Multifunctional Interfacial Molecular Bridging Strategy Enables Efficient and Stable Inverted Perovskite Solar Cells

Interface engineering in inverted perovskite solar cells (PSCs) faces critical challenges arising from nonideal interfacial contact, defect accumulation, impeded carrier transport, and energy-level misalignment between the perovskite and electron transport layer, for example, phenyl-C61-butyric acid methyl ester (PCBM). These interfacial deficiencies collectively induce nonradiative recombination and degrade device stability. Herein, a multifunctional interfacial molecular bridging strategy using (benzhydrylthio)acetic acid (DSA) addresses the upper interfacial issues of inverted PSCs, achieving three synergistic roles. 1) Interfacial stabilization. A stable molecular-bridging layer is constructed with DSA at the perovskite/PCBM interface through carboxylate-Pb²⁺ coordination bonds, along with π-π stacking interactions between DSA and PCBM. 2) Defect passivation. Multiple active sites in DSA molecules, such as thioether and carboxylic acid groups, can synchronously achieve chemical passivation with undercoordinated Pb²⁺ sites. 3) Energy band alignment: DSA induces n-type band bending through electron donation by the thioether, reducing the work function and enhancing the electron-extraction kinetics. As a result, DSA-treated devices achieve a champion power conversion efficiency of 26.08% along with an open-circuit voltage loss of only 53 mV. Finally, the DSA-treated devices demonstrate remarkable operational stability, retaining 96% of the initial efficiency after being tracked at the maximum power point for 2000 h.