Using Aromatic‐Bridge‐Tuned Dimer Acceptors to Harmonize Photoluminescence Quantum Yield and Crystallinity for Organic Solar Cells Exceeding 21% Efficiency

ABSTRACT Suppressing non‐radiative energy loss (Δ E 3 ) by enhancing the photoluminescence quantum yield (PLQY) of active‐layer materials, particularly the acceptor component, is important for achieving high‐performance organic solar cells (OSCs). A key challenge is how to design acceptor materials that attain high PLQY while preserving favorable crystallinity and aggregation behavior, as these properties are often mutually conflicting. Here, we address this challenge by developing a series of dimeric acceptors linked via benzene, naphthalene, and anthracene bridges (named Ph‐dimer, Naph‐dimer, and Ant‐dimer). Although the conjugation length and intrinsic emission of these cores increase from benzene to anthracene, the photovoltaic performance of the resulting dimeric acceptors shows no linear correlation with this trend. Among them, the Naph‐dimer optimally balances crystallinity and PLQY, with enhanced molecular packing and reduced disorder, suppressing energy loss ( E loss ) and facilitating charge extraction. Consequently, the PM6:Naph‐dimer OSC exhibits a power conversion efficiency (PCE) of 18.90%, an open‐circuit voltage ( V oc ) of 0.974 V and a low Δ E 3 of 0.192 eV, outperforming PM6:Ph‐dimer and PM6:Ant‐dimer counterparts. Moreover, incorporating Naph‐dimer into a PM6:L8‐BO host yields a PCE of 21.02%. These findings indicate that precise bridge modulation is an effective strategy for harmonizing high PLQY with crystalline order in OSCs.