Efficient flexible quantum-dot light-emitting diodes with unipolar charge injection

Abstract

The exfoliation between the electrode film and the adjacent functional layer is still a big challenge for the flexible light emitting diodes, especially for the devices dependent on the direct charge injection from the electrodes. To address this issue, we design a flexible quantum-dot light-emitting diodes (QLEDs) with a charge-generation layer (CGL) on the bottom electrode as the electron supplier. The CGL consisting of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/ZnO can provide sufficient electron injection into the QDs, enabling a balanced charge injection. As a result, the CGL-based QLED exhibits a peak external quantum efficiency 18.6%, over 25% enhancement in comparison with the device with ZnO as the electron transport layer. Moreover, the residual electrons in the ZnO can be pulled back to the PEDOT:PSS/ZnO interface by the storage holes in the CGL, which are released and accelerates the electron injection during the next driving voltage pulse, hence improving the electroluminescence response speed of the QLEDs.