• Applied Chemistry for Engineering
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• v.32 no.6
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• pp.690-694
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• 2021

Carbon spheres (CS) were fabricated using glucose as a precursor in the hydrothermal method. Hollow TiO₂ (H-TiO₂) spheres with 200 nm, 500 nm, and 1,200 nm were synthesized by CS/TiO₂ core-shell particles via a sol-gel and calcination method. H-TiO₂ spheres with nano and micron sizes were characterized using FE-SEM, HR-TEM, and X-ray diffraction. The CIE color coordinate, solar reflectance, and heat shield temperatures of H-TiO₂/polyacrylate (PA) composite film were investigated using a UV-Vis-NIR spectrometer and homemade heat insulation temperature measuring device. H-TiO₂/PA composites exhibit excellent thermal insulation since the hollow structure filled with dry air has low thermal conductivity and near infrared light reflecting performance. The thermal insulation increased with increasing the hollow sphere (HS) size on H-TiO₂/PA composites. The PA composite film mixed with H-TiO₂ filled with 1200 nm HS reduced the heat shield temperature by 26 ℃ compared to that of the transparent glass counterpart.

• Applied Chemistry for Engineering
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• v.30 no.3
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• pp.358-364
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• 2019

To improve the optical characteristics and antifouling of anti-reflective coating (AR) films, various AR coating films were prepared by varying the mixing ratio of tetraethylorthosilicate (TEOS)/base and methyltrimethoxysilane (MTMS)/acid hybrid solution. Prepared AR coating films were characterized by UV-Vis spectroscopy, contact angle analyzer, atomic force microscope (AFM), FT-IR and pencil scratch hardness test. In an AR coating film that prepared from the hybrid solution with a 10 wt% MTMS/acid solution, the glass substrate showed an excellent optical property (97.2% transmittance), good antifouling ($121^{\circ}$ water contact angle and $90^{\circ}\;CH_2I_2$ contact angle) and moderate mechanical strength (pencil hardness of 4 H). In particular, it is considered that the good antifouling was due to the well dispersion of the methyl group ($-CH_3$), derived from a small amount of MTMS/acid solution in the hybrid solution, on the substrate surface. From results of the pencil hardness test, the mechanical strength of AR coating film was improved as the content of MTMS/acid solution increased.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.240-246
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• 2023

This study was performed to convert NO_x in atmosphere by photochemical reaction utilizing the eco-friendly solar energy. The mortar specimen coated with photocatalyst was fabricated and the photochemical conversion efficiency of NO_x was analyzed. The photocatalyst coated concrete was fabricated by first adding TiO₂ photocatalyst on the bottom of mold first and next adding cement mortar and, then, curing the concrete mortar. The grease was sprayed on the bottom of mold in advance so that the concrete can be demolded easily after curing. The conversion efficiencies of NO_x by photochemical reactions were investigated systematically by changing the process variable conditions of amount of TiO₂ coating, UV-A light intensity, total gas flow rate, relative humidity and initial NO_x concentration. It was confirmed that the photocatalyst coated concrete fabricated in this study could convert NO_x successfully for various process conditions in atmosphere. In future, we believe this research result can be utilized as basic data to design the infrastructure of building, tunnel and road for controlling efficiently the air pollutants such as NO_x, SO_x, and VOCs.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.97.1-97.1
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• 2010

