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

Abstract 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.