Dresden 2017 – wissenschaftliches Programm
CPP 32.14: Vortrag
Mittwoch, 22. März 2017, 13:00–13:15, CHE 91
Influence of radiative efficiency and dipole orientation on optimal layer thicknesses of monochrome OLEDs for maximum EQE — •Paul-Anton Will, Cornelius Fuchs, Reinhard Scholz, Simone Lenk, and Sebastian Reineke — Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP) and Institute for Applied Physics, Technische Universität Dresden, Germany
For realizing highly efficient organic light-emitting diodes (OLEDs), the light-emitting molecule has to meet several requirements. Among chemical, energetic, and optical characteristics two crucial properties are the radiative efficiency ηrad and the emissive dipole orientation described by the anisotropy factor a. While the first is already close to its maximum for commonly used emitter molecules, a lot of research is currently ongoing to understand and control the dipole orientations of organic molecules. However, the external quantum efficiency (EQE) of OLEDs depends on the optical enviroment of the emitting molecules. As known, the Purcell effect leads to an effective radiative efficiency ηrad* for emitters in a cavity. In this work, we show how the radiative efficiency ηrad and the anisotropy factor a influence the optimal layer thickness of monochrome OLEDs to reach maximum EQE. We find that for emitters with ηrad < 100 % the product of ηrad* and the outcoupling efficiency ηout needs to be optimized, instead of solely optimizing ηout. When doing so, the EQE of planar OLEDs with highly oriented molecules but imperfect radiative efficiency can be pushed further. In this way, the full potential of planar OLEDs can be exploited.