Abstract
The charge-carrier distribution has been an important parameter in determining the efficiency of quantum-dot-based light-emitting diodes (QLEDs). In this Letter, we demonstrate a new inverted device structure of ITO/ZnO/polyethylenimine/quantum dots (QDs)/1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi)/4,4'-bis(9-carbazolyl)-2,2'-biphenyl (CBP)/MoO3/Al for improving the efficiency of InP-QD-based QLEDs. By introducing a thin layer of electron transport materials, the hole accumulation at the hole transport layer and the QD interface is largely reduced, which suppresses the quenching effect of holes on the QD emission. Compared with the conventional device structure with the emitters at ZnO/CBP pn junction, the peak current efficiency (external quantum efficiency) increases from 3.83 (5.17 cd/A) to 6.32% (8.54 cd/A) by imbedding the QDs at the electron-dominating interface of ZnO/TPBi. The analysis reveals that an internal quantum efficiency of nearly 100% is achieved for the InP-QD-based device (with a photoluminescence quantum yield of 32%). This work provides an alternative device structure for achieving high-efficiency QLED devices.
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