Gu Young Kim

Ligand Effects on Luminescence of New Type Blue Light-Emitting Mono(2-phenylpyridinato)iridium(III) Complexes

Newly prepared hydrido iridium(III) complexes [Ir(ppy)(PPh3)2(H)L](0,+) (ppy = bidentate 2-phenylpyridinato anionic ligand; L = MeCN (1b), CO (1c), CN(-) (1d); H being trans to the nitrogen of ppy ligand) emit blue light at the emission lambda(max) (452-457, 483-487 nm) significantly shorter than those (468, 495 nm) of the chloro complex Ir(ppy)(PPh3)2(H)(Cl) (1a). Replacing ppy of 1a-d with F2ppy (2,4-difluoro-2-phenylpyridinato anion) and F2Meppy (2,4-difluoro-2-phenyl-m-methylpyridinato anion) brings further blue-shifts down to the emission lambda(max) at 439-441 and 465-467 nm with CIE color coordinates being x = 0.16 and y = 0.18-0.20 to display a deep-blue photoemission. No significant blue shift is observed by replacing PPh3 of 1a with PPh2Me to produce Ir(ppy)(PPh2Me)2(H)(Cl) (1aPPh 2Me), which displays emission lambda max at 467 and 494 nm. The chloro complexes, [Ir(ppy)(PPh3)2(Cl)(L)](0,+) (L = MeCN (2b), CO (2c), CN(-) (2d)) having a chlorine ligand trans to the nitrogen of ppy also emit deep-blue light at emission lambda(max) 452-457 and 482-487 nm.

Dependence of Effective Doping Concentration on the Molecular Structure of Dopant: ABCV-P Doped OLEDs with Broad Range of and High Doping Concentration

A new red fluorescent material, (2Z,2′Z)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′,1″-terphenyl-2′,5′-diyl]bis(2-phenylacrylonitrile) (ABCV-P), preventing concentration quenching in solid state was synthesized. Studies on the device performance of ABCV-P doped OLEDs with variation of the doping concentration and thickness of the emitting layer as well as the optical properties of ABCV-P were carried out. The effective doping concentration of ABCV-P dopant was in the range of 40%–50%. ABCV-P doped OLEDs showed maximum luminance of 11000 cd/m2 (40%) and 6800 cd/m2 (50%), CIExy coordinates of (0.588, 0.410) (40%) and (0.597, 0.402) (50%) and full width at half maxima of 71 nm and 72.5 nm, respectively. Accordingly, ABCV-P doped OLED showed much lower sensitivity to doping concentration than the typical red doped ones.

A Study on the Phosphorescent Blue Organic Light-Emitting Diodes Using Various Host Materials

We investigated the electrical characteristics of three devices which were fabricated with phosphorescent blue emitter, iridium(III) bis(4,6-difluorophenylpyridinato-N,C2′)picolinate (FIrpic), doped in host materials, 4,4,N,N′-dicarbazolebiphenyl (CBP), N,N′-dicarbazolyl-3,5-benzene (mCP) of the carbazole-type and p-bis(triphenylsilyly)benzene (UGH2) of the wide-energy-gap, respectively. We demonstrated the efficient blue electrophosphorescence using exothermic energy transfer between mCP and FIrpic with triplet energy level of 2.90 eV and 2.65 eV, respectively. Device property for a mCP-based structure was found to be superior to that employing the endothermic host-guest combination consisting of the CBP and FIrpic with triplet energy level of 2.57 eV and 2.65 eV, respectively. In case the device with UGH2, despite of the very wide band gap (4.40 eV), it is inefficient given the large energy barrier (1.70 eV) for hole injection into the highest occupied molecular orbital (HOMO) of UGH2 as the drive voltage increases. The device with mCP host material shows a maximum luminous efficiency and power efficiency of 17.00 cd/A and 10.9 lm/W, respectively.

The Structure Optimization of White Organic Light-Emitting Diodes for High Efficiency

We have demonstrated the structure optimization of white organic light-emitting diodes with two separated emissive layers for better efficiency. For efficient optimization of white organic light-emitting diodes, we carried out a insertion of hole buffer layer, a thickness change of emission layer, and a change of electron transport layer. The optimized device showed maximum luminance of 29 600 cd/m2 at 14 V and the maximum luminous efficiency of 14.30 cd/A at 7.34 mA/cm2, respectively. All devices showed white emission at operating voltages without change of CIEx,y coordinates.

Asymmetric Monotriphenylamine-Substituted Anthracenes for Blue-Organic Light-Emitting Diodes

A series of blue fluorescent materials based on asymmetric mono-triphenylamine-substituted anthracenes have been synthesized and characterized using spectroscopic analysis. Multilayered organic light-emitting diodes (OLED) were fabricated using these materials as dopants. A maximum luminance of 27900 cd/m2 at 11 V and a luminous efficiency of 10.1 cd/A at 20 mA/cm2 were achieved. The peak wavelength of the electroluminescence was 459 nm with CIE coordinates of (0.174, 0.288) at 10 V and the device also showed a stable color chromaticity at various voltages.