Min-Kyu Son

Study on characteristics of CdS quantum dot-sensitized solar cells prepared by successive ionic layer adsorption and reaction with different adsorption times

Cadmium sulfide (CdS) quantum dots (QDs) were adsorbed on a titanium dioxide (TiO2) nanoporous film by successive ionic layer adsorption and reaction (SILAR) method with different adsorption times to study the influences of different SILAR adsorption times on CdS quantum dot-sensitized solar cells (QDSCs). The optical properties of CdS sensitized TiO2 films were studied by scanning electron microscopy and UV-Vis absorbance spectroscopy. The particle size of the CdS QDs was approximated using the effective mass approximation theory from the absorbance spectra. The photovoltaic characteristics of the CdS QDSCs were analyzed by I–V characteristics and electrochemical impedance spectroscopy under air mass 1.5 illumination. As a result, the particle size of the CdS QDs became larger and light harvesting was enhanced with increasing SILAR adsorption time. The maximum photovoltaic conversion efficiency of the CdS QDSCs (1.86%) was obtained at the SILAR adsorption time of 30 min with the highest short circuit current density and lowest charge transfer resistance.

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%.

The effects of electrolyte additives on the cell performances of CdS/CdSe quantum dot sensitized solar cells

The electrolyte for QDSSCs is normally a polysulfide, S2−/Sx2−, redox couple. This couple plays an important role for the regeneration of quantum dots. This study examined the effects of the electrolyte for CdS/CdSe QDSSCs. Electrolytes consisting of 1M Na2S, 2M S in a methanol and water-mixed solution at a 7: 3 ratio with or without additives such as KCl, NaOH, KOH and NaCl were used for QDSSC. The electrolyte with NaOH showed the highest conversion efficiency, 3.18%. The reasons for the improved photovoltaic characteristics were analyzed using a range of techniques.

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.

Enhanced Photocurrent from CdS Sensitized ZnO Nanorods

Structure and optical properties of cadmium sulphide-zinc oxide composite nanorods have been evaluated by suitable characterization techniques. The X-ray diffraction spectrum contains a series of peaks corresponding to reflections from various sets of lattice planes of hexagonal ZnO as well as CdS. The above observation is supported by the Micro-Raman spectroscopy result. The optical reflectance spectra of CdS-ZnO is compared with that of ZnO where we observe an enhanced absorption and hence diminished reflection from CdS-ZnO compared to that from only ZnO. A very small intensity of the visible photoluminescence peak observed at 550 nm proves that the ZnO nanorods have very low concentrations of point defects such as oxygen vacancies and zinc interstitials. The photocurrent in the visible region has been significantly enhanced due to deposition of CdS on the surface of the ZnO nanorods. CdS acts as a visible sensitizer because of its lower band gap compared to ZnO.

Effect of Acetic Acid in TiCl4 Post-Treatment on Nanoporous TiO2 Electrode in Dye-Sensitized Solar Cell

Titanium tetrachloride (TiCl4) is adopted as a post-treatment on the nanoporous titanium oxide (TiO2) layers to enhance the performance of dye-sensitized solar cells (DSCs). A TiCl4 post-treatment is capable of improving electron transport and dye-loading on the surface of TiO2 layers. In this study, the TiCl4 solution mixed with acetic acid was employed to enhance the condition of the TiCl4 post-treatment. Since acetic acid in the TiCl4 solution prevents the formation of impurities and facilitates the crystallization, it improves dye adsorption and electron transport properties. To analyze the performance of the cell, we measured X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface measurements, UV–vis spectroscopy and electrochemical impedance spectroscopy (EIS) and photocurrent–voltage (I–V) measurements.

Improvement on the Long-Term Stability of Dye-Sensitized Solar Module by Structural Alternation

Dye-sensitized solar cell (DSC) module still lacks the long-term stability because of a volatile electrolyte. In this work, structural alternation of DSC parallel modules was proposed for high performance and stability. In the conventional module, the adhesion with the photo/counter electrodes was not stable with only one layer of sealant so that the stability was poor. On the other hand, buried grid module proposed in this work is possible to be stably sealed with only one layer of sealant. In this structure, grid electrodes are leveled with the same height of transparent conductive oxides (TCOs) because grid electrodes are inserted under furrows of etched TCOs. Consequently, the buried grid module had better long-term stability than conventional module. Additionally, the photo-current and efficiency were improved by the sonicated grid and the light scattering layer.

Analysis on the Light-Scattering Effect in Dye-Sensitized Solar Cell according to the TiO2 Structural Differences

A light-scattering layer is widely used in highly efficient dye-sensitized solar cells (DSCs) because it improves the light-harvesting ability of a DSC by reflecting the light passing through the transparent TiO2 layer. Among many parameters affecting this light-scattering effect, the thickness of the TiO2 photoelectrode is also a significant parameter. However, most studies regarding the influence of the TiO2 photoelectrode thickness on the light-scattering effect have only focused on the thickness of the transparent TiO2 layer and have ignored the light-scattering layer thickness itself. Therefore, in this study, we analyzed the light scattering effect according to the thickness of the light-scattering layer and the resulting photovoltaic performance of the DSC. Finally, it was confirmed that the light-scattering effect is enhanced to some degree with the increase of the light-scattering layer thickness, while it is weakened when the light-scattering layer thickness is further increased.

A Study on FTO-less Dye Sensitized Solar Cell with Ti Deposited Glass

Dye-sensitized solar cells (DSCs) have taken much attention due to their low cost and easy fabrication method compare to silicon solar cells. But research on cost effective DSC is prerequisite for commercialization. Fluorine doped tin oxide (FTO) which have been commonly used for electrode substrate as electron collector occupied most percentage of manufacturing cost. Therefore we studied FTO-less DSC using sputtered Ti deposited glass as photoelectrode instead of FTO to reduce manufacturing cost. Ti films sputtered on the glass for different time, 5 to 20 minutes with decreasing sheet resistance as deposition time increases. A light source illuminated to counter electrode in order to overcome opaque Ti films. The efficiency of DSC (Ti20) made Ti sputtered glass for 20 min as photoelectrode was 5.87%. There are no significant difference with conventional cell despite lower manufacturing cost.

The Enhancement of the Performance of Dye Sensitized Solar Cells Using Nb 2 O 5 -TiO 2 Compound

Niobium oxide () has a strong chemical coherence and good electrical conductivity. Therefore, this material is helpful to enhance the performance of the dye sensitized solar cells (DSC) by improving the electron mobility. In this study, was mixed with and this compound was applied to the DSC to improve its performance. As a result, the current density of the DSC using the compound on the photoelectrode was increased, because the internal resistance concerned to the electron transfer in the photoelectrode of DSC was decreased. However, large amount of the induces the decrease of the efficiency of the DSC because the surface area to attach dye molecules is decreased due to the large particle of . Therefore, it is important to optimize the mixture ratio of the compound for maximizing the performance of the DSC. Finally, the most optimum performance of the DSC was shown in case of the concentration of 10 wt% of the compound.