• Korean Journal of Materials Research
• /
• v.24 no.10
• /
• pp.565-571
• /
• 2014

Nitrogen-doped ZnO nanoparticle-carbon nanofiber composites were prepared using electrospinning. As the relative amounts of N-doped ZnO nanoparticles in the composites were controlled to levels of 3.4, 9.6, and 13.8 wt%, the morphological, structural, and chemical properties of the composites were characterized by means of field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In particular, the carbon nanofiber composites containing 13.8 wt% N-doped ZnO nanoparticles exhibited superior catalytic properties, making them suitable for use as counter electrodes in dye-sensitized solar cells (DSSCs). This result can be attributed to the enhanced surface roughness of the composites, which offers sites for $I_3{^-}$ ion reductions and the formation of Zn3N2 phases that facilitate electron transfer. Therefore, DSSCs fabricated with 13.8 wt% N-doped ZnO nanoparticle-carbon nanofiber composites showed high current density ($16.3mA/cm^2$), high fill factor (57.8%), and excellent power-conversion efficiency (6.69%); at the same time, these DSSCs displayed power-conversion efficiency almost identical to that of DSSCs fabricated with a pure Pt counter electrode (6.57%).

• 한국신재생에너지학회:학술대회논문집
• /
• 2010.06a
• /
• pp.64.2-64.2
• /
• 2010

In order to improve the overall power conversion efficiency in dye-sensitized solar cells (DSSCs), it is very important to secure the sufficient surface area of photocatalytic nanoparticles layer for absorbing dye molecules. It is because increasing the amount of dye absorbed generally results in increasing the amount of light harvesting. In this work, we proposed a new method for increasing the specific surface area of photocatalytic titanium oxide ($TiO_2$) nanoparticles by using an inorganic templating method. Salt-$TiO_2$ composite nanoparticles were synthesized in this approach by spray pyrolyzing both the titanium butoxide and sodium chloride solution. After aqueous removal of salt from salt-$TiO_2$ composite nanoparticles, mesoporous $TiO_2$ nanoparticles with pore size of 2~50 nm were formed and then the specific surface area of resulting porous $TiO_2$ nanoparticle was measured by Brunauer-Emmett-Teller (BET) method. Generally, commercially available P-25 with the average primary size of ~25 nm $TiO_2$ nanoparticles was used as an active layer for dye-sensitized solarcells, and the specific surface area of P-25 was found to be ~50 $m^2/g$. On the other hand, the specific surface area of mesoporous $TiO_2$ nanoparticles prepared in this approach was found to be ~286 $m^2/g$, which is 5 times higher than that of P-25. The increased specific surface area of $TiO_2$ nanoparticles will absorb relatively more dye molecules, which can increase the short curcuit current (Jsc) in DSSCs. The influence of nanoporous structures of $TiO_2$ on the performance of DSSCs will be discussed in terms of the amount of dye molecules absorbed, the fill factor, the short circuit current, and the power conversion efficiency.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.19 no.6
• /
• pp.87-93
• /
• 2019

We discuss the design of a radiometer using a millimeterwave(Ka-band) seeker. We applied a total power radiometer, thus the radiometer is composed of a IF-drive amp, band-pass filter, detector and an Op-amp additionally. As a radiometer measure a radiated signal of an object which is noise-like, a radiometer is easily affected by the variance of system temperature. To mitigate an adverse effect, we propose a compensation method in a radiometer without brightmess temperature compensation circuits. Through some experiments such like a distinction a target and the background, we have verified that the designed radiometer system has distingushed a car from the ground completely.

