Enhanced Lifetime and Efficiency of Red Quantum Dot Light‐Emitting Diodes with Y‐Doped ZnO Sol–Gel Electron‐Transport Layers by Reducing Excess Electron Injection

Abstract

Charge balance between electrons and holes, which are injected into the quantum dot (QD) emission layer (EML), is critical for realizing stable and efficient QD light‐emitting diodes (QLEDs). ZnO has been widely used as an electron‐transport layer (ETL) because of its superior performance compared to other metal oxides. However, nearly barrier‐free electron injection into the QD EML leads to spontaneous charge transfer and excess electron injection, resulting in reduced device performance. Here, to adjust electron–hole balance and thereby improve the lifetime and efficiency of QLEDs, we introduce an yttrium (Y)‐doped ZnO (YZO) ETL into QLEDs. The sol–gel processed YZO film, with a mobility that could be simply tuned by varying the Y concentration, provides enhanced charge‐transport balance by suppressing excess electron flow to the QD EML. Furthermore, YZO helps suppress QD charging and smooth the surface morphology. Applying the YZO ETL into the inverted‐structure QLED enables us to achieve color‐saturated red emission, an improved external quantum efficiency of up to 8.6%, and an eight times longer lifetime compared to the device with undoped ZnO. This result provides a simple method for enhancing the performance of QLEDs by easily controlling metal doping concentration in the sol–gel processed ZnO ETL.

Highly Efficient, Surface Ligand Modified Quantum Dot Light‐Emitting Diodes Driven by Type‐Controllable MoTe2 Thin Film Transistors via Electron Charge Enhancer

“…To resolve the poor electron-hole balance, several attempts have been reported such as inserting a electron blocking layer and adopting a Y-doped ZnO NPs as an electron transport layer (ETL) to decrease the electron injection into QDs. [1,40,41] However, these strategies cause the device instability in QLEDs. Hence in this study, we utilized a robust ligand exchange strategy to optimize the balance of electron/hole injection and lower the energy barrier between QD and the adjacent layer.…”

P‐120: Degradation Mechanism and Lifetime Improvement of Blue Quantum‐Dot Light‐Emitting Diodes

“…However, operation lifetime is still an issue for QLED. Several methods for elongating QLED lifetime had been reported, such as using blocking layer and ameliorating transporting materials, for improving carrier balance in a QLED [3,4,5]. In this work, we demonstrate that the crucial factor of operation lifetime in our blue QLED is organic hole-transporting layer (HTL).…”

An efficient organic and inorganic hybrid interlayer for high performance inverted red cadmium-free quantum dot light-emitting diodes

“…Another simple and effective approach is by modulating the electronic structures of ZnO by doping metals such as magnesium (Mg), yttrium(Y), gallium (Ga), and aluminium (Al) to improve the charge balance or suppress the exciton quenching of the QD interface. [19][20][21][22][23] Cesium azide (CsN 3 ) 24 , polyvinylpyrrolidone (PVP), 25 and Lithium 8-quinolate (LiQ) 26 materials also have been studied as dopants to modulate the mobility of ZnO. To improve the device performance of device on insulating or organic polymer interlayers, thickness control is crucial, which forms a tunneling barrier in the QLED device.…”