• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.599-601
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• 2004

A new blue electroluminescent conjugated polymer, poly(BP-alt-BCV), was prepared by Hornor-Emmons polycondensation and used as a host polymer for the phosphorescent dopant, $(bsn)_2Ir(acac)$. Poly(N-vinylcarbazole) (PVK), known as a blue EL material, was also used for comparison with poly(BP-alt-BCV). Electrophosphorescence of PLEDs with these dopant/host systems was investigated in terms of luminescence, efficiency, emission color, and energy transfer.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.9
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• pp.682-685
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• 2013

We have fabricated blue phosphorescent organic light-emitting devices (OLEDs) on a plastic substrate. The solution coated poly (9-vinylcarbazole) (PVK) host doped with Bis (3,5-difluoro-2-(2-pyridyl)phenyl_(2-carboxypyridyl)irdium(III) (FIrPic) guest molecules was used as an hole transporting emission layer. The device structure was ITO/PVK:FIrpic (50 nm, xwt%)/TAZ 50 nm)/LiF (0.5 nm)/Al (100 nm). The concentration of FIrpic molecule was varied from 1 wt% to 10 wt%. The OLED on plastic substrate exhibited maximum current efficiency of 18 cd/A with 5 wt% FIrpic molecules were doped into the PVK layer.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.192-195
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• 2009

We developed highly efficient blue PHOLEDs with reduced roll-off by using a mixed host structure. The balanced charge carrier injection and the distributed recombination zone within emissive layer resulted in a highly stable efficiency roll-off with quantum efficiencies of 20.1 and 18.1 % at a luminance of 1000 and 10000 cd/$m^2$.

• Transactions on Electrical and Electronic Materials
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• v.12 no.2
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• pp.80-83
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• 2011

We have fabricated phosphorescent white organic light-emitting devices (WOLEDs) with a spin-coated poly(Nvinylcarbazole) [PVK] host layer. Iridium(III) bis[(4,6-difluorophenyl)-pyridinato-N,$C^{2'}$]picolinate (FIrpic), tris(2-phenylpyridine)iridium(III) [$Ir(ppy)_3$], and tris(2-phenyl-1-quinoline)iridium(III) [$Ir(phq)_3$], were used as the blue, green, and red guest materials, respectively. The PVK was mixed with FIrpic, $Ir(ppy)_3$, and $Ir(phq)_3$ molecules in a chlorobenzene solution and spin-coated in order to prepare the emission layer; 3-(4-biphenylyl)-4-phenyl-5-(4-tertbutylphenyl)-1,2,4-triazole (TAZ) was used as an electron transport material. The resultant device structure was ITO/PVK:FIrpic:$Ir(ppy)_3:Ir(phq)_3$/TAZ/LiF/Al. The electroluminescence, efficiency, and electrical conduction characteristics of the WOLEDs based on the doped PVK host layer were investigated. The maximum current efficiency of the three wavelength WOLED with the doped PVK host was 19.2 cd/A.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.767-770
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• 2009

We synthesized a spirobenzofluorene type phosphine oxide (SPPO2) as a new triplet host and an universal electron transport material for phosphorescent organic light-emitting diodes(PHOLEDs). Red PHOLEDs with the SPPO2 host material showed a high quantum efficiency of 14.3 % with a current efficiency of 20.4 cd/A. In addition, the SPPO2 could be applied as an electron transport material which can be matched with any host material due to the lowest unoccupied molecular orbital of 2.4 eV. Electron injection from a cathode to the SPPO2 electron transport layer was better than common electron transport materials. In particular, the SPPO2 was effective as the electron transport material in blue PHOLEDs and the quantum efficiency was more than doubled and driving voltage was lowered by more than 3 V using the SPPO2 instead of common electron transport material.

• Journal of the Korean institute of surface engineering
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• v.46 no.2
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• pp.93-97
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• 2013

We studied the emission characteristics of white phosphorescent organic light-emitting diodes (PHOLEDs), which were fabricated using a two-wavelength method. To optimize emission characteristics of white PHOLEDs, white PHOLEDs with co-doping and blue/co-doping emitting layer (EML) structures were fabricated using a host-dopant system. The total thickness of light-emitting layer was 25 nm and the dopant of blue and red was FIrpic and $Bt_2Ir(acac)$ in UGH3, respectively. In case of co-doping structure, applying micro lens array film showed efficiency improvement from the current efficiency 78.5 cd/A and power efficiency 40.4 lm/W to the current efficiency 131.1 cd/A and power efficiency 65 lm/W and blue / co-doping structure showed efficiency improvement from the current efficiency 43.8 cd/A and power efficiency 22 lm/W to the current efficiency 69 cd/A and power efficiency 32 lm/W.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.208-211
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• 2009

