Herbert Friedrich Börner

High efficiency polymer LEDs: triplets and novel devices

We present results and a discussion of highly efficient polymer Light-Emitting Diodes (polymer LEDs, PLEDs). The external quantum efficiency in current standard devices reaches up to 2-4% only. We have explored two routes to enhance this value. In the first route, PEDOT/PSS is replaced with a novel anode or hole injection layer. The efficiency with some Light Emitting Polymers (LEP) is improved significantly, resulting in an efficacy of 35 cd/A for a yellow emitting poly-(para-phenylene-vinylene) and 20 cd/A for a blue emitting poly-(spirobifluorene). We attribute the major improvement compared to standard devices, where about 10 and 5 cd/A are obtained, respectively, to a combination of improved exciton formation efficiency and light out-coupling efficiency, and to less quenching of the radiative decay under actual device operating conditions. In the second route, we developed a new host polymer with high triplet energy such that transition metal-based green-emitting phosphorescent dyes can be used without significant back transfer of triplet excitons to the polymer host. First results using this system showed about 25 cd/A using a soluble green Ir-based emitter. Importantly, all data are obtained in a standard two-layer device of a hole transport/injection layer and the LEP.

67.2: Invited Paper: High‐Efficiency Phosphorescent Polymer LEDs

In this paper, we present the results of our ongoing work towards achieving high-efficiency high-energy (i.e. green and blue) phosphorescent polymer light-emitting diodes (pLEDs). Green phosphorescent pLEDs have been prepared with efficiencies that are comparable to those of state-of-the art OLEDs based on small molecules (smOLEDs), and the first steps towards extending these concepts to blue phosphorescent pLEDs are shown.