Side‐Chain Engineering on Y‐Series Acceptors with Chlorinated End Groups Enables High‐Performance Organic Solar Cells

Abstract Chemical modifications of non‐fullerene acceptors (NFAs) play vital roles in the development of high efficiency organic solar cells (OSCs). In this work, on the basis of the previously reported molecule named Y6‐1O, chlorination and inner side‐chain engineering are adopted to endow the corresponding devices with higher open‐circuit voltage ( V OC ) and short‐circuit current density ( J SC ) as well as good morphology for high fill factor (FF). As a result, the molecule named BTP1O‐4Cl‐C12 can help achieve a higher power conversion efficiency (PCE) of 17.1% than that of Y6‐1O (16.1%). Furthermore, the following comparisons between BTP1O‐4Cl‐C12 and the two symmetric acceptors named BTP2O‐4Cl‐C12 and BTP‐4Cl‐C12 demonstrate the effect of asymmetric alkoxy substitution on the outer side chains, which not only achieves a balance between V OC and J SC , but also help obtain appropriate morphology for efficient charge dissociation and suppressed charge recombination. Therefore, the asymmetric BTP1O‐4Cl‐C12 can achieve a higher PCE compared to the symmetric BTP2O‐4Cl‐C12 and BTP‐4Cl‐C12. The work not only reports an excellent NFA for high‐performance OSCs, but also puts forward a series of methods for consecutive chemical modifications on Y‐series acceptors, which can be further applied to boost the PCE of OSCs to a higher level.