In this paper, we reported superior performance of solution-processed top-emission quantum dot light-emitting diodes (TE-QLEDs) with Mg-doped ZnO nanoparticle (NP) electron transport layer (ETL). The Mg-doped ZnO NPs were synthesized by the sol-gel method. Transmission electron microscopy
(TEM) analysis of the Mg-doped ZnO NPs with 0 wt%, 5 wt%, 10 wt%, and 15 wt% Mg-doping concentrations revealed average diameters of 5.86 nm, 5.33 nm, 4.52 nm, and 4.37 nm, respectively. The maximum luminance, the current efficiency, and external quantum efficiency (EQE) were 178,561.8 cd/m2,
56.0 cd/A, and 14.43%, respectively. However, for the best performance of TE-QLED without Mg-doping in the ZnO NPs, the maximum luminance was only 101,523.4 cd/m2, the luminous efficiency was 27.8 cd/A, and the EQE was 6.91%. The improvement of the performance is attributed to the
suppression of electron transfer by an increase in the energy barrier between the cathode and Mg-doped ZnO NP ETL and the reduction in the Hall mobility of electron with increasing the Mg-doping in the ZnO NPs, resulting in the enhanced charge balance in the quantum dot (QD) emitting layer
(EML).
Herein, the outstanding efficiency of solution‐processed quantum‐dot (QD) light‐emitting diodes (QLEDs) is demonstrated, which is achieved by adjusting the thickness of their Zn0.9Mg0.1O nanoparticle (NP) electron transport layer (ETL).The NPs are prepared by the sol‐gel method. As the thickness increases, the current density of the QLEDs decreases because of the increased resistance of the Zn0.9Mg0.1O NP ETL. As the thickness increases from 10 to 35 nm, the luminance, luminous efficiency, and external quantum efficiency (EQE) also increase because of the improved charge balance between electrons and holes in the QD emissive layer (EML). In contrast, as the thickness increases beyond 35–120 nm, these three variables decrease because of the worsening charge balance, which is attributing to deficient electron injection from the cathode into the QD EML compared with hole injection from the anode into the EML. The QLED with a 35 nm thick Zn0.9Mg0.1O NP ETL exhibits the highest luminance, luminous efficiency, and EQE, with values of 128 084 cd m−2, 88.8 cd A−1, and 21.3%, respectively. The superior device performance and good charge balance to the appropriate ETL thickness are attributed.
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