Phenanthrene Treatment for O‐xylene‐Processed PM6:Y6‐Based Organic Solar Cells Enables Over 19% Efficiency

Abstract Achieving excellent charge transport properties in high‐performance organic solar cells (OSCs) generally requires photovoltaic materials to have strong crystallinity. Meanwhile, non‐halogenated solvent processing is very important for future application of the OSCs. However, highly crystalline materials will pose challenges for the control of molecular aggregation behavior in donor/acceptor blend films processed with high boiling point non‐halogenated solvents. Herein, a new approach to effectively regulate the aggregation of represented strong crystallinity material Y6 in high boiling point processing solvents is developed by employing phenanthrene (PAT) with unique crystallinity and relatively loose molecular stacking as volatile solid additive. It is elucidated that PAT treatment shows a significant effect in inhibiting the excessive self‐aggregation of Y6 in high boiling point solvent during the film formation process and reducing the crystallization rate of Y6 molecules under thermal annealing, resulting in highly ordered molecular packing and favorable phase‐separated morphology. As a result, the PM6:Y6‐based device processed with chlorobenzene, toluene, and o ‐xylene achieve excellent power conversion efficiencies (PCEs) of 17.71%, 17.99%, and 19.04%, respectively. The efficiency of 19.04% represents the highest value so far for the PM6:Y6‐based binary OSCs processed with high boiling point non‐halogenated solvents.