유연금속기판위에 DC 마그네트론 스퍼터링을 이용하여 Ag/ZnO 이중구조의 후면반사막을 증착하고 Ag 표면조도 변화에 따른 후면반사막의 반사특성 변화와 플렉서블 비정질 실리콘 박막 태양전지의 셀 특성에 미치는 영향을 조사하였다. Substrate구조를 갖는 플렉서블 실리콘 박막 태양전지에서는 실리콘 박막 광흡수층의 상대적으로 낮은 광 흡수율로 인하여 입사광에 대한 태양전지 내에서의 광 산란 및 포획이 태양전지 효율을 증대시키는데 매우 중요한 역할을 하는 것으로 알려져 있다. 플렉서블 실리콘 박막 태양전지에서의 후면반사막은 광 흡수층에서 흡수되지 않는 입사광을 다시 반사시켜 광 흡수를 증대시키며 이때 후면반사막 표면에서 반사 빛을 효율적으로 산란시켜 이동경로를 증대시킴으로써 광 흡수율을 더욱 향상시킬 수 있다. 본 연구에서는 유연금속 기판위에 Ag와 ZnO:Al($Al_2O_3$ 2.5wt%) 타겟을 사용한 DC 마그네트론 스퍼터링법으로 Ag/AZO 이중구조의 후면반사막을 제조하고, Ag 박막의 표면형상 변화와 이에 따른 후면반사막의 반사도 변화를 비교, 분석하였다. 증착 조건 변화에 따른 표면 형상 및 반사 특성은 Atomic Force Mircroscope(AFM), Scanning electron miroscopy(SEM), UV-visible-nIR spectrometry를 통하여 분석하였다. 서로 다른 표면 거칠기를 갖는 후면반사막 위에 n-i-p구조의 a-Si:H 실리콘 박막 태양전지를 제조한 후 태양전지 동작 특성에 미치는 영향을 조사하였다. n,p층은 13.56MHz PECVD, i층은 60MHz VHF CVD를 사용하여 각각 제조 하였으며, Photo I-V, External Quantum Efficiency(EQE) 분석을 통하여 태양전지 특성을 조사 하였다. SEM 분석결과 공정 온도가 증가 할수록 Ag 박막의 표면 결정립 크기도 증가하였으며, AFM분석을 통한 Root-mean-square(Rms)값은 상온에서 $500^{\circ}C$로 증착온도가 증가함에 따라 6.62nm에서 46.64nm까지 증가하였다. Ag 박막의 표면 거칠기 증가에 따라 후면반 사막의 확산 반사도도 함께 증가하였다. 공정온도 $500^{\circ}C$에서 증착된 후면반사막을 사용하여 a-Si:H 태양전지를 제조하였을 때 상온에서 제조한 후면반사막에 비하여 단락전류밀도 (Jsc)값은 9.94mA/$cm^2$에서 13.36mA/$cm^2$로 증가하였으며, 7.6%의 가장 높은 태양전지 효율을 나타내었다.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.42 no.1
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• pp.57-64
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• 2016

Just like UV radiation, heat increases collagen degradation and accumulation of abnormal elastin fiber and this is termed thermal skin aging. Dunaliella salina (DS), a green alga, is known for its beta-carotene accumulation, having various applications in the health and nutritional products. However, the effects of DS on heat-induced skin aging remain unexplored. In this study, we performed anti-thermal aging tests of the ethanol extract of DS (DSE). We measured the cellular levels of type I procollagen and MMP-1 using ELISA in human dermal fibroblast cells after heat shock. DSE reduced the expression of MMP-1 protein and increased the expression of type I procollagen. In addition, DSE upregulated the mRNA expression of HSP47 reduced by heat shock, which is involved in collagen synthesis. Also, DSE reduced the expression of inflammation mediator (TGF-${\beta}$, IL-12, etc). We demonstrate that DSE regulates the heat-induced solar elastosis through the regulation of tropoelastin and fibrillin-1, two major proteins of elastic fibers, and MMP-12 expression. These results suggest that DSE may be effective for preventing thermally induced skin aging.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.417-423
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• 2011

