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.