The authors have demonstrated the various characteristics of hybrid white organic light-emitting diodes (HWOLED) using fluorescent blue and phosphorescent red emitters. We also demonstrated that two devices showed different characteristics in accordance with thickness of the 4,4′-N,N′-dicarbazole-biphenyl (CBP) spacer (CS) inserted between the blue and the red emitting layer. It was found that the device with a CS thickness of 70 $\AA$ showed a current efficiency 2.5 times higher than that of the control device with a CS thickness of 30 $\AA$ by preventing the triplet Dexter energy transfer from the red to the blue emitting layer. The HWOLED with the CS thickness of 70 $\AA$ exhibited a maximum luminance of 24500 cd/$m^2$, a maximum current efficiency of 42.9 cd/A, a power efficiency of 37.5 lm/W, and Commission Internationale de I'Eclairage coordinates of (0.37, 0.42).

• Bulletin of the Korean Chemical Society
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• v.33 no.11
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• pp.3645-3650
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• 2012

Two new blue emitting cationic iridium(III) complexes with two substituted 2-phenlypyridine ligands as main ligands and one 2,2'-biimidazole as an ancillary ligand, $[(L1)_2Ir(biim)]Cl$ (1) and $[(L2)_2Ir(biim)]Cl$ (2), where L1 = 2-(2',4'-difluorophenyl)-4-methylpyridine, L2 = 2-(2',4'-difluoro-3'-trifluoromethylphenyl)-4-methylpyridine and biim = 2,2'-biimidazole, were synthesized for applications in phosphorescent organic light-emitting diodes (PhOLEDs). Their photophysical, electrochemical and electroluminescent (EL) device performances were examined. The photoluminescent (PL) spectra revealed blue phosphorescence in the 450 to 485 nm range with a quantum yield of more than 10%. The iridium(III) compounds studied showed good solubility in organic solvents with no solvatochromism dependent on the solvent polarity. The solution-processed OLEDs were prepared with the configuration, ITO/PEDOT:PSS (40 nm)/mCP:Ir(III) (70 nm)/OXD-7 (20 nm)/LiF (1 nm)/Al (100 nm), by spin coating the emitting layer containing the mCP host doped with the iridium phosphors. The best performance of the fabricated OLEDs based on compound 1 showed an external quantum efficiency of 4.5%, luminance efficiency of 8.52 cd $A^{-1}$ and blue emission with the CIE coordinates (x,y) of (0.16, 0.33).

• Korean Chemical Engineering Research
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• v.49 no.3
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• pp.325-329
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• 2011

$Ir(pmb)_{3}$(Iridium(III)Tri(1-phenyl-3-methylbenzimidazolin-2-ylidene-$C,C^{2'}$ ) was synthesized to develop a deep blue-emitting Ir(III) complex. We suggested the ultrasonic reactor to enhance the poor reaction yield of $Ir(pmb)_{3}$. The ultrasonic wave enhanced the reaction yield of $Ir(pmb)_{3}$ because the ultrasound helped non-soluble reactants disperse efficiently and produced free radial during the reaction. The maximum yield of $Ir(pmb)_{3}$ was 42.5%, which was 4 times higher than conventional method. Organic light emitting devices were fabricated with the synthesized mer-$Ir(pmb)_{3}$ which emitted at 405 nm. A range of host materials with large bandgaps (UGH2, mCP and CBP) were tested for developing a deep blue emitting device. In case of the device with mCP as the host material, it emitted deep blue and performed quite well relative to the other host materials tested.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.6
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• pp.486-490
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• 2011

To investigate the effect of two-emission-layer structure on the emission characteristics of the phosphorescent white organic light-emitting diodes (PHWOLEDs), the PHWOLEDs with two different emission layers, blue EML(29 nm, FIrpic-doped mCP) and red EML(1 nm, Ir(pq)$_2$acac-doped CBP)), following host-guest system were fabricated. The bi-layered blue EML was composed of mCP:FIrpic (20 nm, 7 vol.%) and mCP:FIrpic (9 nm, 7, 10, 15, 20, and 25 vol.%, respectively). When the concentration of FIrpic was increased from 7 to 15 vol.%, light emission luminance, current efficiency, and external quantum efficiency were increased. On the contrary, when the concentration of FIrpic was increased to more than 20 vol.%, light emission luminance, current efficiency, and external quantum efficiency were decreased. The PHWOLEDs with the bi-layered blue EML structure of mCP:FIrpic (20 nm, 7 vol.%) and mCP:FIrpic (9 nm, 15 vol.%) showed current efficiency of 29.7 cd/A and external quantum efficiency (EQE) of 16.6% at 1,000 $cd/cm^2$.