• Journal of Sensor Science and Technology
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• v.28 no.6
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• pp.407-413
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• 2019

Using 3D printing technology, we created a biomimetic water strider robot that can monitor environments. We found ways to increase the bearing capacity of the fluid-driven water strider robot by conducting experiments then comparing with more stable robots. The controller of the robot is based on Arduino, and can be controlled wirelessly with a Bluetooth module. The speed of the robot is 7.37 cm/s, and the bearing capacity is 29 g. A lithium polymer battery that can be charged with a solar cell was used as a power source, and both the charging and driving times were also explored.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2015.05a
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• pp.101-101
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• 2015

Photoelectrochemical water splitting is considered as a promising method of transforming solar energy into chemical energy stored in the type of hydrogen. An n-type $WO_3$ semiconductor is one of the most promising photoanodes for hydrogen production from water splitting. Films annealed at lower temperatures consisted of amorphous, whereas films annealed above $500^{\circ}C$ comprised solely of monoclinic $WO_3$. In this study, we observed photoactivity of $WO_3$ as increasing thickness of $WO_3$. And it shows good photoacivity as thickness increases. Also we tried to improve photoactivity through surface modification and bulk modification by using hydrogen treatment and conducting polymer. The photocurrent was measured in potentiostatic method with the three electrode system. A Pt wire and Ag / AgCl electrode were used as the counter electrode and the reference electrode, respectively. photocurrent-time (I-T) curve was measured at a bias potential of 0.79 V.

• Korean Chemical Engineering Research
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• v.61 no.2
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• pp.202-207
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• 2023

In the case of driving water electrolysis by receiving surplus electricity from solar and wind power generation, operation and stopping must be repeated according to weather fluctuations. When the PEMWE(Polymer Electrolyte Membrane Water Electrolysis) is driven and stopped, the PEM fuel cell is in the same state as the PEM fuel cell due to the residual hydrogen and oxygen, and the high potential of the water electrolysis formed during operation is highly likely to cause degradation of the electrode and membrane even during stopping. In this study, in order to check how much degradation of the electrode and membrane progresses during the repeated driving/shutdown process of PEM water electrolysis, the performance decrease was measured by changing the number of driving/shutdown for 144 hours. Changes in electrode catalyst active area, hydrogen permeability and fluorine emision rate of membranes were analyzed to measure changes in the properties of electrodes and polymer membranes. Overall, the PEMWE performance decreased as the number of stops increased. When stopped 5 times in 144 hours, the IrO_x catalyst activity decreased by more than 30%, and the hydrogen permeability increased by 80%, confirming that both the electrode and the membrane were deteriorated.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.343-343
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• 2014

We reported on the electrical, optical, structural and morphological properties fabricated by co-sputtering for use as an anode for organic solar cells (OSCs). By adjusting RF and DC power of $MoO_3$ and IZO targets during co-sputtering, we fabricated the $MoO_3$-IZO electrode with graded content of the $MoO_3$ on the IZO films. At optimized $MoO_3$ thickness of 20 nm, the $MoO_3$ graded IZO electrode showed a higher mobility ($33cm^2/V-Sec$) than directly deposited $MoO_3$ on IZO film ($26cm^2/V-Sec$). At visible range (400nm~800nm), optical transmittance of the $MoO_3$ graded IZO electrode is higher than that of directly deposited $MoO_3$ on IZO film. High mobility of $MoO_3$ graded on IZO is attributed to less interface scattering between $MoO_3$ and IZO. To investigate the feasibility of $MoO_3$ graded IZO films, we fabricated conventional P3HT:PCBM based OSCs with $MoO_3$ graded IZO as a function of MoO3 thickness. The OSC fabricated on the $MoO_3$ graded IZO anode showed a fill factor of 66.53%, a short circuit current of $8.121mA/cm^2$, an open circuit voltage of 0.592 V, and a power conversion efficiency of 3.2% comparable to OSC fabricated on ITO anode and higher than directly deposited $MoO_3$ on IZO film. We suggested possible mechanism to explain the high performance of OSCs with a $MoO_3$ graded IZO.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.394.2-394.2
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• 2014

