Dual-Functionalized Bonding Management via Aromatic Formamidine Ligands Enables 25.57%-Efficient Ambient-Printed...

Ambient printing of perovskite solar cells (PSCs) faces severe challenges in controlling crystallization under humid conditions, leading to substantial performance losses compared to inertly processed devices. While ligand-assisted coordination is known to modulate crystal growth, a precise understanding of how specific chemical bonds influence crystallization dynamics during ambient printing remains elusive. Herein, we unveil a dual-functionalized bonding (DFB) mechanism enabled by aromatic formamidine ligands that concurrently coordinate with both the inorganic framework and organic cations during ambient printing. The key mechanistic insight lies in the ability of ligands to form simultaneous coordination bonds with [PbI₆]^4- octahedra and hydrogen bonds with formamidinium ions (FA⁺), which collectively delay nucleation, suppress the δ-phase formation, and widen the recrystallization window. By incorporating an electron-deficient triazole ring into the ligand backbone, we enhance this bifunctional binding effect, leading to superior crystallization control and defect suppression. The resulting perovskite films exhibit remarkable homogeneity, low trap density, and enhanced carrier diffusion. Consequently, ambient-printed devices achieve champion power conversion efficiencies of 25.57% for 0.09 cm², 23.98% for 1.04 cm², and 22.98% in 5 × 5 cm² mini-modules. The optimized devices retain over 90% of their initial performance after 1,000 h of continuous operation. This work provides a profound mechanistic framework for molecular-level crystallization control in printed photovoltaics.