• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.340-343
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• 2002

We report here our recent progress in the development and commercialization of polyfluorenes emitting red, green and blue (ROB) colors as materials for light emitting diodes (LEDs). Our patented version of the Suzuki coupling process has been used to synthesize a variety of fluorenebased homopolymers and copolymers emitting colors across the entire visible spectrum. The optical and electronic properties of the polymers are tailored through selective incorporation of different aromatic units into the polyfluorene backbone. Our latest green emitter, reported herein, provides very efficient devices with a low turn-on voltage of 2.25 V, a peak efficiency of 10.5 Cd/A at 6,600 Cd/$m^2$ at 4.85 V. These devices maintain an efficiency of greater than 10 Cd/A up to 50,000 Cd/$m^2$ and demonstrate very good stability as exemplified by a device half-life of greater than 1,500 hours starting from 1,100 Cd/$m^2$. Considerable progress has also been made with red and blue emitters and will be the subject of this presentation.

• Journal of Life Science
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• v.32 no.7
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• pp.578-587
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• 2022

Korea, as the world's 7^th largest emitter of greenhouse gases, has raised the national greenhouse gas reduction target as international regulations have been strengthened. As it is possible to utilize coastal and marine ecosystems as important nature-based solutions (NbS) for implementing climate change mitigation or adaptation plans, the blue carbon ecosystem is now receiving attention. Blue carbon refers to carbon that is deposited and stored for a long period after carbon dioxide (CO₂) is absorbed as biomass by coastal ecosystems or oceanic ecosystems through photosynthesis. Currently, there are only three blue carbon ecosystems officially recognized by the Intergovernmental Panel on Climate Change (IPCC): mangroves, salt marshes, and seagrasses. However, the results of new research on the high CO₂ sequestration and storage capacity of various new blue carbon sinks, such as seaweeds, microalgae, coral reefs, and non-vegetated tidal flats, have been continuously reported to the academic community recently. The possibility of IPCC international accreditation is gradually increasing through scientific verification related to calculations. In this review, the current status and potential value of seaweeds, seagrass fields, and non-vegetated tidal flats, which are sources of blue carbon on the east coast, are discussed. This paper confirms that seaweed resources are the most effective NbS in the East Sea of Korea. In addition, we would like to suggest the direction of research and development (R&D) and utilization so that new blue carbon sinks can obtain international IPCC certification in the near future.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.11
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• pp.55-61
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• 1998

Organic light emitting devices from a single layer thin film with a hole transport polymer, poly(N-vinylcarbazole) (PVK) doped with 2-(4-bi phenyl)-5-(4-t-butyl-phenyl) -1,3,4-oxadiazole (Bu-PBD) as electron transporting molecules and Coumurine 6(C6), 1,1,4,4-tetraphenyl-1,3-butadiene (TPB), Rhodamine B as a emitter dye were fabricated. The sing1e layer structure and the use of soluble materials simplify the fabrication of devices by spin coating technique. The active layer consists of one polymer layer that is simply sandwiched between two electrodes, indium-tin oxide (ITO), and aluminum. In this structure, electron and hole inject from the electrodes to the PVK : Bu-PBD active layer. Respectively, Blue, green and orange colored emission spectrum by the use of TPB, C6, Rhodamine B dye emitted at 481nm, 500nm and 585nm were achieved during applied voltages. PVK materials can be useful as the host polymer to be molecularly doped with other organic dyes of the different luminescence colors. And EL color can be tuned to the full visible wavelength.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.3
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• pp.192-197
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• 2017

Hydrogenated Amorphous Silicon (a-Si:H) is used as an emitter layer in HIT (heterojunction with Intrinsic Thin layer) solar cells. Its low band gap and low optical properties (low transmittance and high absorption) cause parasitic absorption on the front side of a solar cell that significantly reduces the solar cell blue response. To overcome this, research on CSC (carrier Selective Contacts) is being actively carried out to reduce carrier recombination and improve carrier transportation as a means to approach the theoretical efficiency of silicon solar cells. Among CSC materials, molybdenum oxide ($MoO_x$) is most commonly used for the hole transport layer (HTL) of a solar cell due to its high work function and wide band gap. This paper analyzes the electrical and optical properties of $MoO_x$ thin films for use in the HTL of HIT solar cells. The optical properties of $MoO_x$ show better performance than a-Si:H and ${\mu}c-SiO_x:H$.

