Solution-processible multilayer phosphorescent PLEDs based on copolystyrenes

We synthesised novel styrene monomers and their polymers with triphenylamine based bodies and compared their hole-transporting behaviour in polymer light emitting diodes (PLEDs) with well known structures. As base body of all monomers a triphenylamine structure was selected, functionalised with the following side groups: diphenylaminc, 3-methylphenylaniline, 1- and 2-naphthylamine, carbazole, and phenothiazine. Furtheremore we used the well known hole-transporting polymer N,N'-bis(3-methylphenyI)-N,N'-diphenylbenzidine (TPD). The energy levels of all polymers were measured with photo-emission spectroscopy and compared with cyclovoltammetric investigations. The polymers were applicated in PLEDs as polymer blend systems with the following device assembly: glass/ITO/PEDOT-PSS/polymer-blend/CsF/Ca/Ag. 2-(4-biphenyl)-5-(4-tert-butylpheny1)-1,3,4-oxadiazole (tertBuPBD) acts in all cases as 30 wt-% electron-transporting material and 8 wt-% Ir(2-(4-toly1)-pyridinato)(3) (Ir(Meppy)(3)) was used as triplet emitting complex. It was shown that two polymers are favored, because of their best overall electrolumincscent performances and their highest glass transition temperatures. With the carbazole substituted polymer (Tg = 246 degrees C) a luminous efficiency of 35 cd A(-1) by a brightness of 6700 cd m(-2) at 10 V was asseccible. The phenothiazine functionaliscd polymer (Tg = 220 degrees C) showed at 10 V a luminous efficiency of 29.0 cd A(-1) and a brightness of 6100 cd m(-2). Both polymers exhi-bited better performances compared to the well investigated TPD derivative (with a luminous efficiency of 7.9 cd A(-1) and a brightness of 2500 cd m(-2) at 10 V) and should be preffered as hole-transporting materials in further investigations.