Achieving Near 21% Efficiency Organic Solar Cells with Minimal Nonradiative Energy Loss through Controlled Packing of Fused-Ring Electron Acceptors

This work has successfully designed and synthesized two novel acceptor materials, Y6-2Cl and Y6-4Cl, which are distinguished by bulky chlorobenzene moieties at the terminal positions of their inner side chains. The introduction of chlorobenzene groups at the side-chain termini substantially enhances the solubility of the acceptors, while also boosting the photoluminescence quantum yield and inducing a distinct molecular packing mode in Y6-2Cl and Y6-4Cl. Rather than following the conventional three-dimensional network structure observed in Y-series acceptors, these materials form a highly ordered, array-like arrangement while maintaining excellent crystalline characteristics. This unique structural feature not only preserves outstanding charge-transport properties but also optimizes aggregation behavior and morphology of the active layer of these materials. In practical device applications, the binary device based on the D18:Y6-2Cl blend demonstrates a PCE of 20.0% with reduced non-radiative energy loss (0.212 eV). Furthermore, the ternary device composed of D18:L8-BO:Y6-2Cl achieves a remarkable PCE of 20.92%, accompanied by a fill factor of 82.93%. These results highlight the significant potential of our designed materials. Overall, the side-chain functionalization strategy proposed in this study provides a valuable and innovative direction for the future development of high-performance NFAs, paving the way for further advancements in the field of OSCs.