High-Efficiency Red Perovskite Light-Emitting Diodes by Designing the Landscapes of MoO_x

Perovskite quantum dot light-emitting diodes (Pe QLEDs) hold significant application potential in next-generation displays, but the device performance remains compromised by the acidity and hygroscopicity of the widely adopted hole injection layer (HIL), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Molybdenum oxide (MoO_x) has garnered significant attention due to its excellent environmental stability; however, there is still a lack of research on the influence of different molybdenum ion contents on the physicochemical properties of molybdenum oxide itself and its application as a hole injection layer (HIL) in red Pe QLEDs. In this work, three MoO_x solutions with the conduction band level from -4.70 to -5.15 eV were prepared by modulating the H₂O₂ ratio to regulate the Mo⁵⁺ and Mo⁶⁺ content, and different MoO_x were adopted as HIL to systematically investigate the influence of energy landscapes on device performance. A gradient conduction band energy was realized, and optimal hole injection was obtained when the ratio of Mo⁵⁺ is 48.1%, with an external quantum efficiency (EQE) of 28.6% realized. This efficiency is comparable to that of PEDOT:PSS-based devices and represents the highest value reported for MoO_x-based red Pe QLEDs. Besides, the operational stability was enhanced from 3.0 to 10.6 h, and after being stored for 48 h in a high-humidity environment, the half-life (T₅₀) remained above 3.0 h, far exceeding that of PEDOT:PSS-based devices, which nearly lost their operational stability. The proposed MoO_x-based Pe QLEDs exhibited significantly improved operational and storage stabilities.