We fabricated highly transparent and flexible Ti doped In2O3 (TIO)/Ag nanowire(NW)/TIO (TAT) multilayer electrodes by linear facing target sputtering (LFTS) and brush-painting for used as flexible for anode organic solar cells(FOSCs). The characteristics of TAT transparent anode as a function of number of brush-painting cycles was also investigated. At optimized conditions we achieved highly flexible TAT multilayer electrodes with a low sheet resistance of $9.01{\Omega}/square$ and a high diffusive transmittance more than 80% in visible region as well as superior mechanical stability. The effective embedment of the Ag NW network between top and bottom TIO films led to a metallic conductivity, high transparency. Based on FE-SEM HRTEM, and XRD analysis, we can find that the Ag NW network was effectively embedded between top and bottom TIO layers due to good flexibility of Ag NW, the TAT multilayer showed superior flexibility than single TIO layer. Successful operation of FOSCs with high power conversion efficiency of 3.01% indicates that TAT hybrid electrode is a promising alternative to conventional ITO electrode for high performance FOSCs.

• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.253-260
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• 2024

Proton exchange membrane water electrolysis (PEMWE) is an efficient method for utilizing renewable energy sources such as wind and solar powers to produce green hydrogen. For PEMWE powered by renewable energy sources, its durability is a crucial factor in its performance since irregular and fluctuating characteristics of renewable energy sources, especially for wind power, can deteriorate the stability of PEMWE. Triangular voltage cycle is well able to simulate fluctuating wind power, but its effect on the durability has not been investigated extensively. In this study, the performance degradation of the PEMWE cell operated with the triangular voltage cycling was investigated at different ramping rates. The measured current responses during the cycling gradually decreased for both ramping rates, and I-V curve measurements before and after the cycling confirmed the degradation of the performances of PEMWE. For both measurements, the degradation rate was larger for 300 mV s^-1 than 30 mV s^-1, and they were determined as 0.36 and 1.26 mV h^-1 (at the current density of 2 A cm^-2) at the ramping rates of 30 and 300 mV s^-1, respectively. The comparison with other studies on triangular voltage cycling also indicate that an increase in the ramping rate accelerates the deterioration of the PEMWE performance. X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the Ir catalyst was oxidized and did not dissolve during the voltage cycling. This study suggests that the ramping rate of the triangular voltage cycling is an important factor for the evaluation of the durability of PEMWE cells.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.1838-1843
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• 2014

Nanoimprint lithography (NIL) fabrication process is regarded as the main alternative to existing expensive photo-lithography in areas such as micro- and nano-electronics including optical components and sensors, as well as the solar cell and display device industries. Functional patterns, including anti-reflective moth-eye pattern, photonic crystal pattern, fabricated by NIL can improve the overall efficiency of such devices. To successfully imprint a nano-sized pattern, the process conditions such as temperature, pressure, and time should be appropriately selected. In this paper, a cavity-filling process of the moth-eye pattern during the thermal-NIL within the temperature range, where the polymer resist shows the viscoelastic behaviors with consideration of stress relaxation effect of the polymer, were investigated with three-dimensional finite element analysis. The effects of initial thickness of polymer resist and imprinting pressure on cavity-filling process has been discussed. From the analysis results it was found that the cavity filling can be completed within 100 s, under the pressure of more than 4 MPa.

