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Light outcoupling enhancement from top-emitting organic light-emitting diodes made on a nano-sized stochastic texture surface

Woo-Young Park, Yongwon Kwon, Changhee Lee, and Ki-Woong Whang

Open Access Open Access

Abstract

An effective method for enhancing the light outcoupling efficiency from top-emitting organic light-emitting diodes (TEOLEDs) with a nano-sized stochastic texture surface (NSTS) is suggested. The broadly distributed pitch and the randomly sized of islands in the NSTS enable the photons that are otherwise trapped to be emitted over the broad emission wavelength range. The NSTS-embedded TEOLEDs have wide angular-dependent emission characteristics and an enhanced external quantum efficiency (EQE). Theoretical and full-wave optical calculations were performed to understand the mechanisms of the efficiency enhancement. Optimized TEOLEDs achieved a 32% EQE enhancement compared with the reference devices without the NSTS.

© 2014 Optical Society of America

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Figures (5)
Fig. 1
Fig. 1 The procedure used to fabricate the NSTS. The Ag thin film was first deposited on the glass substrate followed by the formation of stochastic Ag islands using a thermal dewetting process.

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Fig. 2
Fig. 2 (a) A schematic illustration of the NSTS-based OLEDs (b) The three-dimensional atomic force microscope (AFM) image of the NSTS on the glass substrate with the dimensions 5.0 × 5.0 μm.

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Fig. 3
Fig. 3 (a) The current density‒voltage‒luminance characteristics and the angular dependence of the electroluminescence (EL) intensity (b) The EQE as a function of luminance (c) The normalized EL spectra of a device without the NSTS as a function of observation angle (d) The normalized EL spectra of a device with the NSTS as a function of observation angle.

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Fig. 4
Fig. 4 (a) The normalized intensity distribution (b) the outcoupling angle of the emitted light (c) emission wavelength, and (d) outcoupling efficiency and enhancement factor as a function of the grating pitch.

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Fig. 5
Fig. 5 The normalized electric field distributions of (a) the reference and (b) the NSTS-based devices.

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Equations (3)

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k ∥ = k 0 sin θ = k w g ± m G ,
θ = ( λ , Λ ) = arc sin [ Re ( n e f f ) ± m λ / Λ ] ,
E ⇀ =∇( ∇⋅ Π ⇀ )+ k 2 n 2 Π ⇀ H ⇀ =jω ε 0 n 2 ∇× Π ⇀ ,
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