Hole-transporting host-polymer series consisting of triphenylamine basic structures for phosphorescent polymer light-emitting diodes

A series of novel styrene derived monomers with triphenylamine-based units, and their polymers have been syn- thesized and compared with the well-known structure of poly- mer of N,N 0 -bis(3-methylphenyl)-N,N 0 -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 poly- mers for blend systems with the following device configura- tion: glass/indium-tin-oxide/PEDOT:PSS/polymer-blend/CsF/Ca/ Ag. In addition to the hole-transporting host polymer, the poly- mer blend includes a phosphorescent dopant (Ir(Me-ppy)3) and an electron-transporting molecule (2-(4-biphenyl)-5-(4-tert- butylphenyl)-1,3,4-oxadiazole). We demonstrate that two poly- mers are excellent hole-transporting matrix materials for these blend systems because of their good overall electrolumines- cent performances and their comparatively high glass transi- tion temperatures. For the carbazole-substituted polymer (Tg ¼ 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-function- alized polymer (Tg ¼ 220 � C) shows nearly the same outstand- ing PLED behavior. Hence, both these polymers outperform the well-known polymer of N,N 0 -bis(3-methylphenyl)-N,N 0 - diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A � 1 and a brightness of 2500 cd m � 2 (10 V). V C 2010 Wiley