Efficient Structure for InP/ZnS based Electroluminescence Device by Embedding the Emitters in the Electron-Dominating Interface.

The charge carrier distribution has been an important parameter in determining the efficiency of quantum dots 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-QDs based QLEDs. By introducing a thin layer of electron transport materials, the hole accumulation at hole transport layer and 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 electron-dominating interface of ZnO/TPBi. The analysis reveals that an internal quantum efficiency of nearly 100% is achieved for the InP-QDs (with photoluminescence quantum yield of 32%) based device. This work provides alternative device structure for achieving high efficiency QLED devices.