Polymer Donor Based on a Bis([1,2,5]thiadiazolo)[3,4-a:3′,4′-c]dithieno[3,2-h:2′,3′-j]phenazine Unit for Organic Solar Cells

Polymer donors occupy a vital position within the active layer of organic solar cells (OSCs), and their rational molecular design and structural modulation are indispensable for the advancement of OSCs. Designing electron-withdrawing units with fused-ring skeletons is an effective strategy for constructing promising polymer donors. Herein, we report a wide-bandgap donor–acceptor (D-A)-type polymer donor, PBDQB-TF, constructed using a seven-membered fused-ring bis[1,2,5]thiadiazolo[3,4-a:3′,4′-c]dithieno[3,2-h:2′,3′-j]phenazine as the electron-withdrawing moiety. This fused aromatic skeleton exhibits strong electron-deficient character and a large conjugated plane. Benefiting from the structural merits, PBDQB-TF features a deep highest occupied molecular orbital (HOMO) energy level, broad visible-light absorption, and tunable aggregation behavior, enabling excellent spectral complementarity and energy-level alignment with classic non-fullerene acceptors BTP-eC9 and L8-BO. Photovoltaic devices fabricated from PBDQB-TF blended with either acceptor achieve promising power conversion efficiency near 10%. The PBDQB-TF:BTP-eC9 device delivers a favorable short-circuit current density of 20.03 mA cm−2, while the PBDQB-TF:L8-BO system affords a higher open-circuit voltage of 0.964 V and a fill factor of 52.15%. Overall, this work validates the great potential of this new seven-membered, fused-ring electron-withdrawing unit and offers a reliable design principle for the development of next-generation potential polymer donor materials.