Hyeong Woo Bae

High efficiency red top-emitting micro-cavity organic light emitting diodes

In this study, we present optical simulation versus real fabricated device results in the micro-cavity red top-emitting organic light emitting diodes (TEOLEDs). The optical simulation results indicate that the two kinds of possible emissive layer (EML) positions exist in the second order micro-cavity effect and each EMLs could emit the similar radiance with near National Television System Committee (NTSC) color coordinate. Expected current efficiency and external quantum efficiency by the optical simulation toward the surface normal in the red tandem TEOLED are 98.8 cd/A and 22.6% for two EMLs, while fabricated device shows 95.8 cd/A and 26.5%, respectively.

Spirobifluorene Core-Based Novel Hole Transporting Materials for Red Phosphorescence OLEDs

Two new hole transporting materials, named HTM 1A and HTM 1B, were designed and synthesized in significant yields using the well-known Buchwald Hartwig and Suzuki cross- coupling reactions. Both materials showed higher decomposition temperatures (over 450 °C) at 5% weight reduction and HTM 1B exhibited a higher glass transition temperature of 180 °C. Red phosphorescence-based OLED devices were fabricated to analyze the device performances compared to Spiro-NPB and NPB as reference hole transporting materials. Devices consist of hole transporting material as HTM 1B showed better maximum current and power efficiencies of 16.16 cd/A and 11.17 lm/W, at the same time it revealed an improved external quantum efficiency of 13.64%. This efficiency is considerably higher than that of Spiro-NPB and NPB-based reference devices.

Luminance uniformity study of OLED lighting panels depending on OLED device structures

This paper describes the luminance uniformity of OLED lighting panels depending on OLED device structures of single emission layer (single-EML), 2-tandem, and 3-tandem. The luminance distribution is evaluated through the circuit simulation and the fabricated panel measurement. In the simulation results with yellow-green color panels of 30 × 80 mm2 emission area, a 3-tandem structure shows the lowest non-uniformity (1.34% at 7.5V), compared to single-EML (5.67% at 2.8V) and 2-tandem (2.78% at 5.3 V) structures at 1,000 cd/m2. The luminance non-uniformity is germane to the OLED conductance showing that the high luminance-current efficiency is of the most importance to achieve the uniform voltage and luminance distribution. In measurement, a 3-tandem structure also achieves the most uniform luminance distribution with non-uniformity of 4.1% while single EML and 2-tandem structures accomplish 9.6%, and 6.4%, respectively, at ~1,000 cd/m2. In addition, the simulation results ensure that a 3-tandem structure panel is allowed to be enlarged the panel size up to about 5,000 mm2 for lower luminance non-uniformity than 10% without any auxiliary metal electrodes.