Synergistic Effects of Polymer Donor Backbone Fluorination and Nitrogenation Translate into Efficient Non-Fullerene Bulk-Heterojunction Polymer Solar Cells

• Published in: ACS applied materials & interfaces Vol. 12; no. 8; pp. 9545 - 9554
• Main Authors: Cao, Zhixiong, Chen, Jiale, Liu, Shengjian, Jiao, Xuechen, Ma, Shanshan, Zhao, Jiaji, Li, Qingduan, Cai, Yue-Peng, Huang, Fei
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 26.02.2020
• Subjects: nitrogenation; fluorination; bulk-heterojunction; polymer solar cells; large band gap
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.9b22987

State-of-the-art non-fullerene bulk-heterojunction (BHJ) polymer solar cells outperform the more extensively studied polymer–fullerene BHJ solar cells in terms of efficiency, thermal-, and photostability. Considering the strong light absorption in the near-infrared region (600–1000 nm) for most of the efficient acceptors, the exploration of high-performing large band gap (LBG) polymer donors with complementary optical absorption ranging from 400 to 700 nm remains critical. In this work, the strategy of concurrently incorporating fluorine (−F) and unsaturated nitrogen (−N) substituents along the polymer backbones is used to develop the LBG polymer donor PB­[N]­[F]. Results show that the F- and N-substituted polymer donor PB­[N]­[F] realizes up to 14.4% efficiency in BHJ photovoltaic devices when paired with a benchmark molecule acceptor Y6, which largely outperforms the analogues PB with an efficiency of only 3.6% and PB­[N] with an efficiency of 11.8%. Systematic examinations show that synergistic effects of polymer backbone fluorination and nitrogenation can significantly increase ionization potential values, improve charge transport, and reduce bimolecular recombination and trap-assisted recombination in the PB­[N]­[F]:Y6 BHJ system. Importantly, our study shows that the F- and N-substituted conjugated polymers are promising electron-donor materials for solution-processed non-fullerene BHJ solar cells.