Effect of Air Exposure of ZnMgO Nanoparticle Electron Transport Layer on Efficiency of Quantum-Dot Light-Emitting Diodes

Abstract

We demonstrate the effect of air exposure on optical and electrical properties of ZnMgO nanoparticles (NPs) typically exploited as an electron transport layer in Cd-based quantum-dot light-emitting diodes (QLEDs). We analyze the roles of air components in modifying the electrical properties of ZnMgO NPs, which reveals that H 2 O enables the reduction of hole leakage while O 2 alters the character of charge transport due to its ability to trap electrons. As a result, the charge balance in the QDs layer is improved, which is confirmed by voltage-dependent measurements of photoluminescence quantum yield. The maximum external quantum efficiency is improved over 2-fold and reaches the value of 9.5% at a luminance of 10 4 cd/m 2 . In addition, we investigate the problem of electron leakage into the hole transport layer and show that trap-mediated electron transport in the ZnMgO layer caused by adsorbed O 2 ensures a higher leakage threshold. This work also provides an insight into the possible disadvantages of device contact with air as well as problems and challenges that might occur during open-air fabrication of QLEDs.

Double-type-I charge-injection heterostructure for quantum-dot light-emitting diodes

“…The characteristics show little current leakage below 2 V, less than 0.1 mA cm À2 , indicating that the ZnMgO layer here is 'optimal', with similar behavior as aged films. 37,38 The full-cycle sweep shows that electron injection improves in the returning half-cycle. This hysteresis is characteristic of the ZnMgO contact but often neglected in the literature.…”

Tailored ZnO Functional Nanomaterials for Solution‐Processed Quantum‐Dot Light‐Emitting Diodes

“…According to Chrzanowski et al, [ 108 ] lifetime measurements revealed that the air‐exposed devices could exhibit much‐improved operational stability (Figure 17e). Two different regimes were identified: Repeating scans under 3 V resulted in reproducible performance, but scanning up to 6 V quickly irreversibly degraded the device performance (Figure 17f).…”

“…Chrzanowski et al reported controlled (humid) air exposure of ZnO‐based ETLs as a suitable approach to improve the charge balance in their QLEDs. [ 108 ] The authors investigated the effect of water and oxygen on the carrier density in the ETL. It was observed that exposure of the ZnMgO ETL to humid air at room temperature resulted in reduced hole leakage and improved charge balance in the device.…”

Finely Controlled Synthesis of Zn1–xMgxO Nanoparticles with Uniform Size Distribution Used as Electron Transport Materials for Red QLEDs

“…Quantum light-emitting diodes (QLEDs) have triggered a tremendous increase in research interest in recent years since the discovery of cadmium selenide nanocrystal-based QLEDs, , and they are expected to be one of the mainstream next-generation display technologies. One of the core techniques in QLEDs is the use of inorganic nanoparticles to substitute the traditional organic molecules as the electron transport layer (ETL) to achieve color controllability and purity, narrow full-width at half-maximum (fwhm) emission wavelength, and long lifetime. − ZnO nanoparticles (NPs) are the most widely used ETL, − mainly because of their high electron mobility, strong coupling effect, and conductive band edge matched with that of the emissive layer (EML), which enables the excellent injection of electrons from ZnO NPs to the emissive layer. However, the low hole mobility of the organic hole transport layer (HTL) does not match the high electron mobility in the ETL layer, resulting in the unbalanced injection of electrons and holes to the EML and the excessive accumulation of electrons in the EML, which degrades the performance and lifetimes of the QLEDs .…”