Synergistic Bimolecular Passivation Enabling High-Performance Inverted Perovskite Solar Cells

Surface and interfacial defects represent the primary loss pathways limiting the power conversion efficiency (PCE) and the operational stability of inverted perovskite solar cells (PSCs). Here, we report a sequential bimolecular passivation strategy employing propane-1,3-diammonium diiodide (PDAI) followed by (E)-[(4-trifluoromethyl)styryl]phosphonic acid (4TF) to simultaneously mitigate grain boundary and surface-state traps. PDAI acts as a deep-level defect passivant by penetrating grain boundaries, effectively eliminating interfacial pinholes and inducing a Fermi level (E_F) shift that reduces the work function (W_F) from 4.40 to 4.28 eV. Subsequent 4TF treatment facilitates coordination bonding with undercoordinated Pb²⁺ sites, establishing a positive surface dipole that shifts the W_F to 4.54 eV. This dual-functional approach optimizes band alignment with the C₆₀ electron transport layer, while yielding a compact, pinhole-free morphology. Consequently, PSCs treated with PDAI/4TF deliver a champion PCE of 24.6%, significantly surpassing the PDAI-only (PCE = 23.17%) and control (PCE = 21.21%) devices. These findings underscore the effectiveness of combined defect and dipole control for tailoring the perovskite/ETL interface in high-performance perovskite solar cells.