Effect of Electron Injection Layer on the Parasitic Recombination at the Hole Transport Layer/Quantum Dot Interface in Quantum Dot Light-Emitting Diodes

Zinc oxide (ZnO) nanoparticles layers are used as a substitute for organic electron transport layer due to high electron mobility, higher thermal stability and less sensitivity to the oxygen/moisture. In this study, we investigated the electron injection properties of ZnO nanoparticles in QLED compared with TPBi commonly used as injection layer in OLEDs. The expected electron injection barrier from energy diagram is similar in both devices, but the current density of the ZnO injection layer was slightly high compared with the TPBi injection layer. The current efficiency of ZnO and TPBi devices were 5.21 cd/A and 2.24 cd/A, respectively. The current efficiency of TPBi device is below half of ZnO device. We found that the electron-hole recombination occurs not only in the QD but also in the poly-TPD for TPBi device.