Improved Hole Injection by Enhancing Electron Extraction of Solution-Processed MoOx in Quantum Dot Light-Emitting Diodes

Hole injection layers (HILs) are pivotal for the performance of quantum dot light-emitting diodes (QLEDs), with solution-processed inorganic HIL materials being a primary means for the commercial application of QLEDs. Transition metal oxides (TMOs), due to their excellent stability, have been widely employed as inorganic HILs by thermal evaporation in QLEDs; however, the hole injection ability of solution-processed TMO film necessitates further enhancement owing to inferior film quality. In this study, a solution-processed molybdenum oxide (MoOx) film was used as a HIL, and its hole injection ability in the QLED was improved by tuning the oxygen states. Oxidation treatments on the MoOx layer can effectively mitigate oxygen vacancies, and consequently, the conduction band minimum (CBM) of MoOx is elevated, which enhances the hole injection through easier electron extraction from the highest occupied molecular orbitals (HOMO) of the hole transport layer. The MoOx-based red QLED exhibits significantly longer working lifetimes (T50@100 cd·m-2 of ∼66,892 h) and comparable current efficiencies (13.7 cd·A-1) compared to the Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)-based QLEDs. Our research not only proposes a promising approach to high-performance MoOx-based QLEDs but also paves the way for further applications of TMOs in QLEDs.