Buried Interface Modulation via Molecular Dipole Passivation for High‐Efficiency Methylammonium‐Free Pb–Sn Perovskite Solar Cells

ABSTRACT

Methylammonium‐free (MA‐free) Pb–Sn perovskites are highly attractive for next‐generation materials due to their ideal bandgaps. However, the efficiency and stability of Pb–Sn perovskite solar cells (PSCs) are still limited by severe Sn ²⁺ oxidation and mismatched energy‐level alignment at the buried interface. Herein, a dipole passivation strategy is developed by introducing 4‐(trifluoromethyl) benzamidine hydrochloride (TFBA) at the PEDOT: PSS/perovskite interface of Pb–Sn PSCs. Benefiting from its multifunctional chemical groups and strong dipole properties, TFBA simultaneously passivates the Pb–Sn perovskite‐related defects and inhibits the deprotonation of –SO ₃ H in PSS through hydrogen‐bonding and coordination interactions, thereby suppressing acidity‐induced interfacial degradation. Consequently, the TFBA‐modified interface exhibits highly quality Pb–Sn perovskite films and more favorable energy‐level alignment. As a result, the optimized Pb–Sn PSCs deliver a power conversion efficiency (PCE) of 22.48%, with an open‐circuit voltage ( V _oc ) of 0.894 V and a fill factor (FF) of 81.74%, which is highest values of V _oc × FF among the reported MA‐free Pb–Sn PSCs. Moreover, the unencapsulated device retains 88.7% of its initial efficiency after 1500 h storage in N ₂ atmosphere.