Highly efficient inverted organic light-emitting diodes based on thermally activated delayed fluorescence

Abstract

Green inverted organic light-emitting diodes (OLEDs) based on a thermally activated delayed fluorescent (TADF) emitter, 2-pheyl-4-carbazole-9-H-thioxanthen-9-one-10,10-dioxide, with a cathode of indium tin oxide (ITO)/ZnO injecting electrons efficiently into the electron transporting layer of Alq3, are demonstrated for the first time. The insertion of 7-nm Cs2CO3 can further enhance the electron injection. The optimized device with 25-nm ZnO and 7-nm Cs2CO3 affords the highest performance of the inverted devices with a current efficiency of 28.1 cd A−1, a power efficiency of 16.1 lm W−1, and an external quantum efficiency of 9.8%. The inverted OLEDs based on TADF emitters are competitive compared with conventional OLEDs because of their air-stable electrodes and TADF emitters, which enable simpler encapsulation.