• Bulletin of the Korean Chemical Society
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• v.30 no.9
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• pp.2057-2060
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• 2009

Conducting poly-N-isopropylacrylamide-N-vinyl carbazole (PNI-nvc) copolymers were synthesized via in situ deposition technique by dissolving different weight percentages of N-vinyl carbazole (10, 20, 30, and 40%). The structural morphology and FT-IR studies support the interaction between PNI and N-vinyl carbazole. The temperaturedependent DC conductivity of PNI-nvc was studied within the range of 300 ${\leq}\;T\;{\leq}$ 500 K, presenting evidence for the transport properties of PNI-nvc. The DC conductivity of PNI-nvc copolymers signifies the future development of new nanocopolymers that acts as a multifunctional material.

• Proceedings of the Korean Vacuum Society Conference
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• 2008.02a
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• pp.204-204
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• 2008

• Journal of Adhesion and Interface
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• v.18 no.3
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• pp.109-117
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• 2017

Poly(N-vinyl carbazole) (PVK) homopolymer, poly(4-vinylpyridine) (PVP) homopolymer, and PVK-b-PVP block copolymer were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and the polymers were used to prepare non-aqueous graphene dispersions with four different solvents, ethanol, N-methyl-2-pyrrolidone (NMP), dichloromethane (DCM), and tetrahydrofuran (THF). $^1H-$ and $^{13}C-NMR$ spectroscopy, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) were carried out to confirm the chemical structure of the polymers. Stability of graphene dispersions was measured by on-line turbidity measurement. Time-dependent Turbiscan Stability Index (TSI) values were interpreted in terms of surface tension (${\sigma}$) and solubility parameter (${\delta}$) among solvents, polymers, and graphene. It was confirmed that the solubilities of polymer and surface tension between solvent and graphene affected the dispersion stability of graphene. PVK-b-PVP block copolymer could effectively maintain the low TSI values of graphene dispersions in ethanol and THF, which have been known as poor solvents for graphene dispersions. It can also be noted that DCM shows good dispersion stability comparable to NMP, which has been known as the best solvent for graphene dispersion.

• Journal of the Microelectronics and Packaging Society
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• v.13 no.4
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• pp.51-56
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• 2006

Polymer light emitting diodes (PLEDs) with ITO/EDOT:PSS/PVK/PFO-poss/LiF/Al structures were prepared by the spin coating method on ITO(indium tin oxide)/glass substrates. PFO-poss[Poly(9,9-dioctylfluorenyl-2,7-diyl) end capped with poss] was used as light emitting polymer. PVK[poly(N-vinyl carbazole)] and PEDOT:PSS [poly(3,4-ethylenedioxythiophene):poly(styrene sulfolnate)] polymers were used as the hole injection and transport materials. The effect of PFO-poss concentration and the heating temperatures on the electrical and optical properties of the devices were investigated. At the same concentration of PFO-poss solution, the current density and luminance of PLED device tend to increase as the annealing temperature increase from $100^{\circ}C$ to $200^{\circ}C$. The maximum luminance was found to be about 958 cd/m2 at 13V for the PLED device with 1.0 wt% PFO-poss at the annealing temperature of $200^{\circ}C$. In addition, the PLED device showed bluish white emission through the strong greenish peak with 523 nm in wavelength. As the concentration of PFO-poss increase from 0.5 wt% to 1.0 wt% and temperature of PLEDs increase from $100^{\circ}C$ to $200^{\circ}C$, the emission color tend to be shifted from blue with (x, y) = (0.17,0.14) to bluish white with (x, y) : (0.29,0.41) in CIE color coordinate.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2006.10a
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• pp.154-157
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• 2006

ITO(indium tin oxide)/glass 기판 위에 PEDOT:PSS[poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)]와 PVK[poly(N-vinyl carbazole)] 고분자 물질을 정공 주입 및 수송층으로, 발광층으로 PFO-poss[Poly(9,9-dioctylfluorenyl-2,7-diyl) end capped with POSS]를 사용하여 스핀코팅법과 열 증착법으로 ITO/PEDOT:PSS/PVK/PFO-poss/LiF/Al 구조의 고분자 발광 다이오드를 제작하였다. PFO-poss 유기발광 층의 열처리 조건 (온도, 시간)이 PLED 소자의 전기적, 광학적 특성에 미치는 영향을 조사하였다. 1 wt%의 농도를 갖는 PFO-poss 유기물 발광 층을 200C 온도로 3시간 열처리 할 경우 11 V 인가전압에서 $1497\;cd/m^2$의 최대 휘도를 나타내었다. 동일온도에서 열처리 시간을 1시간에서 3시간으로 증가시킬 경우 휘도의 증가와 함께 발광 개시온도가 감소하는 경향을 보여주었다. 또한 열처리 온도와 시간을 증가시킬 경우 제2발광피크인 excimer 피크가 크게 나타났으며 청색에서 황색 발광 쪽으로 천이되는 경향을 나타내었다.

