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Silicon oxide thin film was formed using reaction of spin-coated dimethyl-silicone-oil and 5% ozone gas at low temperature of 300°C. Silicone oil is used for lubrication, insulation, and so on, and it is inexpensive and easy to deal with owing to its stability. FT-IR spectrum of the formed silicon oxide film was similar to that of the thermally oxidized film, and we hardly observed peaks of Si-CH3and C-H bonds originated in silicone oil. The Si-OH bonds in the film were observed. The Si-OH bond causes the degradation of the electric properties of the insulator. In order to remove the Si-OH bonds, the silicon oxide film was treated with an argon excimer light at room temperature. The wavelength of the light was 126 nm. The amount of Si-OH bond was drastically reduced by the UV annealing. The energy of the UV light is high and the value is 9.8 eV. The high energy light may cut the bond of Si-OH. Therefore, the amount of Si-OH bond could be reduced.

Reflection losses of light at the silicon surface cause a reduction in conversion efficiency of silicon solar cell. There is anisotropic etching silicon to form a textured structure on the silicon surface by a simple wet process as a method of reducing the reflectivity. Further, miniaturization of the textured structure to the nanosize will improve the conversion efficiency by reducing the reflectivity. In this study, we formed texture structure of 1 μm size by applying the particles on a silicon surface as an etching mask.

Temperature characteristic analysis of the triple-junction solar cell was carried out using circuit simulator under concentration conditions. The temperature exponent of saturation current density for each single-junction solar cell was derived. Extracted temperature exponents were used in the equivalent circuit model for the triple-junction solar cell, and the calculations of solar cell performance were carried out at various temperatures and concentration ratios. The calculation results agreed well with the measured results.

Using an equivalent circuit model, the output characteristics of a bifacial photovoltaic solar module under various shaded conditions of the back side of the module were analyzed in detail. From the dark current-voltage (I-V) characteristics of bifacial photovoltaic solar cell, the diode parameters were extracted. The extracted diode parameters were applied to the equivalent circuit model for the bifacial photovoltaic solar module, and the solar-module performance was calculated. There was good agreement between the measured and calculated IV characteristics of the bifacial photovoltaic solar module under various shaded conditions.

In order to fabricate the SiO2 thin film using dimethyl silicone oil and ozone on protective covering glass for solar panels, the hydrophilicity and the transmittance of the film was investigated. We fabricated the film at different temperatures of 150°C, 175°C, 200°C, 225°C and 250°C on the glass substrates. The hydrophilicity of the film fabricated at 150°C showed very good hydrophilicity (water contact angle: ~8°), and transmittance was improved compared to the non-coated glass.

When installing concentrator photovoltaic (CPV) systems in desert areas, we must consider the impact of sandstorms on the Fresnel lens in CPV modules. CPV systems are much more sensitive to sandstorms than flat-panel PV systems because they can only use the direct beam component of sunlight. In this study, the transmittance of a PMMA substrate after sandblasting was evaluated and the influence of sandblasting on the output of a CPV system was assessed. The transmittance of PMMA decreased with an increase in the momentum of blown sand. The conversion efficiency of a CPV module was determined by equivalent circuit calculation. The conversion efficiency decreased with increasing momentum. The coefficient of degradation was 0.17 point per unit momentum.

SiC was prepared from Shirasu volcanic ash using solar furnace. The solar furnace is composed by two parts; Fresnel lens and reacting furnace. Fresnel lens is used to concentrate sunlight onto the reacting furnace where the sample was put on. The sample was made from the mixture of SiO2 formed using Shirasu volcanic ash and graphite, and placed in the carbon crucible inside the reacting furnace. By using light of sun concentrated with Fresnel lens, the sample was irradiated for 15 minutes and the furnace was left until it cooled down to room temperature. Both irradiated and cooling processes were done under Ar atmosphere. After the experiment, the sample was evaluated by XRD and Raman spectroscopy and the result indicated that β-SiC was formed.

The output characteristics of concentrator photovoltaic (CPV) system were analyzed in the data period of a year from November 2010 to October 2011. Characteristics of CPV are more sensitive to environmental factors as compared to flat-plate PV system. Especially, solar spectrum distribution has considerable influence on the output of CPV because CPV uses multi-junction solar cells. In this study, we analyzed the influence of environmental factors using average photon energy (APE) and temperature of solar cell (Tcell). Most frequent condition during operation was APE = 1.87 ± 0.005 eV and Tcell = 65 ± 2.5 °C. Performance ratio at the most frequent condition was 83.9%. These results indicated the importance of the understanding of the behavior of the outdoor performance and the accurate data of environmental conditions where the PV systems were installed.

The most common method for solar cell installation is the inclining mounting method, this method can also be used with the bifacial solar cell. For the installation, its important to understand the properties of light which is entering the back surface of the bifacial solar cell. In this study, we measured the incidence light of the back surface of bifacial solar cell and compared its output power to the common single-surface solar cell to investigate the optimal condition for its installation in terms of (1) tilt angle, (2) height, (3) optimal region and (4) ground surface condition where the panel should be installed.

The micro/nanocomposite structure on silicon surface was formed by a simple 2-step chemical etching with a potassium hydroxide anisotropic etching and a stain etching in order to obtain a superhydrophobic silicon surface. Micro-sized pyramids structure was formed in a mixture of 3 wt.% potassium hydroxide with 8 vol.% isopropyl alcohol solution at 80C for 60 min. The formation of the nanosized structure was performed by stain etching at room temperature using nitric acid (HNO3) / hydrofluoric acid (HF) aqueous solutions. The silicon surface had the superhydrophobic surface. The contact angle was measured and the maximum value was 167o for the condition of second etching with HF : HNO3 : H2O = 11 : 1 : 3.

High purity nanoporous silica was fabricated using Shirasu a volcanic ash as a starting material. The starting materials were melted at 1400°C. A mother glass was formed by quenching the melt in pure water. Leaching was performed by immersing the mother glass into an HCl solution. Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure and had pore size smaller than 2 nm. In order to control the pore size, post heat treatment was performed. The treatment temperature was varied from 540 to 600°C for 12 h. The treatment time was varied from 6 to 12 hours at 600°C. The pore size was controlled from 3.1 to 23.4 nm with changing temperature and time for the post heat treatment.

The anti-soiling layer was coated on the surface of Fresnel lens for concentrator photovoltaic. The anti-soiling layer was prepared by coating the acrylic urethane capping layer, the inorganic/organic nanograded intermediate layer, and the photocatalytic surface layer including modified WO3 and partial hydrolyzed tetraethyl orthosilicate. The adherent sand for the sample without coating was 0.023 g and that for the sample with coating was 0.008 g. The adhesion of sand was suppressed owing to the effect of the anti-soiling coating. The electrostatic potential for the sample without coating was 0.23 kV, and the value was much higher than that for the sample with coating. The electrostatic charge at the surface of sample was suppressed with the anti-soiling coating.

High purity nanoporous silica was fabricated using Shirasu volcanic ash as a starting material. The starting materials were placed into a platinum crucible and were melted at 1400°C. A mother glass was formed by quenching the melt in pure water. Leaching was performed by immersing the mother glass into an HCl solution. Nonsilica phases formed by phase separation in the mother glass were leached out with acid solution. The obtained porous silica was more than 99% pure and had pore size smaller than 2 nm. In order to control the pore size, post heat treatment was performed. The pore size could be controlled from 3.1 to 21.7 nm by changing the post treatment temperature.