Zn-Doped SnO2 NPs as Electron Transport Layer in Green CdSe/ZnS Quantum Dot Light-Emitting Diodes

SnO2 nanoparticles (NPs) have been used as an electron transport layer (ETL) in quantum dot light-emitting diodes (QLEDs) to achieve stable and high-performance devices. However, SnO2 NPs with high electron mobility cause the problem of imbalanced charge injection and transport in QLEDs. Meanwhile, the SnO2 NPs synthesized at low temperature have hydroxyl (−OH) groups, which could damage the performance of QLEDs. Here, Zn doping was applied to modulate the properties of SnO2 NPs and achieve better carrier balance in green CdSe/ZnS QLED. The maximum current efficiency (CE) of QLED with 5 wt % Zn-doped SnO2 NPs is 2.3-fold higher than that of SnO2-based QLED. In addition, a small-molecule 4,4′-bis(carbazole-9-yl)-1,1′-biphenyl (CBP)-mixed poly(9-vinylcarbazole) (PVK) layer was used as a hole transport layer to facilitate the hole injection and charge balance. As a result, a maximum external quantum efficiency (EQE) of 5.03% is obtained for the best performance device. The T50 lifetime at a luminance of 100 cd/m2, for a device based on 5 wt % Zn-doped SnO2 ETL, is 9141 h, which is 2.29-fold longer than the reference one. This work provides a new strategy to obtain high-performance and stable display arrays.