Bi-directional organic light-emitting diodes containing nanoparticles to enhance light outcoupling
Journal
Laser & Photonics Reviews
Journal Volume
7
Journal Issue
6
Pages
1079-1087
Date Issued
2013-10
Author(s)
Hong-Wei Chang
Jonghee Lee
Tae-Wook Koh
Simone Hofmann
Yong Hyun Kim
Bjö
rn Lü
ssem
Seunghyup Yoo
Chung-Chih Wu
Karl Leo
Malte C. Gather
Abstract
AbstractAn effective method is presented for enhancing the outcoupling efficiency of translucent/bi‐directional organic light‐emitting diodes (TL/BD‐OLEDs) with a bottom indium tin oxide (ITO) anode and a top cathode comprised of a thin Ag layer covered with an organic capping layer. Upon insertion of a nanoparticle (NP)‐based scattering layer (NPSL) between the substrate and the ITO anode, the TL/BD‐OLEDs exhibit significantly enhanced external quantum efficiency (EQE) in both emission directions. Furthermore, the NPSL improves the color stability of the TL/BD‐OLEDs over a wide range of viewing angles. Simulations based on geometrical and statistical optics are performed to elucidate the mechanism by which the efficiency is enhanced and to establish strategies for further optimization. Simulations performed on the scattering layers with varying NP volume percentage reveal that the bottom‐side emission is governed by competition between waveguide‐mode extraction and backward scattering by NPs in the film, while the top‐side emission is largely dominated by the latter. Optimized bi‐directional OLEDs achieve a 1.64‐fold enhanced EQE compared to reference devices without NPSL.
Type
journal article