High-efficiency quantum-dot light-emitting devices with enhanced charge injection

We report a colour-saturated, red quantum-dot light-emitting device (QLED) using an inverted organic–inorganic hybrid device structure and colloidal CdSe–CdS (core–shell) quantum-dot emitters. The strong electronic coupling of quantum dots to an adjacent layer of ZnO nanocrystals (which form the electron transport layer) facilitates charge transfer, which is responsible for both injecting electrons and maintaining an optimal charge balance for the quantum dot emitters. We show that QLED performance can be modified by controlling the distance of the electroluminescence recombination zone within the quantum dot film from the quantum dot–ZnO interface. Devices are reported with a luminous efficiency of 19 cd A −1 , corresponding to an external quantum efficiency of 18% (which is close to the theoretical maximum of 20%) and an internal quantum efficiency of 90%. The corresponding luminous power efficiency exceeds 25 lm W −1 due to the low operating voltage of the device. Red quantum-dot light-emitting diodes with an external quantum efficiency of 18%, close to the theoretical maximum of 20%, are reported. Using a layer of zinc oxide nanocrystals provides highly effective electron transport, resulting in devices with a low operating voltage and a high luminous power efficiency of 25 lm W −1 .