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The impact of fluorination on both donor polymer and non-fullerene acceptor: The more fluorine, the merrier

Abstract

Fluorination of the donor polymer or non-fullerene acceptor (NFA) in an organic photovoltaic device is an effective method to improve device efficiency. Although there have been many studies on donor polymer fluorination, blends containing both a fluorinated donor and fluorinated NFA have rarely been reported. In this study, we use two donor polymers (4′-FT-HTAZ and 4′-FT-FTAZ) and two NFAs (ITIC-Th and ITIC-Th1) with different amounts of fluorine (from 2F to 6F) to investigate how the degree of fluorination in a blend impacts device performance. We find that fluorinating the NFA leads to a higher short-circuit current density (Jsc) and fill factor (FF), however, the open-circuit voltage (Voc) is decreased due to a depressed lowest unoccupied molecular orbital (LUMO) level. Adding additional fluorine to the donor polymer does not have a large effect on the Jsc or FF, but it does lead to an improved Voc. By fluorinating the NFA and having more fluorine on the donor polymer, we obtain both a high Jsc and Voc simultaneously, leading to a power conversion efficiency over 10% in the case of 4′-FT-FTAZ:ITIC-Th1, which has the most amount of fluorine (6F).

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Acknowledgements

N. B., Q. Z., J. R., Z. P., H. A., and W. Y. were supported by an NSF grant (CBET-1639429). N.B. was also supported by the Dissertation Completion Fellowship from the Graduate School at UNC. S. D., J. W., and X. Z. thank the National Natural Science Foundation of China (Nos. 51761165023 and 21734001). X-ray data was acquired at beamlines 11.0.1.2 and 7.3.3 at the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. C. Wang, C. Zhu, and A.L.D. Kilcoyne are gratefully acknowledged for providing the beamline support at beamlines 7.3.3 and 11.0.1.2.

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Correspondence to Wei You.

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Bauer, N., Zhang, Q., Rech, J.J. et al. The impact of fluorination on both donor polymer and non-fullerene acceptor: The more fluorine, the merrier. Nano Res. 12, 2400–2405 (2019). https://doi.org/10.1007/s12274-019-2362-3

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Keywords

  • organic solar cells
  • non-fullerene acceptors
  • fluorination
  • bulk heterojunction