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

Abstract

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,N'-bis(3-methylphenyl)-N,N'-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-tert-butylphenyl)-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 (T-g = 246 degrees 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 (T-g = 220 degrees C) shows nearly the same outstanding PLED behavior. Hence, both these polymers outperform the well-known polymer of N,N'-bis(3-methylphenyl)-N,N'diphenylbenzidine, showing only a luminous efficiency of 7.9 cd A(-1) and a brightness of 2500 cd m(-2) (10 V)

Ordering the amorphous – Structures in PBD LED materials

“…Older solid state X-ray investigations result in a perfectly planar molecule with coplanar rings [4,56], attributed to intermolecular forces within the crystal. With an interring bond length of 1.50 Å a possible conjugation between both rings is ruled out.…”

“…Molecules and polymers containing the 1,3,4-oxadiazole moiety are interesting candidates for applications like thin-film transistors or light emitting devices [1][2][3][4][5] and are among the most widely studied electron transporting materials for organic light emitting diodes (LEDs) [4,6]. These substances are of interest as electron transport materials or emitting layers in electroluminescent diodes.…”

Carbazole-based polymers as hosts for solution-processed organic light-emitting diodes: Simplicity, efficacy

“…Considering the similarity of structure between carbazole and triphenylamine, PTAs can also act as hole-transport materials and thus hosts. Hole-transportation of PTAs can be reinforced if carbazole groups are appended to PTA [127]. Using this strategy, the blend composed of P32, 30 wt% of tert-BuPBD as the electron-transporting material and 8 wt% of Ir(mppy) 3 gave remarkable performances with a luminous efficiency of about 35.1 cd/A at 100 cd/m 2 , a brightness of 6700 cd/m 2 at 10 V. While searching other side-groups that could further improved performances, only the phenothiazine-functionalized polymer P33 showed performances approaching those obtained with P32 (29 cd/A at 100 cd/m 2 , 6100 cd/m 2 at 10 V).…”

Hole-transporting side-chain polystyrenes based on TCTA with tuned glass transition and optimized electronic properties

“…8 In this polymer, a tris(4-(9H-carbazol-9-yl)phenyl)amine (TCTA) analogue is bound as pendant group to a polystyrene backbone. Polystyrene-based side chain functionalized polymers are known for excellent lm formation and the morphological stability of such layers.…”

“…17,18 2-((2-Ethylhexyl)oxy)-9H-carbazole (c) was obtained by simple etherication of the aryl ether and the corresponding 2-hydroxy-9H-carbazole. The following reactions towards the polymers 3b-f (top of Scheme 5) were performed according to a procedure published by Thesen et al 8 The incorporation of the alkoxy groups leads to a notable decrease of T g (see Table 1). As compared to unsubstituted poly-TCTA, there is a minor T g reduction of 26 K for polymer 3b with two methoxy groups, a 62 K decrease for polymer 3e with four ethoxy groups, and a decrease of 100 K for polymers 3c, 3d, and 3f with four butoxy or two ethylhexyloxy substituents.…”