Configurational Isomers Induced Significant Difference in All‐Polymer Solar Cells

• Published in: Advanced functional materials 2021-06, Vol.31 (26), p.n/a
• Main Authors: Wang, Hengtao, Chen, Hui, Xie, Weicheng, Lai, Hanjian, Zhao, Tingxing, Zhu, Yulin, Chen, Lin, Ke, Chunxian, Zheng, Nan, He, Feng
• Format: Article
• Language: English
• Subjects: all‐polymer solar cells; bromination; configurational isomers; Energy conversion efficiency; Isomers; Materials science; Monomers; Photovoltaic cells; polymer acceptors; Polymerization; Polymers; Solar cells
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.202100877

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 configurational controlled polymers are reported here. The γ‐position based polymer exhibits good solubility, broadened UV absorption, and enhanced charge mobility, while the δ‐position based polymer shows excessive aggregation and is difficult to process in solution. When blended with PM6, PBTIC‐γ‐2F2T achieves excellent device performance with a PCE of 14.32%, but the PBTIC‐δ‐2F2T delivers a PCE of almost zero (0.02%).