Wide‐Bandgap Dithienobenzothiadiazole–Terthiophene Polymer Enabling Efficient Polymer Solar Cells

In this work, a polymer donor PDTfBT-3T based on dithienobenzothiadiazole (DTfBT) and alkyl-substituted thiophenes was synthesized for application in non-fullerene organic solar cells (OSCs). PDTfBT-3T shows a film absorption maximum at 614 nm with an absorption edge near 650 nm, corresponding to an optical bandgap of ≈1.90 eV. Complementary absorption and sufficiently favorable energetic offsets are achieved between PDTfBT-3T and the benzotriazole-fused Y-series acceptor Y14. The optimized PDTfBT-3T:Y14 active layer delivers a power conversion efficiency (PCE) of 11.69%. Packing evolution from predominantly edge-on in neat films to enhanced face-on orientation in blends, together with an interpenetrating nanoscale morphology, underpins efficient charge generation and transport. Moreover, employing PDTfBT-3T as a guest donor in ternary OSCs based on PM6:Y6 and D18:L8-BO increases the PCEs to 17.81% and 18.59%, respectively. These results indicate that DTfBT is a powerful electron-deficient unit and that PDTfBT-3T provides a simple and versatile platform for constructing efficient NFA-based PSCs.