• Polymer(Korea)
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• v.32 no.4
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• pp.372-376
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• 2008

Vacuum deposited 4,4',4"-tris(N-(2-naphthyl)-N-phenylamino)-triphenylamine (2-TNATA), used as a hole injection (HIL) material in OLEDs, is placed as a thin interlayer between indium tin oxide (ITO) electrode and a hole transporting layer (HTL) in the devices. C60-doped 2-TNATA:C60 (20 wt%) film was formed via co-evaporation process and molecular ordering and topology of 2-TNATA:C60 films were investigated using XRD and AFM. The J-V, L-V and current efficiency of multi-layered devices were characterized as well. Vacuum-deposited C60 film was molecularly oriented, but neither was 2-TNATA:C60 film due to the uniform dispersion of C60 molecules in the film. By using C60-doped 2-TNATA:C60 film as a HIL, the current density and luminance of a multi-layered ITO/2-TNATA:C60/NPD/$Alq_3$/LiF/Al device were significantly increased and the current efficiency of the device was increased from 4.7 to 6.7 cd/A in the present study.

• Bulletin of the Korean Chemical Society
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• v.26 no.11
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• pp.1807-1818
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• 2005

New PPV based conjugated polymers, containing terphenyl units, were prepared as the electroluminescent (EL) layer in light-emitting diodes (LEDs). The prepared polymers, poly[2,5-bis(4-(2-etylhexyloxy)phenyl)-1,4-phenylenevinylene] (BEHP-PPV), poly[2-(2-ethylhexyloxy)-5-(4-(4-(2-etylhexyloxy)phenyl)phenyl)-1,4-phenylenevinylene] (EEPP-PPV) and poly[2-(2-ethylhexyloxy)-5-(9,9-bis(2-etylhexyl)fluorenyl)-1,4 phenylenevinylene] (EHF-PPV), were soluble in common organic solvents and used as the EL layer in double layer light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). The polymers were prepared by the Gilch reaction. The number-average molecular weight $(M_n)$, weight-average molecular weight $(M_w)$, and the polydispersities (PDI) of these polymers were in the range of 9000-58000, 27000-231000, 2.9-3.9, respectively. These polymers have quite good thermal stability with decomposition starting above 320-350. The polymers show photoluminescence (PL) with maximum peaks at around 526-562 nm (exciting wavelength, 410 nm) and blue EL with maximum peaks at around $\lambda_{max}$ = 526-552 nm. The current-voltageluminance (I-V-L) characteristics of polymers show turn-on voltages of 5 V. Even though both of EEPP-PPV and BEHP-PPV have the same terphenyl group in the repeating unit, EEPP-PPV with directly substituted alkoxy group in the back bone has longer effective conjugation length than BEHP-PPV, and exhibits red shift in the PL spectra. Both of EEPP-PPV and EHF-PPV have ter-phenyl units and directly substituted alkoxy group in back bone. EHF-PPV with fluorenyl unit attached to the PPV backbone has shorter effective conjugation length than EEPP-PPV with biphenyl unit, and exhibits blue shift in the PL spectra.

• Polymer(Korea)
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• v.33 no.5
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• pp.407-412
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• 2009

Vacuum deposited N,N-di-1-naphthyl-N,N-diphenyl-1,1'-biphenyl-4,4'-diamine (NPD) as a hole transporting (HTL) materials in OLEDs was placed on PEDOT-PSS, a hole injection layer (HIL). PEDOT-PSS was spin-coated on to the ITO glass. $C_{60}$-doped NPD-$C_{60}$(10 wt%) film was formed via co-evaporation process and the morphology of NPD-$C_{60}$ films was investigated using XRD and AFM. The J - V, L - V and current efficiency of multi -layered devices were characterized. According to XRD results, the deposited $C_{60}$ thin film was partially crystalline, but NPD-$C_{60}$ film was observed not to be crystalline, which indicates that $C_{60}$ molecules are uniformly dispersed in the NPD film. By using $C_{60}$-doped NPD-$C_{60}$ film as a HTL, the current density and luminance of multi-layered ITO/PEDOT-PSS/NPD-$C_{60}/Alq_3$/LiF/Al device were significantly increased by about 80% and its efficiency was improved by about 25% in this study.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.11-11
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• 2008

