Enhanced Light Extraction from Bottom Emission OLEDs by High Refractive Index Nanoparticle Scattering Layer.

Park Park,Choi Choi

doi:10.3390/nano9091241

Abstract

High refractive index nanoparticle material was applied as a scattering layer on the inner side of a glass substrate of a bottom emission organic light emitting diode (OLED) device to enhance light extraction and to improve angular color shift. TiO2 and YSZ (Yttria Stabilized Zirconia; Y2O3-ZrO2) were examined as the high refractive index nanoparticles. The nanoparticle material was formed as a scattering layer on a glass substrate by a coating method, which is generally used in the commercial display manufacturing process. Additionally, a planarization layer was coated on the scattering layer with the same method. The implemented nanoparticle material and planarization material endured, without deformation, the subsequent thermal annealing process, which was carried out at temperature ranged to 580 °C. We demonstrated a practical and highly efficient OLED device using the conventional display manufacturing process by implementing the YSZ nanoparticle. We obtained a 38% enhanced luminance of the OLED device and a decreased angular color change compared to a conventional OLED device.

Highlights

In flat-panel display devices, organic light emitting diodes (OLEDs) are widely used, from mobile phones to large size TVs because OLED has excellent electro-optical properties for display products compared to widely used liquid crystal displays (LCDs)
The efficiency of OLED devices is an important factor for practical OLED display products
Several methods have been proposed to enhance the light extraction from OLEDs, including mesh structures on the glass substrate [8], silica micro spheres [9], scattering layers [10], embedded low-index grids [11], photonic crystals [12,13], micro pyramids [14], and micro lens arrays [15,16,17,18]

Summary

Introduction

In flat-panel display devices, organic light emitting diodes (OLEDs) are widely used, from mobile phones to large size TVs because OLED has excellent electro-optical properties for display products compared to widely used liquid crystal displays (LCDs). Several methods have been proposed to enhance the light extraction from OLEDs, including mesh structures on the glass substrate [8], silica micro spheres [9], scattering layers [10], embedded low-index grids [11], photonic crystals [12,13], micro pyramids [14], and micro lens arrays [15,16,17,18]. These methods could be used for limited applications such

Materials and Methods

Conclusions

Findings