Core chlorination position governs charge transport and efficiency in small-molecule acceptors for organic solar cells.

Halogen positional isomerism provides an effective strategy to regulate the solid-state organization of non-fullerene acceptors. Two dibenzo[b,f]oxepine-based acceptors with para- and meta-chlorination were designed. Meta-chlorination enhances intermolecular packing and charge transport, enabling efficient charge extraction and a high power conversion efficiency of over 18.5%, outperforming the para-substituted analogue.