and outstanding stability, retaining >91% initial efficiency after 1000 hours at 85°C/85% relative humidity and >94% after 2000 hours of maximum power point tracking. Large-area modules (900 square centimeters) deliver 20.25% efficiency (certified 17.75%) with negligible degradation over 4 months. This work establishes a ligand-based dimensional design platform for stable, scalable perovskite photovoltaics.