ZnO has a very large exciton binding energy (60 meV) as well as thermal and chemical stability, which are expected to allow efficient excitonic emission, even at room temperature. ZnO based electronic devices have attracted increasing interest as the backplanes for applications in the next-generation displays, such as active-matrix liquid crystal displays (AMLCDs) and active-matrix organic light emitting diodes (AMOLEDs), and in solid state lighting systems as a substitution for GaN based light emitting diodes (LEDs). Most of these electronic devices employ the electrical behavior of n-type semiconducting active oxides due to the difficulty in obtaining a p-type film with long-term stability and high performance. p-type ZnO films can be produced by substituting group V elements (N, P, and As) for the O sites or group I elements (Li, Na, and K) for Zn sites. However, the achievement of p-type ZnO is a difficult task due to self-compensation induced from intrinsic donor defects, such as O vacancies (Vo) and Zn interstitials ($Zn_i$), or an unintentional extrinsic donor such as H. Phosphorus (P) doped ZnO thin films were grown on c-sapphire substrates by radio frequency magnetron sputtering with various Ar/ $O_2$ gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio with out post-annealing. The P-doped ZnO films grown at a Ar/ $O_2$ ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of $10^{-17}cm^{-3}$ and $2.5cm^2/V{\cdot}s$, respectively. X-ray diffraction showed that the ZnO (0002) peak shifted to lower angle due to the positioning of $p^{3-}$ ions with a smaller ionic radius in the $O^{2-}$ sites. This indicates that a p-type mechanism was due to the substitutional Po. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction LEO showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.117-122
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• 2016

White organic light-emitting diodes with a structure of indium-tin-oxide [ITO]/N,N-diphenyl-N,N-bis-[4-(phenylm-tolvlamino)-phenyl]-biphenyl-4,4-diamine [DNTPD]/[2,3-f:2, 2-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile [HATCN]/1,1-bis(di-4-poly-aminophenyl) cyclo -hexane [TAPC]/emission layers doped with three color dopants/4,7-diphenyl-1,10-phenanthroline [Bphen]/$Cs_2CO_3$/Al were fabricated and evaluated. In the emission layer [EML], N,N-dicarbazolyl-3,5-benzene [mCP] was used as a single host and bis(2-phenyl quinolinato)-acetylacetonate iridium(III) [Ir(pq)2acac]/fac-tris(2-phenylpyridinato) iridium(III) $[Ir(ppy)_3]$/iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate [FIrpic] were used as red/green/blue dopants, respectively. The fabricated devices were divided into five types (D1, D2, D3, D4, D5) according to the structure of the emission layer. The electroluminescence spectra showed three peak emissions at the wavelengths of blue (472~473 nm), green (495~500 nm), and red (589~595 nm). Among the fabricated devices, the device of D1 doped in a mixed fashion with a single emission layer showed the highest values of luminance and quantum efficiency at the given voltage. However, the emission color of D1 was not pure white but orange, with Commission Internationale de L'Eclairage [CIE] coordinates of (x = 0.41~0.45, y = 0.41) depending on the applied voltages. On the other hand, device D5, with a double emission layer of $mCP:[Ir(pq)_2acac(3%)+Ir(ppy)_3(0.5%)]$/mCP:[FIrpic(10%)], showed a nearly pure white color with CIE coordinates of (x = 0.34~0.35, y = 0.35~0.37) under applied voltage in the range of 6~10 V. The luminance and quantum efficiency of D5 were $17,160cd/m^2$ and 3.8% at 10 V, respectively.