• Journal of the Korean Applied Science and Technology
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• v.29 no.3
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• pp.459-465
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• 2012

We had synthesized a green dopant material based on the binaphthyl group, 7,7'-(2,2'dimethoxy-1,1'-binaphthyl-3,3'-diyl) bis(4-(thiophen -2-yl) benzo[e][1,2,5] thiadiazole (TBT). We also fabricated the white organic light emitting diode (OLED) with a phosphorescent blue emitter : iridium(III)bis[(4,6-di-fluoropheny)-pyridinato -N,C2]picolinate (FIrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) of hole transport type host material and both TBT and bis(2-phenylquinolinato)- acetylacetonate iridium(III) (Ir(pq)2acac) doped in 1,3,5-tris(N-phenylbenzimidazole -2-yl)benzene (TPBi) of electron transport type host material. As a result, the property of white OLED using TBT, which demonstrated a maximum luminous efficiency and external quantum efficiency of 5.94 cd/A and 3.23 %, respectively. It also showed the pure white emission with Commission Internationale de I'Eclairage (CIE) coordinates of (0.34, 0.36) at 1000 nit.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.11.2-11.2
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• 2011

Polymer based organic photovoltaics have attracted a great deal of attention due to the potential cost-effectiveness of light-weight and flexible solar cells. However, most BHJ polymer solar cells are not thermally stable as subsequent exposure to heat drives further development of the morphology towards a state of macrophase separation in the micrometer scale. Here we would like to show three different approaches for developing new electroactive polymers to improve the thermal stability of the BHJ solar cells, which is a critical problem for the commercialization of these solar cells. For one of the examples, we report a new series of functionalized polythiophene (PT-x) copolymers for use in solution processed organic photovoltaics (OPVs). PT-x copolymers were synthesized from two different monomers, where the ratio of the monomers was carefully controlled to achieve a UV photo-crosslinkable layer while leaving the ${\pi}-{\pi}$ stacking feature of conjugated polymers unchanged. The crosslinking stabilizes PT-x/PCBM blend morphology preventing the macro phase separation between two components, which lead to OPVs with remarkably enhanced thermal stability. The drastic improvement in thermal stabilities is further characterized by microscopy as well as grazing incidence X-ray scattering (GIXS). In the second part of talk, we will discuss the use of block copolymers as active materials for WOLEDs in which phosphorescent emitter isolation can be achieved. We have exploited the use of triarylamine (TPA) oxadiazole (OXA) diblock copolymers (TPA-b-OXA), which have been used as host materials due to their high triplet energy and charge-transport properties enabling a balance of holes and electrons. Organization of phosphorescent domains in TPA-b-OXA block copolymers is demonstrated to yield dual emission for white electroluminescence. Our approach minimizes energy transfer between two colored species by site isolation through morphology control, allowing higher loading concentration of red emitters with improved device performance. Furthermore, by varying the molecular weight of TPA-b-OXA and the ratio of blue to red emitters, we have investigated the effect of domain spacing on the electroluminescence spectrum and device performance.

• Analytical Science and Technology
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• v.34 no.3
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• pp.128-133
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• 2021

During titration, several chemical reactions result in changes not only in the potential of chemicals, but also in the colors of the indicator. In a potentiometric titration, a titration curve is obtained by measuring the abrupt change in the potential at the endpoint. Generally, acid-base titration is performed by observing the color change caused by an indicator to determine the endpoint. The method of determining the endpoint by measuring the potential difference has been well established and commercialized; however, the devices that can obtain the endpoint by observing the color change are limited. Consequently, in this study, a simple and precise spectral endpoint detector was manufactured using a drop-counter comprising an infrared emitter and a phototransistor, a white light LED as the light source and photodetector, and an analog-to-digital converter (Arduino). Spectrator, a new named, showed excellent results in terms of the reproducibility of acid-base titration using thymol blue as an indicator. Herein, we present the results of the Spectrator-manufacturing process as well as the experimental results.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.293-293
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• 2014

