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Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination

Nature Photonics volume 12, pages 159–164 (2018)Cite this article

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Abstract

The external quantum efficiencies of state-of-the-art colloidal quantum dot light-emitting diodes (QLEDs) are now approaching the limit set by the out-coupling efficiency. However, the brightness of these devices is constrained by the use of poorly conducting emitting layers, a consequence of the present-day reliance on long-chain organic capping ligands. Here, we report how conductive and passivating halides can be implemented in Zn chalcogenide-shelled colloidal quantum dots to enable high-brightness green QLEDs. We use a surface management reagent, thionyl chloride (SOCl2), to chlorinate the carboxylic group of oleic acid and graft the surfaces of the colloidal quantum dots with passivating chloride anions. This results in devices with an improved mobility that retain high external quantum efficiencies in the high-injection-current region and also feature a reduced turn-on voltage of 2.5 V. The treated QLEDs operate with a brightness of 460,000 cd m−2, significantly exceeding that of all previously reported solution-processed LEDs.

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Fig. 1: Chlorination ligand exchange mechanism.
Fig. 2: Characterization of C–S–S–Cl CQDs.
Fig. 3: Conductivity and QLED architecture characterization.
Fig. 4: EQE characterization of QLED devices.
Fig. 5: Electroluminescence spectra under different biases.
Fig. 6: Optoelectronic simulations of charge carrier distributions and recombination rates inside the active layers.

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Acknowledgements

This publication is based in part on work supported by the Ontario Research Fund Research Excellence Program, and by the Natural Sciences and Engineering Research Council (NSERC) of Canada. The authors thank B. Sun, M. Liu, M. Burgelman, P.-C. Li and R. Munir for their help during the course of study.

Author information

Author notes

  1. Fengjia Fan

    Present address: CAS Key Laboratory of Microscale Magnetic Resonance and Department of Modern Physics, University of Science and Technology of China (USTC), Hefei, China

  2. Min Liu

    Present address: Institute of Super-microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, Changsha, China

  3. These authors contributed equally: Xiyan Li and Yong-Biao Zhao.

Authors and Affiliations

  1. Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada

    Xiyan Li, Yong-Biao Zhao, Fengjia Fan, Larissa Levina, Min Liu, Rafael Quintero-Bermudez, Xiwen Gong, Li Na Quan, James Fan, Zhenyu Yang, Sjoerd Hoogland, Oleksandr Voznyy & Edward H. Sargent

  2. Department of Materials Science and Engineering, University of Toronto, Toronto, Ontario, Canada

    Yong-Biao Zhao & Zheng-Hong Lu

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Contributions

X.L. and F.F. conceived the idea. X.L. and F.F. developed the efficient chlorination exchange. X.L. and Y.-B.Z. fabricated and characterized the QLEDs. O.V. performed optoelectronic device simulations. L.L. and X.L. synthesized the CQDs. M.L. undertook SEM imaging. R.Q.-B. performed XPS characterizations. X.L., F.F., O.V., E.H.S. and Y.-B.Z. wrote the manuscript. O.V., E.H.S. and Z.-H.L supervised the project. All authors discussed the results and assisted in manuscript preparation.

Corresponding authors

Correspondence to Fengjia Fan, Oleksandr Voznyy, Zheng-Hong Lu or Edward H. Sargent.

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Li, X., Zhao, YB., Fan, F. et al. Bright colloidal quantum dot light-emitting diodes enabled by efficient chlorination. Nature Photon 12, 159–164 (2018). https://doi.org/10.1038/s41566-018-0105-8

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