Synergistic Interface Engineering via o‐Difluorobenzene‐Mediated HPWO Crystallization and ITO Fluorination for 20.57% Efficiency Organic Solar Cells

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Interfacial energy loss is a critical challenge in achieving high-efficiency organic solar cells (OSCs), primarily due to mismatched energy levels and inefficient charge collection. Herein, a bifunctional interface engineering strategy is proposed, employing an ethanol/o-difluorobenzene (EtOH/o-DFB) dual-solvent system for phosphotungstic acid (HPWO) processing. During film formation, o-DFB regulates HPWO crystallization by suppressing excessive aggregation, while enabling in situ ITO fluorination through the adsorbed o-DFB. This synergistic approach simultaneously mitigates the trap-assisted nonradiative recombination at the hole transport layer while enhancing the electrode work function, resulting in better ohmic contact, minimized trap-state densities, and improved energy level alignment at the electrode/active layer interface. The effectiveness of this strategy is demonstrated across multiple active layer systems. Remarkable power conversion efficiencies of 19.55%, 20.07%, and 20.57% are achieved for PM6/L8-BO, D18/L8-BO, and D18/BTP-eC9-based OSCs, respectively. Notably, the 20.57% PCE represents one of the highest efficiencies reported to date for OSCs, highlighting the potential of this bifunctional interface engineering strategy in advancing high-performance organic photovoltaics.