• Journal of Power System Engineering
• /
• v.10 no.2
• /
• pp.47-53
• /
• 2006

This study concerns the performance of condensation heat transfer in plain and grooved thermosyphons. Distilled water, methanol, ethanol have been used as the working fluids. In the present work, a copper tube of the length of 1200mm and 14.28mm of inside diameter is used as the container of the thermosyphon. Each of the evaporator and the condenser section has a length of 550mm, while the remaining part of the thermosyphon tube is adiabatic section. A study was carried out with the characteristics of heat transfer of the thermosyphon 50, 60, 70, 80, 90 helical grooves in which boiling and condensation occur. The liquid filling as the ratio of working fluid volume to total volume of thermosyphon, the kinds of working fluid, the inclination angle, grooves and operating temperature have been used as the experimental parameters. The experimental results show that the number of grooves, the amount of the working fluid, the kind of working fluid, angle of inclination angle are very important factors for the operation of thermosyphon. The maximum heat transfer was obtained when the liquid fill was about 20 to 25 % of the thermosyphon volume. The relatively high rates of heat transfer have been achieved in the thermosyphon with grooves. The helical grooved thermosyphon having 70 to 80 grooves in water, 60 to 70 grooves in methanol and 70 to 80 grooves in ethanol shows the best heat transfer coefficient in both condensation.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.11a
• /
• pp.297-300
• /
• 2007

In this study, we have attempted a new method to enhance the coloring of dye on the $TiO_2$ surface in the dye sensitized solar cell. In the conventional coloring process in a dye sensitized solar cells, dye is absorbed by the covalent bond between TiO2 and dye molecule while the photo-electrode coated with $TiO_2$ layer is soaked in dye solution for about 12-24 hours. But this process takes long time, so we have researched more effective and faster way than the conventional process by applying electric field. Three kinds of electric power such as direct voltage, alternating voltage and pulse voltage were applied to the transparent conducting oxide during the coloring process. As a result, we achieved improved power, fill factor and efficiency of dye-sensitized solar cell in case of applying direct voltage and pulse voltage. In contrast, alternating voltage tend to reduce the dye adsorption on the $TiO_2$ surface and hence the efficiency. We measured the absorption spectra of dye by UV-VIS spectrophotometer before and after soaking the $TiO_2$ in the dye and found no characteristic change in the dye was observed. In this study, we researched on shortening time of coloring process which spent much time in the whole process.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.343-343
• /
• 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
• /
• 2014.02a
• /
• pp.478.1-478.1
• /
• 2014

We investigated $MoO_3$ graded ITO electrodes for organic solar cells (OSCs) without PEDOT:PSS buffer layer. The effect of $MoO_3$ thickness on the electrical, optical, and structural properties of $MoO_3$ graded ITO anodes prepared by RF/DC magnetron co-sputtering system using $MoO_3$ and ITO targets was investigated. At optimized conditions, we obtained $MoO_3$ graded ITO electrodes with a low sheet resistance of 13 Ohm/square, a high optical transmittance of 83% and a work function of 4.92 eV, comparable to conventional ITO films. Due to the existence of $MoO_3$ on the ITO electrodes, OSCs fabricated on $MoO_3$ graded ITO electrode without buffer layer successfully operated. Although OSCs fabricated on ITO anode without buffer layer showed a low power conversion efficiency of 1.249%, OSCs fabricated on $MoO_3$ graded ITO electrode without buffer layer showed a outstanding cell performance of 2.545%. OSCs fabricated on the $MoO_3$ graded ITO electrodes exhibited a fill factor of 61.275%, a short circuit current of 7.439 mA/cm2, an open circuit voltage of 0.554 V, and a power conversion efficiency of 2.545%. Therefore, $MoO_3$ graded ITO electrodes can be considered a promising transparent electrode for cost efficient and reliable OSCs because it could eliminate the use of acidic PEDOT:PSS buffer layer.

