Configurational Isomers Induced Significant Difference in All‐Polymer Solar Cells

The design of polymer acceptors plays an essential role in the performance of all-polymer solar cells. Recently, the strategy of polymerized small molecules has achieved great success, but most polymers are synthesized from the mixed monomers, which seriously affects batch-to-batch reproducibility. Here, a method to separate gamma-Br-IC or delta-Br-IC in gram scale and apply the strategy of monomer configurational control in which two isomeric polymeric acceptors (PBTIC-gamma-2F2T and PBTIC-delta-2F2T) are produced is reported. As a comparison, PBTIC-m-2F2T from the mixed monomers is also synthesized. The gamma-position based polymer (PBTIC-gamma-2F2T) shows good solubility and achieves the best power conversion efficiency of 14.34% with a high open-circuit voltage of 0.95 V when blended with PM6, which is among the highest values recorded to date, while the delta-position based isomer (PBTIC-delta-2F2T) is insoluble and cannot be processed after parallel polymerization. The mixed-isomers based polymer, PBTIC-m-2F2T, shows better processing capability but has a low efficiency of 3.26%. Further investigation shows that precise control of configuration helps to improve the regularity of the polymer chain and reduce the pi-pi stacking distance. These results demonstrate that the configurational control affords a promising strategy to achieve high-performance polymer acceptors.