• Journal of Adhesion and Interface
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• v.20 no.4
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• pp.146-154
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• 2019

In this study, alkoxysilane-functionalized amphiphilic polymer (AFAP), which have hydrophilic segment and hydrophobic segment functionalized by alkoxysilane group at the same backbone, was synthesized and used as a dispersant and control agent for reaction rate in the preparation of colloidally stable organic-inorganic (O-I) hybrid sols. After reaction with fluorosilane compounds, fluorinated O-I hybrid sols were prepared and coated onto glass substrate to form hydrophobic O-I hybrid coating films through low-temperature curing process. Surface hardness and hydrophobicity of cured coating films were varied with type of solvent and composition of AFAP and fluorinated alkoxysilane compounds. At appropriate solvent and composition of fluorinated alkoxysilane compounds, O-I hybrid coating film having high transparency and surface hardness could be prepared, which could be applicable to cover window of solar cell and displays.

• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.629-635
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• 2012

Two novel conjugated copolymers utilizing 4,7-dithien-2-yl-2,1,3-benzothiadiazole (DTBT) coupled with cyano (-CN) substituted vinylene, as the electron deficient moeity, have been synthesized and evaluated in bulk heterojunction solar cell. The electron deficient moeity was coupled with carbazole and fluorene unit by Knoevenagel condition to provide poly(bis-2,7-((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl)ethenyl)-alt-9-(1-octylnonyl)-9H-carbazol-2-yl-2-butenenitrile) (PCVCNDTBT) and poly(bis-2,7-((Z)-1-cyano-2-(5-(7-(2-thienyl)-2,1,3-benzothiadiazol-4-yl)-2-thienyl)ethenyl)-alt-9,9-dihexyl-9H-fluoren-2-yl) (PFVCNDTBT). The optical band gaps of PCVCNDTBT (1.74 eV) and PFVCNDTBT (1.80 eV) are lower than those of PCDTBT (1.88 eV) and PFVDTBT (2.13 eV), which is advantageous to provide better coverage of the solar spectrum in the longer wavelength region. The high $V_{oc}$ value of the PSC of PCVCNDTBT (~0.91 V) is attributed to its lower HOMO energy level ( 5.6 eV) as compared to PCDTBT ( 5.5 eV). Bulk heterojunction solar cells based on the blends of the polymers with [6,6]phenyl-$C_{61}$-butyric acid methyl ester ($PC_{61}BM$) gave power conversion efficiencies of 0.76% for PCVCNDTBT under AM 1.5, 100 mW/$cm^2$.

• Journal of the Microelectronics and Packaging Society
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• v.20 no.2
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• pp.39-46
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• 2013

In this paper, organic solar cells(OSCs) based on bulk-heterojunction structures were fabricated by spin coating method using polymer P3HT and fullerene PCBM as a photoactive layer. The fabricated OSCs had a simple glass/ITO/PEDOT:PSS/P3HT:PCBM/Al structures. The photoactive layer of mixed P3HT:PCBM was formed with 1:1 weight ratio. The hole transport layer(HTL) was used conducting polymer PEDOT:PSS concentration with gold nanoparticles. The annealing temperature and concentration of nanoparticles in HTL were verified to improve the OSC characterization. The percentage of gold nanoparticles in HTL were 0.5 wt% and 1.0 wt%, and the surface morphology, electrical properties and absorption intensities were investigated. The devices were 0.5 wt%, and the highest 3.1% of the powder conversion efficiency(PCE), 10.2 $mA/cm^2$ of the maximum short circuit current density($J_{SC}$), 0.535V of the open circuit voltage($V_{OC}$) and 55.8% of the fill factor(F.F) could be obtained when the nanoparticle concertration was 0.5 wt%. The annealing temperature of HTL was $110^{\circ}C$, $130^{\circ}C$, $150^{\circ}C$ in vacuum oven and measured the absorption intensities, surface morphology, crystallinity and electrical properties were investigated. The best property was obtained in HTL annealed at $130^{\circ}C$ for gold nanoparticles of 0.5 wt%, showing that $J_{SC}$, $V_{OC}$, F.F and PCE were about 12.0 $mA/cm^2$, 0.525V, 64.2% and 4.0%, respectively.