Fluorobenzene Side Chain‐Engineered Y6 Derivatives for Enhanced Molecular Stacking and High‐Performance Additive‐Free Organic Solar Cells

Abstract Organic solar cells (OSCs) have become a promising photovoltaic technology, achieving high efficiencies over 20%. However, simplifying processing techniques to maintain high performance remains a significant challenge. This work reports a series of Y6‐derived non‐fullerene acceptors (NFAs), namely BTP‐R1F, BTP‐R2F, BTP‐R3F, and BTP‐R5F, featuring fluorinated phenoxyoctyl side chains with varying numbers of fluorine atoms. Systematic fluorination has minimal impact on optical absorption and energy levels but significantly influences molecular packing and morphology. BTP‐R1F, BTP‐R2F, and BTP‐R5F exhibit compact honeycomb‐like stacking patterns with enhanced π–π interactions, while BTP‐R3F displays a looser S‐shaped stacking due to severe side chain folding, thus hindering charge transport. Additive‐free OSCs processed with toluene demonstrate that D18/BTP‐R5F has formed a well‐defined fiber‐like interpenetrating network, achieving a remarkable power conversion efficiency (PCE) of 19.06%. This study highlights the potential of fluorobenzene side chain engineering to enhance molecular stacking and morphology without any additive, offering a pathway toward scalable and high‐performance OSCs with simplified processing conditions. The findings provide valuable insights for designing next‐generation NFAs for efficient and reproducible OSCs.