Cd-Free Quantum-Dot\nLight-Emitting Diodes through\nNanometer-Thick ZnS/ZnMgO Double-Electron Transport Layers

Quantum-dot light-emitting diodes (QLEDs) are gaining\npopularity\nas next-generation display devices due to their outstanding electroluminescent\nproperties. However, conventional metal oxide-based electron transport\nlayers (ETLs) used in QLEDs often suffer from charge imbalance, primarily\ndue to intrinsic oxygen vacancies affecting their electrical properties,\nwhich degrade performance. To address this challenge, we introduce\nZnS nanoparticles possessing a wider bandgap than ZnMgO nanoparticles,\nexcellent chemical robustness and processability, to form a double-layer\nETL of ZnS/ZnMgO in an inverted InP-based QLED. Owing to the higher\nenergy levels and lower electron mobility of ZnS compared to ZnMgO,\nexcess electron injection can be effectively controlled, resulting\nin improved charge balance in the devices. As a result, the InP-based\nQLED with a ZnS/ZnMgO double-layer ETL shows a 1.3-fold higher external\nquantum efficiency and a 1.84-fold longer lifetime than the QLED without\na ZnS layer. Given the facile synthesis and processability of the\nZnS nanoparticles introduced here, they may be applicable to a variety\nof optoelectronic devices, including QLEDs, for effective control\nof electron injection.