Achieving Charge Balance in Red InP-Based QLEDs through a Novel ZnO@hydroxides Electron Transport Layer

Environmentally friendly InP-based quantum dot light-emitting diodes (QLEDs) are promising for next-generation displays but are hindered by charge imbalance and exciton quenching from conventional ZnMgO electron transport layers (ETLs). To address this, we developed a novel ZnO@hydroxides ETL via a simple sol-gel method. The surface-associated hydroxide species, including LiOH·H₂O and Mg(OH)_x, form a passivating layer on the ZnO nanocrystals. This leads to a more compact film, reduced surface defects, and better-matched charge injection. Consequently, the optimized red InP/ZnSe/ZnSe_0.75S_0.25/ZnS QLED achieves a high external quantum efficiency (EQE) of 26.42%, significantly outperforming the ZnMgO-based device (EQE = 18.59%). Operational stability is also markedly improved, with the T₉₅@100 cd·m^-2 lifetime extending from 3,316 to 7,548 h─a greater than 2-fold enhancement. This work demonstrates that rational ETL surface passivation is a highly effective strategy for developing high-efficiency, stable, and cadmium/plumbum-free QLEDs.