Co-passivation of Buried Interfaces in Perovskite Solar Cells with Sulfonate and Amine Salts

Interfacial defects remain a key limitation of the performance of perovskite solar cells (PSCs). Using first-principles density functional theory (DFT) and SCAPS-1D device simulations, we examine how sulfonate and primary amine salts can jointly passivate the SnO 2 /perovskite buried interface. The sulfonate group forms strong S–O–Sn bonds with surface Sn atoms, while the ammonium cation anchors to undercoordinated Pb 2+ through N–H···I interactions, creating a complementary interfacial dipole and lowering the trap density. Calculated adsorption energies up to −4.53 eV confirm robust binding and efficient defect deactivation. Device simulations calibrated to experimental parameters yield an initial efficiency of 20.95% and increase to 28.8% after optimizing thicknesses and defect densities. Efficiencies above 30% arise in the near-ideal trap-free regime and represent theoretical upper limits for this architecture. Overall, the combined DFT and SCAPS analysis shows that cooperative sulfonate–amine passivation effectively mitigates non-radiative recombination and provides molecular guidelines for improving buried interfaces.