Multiple-Site Interface Modification with 3,4,5-Trifluorobenzoic Acid for Efficient and Stable Perovskite Solar Cells

Metal halide perovskites have shown great promise in the photovoltaic field owing to their outstanding optoelectronic properties. However, defect states at the perovskite/electron transport layer interface significantly increase charge recombination losses, becoming a major bottleneck hindering further improvements in the efficiency of perovskite solar cells. Here, we introduce a multiple-site surface modification strategy using 3,4,5-trifluorobenzoic acid (TFBA) to address interfacial defects and energy-level alignment in inverted perovskite solar cells. TFBA anchors strongly onto the perovskite surface via carboxyl coordination with undercoordinated Pb²⁺ ions and hydrogen bonding with FA⁺ cations, thereby significantly reducing trap-state density and suppressing nonradiative recombination. Meanwhile, the multifluorinated structure further induces n-type band bending, optimizing electron transport and improving energy-level alignment, while also providing interfacial hydrophobicity. As a result, the TFBA-modified device achieved a champion power conversion efficiency (PCE) of 25.54% with an open-circuit voltage (V_OC) of 1.183 V and fill factor (FF) of 85.17%, significantly outperforming the reference device's PCE of 24.41% with a V_OC of 1.149 V and FF of 83.10% in the Cs_0.05FA_0.95PbI₃ perovskite system, while maintaining 85% of its initial PCE after 1,000 h of continuous operational stability testing.