Solid Additives for Spontaneously Spreading‐Processed Organic Photovoltaics

The spontaneous spreading (SS) process offers a unique solution-processed platform for fabricating organic photovoltaics (OPVs) under open-air conditions. Yet its development is hindered by limited strategies to achieve uniform film thickness and homogeneous phase morphology. In this work, an SS process is developed using the green solvent o-xylene and mediated by solid additives to regulate interfacial tension, enabling the formation of uniform SS-films on the water surface. The aromatic solid additive phenanthrene (PAT) extended the drying time of the wet film, effectively suppressed excessive acceptor aggregation, enhanced molecular packing order, and optimized phase-separated morphology for the SS-film. The OPV device with SS-film as the active layer achieved a champion efficiency of 16.4%. To the best of current knowledge, this is the first attempt to introduce solid additives in SS-processed OPVs, offering a versatile strategy to simultaneously adjust film-forming kinetics and phase morphology. This study presents a simple approach to fabricating solution OPVs with solution processability and reproducibility.