Dipole Molecular Bridge Engineering Enables Defect Suppression and Charge Transport Enhancement at the Buried Interface of Perovskite Solar Cells

The buried interface between the perovskite and the tin oxide (SnO2) electron transport layer critically governs the efficiency and stability of perovskite solar cells (PSCs). Herein, we engineer a robust buried interface by constructing a dipolar molecular bridge using a multifunctional zwitterion, 4-(1,3,5-triaza-7-phosphaadamantan-1-ium-1-yl)butane-1-sulfonate (PTABS). The sulfonate group (─SO3-) of PTABS chemisorbs onto the SnO2 surface via stable Sn─O─S bonds, effectively passivating oxygen vacancies. Concurrently, the P and N atoms on the cationic side coordinate with undercoordinated Pb2+ in the perovskite, enabling bilateral interface passivation. Moreover, the superior hydrophilicity of PTABS improves the wettability of the SnO2 substrate, guiding the growth of a perovskite film with larger grains, reduced defects, and enhanced coverage. Crucially, the substantial intrinsic dipole moment of PTABS (computed to be 31.61 D) induces a strong interfacial dipole layer. This layer downshifts the work function of SnO2, promotes favorable band bending, and optimizes the energy-level alignment at the interface. Consequently, electron extraction and transport are significantly boosted, while hole back-transfer is effectively suppressed. As a result, PTABS-modified PSCs achieve an increased power conversion efficiency (PCE) of 24.13% compared to 22.37% for the control, along with markedly improved operational stability.