Protonated Molecular Bridging of Buried Interfaces for Stable Inverted Perovskite Solar Cells

Self-assembled monolayers (SAMs) are widely used as hole-selsctive contacts in inverted perovskite solar cells (PSCs). However, their molecular-scale thickness makes the SAM/perovskite buried interface sensitive to molecular coverage, precursor wettability, and initial nucleation, which can lead to insufficient interfacial coupling and defect-assisted recombination. Herein, we introduce 4-aminobenzenesulfonamide hydrochloride (4-Ah·HCl) as a protonation-enhanced molecular bridge between [4-(7H-Dibenzo[c,g]carbazol-7-yl)butyl]phosphonic acid (4PADCB) and the perovskite absorber. Compared to its neutral counterpart, the protonated NH3+ sites in 4-Ah·HCl exhibit stronger positive electrostatic potential, enhanced hydrogen-bonding capability, and pronounced dipolar characteristics. This facilitates robust N-H···O-P interactions with 4PADCB. The S=O and N-H groups within the sulfonamide moiety interact with interfacial Pb2+ and I- sites and contribute to defect passivation. The modification improves precursor wettability and are associated with denser perovskite films and reduced nonradiative recombination. The modified inverted PSCs achieve a champion power conversion efficiency (PCE) of 25.50% and exhibit improved thermal and storage stability. This work presents a viable protonation strategy for engineering phosphonic-acid-based SAM/perovskite interfaces.