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Anomalous circularly polarized light emission in organic light-emitting diodes caused by orbital–momentum locking

Abstract

Chiral circularly polarized (CP) light is central to many photonic technologies, from the optical communication of spin information to novel display and imaging technologies. As such, there has been significant effort in the development of chiral emissive materials that enable the emission of strongly dissymmetric CP light from organic light-emitting diodes (OLEDs). It has been widely accepted that the molecular chirality of the active layer determines the favoured light handedness of the CP emission in such devices, regardless of the light-emitting direction. Here we discover that, unconventionally, oppositely propagating CP light exhibits opposite handedness, and reversing the current flow in OLEDs also switches the handedness of the emitted CP light. This direction-dependent CP emission boosts the net polarization rate by orders of magnitude by resolving an established issue in CP-OLEDs, where the CP light reflected by the back electrode typically erodes the measured dissymmetry. Through detailed theoretical analysis, we assign this anomalous CP emission to a ubiquitous topological electronic property in chiral materials, namely orbital–momentum locking. Our work paves the way to design new chiroptoelectronic devices and probes the close connections between chiral materials, topological electrons and CP light in the quantum regime.

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Fig. 1: Device-structure-dependent CP-EL.
Fig. 2: Emission-direction-dependent CP emissions relative to charge-carrier flow directions.
Fig. 3: Illustration of orbital–momentum locking and the ACPE.
Fig. 4: The chirality and CP emission for stacking two F8BT molecules with a twisted angle.

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Data availability

The main data supporting the findings of this study are available within this Article and its Supplementary Information. Further data are available from the corresponding author on reasonable request. Source data are provided with this paper.

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Acknowledgements

We dedicate this paper to the memory of Professor Alasdair James Campbell (1961–2021). L.W. would like to thank Alasdair James Campbell and J. Nelson for useful discussions at Imperial College London. L.W. would like to thank K. Stjerne (Biolab A/S, Denmark) and T. Brock-Nannestad (University of Copenhagen, Denmark) for access to the CPL-300 spectrometer. L.W. would like to thank R. Zhang (Linköping University) for help with processing the GIWAXS data. B.Y. acknowledges the financial support of the MINERVA Stiftung with the funds from the BMBF of the Federal Republic of Germany and the European Research Council (ERC Consolidator Grant ‘NonlinearTopo’, number 815869). L.W. and M.J.F. would like to thank Cambridge Display Technology Limited (company number 02672530) for providing the F8BT polymers. L.W. and M.J.F. would like to acknowledge EPSRC research grants EP/P000525/1, EP/L016702/1 and EP/R00188X/1. For the purpose of open access, the author has applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising.

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L.W. and B.Y. conceived the project. L.W. collected the spectroscopy and device data. L.W. and M.J.F. analysed the experimental data. Y.L. and B.Y. wrote the theory and performed theoreteical calculations. L.W., Y.L. and B.Y wrote the manuscript. All authors contribute to the discussion and the revision of the manuscript.

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Correspondence to Li Wan or Binghai Yan.

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M.J.F. is an inventor on a patent concerning chiral blend materials (WO2014016611). The remaining authors declare no competing interests.

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Nature Photonics thanks Lorenzo Di Bari and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Wan, L., Liu, Y., Fuchter, M.J. et al. Anomalous circularly polarized light emission in organic light-emitting diodes caused by orbital–momentum locking. Nat. Photon. 17, 193–199 (2023). https://doi.org/10.1038/s41566-022-01113-9

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