Improved performance of quantum dot light-emitting diodes by introducing WO3 hole injection layers

We prepared quantum dot light-emitting diodes (QLEDs) with a tungsten oxide (WO3) hole injection layer (HIL) produced via thermal evaporation. Placement of a WO3 layer between the indium tin oxide (ITO) anode and the poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (poly-TPD) hole transport layer (HTL) reduced the QELD threshold voltage and enhanced luminance, luminous efficiency, and quantum external efficiency. The optimal layer thickness was 10 nm, associated with increases of 57.2% and 72.3% in the maximum luminous efficiency and maximum external quantum efficiency, respectively, compared to the reference QLED without WO3 HIL. The results can be explained from fact that the insertion of WO3 HILs reduced the energy barrier between the ITO and poly-TPD layers, thus facilitating hole injection from ITO into poly-TPD.