Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates
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Bragg scattering at one-dimensional corrugated substrates allows to improve the light outcoupling from top-emitting organic light-emitting diodes (OLEDs). The OLEDs rely on a highly efficient phosphorescent pin stack and contain metal electrodes that introduce pronounced microcavity effects. A corrugated photoresist layer underneath the bottom electrode introduces light scattering. Compared to optically optimized reference OLEDs without the corrugated substrate, the corrugation increases light outcoupling efficiency but does not adversely affect the electrical properties of the devices. The external quantum efficiency (EQE) is increased from 15 % for an optimized planar layer structure to 17.5 % for a corrugated OLED with a grating period of 1.0mm and a modulation depth of about 70 nm. Detailed analysis and optical modeling of the angular resolved emission spectra of the OLEDs provide evidence for Bragg scattering of waveguided and surface plasmon modes that are normally confined within the OLED stack into the air-cone. We observe constructive and destructive interference between these scattered modes and the radiative cavity mode. This interference is quantitatively described by a complex summation of Lorentz-like resonances.
Schwab , T , Fuchs , C , Scholz , R , Zakhidov , A , Leo , K & Gather , M C 2014 , ' Coherent mode coupling in highly efficient top-emitting OLEDs on periodically corrugated substrates ' Optics Express , vol 22 , no. 7 , pp. 7524-7537 . DOI: 10.1364/OE.22.007524
(C) 2014 OSA. This paper was published in Optics Express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
This work was funded by the European Social Fund and the Free State of Saxony through the OrganoMechanics project, and by the AIF/BMWi in the framework IGF under contract no. GF-11/05 resp. AiF-Nr. 16784 BR (project LipsOLED). Support from the excellence cluster cfaed is gratefully acknowledged. We acknowledge support by the German Research Foundation and the Open Access Publication Funds of the TU Dresden.
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