Novel Fused‐Ring Electron Acceptors Based on Double Electron‐Deficient Central Core for High‐Performance Organic Solar Cells

Rapid advances in A‐DA'D‐A fused‐ring electron acceptors have significantly boosted organic solar cells (OSCs), yet non‐radiative energy loss (Δ E 3 ) remains a persistent bottleneck, and reliance on single electron‐deficient cores limits further molecular diversification. Herein, we report CBT‐4F, a novel acceptor featuring a double electron‐deficient bis([1,2,5]thiadiazolo)[3,4‐c:3′,4′‐g]carbazole (CBT) core constructed via stepwise intramolecular Cadogan reductive cyclization. This synthetic strategy circumvents the challenges of carrying multiple nitro groups through key cross‐coupling steps and offers an extensible route to multi‐electron‐deficient‐core acceptors. Compared with the benchmark acceptor Y6, CBT‐4F exhibits extended π‐conjugation, increased backbone curvature, a lower average molecular electrostatic potential, and a distinct packing motif. These coupled molecular and solid‐state characteristics, together with optimized blend morphology and recombination behavior, are associated with significantly suppressed Δ E 3 in PM6:CBT‐4F devices (0.220 vs. 0.262 eV for PM6:Y6). Benefiting from a wider photovoltaic bandgap and reduced Δ E 3 , PM6:CBT‐4F achieves a power conversion efficiency (PCE) of 19.02% with a high open‐circuit voltage ( V OC ) of 0.923 V, substantially outperforming the PM6:Y6 counterpart (17.63%, 0.834 V). Furthermore, incorporating CBT‐4F as a third component into the PM6:BTP‐eC9 system boosts the ternary PCE to 20.57%. This work establishes CBT‐4F as a high‐performance molecular platform and expands synthetic accessibility to multi‐electron‐deficient‐core acceptors.