Epoch‐Making Design Strategies for High‐Efficiency Fused‐Ring A‐DA'D‐A Type Non‐Fullerene Acceptors in Organic Solar Cells

The development of non-fullerene acceptors (NFAs) has driven significant advancements in organic solar cells (OSCs), resulting in power conversion efficiencies (PCEs) approaching 20% and positioning OSCs for practical applications. Notably, the recently introduced fused-ring A-DA'D-A type NFAs, especially those called Y-series NFAs, have propelled the field forward due to their strong near-infrared (NIR) absorption, adaptable structural features, and efficient molecular stacking, which collectively enhance charge transfer, minimize energy losses, and improve OSC performance. This review first summarizes the progression of Y-series NFAs from Y1 to the epoch-making acceptor Y6. Recent advances in fused-ring A-DA'D-A type NFAs are then discussed, with a focus on design strategies that modify structural parameters, such as side-chains, central cores, end-capping groups, and π-spacers. The advantages of each NFA are analyzed in relation to their corresponding polymer donors. The influence of molecular structure and optoelectronic properties of NFAs on the morphology of the donor/acceptor (D/A) active layer, charge transfer dynamics, and device performance is examined. Finally, the review identifies current challenges and outlines future directions for the development of Y-series NFAs in OSCs.