Highly electroluminescent devices made with a conveniently synthesized triazole-triphenylamine derivative

The convenient synthesis of (3-(4-tert-Butylphenyl)-4-phenyl-5-(4′- diphenylaminostilben-4-yl)-1,2,4-triazole) is described. This molecule, labeled TAZ-TPA is composed of triphenylamine (known to transport holes) and triazole (known to transport electrons) moieties. TAZ-TPA is easily obtained as a thin solid film by vacuum evaporation. Devices made with TAZ-TPA as electron transport and electroluminescent layer, in conjunction with an aryl amine hole transport layer, luminesce strongly in the blue green (the luminescence peaks at 484 nm). They are characterized by a 4±0.5 V turn on voltage, a maximum luminance of 10900±1100 Cd/m² and a photometric efficiency of 2.2±0.2 Cd/A. From the dependence of the luminance vs. the thickness of the TAZ-TPA layer, it is deduced that the hole and electron diffusion lengths in TAZ-TPA are 60±12 nm and 100±12 nm, respectively. Adding 1 wt.% rubrene in the hole transport layer improves the maximum luminance to 16100±1600 Cd/m² without practically altering the electroluminescent spectrum of the device.