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 γ‐Br‐IC or δ‐Br‐IC in gram scale and apply the strategy of monomer configurational control in which two isomeric polymeric acceptors (PBTIC‐γ‐2F2T and PBTIC‐δ‐2F2T) are produced is reported. As a comparison, PBTIC‐m‐2F2T from the mixed monomers is also synthesized. The γ‐position based polymer (PBTIC‐γ‐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 δ‐position based isomer (PBTIC‐δ‐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 π–π stacking distance. These results demonstrate that the configurational control affords a promising strategy to achieve high‐performance polymer acceptors.

Two chlorine-substituted isomers, ITIC-2Cl-β and a-ITIC-2Cl, were synthesized for potential use as nonfullerene acceptors. The two molecules differ in the position of chlorine atoms, leading to symmetric (ITIC-2Cl-β) and asymmetric ( a-ITIC-2Cl) molecular configuration. In single crystals, the two molecules exhibit a completely different arrangement and stacking as derived from X-ray diffraction analysis. Whereas ITIC-2Cl-β has a linear packing structure, a-ITIC-2Cl forms a 3D interpenetrating network structure with shorter π–π distances and better molecular planarity. Therefore, a high power conversion efficiency of >12% is obtained by a-ITIC-2Cl-based devices. It is ∼10% higher than that of ITIC-2Cl-β-based devices due to the chlorine substituent effect. Thus the fine-tuning of the Cl-substituted position seems to be a promising strategy to construct a 3D interpenetrating charge transportation network and achieve higher performance organic solar cells (OSCs).

Replacing the halogen atoms on the end group was considered an efficient way to enhance the performance of organic solar cells (OSCs), such as tuning energy levels, and improving sunlight absorption and intermolecular stacking. Herein, three chlorine-substituted asymmetric nonfullerene acceptors, named ITIC-Cl-δ-Th,ITIC-Cl-γ-Th, and ITIC-2Cl–Th, were synthesized to study the impact of the chlorine atom position and numbers on the molecular properties.  Theoretical calculation revealed that a single chlorine at the γ-position on the end group led to a better molecular planarity and lower dimer energy of ITIC-Cl-γ-Th, which is appropriate for intermolecular charge transfer. Although double chlorinatation of ITIC-2Cl–Th can significantly redshift the ultraviolet–visible absorption, the lower LUMO energy level would obstruct the improvement in photoelectric conversion efficiency (PCE) due to a lower open-circuit voltage. Hence, we found that single chlorination at the γ-position helps ITIC-Cl-γ-Th-based devices to achieve a PCE as high as 12.25% with higher electron and hole mobilities. In addition, more efficient exciton dissociation and weaker bimolecular recombination were also realized in ITIC-Cl-γ-Th-based devices.