Knoevenagel Condensation Enables a High‐Dipole Interfacial Molecule for Efficient Wide‐Bandgap Perovskite and Tandem Photovoltaics

Abstract The rational molecular design of interfacial modifiers is critical for optimizing charge transport and defect passivation in wide‐bandgap (WBG) perovskite solar cells (PSCs). Herein, we introduce a novel multifunctional molecule, ( Z )‐4‐(2‐(4‐bromophenyl)‐2‐cyanovinyl) phenylamine (BCPA), synthesized via Knoevenagel condensation reaction, featuring a highly polar architecture with a ground‐state dipole moment of 18.16 Debye, significantly exceeding that of the benchmark Me‐4PACz (1.60 Debye). This pronounced polarity stems from a synergistic combination of an electropositive ammonium group (─NH 3 ⁺) and electronegative cyano (─CN) and bromine (─Br) substituents, which collectively foster strong interfacial dipole–substrate interactions. The ─CN moiety coordinates with Niˣ⁺ in NiO X and Pb 2 ⁺ in perovskites, effectively passivating electronic defects and modulating self‐assembled molecules (SAM) anchoring. Meanwhile, the ─NH 3 ⁺ group forms stable bonds with perovskite lattice, modulating crystal growth kinetics, and improving interfacial contact. The Br atom ensures intrinsic compatibility with bromine‐rich wide‐bandgap perovskites. Notably, the rigid, planar structure of BCPA facilitates ordered SAM packing via π–π interactions, enhancing interfacial charge extraction. BCPA‐modified hole transport layers significantly improve the buried perovskite/substrate interface by reducing trap densities, enhancing crystallinity, and aligning energy levels. As a result, modified WBG PSCs realized a champion efficiency of 19.08% with reinforced durability. Furthermore, when applied in perovskite‐organic tandem configurations, the devices reach a remarkable PCE of 26.10%, highlighting the importance of interfacial modifier for next‐generation high‐efficiency photovoltaics.