High-Performance As-Cast Non-Fullerene Polymer Solar Cells From Benzo[1,2-B:4,5-B ']Difuran Polymer Via A Rational Copolymer Design

In this study, we synthesized a novel benzo[1,2-b:4,5-b ']difuran (BDF) copolymer (F13-R) by introducing ester-substituted thiophene into the PDiFPBDF-TBz (F13) backbone aiming to finely tune the molecular stacking and aggregation for non-fullerene as-cast polymer solar cell (PSC) applications. Compared with F13, F13-R displayed a slight blue-shifted absorption, a deeper highest occupied molecular orbital (HOMO) energy level of -5.60 eV, and improved intermolecular stacking. In PSCs, it is found that the as-cast F13-R : IT-4F device, which does not need any solvent additive and thermal/solvent annealing, could achieve a power conversion efficiency (PCE) of 12.2% with an open-circuit voltage (V-oc) of 0.904 V, a short-circuit current density (J(sc)) of 17.61 mA cm(-2) and a fill factor (FF) of 76.60%. The as-cast F13-R : IT-4F device is the first PSC fabricated from low-cost BDF polymers, and its performance is among the best performances in as-cast PSCs. These results demonstrate that fine-tuning the BDF polymer structure via a copolymer design could be an efficient strategy to develop low-cost and high-performance as-cast PSCs.