Side‐Chains Engineered Self‐Assembly of <i>Ortho</i> ‐Benzodipyrrole‐Based Acceptors: Comprehensive Exploration of Structure‐Interface‐Photovoltaics Correlations

Abstract This research employs inner side‐chain engineering in C‐shaped ortho‐benzodipyrrole‐based (CB) A‐D‐A non‐fullerene acceptors (NFAs) CB8, CB12, CB16, and CB20, where side‐chain configuration crucially influences self‐assembly, single‐crystal structures, and optoelectronic properties. The enthalpy of fusion at the melting point, combined with the intensity of the 730 nm solid‐state absorption shoulder, suggests that the acceptor–acceptor (A–A) interactions follow the order: CB8 &gt; CB12 &gt; CB20 &gt; CB16. Solution small‐ and wide‐angle X‐ray scattering (SWAXS) quantitatively reveals the successively increased donor–acceptor (D–A) association numbers of these CB derivatives with PM6, consistent with the reduction of their A–A self‐assembly. Complementarily and comprehensively, transient absorption spectroscopy (TAS) shows a systematically shortened decay‐time of charge transfer in the series of the binary PM6:CB (1:1.2 wt%) thin films, from 25.40 ps (CB8), to 16.13 ps (CB12), to 15.03 ps (CB20), and to 11.97 ps (CB16), following the increasing trend of CB‐PM6 interaction strength. Correspondingly, the photovoltaic efficiency improves with the enhanced CB‐PM6 interactions from PM6:CB8 (15.24%), to PM6:CB12 (16.66%), to PM6:CB20 (17.12%), and to PM6:CB16 (18.13%). These close correlations between the structures and photovoltaic properties elucidate the importance of minimizing A–A self‐aggregation and enhancing D (PM6)‐A (CBs) interactions via engineering the side chains in the CB‐based acceptors.