Hyunwoong Seo

Enhancement in the photovoltaic performance of a dye-sensitized solar cell by an optimized ZnO barrier layer

A dye-sensitized solar cell (DSC) has been considered as a strong alternative to conventional photovoltaic devices based on semiconductors such as silicon or compound semiconductors. The barrier layer functioned by the use of an electrode consisting of two different conduction band potentials is very effective in increasing the photovoltaic performance of a DSC. Especially, zinc oxide (ZnO) is very effective as a barrier layer because it has a higher energy level of the conduction band than TiO2and good contact with TiO2 and dye molecules. We tried to fabricate the ZnO barrier layer using zinc acetate aqueous solution by the dip-coating method, although ZnO film is usually fabricated by chemical vapor deposition or sputter deposition. The experimental parameters were optimized to achieve an effective ZnO barrier layer. The electrochemical impedance spectroscopy and x-ray diffraction pattern were measured to analyze the ZnO layer. The photovoltaic performance of a completed DSC with an optimized ZnO barrier layer was measured and compared with that of a conventional DSC. Consequently, a DSC with a ZnO barrier layer had an increased VOC up to 0.85 V and an enhanced efficiency of 4.05%.

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.

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.

Deduction of Optimal Conditions for Acrylic Etching Technique by using CO 2 Laser

Laser cutting with the micro-control technique has great potential to be employed for acrylic machining. In this paper, the optimal conditions of acrylic etching have been investigated. The three parameters such as laser power, moving velocity, and thickness of acrylic are experimented to find out optimal conditions. From these experimental results, we have known that it is very important to control accurate power by the TRIAC switching technique. The best condition of acrylic etching is performed 10 Wand 72 ㎜/sec at the plastic thickness of 1.33 ㎜. The other case is performed 10W and 48 ㎜/sec, and 12 Wand 56 ㎜/sec at the acrylic thickness of 2.00㎜, respectively.

Alignment of TiO2 (Anatase) Crystal of Dye-Sensitized Solar Cells by External Magnetic Field

In this study, magnetic field () was applied on TiO2 (anatase) of dye-sensitized solar cell (DSC) for alignment of crystal. Magnetic field was applied on TiO2 when deposited TiO2 on the fluorine tin oxide (FTO) was dried at 373 K for crystalline orientation. And applying time of was varied 0~25 min. Characteristics of the magnetic field applied TiO2 films were analyzed by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). Current-voltage characteristics were also analyzed using solar simulator, and it was confirmed that the energy conversion efficiency of 41% was increased. Finally, it was identified that the magnetic field affected orientation of TiO2, resulting in the enhancement of the performance of the DSC.

Effect of the sputtering thickness and angle of the Pt film on a counter electrode on the efficiency of a dye-sensitized solar cell

The effects of the sputtering thickness and angle of the Pt film on a counter electrode on the efficiency of a dye-sensitized solar cell (DSC) were scrutinized. There has been a research that shows the Pt film thickness had no significant influence on the performance of the DSC. However, we conducted the experiment to get the best sputtering time for the best performance of the DSC. With the sputtering time fixed to 120 seconds, we varied the angle of substrate from 0° to 60°. Under standard test condition, we obtained the efficiency of 4.61% at the 40° of substrate angle with a cell area of 1 cm2.

A study on the fabrication of externally connected module by equivalent circuit analysis of optimized dye-sensitized solar cell

In this study, we attempted an external connection of dye-sensitized solar cells for large scaling, contrary to conventional modules of grid type. Generally, it is well known that series connection is effective but parallel connection cause decrease of efficiency in case of external connection. This is the main reason why researchers avoid external connected module. We proved it by equivalent circuit analysis of dye-sensitized solar cell and made up externally series-parallel connected module as a DC power source. It is difficult to make up practical solar module by only series connection because of extremely low current. Therefore, we make a proper voltage from series connection and a current from parallel connection of dye-sensitized solar cell module without current loss using that analysis. Finally, we made 8V-0.25A large module of series-parallel connected dye-sensitized solar cell based on equivalent circuit analysis.

The effect of dividing the active area of dye-sensitized solar cell

Active area of dye-sensitized solar cell (DSSC) has an effect on the efficiency of DSSC. As the active area increases, the efficiency goes down in a general way. This is caused by the increase of internal resistance in DSSC. The internal resistances are related to various resistant elements. The charge transfer processes at Pt counter electrode and the sheet resistance of TCO are two of these resistant elements. In this study, we try to divide the active area into several small sections in a large sized cell to reduce these two internal resistant elements. As a result, we find out that the fill factor is increased and then the conversion efficiency is improved as the number of dividing active area into several small sections is increased.

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.