Quantum dot light-emitting diodes using a graphene oxide/PEDOT:PSS bilayer as hole injection layer

Quantum dot (QD) light-emitting diode (QLED) displays are highly promising optoelectronic devices, but several critical issues remain to be solved. The hole-electron charge balance is particularly important but hole-injection is more difficult than electron-injection in QLEDs; as a result, good hole injection ability is required. Here, we introduce a graphene oxide (GO) layer between the anode electrode and a typical hole injection layer of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) to improve the hole injection ability of a QLED device. The device with the GO/PEDOT:PSS bilayer hole injection layer exhibits a three-fold increase in brightness and external quantum efficiency as well as doubled current efficiency compared to a counterpart device using a single PEDOT:PSS layer. In addition, the turn-on voltage is improved from 8.35 V to 5.35 V. The dramatic improvements in the optoelectronic performance are attributed to the stepwise energy band structure in the hole injection bilayers; the work function of the GO layer is measured to be 4.98 eV, which reduces the interfacial barrier energy between the anode and PEDOT:PSS layer.