Overcoming the Electroluminescence Efficiency Limitations in Quantum-Dot Light-Emitting Diodes

Development of quantum dots (QDs) based light-emitting diodes (QLEDs) is driven by attractive properties of these fluorophores such as precise Gaussian distribution, tunable emission, and facile solution processability. The performance of QLED devices is limited by intrinsic factors such as luminance quenching in quantum dots due to imbalanced carrier injection predominantly caused by a large hole injection barrier as well as by extrinsic processes such as nonradiative recombination at active layer interfaces. The Auger recombination problem is overcome by charge siphoning at the interfaces between QDs and charge-transporting material. A simplest trilayer (p–i–n) LED structure is fabricated using an all-solution processing method: a carefully engineered p-type polymeric hole transport layer with a gradient work function is incorporated. The gradient work function creates the cascading energy levels from the moderate Fermi level anode to the deep-lying valence band level of QDs. As a result, the QLEDs exhibit significantly improved external quantum efficiencies and luminous efficiencies of 15.9% and 31.8 cd A⁻¹, 17.4% and 59.3 cd A⁻¹, and 12.8% and 14.4 cd A⁻¹ for red, green, and blue light-emitting devices, respectively. It is expected that the concept demonstrated here will facilitate the design and development of efficient solution-processible QLEDs for full-color displays.