Solution-processed optoelectronic and electronic devices are attractive owing to the potential for low-cost fabrication of large-area devices and the compatibility with lightweight, flexible plastic substrates. Solution-processed light-emitting diodes (LEDs) using conjugated polymers or quantum dots as emitters have attracted great interest over the past two decades1,2. However, the overall performance of solution-processed LEDs2,3,4,5—including their efficiency, efficiency roll-off at high current densities, turn-on voltage and lifetime under operational conditions—remains inferior to that of the best vacuum-deposited organic LEDs6,7,8. Here we report a solution-processed, multilayer quantum-dot-based LED with excellent performance and reproducibility. It exhibits colour-saturated deep-red emission, sub-bandgap turn-on at 1.7 volts, high external quantum efficiencies of up to 20.5 per cent, low efficiency roll-off (up to 15.1 per cent of the external quantum efficiency at 100 mA cm−2), and a long operational lifetime of more than 100,000 hours at 100 cd m−2, making this device the best-performing solution-processed red LED so far, comparable to state-of-the-art vacuum-deposited organic LEDs2,3,4,5,6,7,8. This optoelectronic performance is achieved by inserting an insulating layer between the quantum dot layer and the oxide electron-transport layer to optimize charge balance in the device and preserve the superior emissive properties of the quantum dots. We anticipate that our results will be a starting point for further research, leading to high-performance, all-solution-processed quantum-dot-based LEDs ideal for next-generation display and solid-state lighting technologies.
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This work is financially supported by the National High Technology Research and Development Program of China (2011AA050520), the National Natural Science Foundation of China (21233005 and 51172203), the Natural Science Funds for Distinguished Young Scholar of Zhejiang Province (R4110189), the Public Welfare Project of Zhejiang Province (2013C31057), the Jiangsu Natural Science Foundation (BK20130006 and BK20131413), the National Basic Research Program of China (2015CB932200) and the Jiangsu Specially-Appointed Professor programme. We thank L. Liao and L. Zhang for assistance in cross-measuring the QLED and OLED devices. We thank Q. Chen for assistance with atomic force microscopy and scanning Kelvin probe microscopy measurements. We thank Z. Zhang and C. Jin for assistance with cross-sectional transmission electron microscopy experiments. We also thank J. Yu and G. Qian for assistance in obtaining the confocal images.