Flexible quantum dot light-emitting diodes without sacrificing optical and electrical performance

Quantum dot light-emitting diodes (QLEDs) has been developed toward flexibility without sacrificing optical and electrical performances as in the case of organic light-emitting diodes (OLEDs) display. The biggest challenge is replacing the conventional rigid or brittle electrodes, which has not been successful in the QLEDs yet. In this study, the flexible QLEDs without degradation of both optical and electrical performances are demonstrated to exhibit excellent light-emitting properties (maximum luminance of 14,330 cd/m2 and maximum current efficiency of 20.77 cd/A) with a low turn-on voltage of 3.5 V. The double-layered graphene of stepwise-tuned workfunctions was developed as a flexible and transparent anode. The top layer of a graphene film is oxidized by the oxygen plasma, which promotes wettability of the hydrophilic hole injection layer (HIL) and enhances the rate of hole injection by mediating the workfunctions between HIL and the pristine graphene anode. The color shift as a function of brightness could be minimized due to the balanced charge injection through this new electrode. The flexibility of QLEDs could be accomplished with mixture of an Al film and Ag nanowires as a cathode. No significant degradation of flexible QLED performances could be observed through a bending test involving even 1,000 bends.