• Current Photovoltaic Research
• /
• v.7 no.3
• /
• pp.65-70
• /
• 2019

As a demand of higher power photovoltaic modules, shingled, multi-busbar, half-cell, and bifacial techniques are developed. Multi-busbar module has advantage for large amount of light havesting. And, half-cell is high power module for reducing resistive losses and higher shade tolerance. Recently, researches on multi-busbar is focused on reliability according to adhesion and intermetallic compound between Sn-Pb solder and Ag electrode. And half-cell module is researched to comparing with full-sized cell module for structure difference. In this study, we investigated the factors affecting to efficiency and adhesion of multi-wires half-cell module according to wire thickness, solder thickness, and flux. The results of solar simulator and peel test was that peel strength and efficiency of soldered cell is not related. But samples with flux including high solid material showed high efficiency. The results of FE-SEM and EDX line scan on cross-section between wire and Ag electrode for different flux showed thickness of solder joint between wire and Ag electrode is increasing through solid material increasing. Flux including high solid material would affect to solder behavior on Ag electrode. Higher solid material occurred lower growth of IMC layer because solder permeate to sider of wire ribbon than Ag electrode. And it increased fill factor for high efficiency. In soldering process, amount of solid material in flux and solder thickness are the factor related with characteristic of soldered photovoltaic cell.

• Korean Security Journal
• /
• no.1
• /
• pp.283-319
• /
• 1997

Our society witnesses the rapid progress in the areas of politics, economy, society and culture in the process of national modernization since 1960s, which in turn as a reverse function gets to contract a societic pathology, totally lowering the security level of citizens' lives owing to various violent crimes like hostage commotions and murders with rifles and deadly weapons. what is the main reason for that? That may be partly because the chief police force concentrates on the current situation resulting in the vacuum of the public peace. However, the main reason is that the police fall short of man-power and equipments even if the whole police power were put to use in preventing and quelling the crimes. That is true not only of Korea but also of the advanced countries like the U.S.A., England and Japan. We realize that these advanced countries have higher level of security in every individual's life and property than Korea because their progress of the private guard systems can fill in a vacuum of the shortage of the police power, Therefore, we should without delay internationalize our private guard systems expecting the widely opening of the guard service markets in the age of Uruguay Round. To do this, we need to change our ideas for fostering the policy of the private guard from passive defense ideas into positive aggressive ones. Our police should urgently set up a plan to pursue the orientation of vision that we should dispatch our private guards overseas before foreign guards rush into our markets. Accordingly it goes without saying that the private guard group should distinguish their services from the public services initiating their own theory and strategy of private guard services and also readjust themselves between the public duties and the private services with the study of minimizing the reverse function of the private guard systems. The history criminal justice has always shown that the criminal system progressed at the initiative of the civil factor in case its demand and supply do not make both ends meet. Nevertheless, in the process the power of the government never weakens, rather it is built up in general. In conclusion, the necessity of the build-up of the private guard services must duly be acknowledged by the police as well as by the business which has its unique sphere within the criminal justice instead of as the suplemtary services of the simple the police power on the long-term basis. The purpose of the private guard services can be largely classified into the two categories; first it means the function to prevent the crimes against the citizens and secondly to enhance the national interest as an increasing mammoth business with a worldly competition capacity. The police has an absolute responsibility that they should protect the modem public in general from feeling the crisis of the personal threat, tension, anxiety and nervousness. In short, if we develop the complete private guard system to guarantee the societic atmosphere for all citizens, keep the public peace, and protect all citizens' lives and properties, we will sure enjoy a beautiful land, a wholesome society and a happy life in goodharmony of law and order.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.15 no.6
• /
• pp.252-259
• /
• 2005

Single crystal $CuGaSe_2$ layers were grown on thoroughly etched semi-insulating CaAs(100) substrate at $450^{\circ}C$ with hot wall epitaxy (HWE) system by evaporating $CuGaSe_2$ source at $610^{\circ}C$. The crystalline structure of the single crystal thin films was investigated by the photoluminescence (PL) and double crystal X-ray diffraction (DCXD). The carrier density and mobility of single crystal $CuGaSe_2$ thin films measured with Hall effect by Van der Pauw method are $4.87{\times}10^{17}cm^{-3}$ and $129cm^2/V{\cdot}s$ at 293 K, respectively. The temperature dependence of the energy band gap of the $CuGaSe_2$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=1.7998eV-(8.7489{\times}10^{-4}eV/K)T^2/(T+335K)$. The voltage, current density of maxiumun power, fill factor, and conversion, efficiency of $n-CdS/p-CuGaSe_2$, heterojunction solar cells under $80mW/cm^2$ illumination were found to be 0.41 V, $21.8mA/cm^2$, 0.75 and 11.17%, respectively.