Highly Efficient and Bright Quantum‐Dot Light‐Emitting Diodes with Enhanced Charge Balance by Adjusting the Thickness of Zn0.9Mg0.1O Electron Transport Layer

Abstract

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.