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High-efficiency light-emitting devices based on quantum dots with tailored nanostructures

Abstract

We report a full series of blue, green and red quantum-dot-based light-emitting devices (QD-LEDs), all with high external quantum efficiencies over 10%. We show that the fine nanostructure of quantum dots—especially the composition of the graded intermediate shell and the thickness of the outer shell—plays a very important role in determining QD-LED device performance due to its effects on charge injection, transport and recombination. These simple devices have maximum current and external quantum efficiencies of 63 cd A−1 and 14.5% for green QD-LEDs, 15 cd A−1 and 12.0% for red devices, and 4.4 cd A−1 and 10.7% for blue devices, all of which are well maintained over a wide range of luminances from 102 to 104 cd m−2. All the QD-LEDs are solution-processed for ease of mass production, and have low turn-on voltages and saturated pure colours. The green and red devices exhibit lifetimes of more than 90,000 and 300,000 h, respectively.

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Figure 1: Surface elemental composition evolution with reaction time by XPS characterization, TEM characterization and photoluminescence spectra of green quantum dots.
Figure 2: Schematic of device structure, energy levels and electroluminescence performance of green QD-LEDs.
Figure 3: Electroluminescence performance of red and deep blue QD-LEDs.
Figure 4: Electroluminescence spectra, CIE coordinates and operating lifetime of QD-LEDs.
Figure 5: Monochrome active matrix QD-LED display prototypes.

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Acknowledgements

This work was supported financially by the US National Science Foundation (NSF; SBIR Phase I award no. 1248863 and Phase II award no. 1353411) and the Florida High-Tech Corridor Council (FHTCC). Assistance with data collection and reduction by R. Zhou and J. Mudrick (Materials Science and Engineering, University of Florida) is acknowledged. The authors also acknowledge Shanghai Tianma Micro-Electronics Group for assistance with AM QD-LED fabrication. J.X. acknowledges financial support from the NSF Major Research Instrumentation Program for the acquisition of the PHI XPS instrument.

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Contributions

Y.Y. and Y.Z. synthesized material, fabricated devices, collected performance data and postulated mechanisms to explain the performance of the QD-LEDs. W.C. carried out the TEM and XPS measurements. A.T. and J.H. carried out the lifetime test and fabrication of the 4.3-inch AM QD-LED prototypes. J.R.M. carried out the XRD measurement and device efficiency distribution statistics. J.X., P.H.H. and L.Q. supervised the synthesis of materials and devices, directed the collection of performance data, designed tests for the postulated mechanism, and finalized the manuscript.

Corresponding authors

Correspondence to Jiangeng Xue, Paul H. Holloway or Lei Qian.

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The authors declare competing financial interests. Y.Y., A.T., J.H. and J.R.M. are employees of NanoPhotonica Inc., and Y.Z. and L.Q. are Founders of NanoPhotonica Inc., which is the provider of the QD-LEDs display technique and related materials.

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Yang, Y., Zheng, Y., Cao, W. et al. High-efficiency light-emitting devices based on quantum dots with tailored nanostructures. Nature Photon 9, 259–266 (2015). https://doi.org/10.1038/nphoton.2015.36

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