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Proceedings Paper

A micrometer-scale patterning of OLED substrates for the enhancement of outcoupling efficiency by redirection of substrate and organic waveguided modes (Conference Presentation)

Paper Abstract

According to simulated calculations, in our bottom emitting OLED devices, the outcoupling efficiency (ηOUT) is limited to only 17% of light escaping into free space due to light lost as substrate guided (22%), organic waveguided (12%) and evanescent modes (31%) and the air/substrate, substrate/organic and organic/metal interfaces respectively [1]. To extract substrate guided modes, our previous work showed that OLEDs fabricated over sample glass patterned substrates, can simultaneously enhance the ηOUT and reduce view angle dependency [1]. This represents an improvement on past research efforts, wherein some outcoupling structures tended to induce strong viewing angle dependence [2] and those intended suppress this, had no effect on ηOUT [3]. Previous research for extracting organic waveguides, however, may involve complex nm-scale fabrication techniques resulting in 20-25% enhancement in ηOUT [4-5]. In this work, we demonstrate that a novel pattern of ITO-coated glass substrate can extract up to 30.8% of organic waveguided modes, by micrometer-scale patterning of both the ITO and glass beneath the ITO. Using the simulation programme, Setfos, existing patterns at the air/substrate interface were first replicated and then manually optimized in terms of depth, diameter, edge-to-edge distance, the shape of holes and their packing arrangement. A combination of the most optimized dimensions then resulted in a maximum enhancement in ηOUT by 30.36%. Devices fabricated with similar pattern dimensions at the air/substrate interface (albeit slight differences) showed a 27.3% enhancement as a result of extracted substrate guided modes. The substrate/organic side of the device was also patterned with similar dimensions as mentioned above and resulted in a 30.8% enhancement of ηOUT due to extracted organic waveguided modes being redirected as leaky modes, wherein light is then able to escape into the forward viewing direction.

Paper Details

Date Published: 1 April 2020
Proc. SPIE 11365, Organic Electronics and Photonics: Fundamentals and Devices II, 113650V (1 April 2020); doi: 10.1117/12.2555624
Show Author Affiliations
Savanna Lloyd, Japan Advanced Institute of Science and Technology (Japan)
Tatsuya Tanigawa, IMRA America, Inc. (Japan)
Hideyuki Murata, Japan Advanced Institute of Science and Technology (Japan)

Published in SPIE Proceedings Vol. 11365:
Organic Electronics and Photonics: Fundamentals and Devices II
Sebastian Reineke; Koen Vandewal; Wouter Maes, Editor(s)

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