Dresden 2017 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 50: Poster: Organic Electronics and Photovoltaics, Molecular Excitations

CPP 50.9: Poster

Wednesday, March 22, 2017, 18:30–21:00, P3

Comparison of theoretical and actual benefit of birefrigent layers in OLEDs — •Markus Schmid, Thomas Lampe, and Wolfgang Brütting — Institute of Physics, University of Augsburg, 86135 Augsburg, Germany

One of the main factors influencing the efficiency of OLEDs is the microcavity formed by the organic layers enclosed between the electrodes. From a theoretical point of view it was shown that the inclusion of a birefrigent material as transport layer at the reflective cathode can improve the outcoupling efficiency of such devices [1]. The main reason for this is reduced coupling to surface plasmons at the organic-metal interface due to the effects of the anisotropic material.

In this work we present an OLED-layout using a birefrigent electron transport layer and a reference device with isotropic optical constants. However, the main challenge is that most optically anisotropic organics like TCTA or Spiro-2CBP are hole-conductors not suitable for electron-transport. Additionally the use of electron injection layers would prevent the beneficial effects of the anisotropic material. In order to reach the necessary electric properties we doped the organic material. Making use of electrical and optical simulations as well as a heteroleptic phosphorescent emitter, we achieved a highly efficient OLED with a birefrigent layer in contact to the reflective cathode. The devices even show an external quantum efficiency close to their theoretical limit of about 21 %.
Callens, Michiel K. et al.: Anisotropic materials in OLEDs for high outcoupling efficiency. Optics express 23, p.21128–21148 (2015).