Robust ZnMgO Capped with Benzyl‐Phosphonic Acid as Armor Layer Enables Efficient and Stable Quantum Dot Light‐Emitting Diodes

Abstract The Zinc‐Magnesium oxide (ZnMgO, ZMO) nanoparticles (NPs) are well‐documented as electron transport layer (ETL) in quantum dot light‐emitting diodes (QLEDs). However, ZnO/ZMO nanoparticles prepared via low‐temperature sol–gel methods with small grain size and abundant surface defects always suffer from structural and electrical drift, causing lifespan reduction and performance fluctuations of devices. Herein, the benzyl phosphate (BPA) and its derivatives are introduced onto the surface of ZMO NPs as armor layer to stabilize and regulate their properties as ETLs. The prepared ZMO capped with BPA NPs have fine structural and electrical properties stability, which have simultaneously achieves effective defect passivation, enhances nanoparticle dispersibility and stability, and precisely tunes energy levels to balance charge injection. By benefiting from the robust ZMO ETLs, the overall performance of the QLED devices has been greatly boosted. The resulting external quantum efficiency (EQE) of green QLEDs is increased from 20.8% to 29.9%, showing the best performance among currently reported ZMO‐based green QLEDs, and over 3.3‐fold improvement in T ₉₅ operation lifetime at 1000 cd m ^{− 2} . The relevant physical mechanism has also been investigated. Current work will inspire the exploration of ZMO decorating engineering to construct solution‐processed QLEDs device with higher performance.