Highly efficient solution-processed red phosphorescent organic light-emitting diodes employing an interface exciplex host

To cut cost and improve efficiency, an interface exciplex system of N,N′-di(naphth-1-yl)-N,N′-diphenyl-benzidine (NPB)/1,3,5-tris[N-(phenyl)benzimidazole]-benzene (TPBi) was employed as a host in solution-processed red phosphorescent organic light-emitting diodes (PhOLEDs). The optimal red PhOLEDs based on the interfacial exciplex host (IEH) present excellent performance with a maximum power efficiency (PEmax) of 40.4 lm W-1, a maximum external quantum efficiency (EQEmax) of 17.2%, and a pretty low turn-on voltage of 2.6 V. Through ideality factor (η) measurements, the results indicate that Langevin recombination (LR) is the dominant carrier recombination pathway in the devices. And the detailed analysis of carrier recombination pathways reveals the advantages of the IEH in carrier transport and recombination. Our work highlights the working process of the IEH and provides evidence for the superiority of the IEH in high performance PhOLEDs.