Highly efficient charge generation and injection in HAT-CN/TAPC heterojunction for high efficiency tandem organic light-emitting diodes

Abstract

An efficient planar organic heterojunction (OHJ) consisted of 1,4,5,8,9,11-hexaazatriphenylene- hexacarbonitrile (HAT-CN)/1,1-bis [(di-4-tolyamino)phenyl)]cyclohexane (TAPC) is employed simultaneously as both charge generation layer (CGL) and charge injectors to fabricate high efficiency and long lifetime tandem organic light-emitting diodes (OLEDs). It can be seen that compared with conventional tandem OLEDs, the tandem OLEDs utilizing OHJ as both CGL and charge injectors significantly improved not only the current and quantum efficiencies, more importantly, but also the power efficiency and stability. The maximum efficiencies were as high as 42.0%, 159.5 cd A-1 and 92.7 lm W-1, and the lifetime reached 1350 h, which are more higher than the efficiencies of 34.3% 130.2 cd A-1 and 75.0 lm W-1 and the lifetime of 859 h of conventional tandem OLEDs. The more balanced charge generation and injection due to the simultaneous utilization of OHJ as CGL and charge injectors contributed to the significant improvement in the performance of resulting tandem OLEDs. These results fully indicate the validity of OHJ as CGL and charge injectors, and also provide a new route for the development of high performance OLEDs.