Enhancing extraction efficiency of quantum dot light-emitting diodes by surface engineering.

Light extraction efficiency significantly affects the final performance of quantum dot light-emitting diodes (QLED) devices. Surface engineering of the substrate has been proved to be an effective method to increase the light extraction efficiency. However, a facile, low cost, and scalable process to modify the QLED substrate's surface remains a perpetual topic, which calls for further study. We herein use the wet chemical etching process to roughen the substrate's surface, and a "multi-pits" like exit surface is formed. These "multi-pits" act as scattering centers that benefits homogeneity of the output light. On the other hand, they also give a rise in output coupling efficiency by inhibiting light propagation of the internally generated photons, owing to the suppressed optical waveguide mode. The external quantum efficiency (EQE) of QLED with a roughened surface shows a 12% increase in maximum value, and over 2.2 fold increase at a high driving voltage than that without surface roughening.