Polaron spin dynamics in high-mobility polymeric semiconductors

Abstract

Polymeric semiconductors exhibit exceptionally long spin lifetimes, and recently observed micrometre spin diffusion lengths in conjugated polymers demonstrate the potential for organic spintronics devices. Weak spin–orbit and hyperfine interactions lie at the origin of their long spin lifetimes, but the coupling mechanism of a spin to its environment remains elusive. Here, we present a systematic study of polaron spin lifetimes in field-effect transistors with high-mobility conjugated polymers as an active layer. We demonstrate how spin relaxation is governed by the charges’ hopping motion at low temperatures, whereas an Elliott–Yafet-like relaxation due to a transient localization of the carrier wavefunctions is responsible for spin relaxation at high temperatures. In this regime, charge, spin and structural dynamics are intimately related and depend sensitively on the local conformation of polymer backbones and the crystalline packing of the polymer chains.

Fig. 1: IDTBT field-induced ESR devices.
Fig. 2: Relaxation processes in IDTBT.
Fig. 3: Modelling of IDTBT spin dynamics.
Fig. 4: Spin lifetimes of field-induced charges.
Fig. 5: Spin admixtures.

Data availability

The data underlying this publication are available on the University of Cambridge data repository at https://doi.org/10.17863/CAM.34786.

Code availability

The CustomXepr source code is published at https://github.com/OE-FET/CustomXepr.

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Acknowledgements

Funding from ERC Synergy grant SC2 (no. 610115), the Alexander von Humboldt Foundation and the Transregional Collaborative Research Center (SFB/TRR) 173 SPIN+X is acknowledged. S.S. thanks the Winton Programme for the Physics of Sustainability and the Engineering and Physical Sciences Research Council (EPSRC) for funding as well as Z.-G. Yu for discussions, R. Chakalov for assistance with sample fabrication and S.-i. Kuroda, H. Tanaka and S. Watanabe for training and discussions. U.C. is a recipient of a DFG-funded position through the Excellence Initiative by the Graduate School Materials Science in Mainz (GSC 266). The work in Mons was supported by the European Commission/Région Wallonne (FEDER–BIORGEL project), the Consortium des Équipements de Calcul Intensif (CÉCI), funded by the Fonds National de la Recherche Scientifique (FRS-FNRS) under grant no. 2.5020.11 as well as the Tier-1 supercomputer of the Fédération Wallonie-Bruxelles, infrastructure funded by the Walloon Region under grant agreement n1117545, and FRS-FNRS. D.B. is FNRS Research Director. This research was undertaken in part on the SAXS/WAXS beamline at the Australian Synchrotron, part of ANSTO.

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S.S. fabricated the FI-ESR devices and carried out the ESR experiments and analyses. R.L.C. performed the Raman measurements. R.D.P. developed the methods to tune the crystallinity of p(NDI2O–T2) and helped with both the fabrication of samples and the interpretation of results. X.J. and C.R.M. carried out the GIWAXS measurements and analysed the GIWAXS data. I.R. carried out and analysed the Hall effect measurements. U.C. and E.R.M. performed the calculation and analyses of spin admixtures. A.Melnyk and D.A. carried out the simulations of dynamic disorder in IDTBT. Y.O., V.L. and D.B. performed the calculations of torsional autocorrelation functions and intra-chain spin density dynamics. C.J., M.L., A.Marks and I.M. synthesized the materials. S.S. and H.S. wrote the manuscript with input from all authors. H.S. and J.S. supervised the project. All authors discussed the results.

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Correspondence to Henning Sirringhaus.

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The authors declare no competing interests.

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Journal peer review information: Nature Physics thanks Z. Valy Vardeny, Zhi-Gang Yu and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Schott, S., Chopra, U., Lemaur, V. et al. Polaron spin dynamics in high-mobility polymeric semiconductors. Nat. Phys. 15, 814–822 (2019). https://doi.org/10.1038/s41567-019-0538-0

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