Hole-transporting host-polymer series consisting of triphenylamine basic structures for phosphorescent polymer light-emitting diodes
MW Thesen, B Höfer, M Debeaux, S Janietz, A Wedel, A Köhler, HH Johannes, H Krueger
J. Pol. Sc. A 48 (2010) 3417-3430
A series of novel styrene derived monomers with triphenylamine-based units, and their polymers have been synthesized and compared with the well-known structure of polymer of N,N0-bis(3-methylphenyl)-N,N0-diphenylbenzidine with respect to their hole-transporting behavior in phosphorescent polymer light-emitting diodes (PLEDs). A vinyltriphenylamine structure was selected as a basic unit, functionalized at the para positions with the following side groups: diphenylamine, 3-methylphenyl-aniline, 1- and 2-naphthylamine, carbazole, and phenothiazine. The polymers are used in PLEDs as host polymers for blend systems with the following device configuration: glass/indium–tin–oxide/PEDOT:PSS/polymer-blend/CsF/Ca/Ag. In addition to the hole-transporting host polymer, the polymer blend includes a phosphorescent dopant [Ir(Me-ppy)3] and an electron-transporting molecule (2-(4-biphenyl)-5-(4-tertbutylphenyl)-1,3,4-oxadiazole). We demonstrate that two polymers are excellent hole-transporting matrix materials for these blend systems because of their good overall electroluminescent performances and their comparatively high glass transition temperatures. For the carbazole-substituted polymer (Tg = 246°C), a luminous efficiency of 35 cd A-1 and a brightness of 6700 cd m-2 at 10 V is accessible. The phenothiazine-functionalized polymer (Tg= 220°C) shows nearly the same outstanding PLED behavior. Hence, both these polymers outperform the well-known polymer of N,N0-bis(3-methylphenyl)-N,N0- diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A-1 and a brightness of 2500 cd m -2 (10 V).