Thermally stable organic light-emitting diodes using new families of hole-transporting amorphous molecular materials

A new family of hole-transporting amorphous molecular materials with high glass-transition temperatures (Tg) have been designed and synthesized. They include 4,4',4-tris[biphenyl-2-yl(phenyl)amino]triphenylamine (o-PTDATA), 4,4',4-tris[biphenyl-3-yl(phenyl)amino]triphenylamine (m-PTDATA), and 4,4',4-tris[biphenyl-4-yl(3'-methylphenyl)amino]triphenylamine (p-PMTDATA). These compounds were found to form readily stable amorphous glasses with high T-g, and to function as materials for hole-injection layers in contact with the ITO electrode in multilayer organic light-emitting diodes (OLEDs). Such devices consisting of double hole-transport layers of o-PTDATA or p-PMTDATA and N,N'-di(biphenyl-4-yl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine and the emitting layer of tris(8-quinolinolato)aluminum were found to exhibit high performance and thermal stability. The devices operated at 150 degrees C, retaining a luminance of 80% of the initial value measured at 20 degrees C. (C) 2000 Elsevier Science S.A. All rights reserved.