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Title: General method to evaluate substrate surface modification techniques for light extraction enhancement of organic light emitting diodes
Authors: Choulis, Stelios A. 
Krummacher, Benjamin C. 
Mathai, Mathew K. 
metadata.dc.contributor.other: Χούλης, Στέλιος Α.
Major Field of Science: Engineering and Technology
Keywords: Electroluminescence;Light emitting diodes
Issue Date: 1-Sep-2006
Source: Journal of applied physics, 2006, vol.100, no. 5, pp. 1-6
Volume: 100
Issue: 5
Start page: 1
End page: 6
Journal: Journal of Applied Physics 
Abstract: The external light output of organic light emitting diodes (OLEDs) can be increased by modifying the light emitting surface. The apparent light extraction enhancement is given by the ratio between the efficiency of the unmodified device and the efficiency of the modified device. This apparent light extraction enhancement is dependent on the OLED architecture itself and is not the correct value to judge the effectiveness of a technique to enhance light outcoupling due to substrate surface modification. We propose a general method to evaluate substrate surface modification techniques for light extraction enhancement of OLEDs independent from the device architecture. This method is experimentally demonstrated using green electrophosphorescent OLEDs with different device architectures. The substrate surface of these OLEDs was modified by applying a prismatic film to increase light outcoupling from the device stack. It was demonstrated that the conventionally measured apparent light extraction enhancement by means of the prismatic film does not reflect the actual performance of the light outcoupling technique. Rather, by comparing the light extracted out of the prismatic film to that generated in the OLED layers and coupled into the substrate (before the substrate/air interface), a more accurate evaluation of light outcoupling enhancement can be achieved. Furthermore we show that substrate surface modification can change the output spectrum of a broad band emitting OLED
ISSN: 10897550
DOI: 10.1063/1.2234550
Rights: © American Institute of Physics
Attribution-NonCommercial-NoDerivs 3.0 United States
Type: Article
Affiliation: Osram Opto Semiconductors, Inc. 
Affiliation : University of Erlangen-Nuremberg 
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