Triazole and Pyridine Hybrid Molecules as Electron-Transport Materials for Highly Efficient Green Phosphorescent Organic Light-Emitting Diodes.

A series of triazole and pyridine hybrid molecules, with a triazole core and pyridine periphery, were designed and synthesized as an electron-transport layer (ETL) and a hole/exciton-block layer for green phosphorescent organic light-emitting diodes. Compared with the widely-used electron-transport material (ETM) of 3-(biphenyl-4-yl)-5-(4- tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ) with a triazole core, lower-lying HOMO and LUMO energy levels were obtained with the introduction of pyridine rings onto the periphery of the molecules, giving improved electron injection and carrier confinement. Significantly reduced driving voltages were achieved in a device structure of ITO/HATCN (5 nm)/TAPC (40 nm)/CBP:8 wt % Ir(PPy)3 (10 nm)/ETL (40 nm)/LiF (1 nm)/Al (90 nm), giving a maximum power efficiency of 72.2 lm W−1 and an external quantum efficiency of 21.8 %, due to the improved electron injection and transport and thus, more balanced carrier recombination, which are much higher than those of the device based on TAZ. [ABSTRACT FROM AUTHOR]