S. Janietz, H. Krueger, M. Thesen, B. Fischer, A. Wedel
Department Polymer Electronics, Fraunhofer Institute for Applied Polymer Research, Geiselbergstr. 69, D-14476 Potsdam, Germany, +49-331-5681920, email: email@example.com
The interest to apply phosphorescent polymers in organic light emitting devices (OLEDs) lies in the scope for low-cost manufacture of large area displays, facilitated by solution-processing of film forming materials. Polystyrene is used as the corresponding non-conjugated polymer matrix. Hole-transport, electron-transport and phosphorescent molecules with red, green and blue emission were attached covalently as side chains with different spacer lengths to the polystyrene backbone.
Different Ir-complexes, tert.-butylphenyl-5-biphenyl-1,3,4-oxadiazole (TBPO) as electron- transport and triphenylamine as hole-transport materials were selected as components for this polymer based phosphorescent systems. These components were functionalized with styrene groups by multistep organic synthesis. As polymerisation process a radical polymerisation was chosen in THF/DMF with AIBN as initiator. Several terpolymers with different spacer lengths to the active molecules were synthesized with sufficient high molecular weights and film forming properties. The composition of the copolymers is verified concerning the three comonomers to optimize the device parameters. First assumptions for the PLED device structure were obtained from the results of the cyclovoltammetric investigations of the synthesized terpolymers. PLEDs were fabricated and characterized from the terpolymers as emitting layer. The relationship between the terpolymer composition and the achieved PLED device parameters will be discussed in detail.