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

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 Sn2+ 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 -SO3H 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 (Voc) of 0.894 V and a fill factor (FF) of 81.74%, which is highest values of Voc × 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 N2 atmosphere.