Ji-Tae Hong

A Study of the Photo-Electric Efficiency of Dye-Sensitized Solar Cells Under Lower Light Intensity

To elucidate possible challenges for outdoor practical use of dye-sensitized solar cells (DSCs), we compared conventional Si solar cells with DSCs. DSC modules still require a larger area than conventional Si solar modules to attain the same rated output because of lower photoelectron-chemical conversion efficiency. However, in backup systems by using batteries, the measured data shows that DSCs generated 15% more electricity than Si solar cells of the same rated output power in the same interval of cloudy daylight. Moreover, the battery charging time of DSCs is about 1 hour faster than the same rate of Si solar cells under outdoor cloudy daylight. This result also indicates that conversion efficiency obtained by the certified condition less than AM 1.5 condition does not always coincide with the electricity generated outdoors daily, and it is not a crucial measure to evaluate the performance of solar cells.

Sterilization of Escherichia coli Based on Nd: YAG Resonator with a Pulsed Xenon Flashlamp

Sterilization of Escherichia coli (E. coli) is examined using a unique pulsed ultra-violet (UV) elliptical reactor based on Nd:YAG laser resonator, UV radiation from a pulsed xenon flashlamp. The light from the discharge has a broadband emission spectrum extending from the UV to the infrared region with a rich UV contained. Sterilization method by using the UV light is fast, environmentfriendly and it does not cause secondary pollution. A Nd:YAG laser resonator having elliptical shape has advantage of concentrating the radiation of the UV light at two foci as the quart sleeve filled with E. coli. The primary objective of this research is to determine the important parameters such as pulse per second (pps), the applied voltage for sterilizing E. coli by using an UV elliptical reactor. From the experiment result, the sterilization effect of UV elliptical reactor is better than that of UV cylindrical reactor, and it can be 99.9% of sterilization at 800V regardless of the pps within 10 minutes.

Proposal of optimal process parameters for polymethylmethacryl plastic adhesion using a pulsed Nd:YAG laser

In this study, we propose a pulsed Nd:YAG laser system that uses a sequential charge and discharge circuit to adhere polymethylmethacryl (PMMA) plastics. Two PMMA plastics adhere to each other when the red one transmits the laser beam and the black one absorbs it. The optimal adhesion depends on several process parameters, such as the charging voltage of the capacitor, the pulse rate [in pulses per second (pps)], the velocity of the target, and the laser beam diameter. We try to optimize the adhesion process parameters from trial-and-error experiments. It has proposed that the optimal adhesion process parameters are a charging voltage of 650 V, a pulse rate of 11 pps, a target velocity of 4.20 mm/s, and a laser beam diameter of 4.00 mm in this pulsed Nd:YAG laser system. In addition, we generalize the optimal conditions for plastic adhesion, such as energy per pulse, peak power, and the velocity of the target.

The New Design of Dye-Sensitized Solar Cell Adopted by Sputter Deposition of Counter Electrode

The counter electrode widely used in DSCs (dye-sensitized solar cells) is constructed of conducting glass substrates coated with Pt films, where the platinum acts as a catalyst. Pt counter electrodes in DSCs are one important component. It is expected that characteristics of Pt electrodes strongly depend on fabrication process and its surface condition. In this study, Pt counter electrode surface of DSC is deposited by reactive RF magnetron sputtering under the conditions of Ar 5mtorr, RF power of 120W and substrate temperature of 100degC. Surface morphology of Pt electrodes was investigated by FE-SEM and AFM. And this paper shows our recent results and technology to fabricate the new designed cell with Pt electrodes deposited by sputtering method. We have achieved fill factor 68% and photoelectric conversion efficiency around 2.6% as the best results of new designed DSCs structure

Sterilization of Escherichia coli by using near-UV LED and TiO2 nanofibers that were prepared by using electrostatic spray

TiO2 nanofiber films were prepared by a homemade electrostatic spray method at 13 kV using a high power supply. As-prepared TiO2 was used to sterilize enteropathogenic Escherichia coli in polluted water by using near-UV LEDs at three different wavelengths with variable exposure time and frequency of irradiation. Irrespective of the wavelength of the light source used, longer irradiation times such as 1 h completely inactivated the E. coli. However, a wavelength of 375 nm was effective in inactivating in a shorter irradiation time (15 min). When the frequency of irradiation was 1 kHz, almost 95% of the E. coli was inactivated after 30 min exposure.

A Study of DSC Using Ultrasonic and Thermal Treatment on Nano-Crystalline TiO2 Surface

Recently, there were many researches for efficiency improvement of DSC. Among of these works, research of surface treatment is still a prerequisite things for electron diffusion, light-harvesting and surface state of DSC[1]. Using of the surface treatment, it can be raise up porosity of TiO2 nano-crystalline structure on photo-electrode[2–5]. There are many ways to raise up its porosity such as chemical, physical, electrical and optical methods[7–9]. In this paper, we have designed and manufactured MOPA-PLL type ultrasonic circuit (100W, frequency and duty variable). Manufactured ultrasonic circuit to use to force physical vibration into TiO2 paste. Then, we have optimized forcing time, frequency and duty of ultrasonic irradiation for surface treatment of DSC photo-electrodes. In I-V characteristic test of DSC, ultrasonic and thermal treated DSC shows 19% improved its efficiency comparing with established DSC.

A Study on the Optimum Structure of Dye-Sensitized Solar Cell for Expanding the Active Area

A lot of researches about dye-sensitized solar cell are recently being conducted. Because DSC has several advantages over the limits of silicon solar cells such as a low manufacturing expense, a simple manufacturing process and its transparency. But most researches on DSC are still conducted about the unit cell and laboratory-centered. That is, present researches on DSC are not practical. Therefore, researches on large scale cells and modules are the prerequisites for DSC to have the practical applications. Characteristics of large scale DSC are so different from those of small area DSC in aspect of fill factor and efficiency. In this study, we made an experiment to find a suitable size of DSC that has the most effective power according to the variation of active area. The experiment was conducted in detail about the optimum ratio of length to width to find the active area which has the best output by comparing with the ratio of active area to non-active area. As a result, we achieved the optimum ratio of length to width as 4:1.5 and active area of 8cm2 as the optimum size for up-scaling DSC. And we got open circuit voltage of 0.8V, short circuit current of 51.7mA and efficiency of 2.9% from the optimum size DSC.