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 Tg 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°C, retaining a luminance of 80% of the initial value measured at 20°C.