Efficient Hole Injection of MoO_x-Doped Organic Layer for Printable Red Quantum Dot Light-Emitting Diodes

In this letter, we report the high-performance quantum dot light-emitting diodes (QLEDs) with a hybrid hole injection layer (HIL) by doping MoO _x into poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS). By this method, the Fermi level of HIL increases from 4.9 to 5.3 eV, allowing better energy level matching and more efficient hole injection capability. The resultant devices exhibit maximum current efficiency of 18.6 cd/A and peak external quantum efficiency of 18.2%, almost 1.5-folds higher than those (12.7 cd/A and 12.3 %) of the control device based on pristine PEDOT:PSS HIL. Most importantly, the hydrophobicity of PEDOT: PSS on transparent conductive oxide can be dramatically improved upon MoO _x doping, which provides promising potential in ink-jet printing for large-area fabrication of devices.