High-performance multilayered phosphorescent OLEDs by solution-processed commercial electron-transport materials

Highly efficient multilayered polymer-based phosphorescent organic light-emitting diodes (PhOLEDs) are realized by orthogonal sequential solution-processing of commercial small-molecule electron-transport materials (ETMs), including 1,3,5-tri(3-pyrid-3-yl-phenyl) benzene (TmPyPB), 4,7-diphenyl-1,10-phenanthroline (BPhen) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The performance of PhOLEDs with solution-deposited ETMs is found to be far superior compared to devices with vacuum-deposited ETMs. PhOLEDs with a solution-deposited BPhen electron-transport layer gave a luminous efficiency of 53.8 cd A(-1) with an external quantum efficiency of 16.1%. The solution-processed electron-transport layer exhibits a unique rough surface morphology which facilitates charge-injection and transport from the cathode metal. The nanostructured surface morphology and charge carrier mobility of the solution-processed electron-transport layers could be tuned and controlled by the solution concentration. The orthogonal solution-processing demonstrated here is a promising strategy for applications in various solution-processed multilayered organic electronic devices.