Over last decade InGaN alloy structures have become the one of the most promising materials among the numerous compound semiconductors for high efficiency light sources because of their direct band-gap and a wide spectral region (ultraviolet to infrared). The primary cause for the high quantum efficiency of the InGaN alloy in spite of high threading dislocation density caused by lattice misfit between GaN and sapphire substrate and severe built-in electric field of a few MV/cm due to the spontaneous and piezoelectric polarizations is generally known as the strong exciton localization trapped by lattice-parameter-scale In-N clusters in the random InGaN alloy. Nonetheless, violet-emitting (390 nm) conventional low-In-content InGaN/GaN multi-quantum wells (MQWs) show the degradation in internal quantum efficiency compared to blue-emitting (450 nm) MQWs owing higher In-content due to the less localization of carrier and the smaller band offset. We expected that an improvement of internal quantum efficiency in the violet region can be achieved by replacing the conventional low-In-content InGaN/GaN MQWs with ultra-thin, high-In-content (UTHI) InGaN/GaN MQWs because of better localization of carriers and smaller quantum-confined Stark effect (QCSE). We successfully obtain the UTHI InGaN/GaN MQWs grown via employing the GI technique by using the metal-organic chemical vapor deposition. In this work, 1 the optical and structural properties of the violet-light-emitting UTHI InGaN/GaN MQWs grown by employing the GI technique in comparison with conventional low-In-content InGaN/GaN MQWs were investigated. Stronger localization of carriers and smaller QCSE were observed in UTHI MQWs as a result of enlarged potential fluctuation and thinner QW thickness compared to those in conventional low-In-content MQWs. We hope that these strong carrier localization and reduced QCSE can turn the UTHI InGaN/GaN MQWs into an attractive candidate for high efficient violet emitter. Detailed structural and optical characteristics of UTHI InGaN/GaN MQWs compared to the conventional InGaN/GaN MQWs will be given.

• Electrical & Electronic Materials
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• v.12 no.7
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• pp.7-11
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• 1999

Fully sealed field emission display in size of 4.5 inch has been fabricated using single-wall carbon nanotubes-organic vehicle com-posite. The fabricated display were fully scalable at low temperature below 415$^{\circ}C$ and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1V/${\mu}{\textrm}{m}$ and field emis-sion current of 1.5mA at 3V/${\mu}{\textrm}{m}$ (J=90${\mu}{\textrm}{m}$/$\textrm{cm}^2$)were observed. Brightness of 1800cd/$m^2$ at 3.7V/${\mu}{\textrm}{m}$ was observed on the entire area of 4.5-inch panel from the green phosphor-ITO glass. The fluctuation of the current was found to be about 7% over a 4.5-inch cath-ode area. This reliable result enables us to produce large area full-color flat panel dis-play in the near future. Carbon nanotubes (CNTs) have attracted much attention because of their unique elec-trical properties and their potential applica-tions [1, 2]. Large aspect ratio of CNTs together with high chemical stability. ther-mal conductivity, and high mechanical strength are advantageous for applications to the field emitter [3]. Several results have been reported on the field emissions from multi-walled nanotubes (MWNTs) and single-walled nanotubes (SWNTs) grown from arc discharge [4, 5]. De Heer et al. have reported the field emission from nan-otubes aligned by the suspension-filtering method. This approach is too difficult to be fully adopted in integration process. Recently, there have been efforts to make applications to field emission devices using nanotubes. Saito et al. demonstrated a car-bon nanotube-based lamp, which was oper-ated at high voltage (10KV) [8]. Aproto-type diode structure was tested by the size of 100mm $\times$ 10mm in vacuum chamber [9]. the difficulties arise from the arrangement of vertically aligned nanotubes after the growth. Recently vertically aligned carbon nanotubes have been synthesized using plasma-enhanced chemical vapor deposition(CVD) [6, 7]. Yet, control of a large area synthesis is still not easily accessible with such approaches. Here we report integra-tion processes of fully sealed 4.5-inch CNT-field emission displays (FEDs). Low turn-on voltage with high brightness, and stabili-ty clearly demonstrate the potential applica-bility of carbon nanotubes to full color dis-plays in near future. For flat panel display in a large area, car-bon nanotubes-based field emitters were fabricated by using nanotubes-organic vehi-cles. The purified SWNTs, which were syn-thesized by dc arc discharge, were dispersed in iso propyl alcohol, and then mixed with on organic binder. The paste of well-dis-persed carbon nanotubes was squeezed onto the metal-patterned sodalime glass throuhg the metal mesh of 20${\mu}{\textrm}{m}$ in size and subse-quently heat-treated in order to remove the organic binder. The insulating spacers in thickness of 200${\mu}{\textrm}{m}$ are inserted between the lower and upper glasses. The Y\ulcornerO\ulcornerS:Eu, ZnS:Cu, Al, and ZnS:Ag, Cl, phosphors are electrically deposited on the upper glass for red, green, and blue colors, respectively. The typical sizes of each phosphor are 2~3 micron. The assembled structure was sealed in an atmosphere of highly purified Ar gas by means of a glass frit. The display plate was evacuated down to the pressure level of 1$\times$10\ulcorner Torr. Three non-evaporable getters of Ti-Zr-V-Fe were activated during the final heat-exhausting procedure. Finally, the active area of 4.5-inch panel with fully sealed carbon nanotubes was pro-duced. Emission currents were character-ized by the DC-mode and pulse-modulating mode at the voltage up to 800 volts. The brightness of field emission was measured by the Luminance calorimeter (BM-7, Topcon).