A series of new quinoxaline-based thiophene copolymers (PQx2T, PQx4T, and PQx6T) was synthesized via Yamamoto and Stille coupling reactions. The $M_ws$ of PQx2T, PQx4T, and PQx6T were found to be 20,000, 12,000, and 29,000, with polydispersity indices of 2.0, 1.2, and 1.1, respectively. The UV-visible absorption spectra of the polymers showed two distinct absorption peaks in the ranges 350 - 460 nm and 560 - 600 nm, which arose from the ${\pi}-{\pi}^*$ transition of oligothiophene units and intramolecular charge transfer (ICT) between a quinoxaline acceptor and thiophene donor. The HOMO levels of the polymer ranged from -5.37 to -5.17 eV and the LUMO levels ranged from -3.67 to -3.45 eV. The electrochemical bandgaps of PQx2T, PQx4T, and PQx6T were 1.70, 1.71, and 1.72 eV, respectively, thus yielding low bandgap behavior. PQx2T, PQx4T, and PQx6T had open circuit voltages of 0.58, 0.42, and 0.47 V, and short circuit current densities of 2.9, 5.29 and 9.05 mA/$cm^2$, respectively, when $PC_{71}BM$ was used as an acceptor. For the solar cells with PQx2T-PQx6T:$PC_{71}BM$ (1:3) blends, an increase in performance was observed in going from PQx2T to PQx6T. The power conversion efficiencies of PQx2T, PQx4T, and PQx6T devices were found to be 0.69%, 0.73%, and 1.80% under AM 1.5 G (100 mW/$cm^2$) illumination.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.454-454
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• 2014

Silicon microwire array is one of the promising platforms as a means for developing highly efficient solar cells thanks to the enhanced light trapping efficiency. Among the various fabrication methods of microstructures, deep reactive ion etching (DRIE) process has been extensively used in fabrication of high aspect ratio microwire arrays. In this presentation, we show precisely controlled Si microwire arrays by tuning the DRIE process conditions. A periodic microdisk arrays were patterned on 4-inch Si wafer (p-type, $1{\sim}10{\Omega}cm$) using photolithography. After developing the pattern, 150-nm-thick Al was deposited and lifted-off to leave Al microdisk arrays on the starting Si wafer. Periodic Al microdisk arrays (diameter of $2{\mu}m$ and periodic distance of $2{\mu}m$) were used as an etch mask. A DRIE process (Tegal 200) is used for anisotropic deep silicon etching at room temperature. During the process, $SF_6$ and $C_4F_8$ gases were used for the etching and surface passivation, respectively. The length and shape of microwire arrays were controlled by etching time and $SF_6/C_4F_8$ ratio. By adjusting $SF_6/C_4F_8$ gas ratio, the shape of Si microwire can be controlled, resulting in the formation of tapered or vertical microwires. After DRIE process, the residual polymer and etching damage on the surface of the microwires were removed using piranha solution ($H_2SO_4:H_2O_2=4:1$) followed by thermal oxidation ($900^{\circ}C$, 40 min). The oxide layer formed through the thermal oxidation was etched by diluted hydrofluoric acid (1 wt% HF). The surface morphology of a Si microwire arrays was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S-4800). Optical reflection measurements were performed over 300~1100 nm wavelengths using a UV-Vis/NIR spectrophotometer (Cary 5000, Agilent) in which a 60 mm integrating sphere (Labsphere) is equipped to account for total light (diffuse and specular) reflected from the samples. The total reflection by the microwire arrays sample was reduced from 20 % to 10 % of the incident light over the visible region when the length of the microwire was increased from $10{\mu}m$ to $30{\mu}m$.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.672-679
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• 2013

$Fe_4[Fe(CN)_6]_3$ coated on a mica or $TiO_2$/mica surface as infrared reflective blue pigment was prepared by a hydrothermal method. $Fe_4[Fe(CN)_6]_3$, used as coloring agent, was uniformly coated on mica or $TiO_2$/mica under the optimized condition of a 1.2 : 1 weight ratio between iron(III) chloride hexahydrate and potassium ferrocyanidetrihydrate at the initial pH level of 4.5 at $70^{\circ}C$. The infrared (IR)-reflective pigments were characterized by SEM, Zeta-potenial, FT-IR, and UV-VIS NIR spectrophotometry. Especially the CIE color coordinate and total solar reflectance(TSR) properties of the pigments were investigated in relation to variation of the coating and coated substrate thicknesses. Isolation-heat paint was prepared with 20 wt% blue pigments fully dispersed in acryl-urethane resin and several additives to coat the film uniformly. The films were also measured with CIE color coordinate, TSR, and the surface temperature was recorded by an isolation-heat measuring system. The pigments and films of $Fe_4[Fe(CN)_6]_3$ coated on mica and $TiO_2$/mica showed high TSR values compared with the TSR value of $Fe_4[Fe(CN)_6]_3$ itself. According to the increase of TSR value, the property of isolation-heat is effective. To realize the optimal blue color, we applied the the pigment to $TiO_2$ coated mica(TM(b)) which has blueish interference color. The pigment of $Fe_4[Fe(CN)_6]_3$ coated on TM(b) shows a strong blue color compared with that of $Fe_4[Fe(CN)_6]_3$ coated on $TiO_2$/Mmca(TM(w)), which has a whitish interference color.

