Vinyl‐Functionalized Linear Alkyl Chains in Nonfullerene Acceptors Enable 19.2% Efficiency and Stable As‐Cast Organic Solar Cells

Abstract Developing efficient and stable as‐cast organic solar cells (OSCs) is imperative for alleviating costs and complexity for large‐scale commercial applications. Nevertheless, achieving the desired double‐fibril morphology of active layer through single‐step processing is challenging. Herein, two nonfullerene acceptors, namely BTP‐N6 and BTP‐V6, are designed and synthesized to construct as‐cast OSCs by introducing linear alkyl chains adjacent to the pyrrole moiety. The reduction of steric hindrance attributable to linear chains engenders diminished dihedral angles of molecular skeletons, thereby promoting compact and face‐on oriented molecular stacking. Moreover, BTP‐V6 featuring vinyl‐functionalized linear chains manifests additional interaction sites with neighboring molecules to instigate enhanced π–π stacking during rapid film‐formation process and engenders the formation of a refined double‐fibril network morphology, which facilitates exciton dissociation, bolsters charge carrier transport, and suppresses recombination loss. Consequently, the D18:BTP‐V6 based device attained a record‐shattering efficiency of 19.2% with a high fill factor (FF) of 80.7%, and also demonstrated robust thermal and shelf stability. Moreover, the meticulously optimized layer‐by‐layer (LBL) structured devices achieved an excellent efficiency up to 20.1%. This study introduces a viable strategy for alkyl chain modification to fabricate efficient and stable as‐cast devices, with the anticipation of expediting the progression toward widespread commercialization of OSCs.