Revealing the Side-Chain Dependent Ordering Transition of Highly-Crystalline Double-Cable Conjugated Polymers

Abstract
Highly-crystalline conjugated polymers are important for microstructure analysis and charge transport in organic electronics. In this work, we have developed a series of highly-crystalline double-cable conjugated polymers for application in single-component organic solar cells (SCOSCs). These polymers contain conjugated backbones as electron donor and pendant perylene bisimide units (PBIs) as electron acceptor. PBIs are connected to the backbone via alkyl units varying from hexyl (C6H12) to eicosyl (C20H40) as flexible linkers. The highly-crystalline nature of these materials allows us to systematically study the effect of the length of the alkyl linkers on the nanostructure and photovoltaic performance. In particular, we find that for double-cable polymers with short linkers, the PBIs tend to stack in a head-to-head fashion, resulting in large d-spacing (e.g. 64 Å for the polymer P12 with C12H24 linker) along the lamellar stacking direction. When the length of the linker groups is longer than a certain length, the PBIs instead adopt a more ordered packing likely via H-aggregation, resulting in short d-spacings (e.g. 50 Å for the polymer P16 with C16H32 linker). Evidence for this transition is provided by X-ray diffraction measurements along with cryo-transmission electron microscopy measurements, where different packing motifs of the PBI units are clearly imaged. The different packing facilitated by longer linker groups is associated with improved exciton separation and charge transport, resulting in enhanced efficiencies of SCOSCs based on the polymer P16. The findings in this work demonstrate that double-cable conjugated polymers can be an important family of highly-crystalline conjugated polymers. Furthermore, this work demonstrates how the precise molecular packing of the acceptor units influences the photovoltaic performance of SCOSCs.

Citation
Feng, G., Tan, W., Karuthedath, S., Li, C., Jiao, X., Liu, A. C. Y., … Li, W. (2021). Revealing the Side-Chain Dependent Ordering Transition of Highly-Crystalline Double-Cable Conjugated Polymers. Angewandte Chemie International Edition. doi:10.1002/anie.202111192

Acknowledgements
This study is jointly supported by MOST (2017YFA0204702, 2018YFA0208504,) and NSFC (52073016, 51773207, 51973031, 21905018, 21905158) of China. This work was further supported by the Fundamental Research Funds for the Central Universities (buctrc201828, XK1802-2), Open Project of State Key Laboratory of Supramolecular Structure and Materials (sklssm202043), Jiangxi Provincial Department of Science and Technology (No. 20192ACB20009) and Hong Kong Scholars Program (Grant No. XJ2020051). The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). A.C.Y.L. acknowledges support from the Australian Research Council (FT180100594). The authors acknowledge the use of instruments and assistance at the Monash Ramaciotti Centre for Cryo-Electron Microscopy, a Node of Microscopy Australia, including the Titan Krios (Australian Research Council LE120100090). This work was performed in part at the SAXS/WAXS beamtline at the Australian Synchrotron, part of ANSTO. Z. T. acknowledges the Shanghai Pujiang Program (Grant No. 19PJ1400500).

Publisher
Wiley

Journal
Angewandte Chemie

DOI
10.1002/anie.202111192
10.1002/ange.202111192

PubMed ID
34546627

Additional Links
https://onlinelibrary.wiley.com/doi/10.1002/anie.202111192

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