Dimeric Acceptors Enable over 20% Efficiency Organic Solar Cells via Electron‐Deficiency Engineering of Quinoxaline Linkers

Dimeric acceptors attract intense interest in organic solar cells (OSCs) for their well-defined structures and solution processability, yet the electronic role of the linking unit, particularly in electron-deficient heteroarenes, remains largely unexplored. Here, we establish the quinoxaline skeleton as a versatile and tunable linking unit and accordingly have designed and synthesized three dimers, namely WD1, WD2, and WD4. By systematically changing the substituents with 4-methoxyphenyl, methyl, and 4-fluorophenyl groups on the quinoxaline-based linkers, their optoelectronic properties can be precisely adjusted. Among the three quinoxaline-based dimers, the most electron-deficient variant WD4, which bears a 6,7-difluoro-2,3-bis(4-fluorophenyl)quinoxaline linking unit, exhibits superior optoelectronic properties. Consequently, the devices with PM6:WD4 as the active layer obtained a power conversion efficiency (PCE) of 17.95% with excellent stability, and the PM6:L8-BO:WD4 ternary devices deliver an impressive PCE of 20.15%. This work demonstrates that fine-tuning the electron delocalization of dimeric linking units represents a straightforward strategy to simultaneously boost efficiency and stability, offering a clear molecular design blueprint for next-generation oligomeric acceptors.