Highly power efficient organic light-emitting diodes based on p-doped and novel n-doped carrier transport layers

Abstract

The power efficiency of organic light-emitting diodes was significantly improved by introducing a novel n-doping (4'7- diphyenyl-1, 10-phenanthroline: 33 wt% 8-hydroxy-quinolinato lithium) layer as an electron transport layer and a p-doping layer composed of 4, 4', 4''-tris (3-methylphenylphenylamono) triphenylamine (m-MTDATA) and tetrafluro-tetracyano-quinodimethane (F4-TCNQ) as a hole transport layer. Hole-only and electron-only devices were demonstrated to observe an improvement in the conductivity of the transport layers. With this strategy, we demonstrated that the power efficiency was enhanced by ∼100%, luminous efficiency was enhanced by ∼54% while driving voltage was reduced by 32% as compared with the control device. We obtained a power efficiency of 4.44 Lm W−1, which is the best value so far reported for tris (8- hydroxyquinolinato) aluminium (Alq3)-based emitters. This improvement was ascribed to the improved conductivity of the transport layers and to the better charge balance in the emission zone.