Synergistic Buried Interface Engineering via Ion Exchange and Passivation for High-Performance Inverted Perovskite Solar Cells

The buried interface of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS/perovskite in inverted perovskite solar cells (PSCs) presents several challenges, such as low work function (WF) causing energy level mismatch, poor conductivity limiting transport, and defect states inducing nonradiative recombination and carrier loss. To address these issues, this work introduced the interfacial modifier sodium acetate (NaOAc) into the PEDOT:PSS precursor solution, enabling molecular-level modulation of the physicochemical properties of the buried interface. Experimental results confirm that sodium ions (Na + ) preferentially coordinate with the sulfonic acid groups at the termini of PEDOT:PSS molecular chains, displacing the nonconductive H + and forming a more ordered molecular packing. This ion-exchange process increases the WF of the PEDOT:PSS film at the buried interface (from 4.27 to 4.38 eV) while enhancing its conductivity by 55%, effectively optimizing interfacial energy level alignment and reducing the hole transport barrier. More importantly, the residual acetate anions exert an in situ passivation effect during the subsequent perovskite crystallization, coordinating with unreacted Pb 2+ at the buried interface, thereby reducing the defect density by 11%. The optimized buried interface exhibits excellent carrier dynamics characteristics, with photoluminescence spectroscopy and electrochemical impedance spectroscopy confirming that the sodium acetate treated PEDOT:PSS buried interface reduces nonradiative recombination and enhances charge extraction. As a result, the device fill factor exceeds 81.7%, and the efficiency improves to 19.38%. When applied to mixed tin lead perovskite (FASnI 3 ) 0.6 (MAPbI 3 ) 0.4, the optimized buried interface further demonstrates universal advantages, achieving an efficiency exceeding 21%. This work reveals the synergistic modulation mechanism of ion coordination engineering at the buried interface on carrier transport and recombination dynamics, providing a new paradigm for the development of high-performance inverted perovskite solar cells.