• Transactions on Electrical and Electronic Materials
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• v.6 no.3
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• pp.101-105
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• 2005

Electroluminescence(EL) and current-voltage(I-V) characteristics of hybrid EL devices containing Pr and Mn co-doped ZnS nanoparticles were investigated in this study. For the insertion of a hole transport layer of poly (N-vinyl carbazole)(PVK), the current level became lower due to the accumulation of electrons at the interface between PVK and nanoparticles. When both PVK and buffer layer $BaF_2$ were simultaneously introduced, the enhanced EL efficiency and improved I-V characteristics were obtained. This results from the additional increase of hole injection owing to the internal field induced by the significant accumulation of electrons at the interface. The presence of buffer layer $BaF_2$ together with PVK makes it possible the charge accumulation enough to induce the sufficient internal field for further hole injection.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1511-1514
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• 2009

Organic light emitting layer in OLED device was formed by gravure printing process in this work. Organic surface coated by gravure printing typically showed relatively bad uniformity. Thickness and roughness control was characterized by applying various mixed solvents in this work. Poly (N-vinyl carbazole) (PVK) and fact-tris(2-phenylpyridine)iridium($Ir(ppy)_3$) are host dopant system materials. PVK was used as a host and Ir(ppy)3 as green-emitting dopant. To luminance efficiency of the plasma treatment on etched ITO glass and then PEDOT:PSS spin coated. The device layer structure of OLED devices is as follow Glass/ITO/PEDOT:PSS/PVK+Ir(ppy)3-Active layer /LiF/Al. It was printed by gravure printing technology for polymer light emitting diode (PLED). To control the thickness multi-printing technique was applied. As the number of the printing was increased the thickness enhancement was increased. To control the roughness of organic layer film, thermal annealing process was applied. The annealing temperature was varied from room temperature, $40^{\circ}C$, $80^{\circ}C$, to $120^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.65-65
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• 2015

In this talk, I will introduce two topics. The first topic is the polymer light emitting diodes (PLEDs) using graphene oxide quantum dots as emissive center. More specifically, the energy transfer mechanism as well as the origin of white electroluminescence in the PLED were investigated. The second topic is the facile synthesis of eco-friendly III-V colloidal quantum dots and their application to light emitting diodes. Polymer (organic) light emitting diodes (PLEDs) using quantum dots (QDs) as emissive materials have received much attention as promising components for next-generation displays. Despite their outstanding properties, toxic and hazardous nature of QDs is a serious impediment to their use in future eco-friendly opto-electronic device applications. Owing to the desires to develop new types of nanomaterial without health and environmental effects but with strong opto-electrical properties similar to QDs, graphene quantum dots (GQDs) have attracted great interest as promising luminophores. However, the origin of electroluminescence (EL) from GQDs incorporated PLEDs is unclear. Herein, we synthesized graphene oxide quantum dots (GOQDs) using a modified hydrothermal deoxidization method and characterized the PLED performance using GOQDs blended poly(N-vinyl carbazole) (PVK) as emissive layer. Simple device structure was used to reveal the origin of EL by excluding the contribution of and contamination from other layers. The energy transfer and interaction between the PVK host and GOQDs guest were investigated using steady-state PL, time-correlated single photon counting (TCSPC) and density functional theory (DFT) calculations. Experiments revealed that white EL emission from the PLED originated from the hybridized GOQD-PVK complex emission with the contributions from the individual GOQDs and PVK emissions. (Sci Rep., 5, 11032, 2015). New III-V colloidal quantum dots (CQDs) were synthesized using the hot-injection method and the QD-light emitting diodes (QLEDs) using these CQDs as emissive layer were demonstrated for the first time. The band gaps of the III-V CQDs were varied by varying the metal fraction and by particle size control. The X-ray absorption fine structure (XAFS) results show that the crystal states of the III-V CQDs consist of multi-phase states; multi-peak photoluminescence (PL) resulted from these multi-phase states. Inverted structured QLED shows green EL emission and a maximum luminance of ~45 cd/m2. This result shows that III-V CQDs can be a good substitute for conventional cadmium-containing CQDs in various opto-electronic applications, e.g., eco-friendly displays. (Un-published results).