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

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 (─NH3⁺) and electronegative cyano (─CN) and bromine (─Br) substituents, which collectively foster strong interfacial dipole-substrate interactions. The ─CN moiety coordinates with Niˣ⁺ in NiOX and Pb2⁺ in perovskites, effectively passivating electronic defects and modulating self-assembled molecules (SAM) anchoring. Meanwhile, the ─NH3⁺ 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.