Jwajin Kim

Efficient bipolar host materials based on carbazole and 2-methyl pyridine for use in green phosphorescent organic light-emitting diodes

Two host materials based on the carbazole/pyridine end-capping group were designed and synthesized to produce green phosphorescent organic light-emitting diodes. One of the host materials, 9-[9,9-diethyl-2-(6-methylpyridin-2-yl)-9H-fluoren-7-yl]-9H-carbazole (2), exhibited excellent properties for use in efficient green phosphorescent organic light-emitting diodes. A device using compound 2 as the host material with the green phosphorescence dopant bis[2-(1,1′,2′,1′′-terphen-3-yl)pyridinato-C,N]iridium(III)(acetylacetonate) had an external quantum efficiency of 10.7%, a power efficiency of 17.27 lm W−1 and a luminance efficiency of 39.72 cd A−1 at 20 mA cm−2, with CIE chromaticity coordinates of (0.34, 0.62) at 8.0 V.

9,9-Diethyl-N,N-diphenyl-9H-fluoren-2-amine derivatives end-capped with various aromatics as blue emitters for OLEDs

ABSTRACT To develop efficient blue emitters, we synthesized a series of 9,9-diethyl-N,N-diphenyl-9H-fluoren-2-amine derivatives end-capped with various aromatics using Suzuki coupling reaction and Buchwald-Hartwig amination. To investigate their electroluminescent properties, multilayer devices were fabricated in following structures: Indium-tin-oxide (ITO) (180 nm)/ N,N′-diphenyl-N,N′-(1-napthyl)-(1,1′-phenyl)-4,4′-diamine (NPB) (50 nm)/ blue emitters (30 nm)/ bathophenanthroline (Bphen) (30 nm)/ 8-hydroxyquinolatolithium (Liq) (2 nm)/ Al (100 nm). All devices showed the blue emissions. Particularly, a device using 9,9-diethyl-7-(10-(10-(naphthalen-2-yl)anthracen-9-yl)anthracen-9-yl)-N,N-diphenyl-9H-fluoren-2-amine showed the efficient blue emission with 5.12 cd/A, 2.33 lm/W, and 3.94% of a luminous, power, and external quantum efficiency at 20 mA/cm2, respectively and CIE (x, y) coordinates of (0.15, 0.15) at 6.0 V.

Electroluminescent properties of naphthalene end-capping bis-anthracene derivatives

ABSTRACT We designed naphthalene moieties end-capping bis-anthracene derivatives and characterized their photophysical properties. We fabricated two set of devices with the structure of ITO /2-TNATA (60 nm) /NPB (10 nm) /emitter (1–3) (40 nm) /Alq3 (15 nm) /Liq (2 nm) /Al for devices 1B–3B and same structure without 2-TNATA for 1A–3A. A device using 2-TNATA exhibited luminous efficiency of 5.98 cd/A, power efficiency of 3.09 lm/W and external quantum efficiency of 3.49% at 200 cd/m2, respectively, while a same device without 2-TNATA layer showed 3.52 cd/A, 1.79 lm/W, and 2.22% at 200 cd/m2, respectively.

Efficient hybrid white organic light-emitting diodes for application of triplet harvesting with simple structure

In this study, we fabricated hybrid white organic light-emitting diodes (WOLEDs) based on triplet harvesting with a simple structure. All the hole transporting material and host in the emitting layer (EML) of devices utilized the same material N,N′-di-1-naphthalenyl-N,N′-diphenyl [1,1′:4′,1″:4″,1‴-quaterphenyl]-4,4‴-diamine (4P-NPD), which is known to be blue fluorescent material. Simple hybrid WOLEDs were fabricated with blue fluorescent, green and red phosphorescent materials. We investigated the effect of triplet harvesting (TH) by an exciton generation zone on simple hybrid WOLEDs. The simple hybrid WOLEDs characteristically had a dominant hole mobility, so an exciton generation zone was expected in the EML. Additionally, the optimal the thickness of the hole transporting layer and electron transporting layer was fabricated a simple hybrid WOLEDs. The simple hybrid WOLED exhibits a maximum luminous efficiency of 29.3 cd/A and a maximum external quantum efficiency of 11.2%. The Commission Internationale de l′Éclairage (International Commission on Illumination) coordinates were (0.45, 0.43) at about 10,000 cd/m2.