Highly efficient inverted polymer light-emitting diodes using surface modifications of ​ZnO layer

Abstract

Organic light-emitting diodes have been recently focused for flexible display and solid-state lighting applications and so much effort has been devoted to achieve highly efficient organic light-emitting diodes. Here, we improve the efficiency of inverted polymer light-emitting diodes by introducing a spontaneously formed ripple-shaped nanostructure of ​ZnO and applying an amine-based polar solvent treatment to the nanostructure of ​ZnO. The nanostructure of the ​ZnO layer improves the extraction of the waveguide modes inside the device structure, and a ​2-ME+​EA interlayer enhances the electron injection and hole blocking in addition to reducing exciton quenching between the polar-solvent-treated ​ZnO and the emissive layer. Therefore, our optimized inverted polymer light-emitting diodes have a luminous efficiency of 61.6 cd A−1 and an external quantum efficiency of 17.8%, which are the highest efficiency values among polymer-based fluorescent light-emitting diodes that contain a single emissive layer.