Bipolar-shell resurfacing for blue LEDs based on strongly confined perovskite quantum dots

Abstract

Colloidal quantum dot (QD) solids are emerging semiconductors that have been actively explored in fundamental studies of charge transport1 and for applications in optoelectronics2. Forming high-quality QD solids—necessary for device fabrication—requires substitution of the long organic ligands used for synthesis with short ligands that provide increased QD coupling and improved charge transport3. However, in perovskite QDs, the polar solvents used to carry out the ligand exchange decompose the highly ionic perovskites4. Here we report perovskite QD resurfacing to achieve a bipolar shell consisting of an inner anion shell, and an outer shell comprised of cations and polar solvent molecules. The outer shell is electrostatically adsorbed to the negatively charged inner shell. This approach produces strongly confined perovskite QD solids that feature improved carrier mobility (≥0.01 cm2 V−1 s−1) and reduced trap density relative to previously reported low-dimensional perovskites. Blue-emitting QD films exhibit photoluminescence quantum yields exceeding 90%. By exploiting the improved mobility, we have been able to fabricate CsPbBr3 QD-based efficient blue and green light-emitting diodes. Blue devices with reduced trap density have an external quantum efficiency of 12.3%; the green devices achieve an external quantum efficiency of 22%.

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Fig. 1: Bipolar-shell resurfacing of perovskite QDs.
Fig. 2: Chemistry and photophysics of bipolar-shell-stabilized CsPbBr3 perovskite QDs.
Fig. 3: Properties of CsPbBr3 perovskite QD solid films cast from bipolar-shell-resurfaced QD inks.
Fig. 4: Blue and green LEDs based on perovskite QD solids.

Data availability

The authors declare that the main data supporting the findings of this study are available within the letter and its Supplementary Information. Extra data are available from the corresponding authors upon reasonable request.

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Acknowledgements

This work was supported by the Ontario Research Fund–Research Excellence Program and the Natural Sciences and Engineering Research Council of Canada (NSERC, grant number 537463-18). M.I.S. acknowledges the support of the Banting Postdoctoral Fellowship Program, administered by the Government of Canada. We acknowledge financial support from the Natural Science Foundation of China (numbers 51821002 and 91733301) and the Collaborative Innovation Centre of Suzhou Nano Science and Technology. Y.-K.W. also acknowledges the financial support of the China Scholarship Council (number 201806920067). We thank Huawei Canada for their financial support. Z.-H.L. and all co-authors from the Department of Materials Science and Engineering at the University of Toronto acknowledge the financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC, grant number 216956-12) and the National Natural Science Foundation of China (grant number 11774304).

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Contributions

Y.D., Y.-K.W. and F.Y. conceived the study. Y.D. and Y.-K.W. synthesized the CsPbBr3 perovskite QDs and developed the ligand exchange method. Y.D. performed steady-state absorption and photoluminescence spectra measurements, time-correlated single-photon counting measurements and transient absorption spectroscopy measurements. Y.-K.W. and F.Y. fabricated the LED devices, performed XRD measurements and characterized the LEDs. B.C., S.-W.B. and M.W. performed TEM, SEM and STEM imaging. J.F. performed FTIR spectroscopy measurements. L.K.S. performed the TGA. M.-J.C. and M.C. performed the ζ-potential measurements. F.Y., P.L. and H.T.K. performed XPS measurements. R.Q.-B. and A.J. performed GISAXS measurements. Y.H., Y.L., B.S., S.L., D.M., P.T., F.D., H.E., E.K. and S.H. contributed to device fabrication and data analyses. Y.D. and O.V. performed the device simulation. M.I.S., Z.-H.L and E.H.S. supervised the project. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Zheng-Hong Lu or Edward H. Sargent.

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Supplementary Information

Supplementary Figs. 1–20, discussion, Tables 1–8 and refs. 1–15.

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Dong, Y., Wang, Y., Yuan, F. et al. Bipolar-shell resurfacing for blue LEDs based on strongly confined perovskite quantum dots. Nat. Nanotechnol. (2020). https://doi.org/10.1038/s41565-020-0714-5

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