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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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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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.
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Supplementary Information
Supplementary Figs. 1–81, Tables 1–12, Methods and references.
Supplementary Table
Statistical source data for Table 1 and Supplementary Tables 3–5, 7 and 10.
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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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DOI: https://doi.org/10.1038/s41560-021-00820-x
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