• Journal of Electrochemical Science and Technology
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• v.9 no.4
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• pp.282-291
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• 2018

The pristine fluorine-doped $SnO_2$ (abbreviated as FTO) inverse opal (IO) was developed using a 410 nm polystyrene bead template. The nanolayered copper tungsten oxide ($CuWO_4$) was decorated on the FTO IO film using a facile electrochemical deposition, subsequently followed by annealing at $500^{\circ}C$ for 90 min. The morphologies, crystalline structure, optical properties and photoelectrochemical characteristics of the FTO and $CuWO_4$-decorated FTO (briefly denoted as $FTO/CuWO_4$) IO film were investigated by field emission scanning electron microscopy, X-ray diffraction, UV-vis spectroscopy and electrochemical impedance spectroscopy, showing FTO IO in the hexagonally closed-pack arrangement with a pore diameter and wall thickness of about 300 nm and 20 nm, respectively. Above this film, the $CuWO_4$ was electrodeposited by controlling the cycling number in cyclic voltammetry, suggesting that the $CuWO_4$ formed during 4 cycles (abbreviated as $CuWO_4$(4 cycles)) on FTO IO film exhibited partial distribution of $CuWO_4$ nanoparticles. Additional distribution of $CuWO_4$ nanoparticles was observed in the case of $FTO/CuWO_4$(8 cycles) IO film. The $CuWO_4$ layer exhibits triclinic structure with an indirect band gap of approximately 2.5 eV and shows the enhanced visible light absorption. The photoelectrochemical (PEC) behavior was evaluated in the 0.5 M $Na_2SO_4$ solution under solar illumination, suggesting that the $FTO/CuWO_4$(4 cycles) IO films exhibit a photocurrent density ($J_{sc}$) of $0.42mA/cm^2$ at 1.23 V vs. reversible hydrogen electrode (RHE, denoted as $V_{RHE}$), while the FTO IO and $FTO/CuWO_4$(8 cycles) IO films exhibited a $J_{sc}$ of 0.14 and $0.24mA/cm^2$ at $1.23V_{RHE}$, respectively. This difference can be explained by the increased visible light absorption by the $CuWO_4$ layer and the favorable charge separation/transfer event in the cascading band alignment between FTO and $CuWO_4$ layer, enhancing the overall PEC performance.

• Journal of the Korean Solar Energy Society
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• v.39 no.5
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• pp.1-10
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• 2019

Recently, the installation capacity of PV (photovoltaic) systems has been increasing not only field installation but also floating PV, farm land, BIPV/BAPV. For this reason, the new design and materials of PV module are needed. In particular, in order to apply a PV system to a building, lightweight of the PV module is essential. PV modules made of generally used texturing glass are excellent in output and reliability, but there is a limit to the weight that can be reduced. For the lightweight of the PV module, it necessary to use a film instead of a glass. However, the application of film rather than a glass may cause various problems such as decrease in photocurrent by decrease in transmittance and a increase of CTM (cell to module) loss, a degradation of the reliability, and so on. In this paper, PV modules using Ultra barrier film, which is recently a lot of interest as a substitute for a glass, its characteristic analysis and reliability test were conducted. The transmittance and UV characteristics of each material were verified, and the output of the fabricated 1 cell PV module was measured. In addition, 24 cell PV modules were fabricated at the lab-scale and its reliability tests were conducted. As a result of the experiment, the reliability characteristics of the ultra barrier film PV module were excellent, and it was confirmed that it could be used as the front material of the PV module instead of glass