Quantum Dot Light Emitting Diodes with ZnO Electron Transport Layer

In order to reduce the turn on voltage and improve the performance of QLED, ZnO film with good electronic transmission property was used as electron transport layer. The structure of the sample was ITO/PEDOT: PSS/Poly-TPD/QDs/ZnO. The models of Folwer-Nordheim tunneling injection and space-charge limited current were employed to analyze the injection current density in QDs layer. The results show that the optimal thickness of poly-TPD is confirmed to 40 nm when ZnO thickness is fixed of 50 nm, and the injection carriers in QDs layer can reach a certain balance. By measuring the current density-voltage-luminance-luminous efficiency of QLED, the influences of hole transport layer thickness on the device performance were studied. Experiment results show that the device with a hole transport layer of 40 nm has the best performances than the other devices, of which the turn on voltage is 1.7 V, the maximum lumious efficiency is 1.18 cd/A, and the maximum brightness can reach 5 225 cd/m2 under the voltage of 9 V.