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Enhanced optical efficiency and color purity for organic light-emitting diodes by finely optimizing parameters of nanoscale low-refractive index grid

Authors
  • Kim, Jae Geun1
  • Hwang, Yooji1
  • Hwang, Ha1
  • Choi, Jun Hee1
  • Park, Young Wook2
  • Ju, Byeong-Kwon1
  • 1 Display and Nanosystem Laboratory, School of Electrical Engineering, Korea University, Seoul, 02841, Republic of Korea , Seoul (South Korea)
  • 2 The School of Mechanical and ICT Convergence Engineering, SUN MOON University, Chungcheongnam-do, 31460, Republic of Korea , Chungcheongnam-do (South Korea)
Type
Published Article
Journal
Scientific Reports
Publisher
Springer Nature
Publication Date
Mar 27, 2020
Volume
10
Issue
1
Identifiers
DOI: 10.1038/s41598-020-62470-5
Source
Springer Nature
License
Green

Abstract

To extract the confined waveguided light in organic light-emitting diodes (OLEDs), inserting a low refractive index (RI) periodic structure between the anode and organic layer has been widely investigated as a promising technology. However, the periodic-structure-based light extraction applied inside devices has been shown to severely distort spectrum and affect EL characteristics. In this study, a simple light extraction technology using periodic low-RI nanodot array (NDA) as internal light extraction layer has been demonstrated. The NDA was fabricated simply via laser interference lithography (LIL). The structural parameters of periodic pattern, distance, and height were easily controlled by the LIL process. From computational analysis using finite-difference time-domain (FDTD) method, the NDA with 300 nm pitch and 0.3 coverage ratio per unit cell with 60 nm height showed the highest enhancement with spectral-distortion-minimized characteristics. Through both computational and experimental systematic analysis on the structural parameters of low-RI NDA-embedded OLEDs, highly efficient OLEDs have been fabricated. Finally, as representative indicators, hexagonal and rectangular positioned NDA-embedded OLEDs showed highly improved external quantum efficiencies of 2.44 (+29.55%) and 2.77 (+57.38%), respectively. Furthermore, the disadvantage originating from the nanoscale surface roughness on the transparent conductive oxide was minimized.

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