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Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells

Nature Energy volume 6, pages 605–613 (2021)Cite this article

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Abstract

Molecular design of non-fullerene acceptors is of vital importance for high-efficiency organic solar cells. The branched alkyl chain modification is often regarded as a counter-intuitive approach, as it may introduce an undesirable steric hindrance that reduces charge transport in non-fullerene acceptors. Here we show the design and synthesis of a highly efficient non-fullerene acceptor family by substituting the beta position of the thiophene unit on a Y6-based dithienothiophen[3,2-b]-pyrrolobenzothiadiazole core with branched alkyl chains. It was found that such a modification to a different alkyl chain length could completely change the molecular packing behaviour of non-fullerene acceptors, leading to improved structural order and charge transport in thin films. An unprecedented efficiency of 18.32% (certified value of 17.9%) with a fill factor of 81.5% is achieved for single-junction organic solar cells. This work reveals the importance of the branched alkyl chain topology in tuning the molecular packing and blend morphology, which leads to improved organic photovoltaic performance.

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Fig. 1: Molecular structures, photophysical properties and photovoltaic properties.
Fig. 2: Single-crystal structures and molecular packing properties of NFAs.
Fig. 3: Morphology characterization of blend films.
Fig. 4: Energy loss analysis in PM6:NFA solar cells.

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Data availability

Source data are provided with this paper. All other data generated or analysed during this study are included in the published article and its Supplementary Information. The X-ray crystallographic coordinates for structures reported in this study have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers 2005533–2005535. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (grant nos 51825301, 21734001, 51973110, 21734009, 21674007, 21733005 and 51761135101), the 111 Project (grant B14009) and Beijing National Laboratory for Molecular Sciences (BNLMS201902). F.G. acknowledges the Swedish Strategic Research Foundation through a Future Research Leader programme (FFL 18-0322). X-ray data were acquired at beamline 7.3.3 at the Advanced Light Source, Lawrence Berkeley National Laboratory, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under contract no. DE-AC02-05CH11231.

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Author notes

  1. These authors contributed equally: Chao Li, Jiadong Zhou.

Authors and Affiliations

  1. School of Chemistry, Beihang University, Beijing, China

    Chao Li, Jiali Song, Xuning Zhang, Yuan Zhang & Yanming Sun

  2. Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, China

    Jiadong Zhou & Zengqi Xie

  3. Frontiers Science Center for Transformative Molecules, In-situ Center for Physical Science, and Center for Hydrogen Science, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Shanghai, China

    Jinqiu Xu, Lei Zhu & Feng Liu

  4. Department of Physics, Chemistry, and Biology, Linköping University, Linköping, Sweden

    Huotian Zhang & Feng Gao

  5. The Institute for Advanced Studies, Wuhan University, Wuhan, China

    Jing Guo & Jie Min

  6. The College of Chemistry and Molecular Engineering, Zhengzhou University, Zhengzhou, China

    Donghui Wei

  7. Beijing National Laboratory for Molecular Science, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China

    Guangchao Han & Yuanping Yi

  8. Department of Chemistry, Hong Kong University of Science and Technology, Kowloon, China

    He Yan

  9. Beijing Advanced Innovation Center for Biomedical Engineering, Beijing, China

    Yanming Sun

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Contributions

C.L. designed and synthesized the L8-R acceptors. J.Z. and Z.X. grew the single crystals, and solved and analysed the single-crystal structures of the L8-R acceptors. J.S. fabricated and characterized the devices. J.X., J.Z. and F.L. performed the morphology characterization and analysed the data. H.Z., F.G., J.G. and J.M. performed the EL and FTPS-EQE experiments and analysed the data. X.Z. and Y.Z. performed the space-charge-limited current method and the transient photo-voltage measurements. D.W., G.H. and Y.Y. performed the theoretical calculations of the Y6 and L8-R acceptors. H.Y. helped analyse the data and revise the manuscript. F.L. and Y.S. supervised and directed this project; C.L., F.L. and Y.S. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Feng Liu or Yanming Sun.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–81, Tables 1–12, Methods and references.

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Supplementary Table

Statistical source data for Table 1 and Supplementary Tables 3–5, 7 and 10.

Source data

Source Data Fig. 1

PCEs of solar cells presented in Fig. 1e.

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Li, C., Zhou, J., Song, J. et al. Non-fullerene acceptors with branched side chains and improved molecular packing to exceed 18% efficiency in organic solar cells. Nat Energy 6, 605–613 (2021). https://doi.org/10.1038/s41560-021-00820-x

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