Mg-Diffusion of ZnO-Based Electron-Transport Layers for Highly Conductive Quantum-Dot Light-Emitting Diodes

Quantum-dotlight-emitting diodes (QLEDs) show great potentialin next-generation display and lighting technologies. Further reducingthe resistances of the high-efficiency QLEDs is critical to improvingtheir luminous efficiencies and lowering their power consumption.However, wet-chemistry methods to improve the conductivities of ZnO-basedelectron-transport layers (ETLs) often lead to trade-offs in the externalquantum efficiencies (EQEs) of QLEDs. Here, we report a facile approachtoward highly conductive QLEDs by in situ diffusion of Mg atoms intothe ZnO-based ETLs. We demonstrate that thermally evaporated Mg canspread deep into the ZnO-based ETL with a long penetration length,generating oxygen vacancies that promote the electron-transport properties.The Mg-diffused ETLs enhance the conductivities and luminous efficienciesof state-of-the-art QLEDs without sacrificing the EQEs. This strategyis applied to QLEDs with various optical architectures, leading tosignificant enhancements in the current densities, luminances, andluminous efficiencies. We expect that our method could be extendedto other solution-processed LEDs using ZnO-based ETLs.