Chinese team report best solution-processed red LED
Solution-processed LEDs using conjugated polymers or quantum dots as emitters have created interest over the past two decades for their potential for low-cost fabrication on flexible plastic substrates. However, the overall performance of such LEDs - including their efficiency, efficiency roll-off at high current densities, turn-on voltage and lifetime under operational conditions - is not as good as the best vacuum-deposited organic LEDs.
Now scientists from Zhejiang University, Chinese Academy of Sciences, and Nanjing Tech University have reported a solution-processed, multilayer quantum-dot-based LED with excellent performance and reproducibility.
Their quantum dot LED, which was the subject of a paper in Nature today, exhibits colour-saturated deep-red emission, sub-bandgap turn-on at 1.7V, high external quantum efficiencies of up to 20.5 percent, 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.
According to to the researchers, this makes making this device the best-performing solution-processed red LED so far, comparable to state-of-the-art vacuum-deposited organic LEDs.
The optoelectronic performance is achieved by inserting an insulating layer between the quantum dot layer and the oxide electron-transport layer to optimise charge balance in the device and preserve the superior emissive properties of the quantum dots.
The researchers anticipate that the 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.
'Solution-processed, high-performance light-emitting diodes based on quantum dots' by Xingliang Dai et al, appears in Nature (2014) doi:10.1038/nature13829
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