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[en] In order to improve the photo energy conversion efficiency of dye-sensitized solar cells (DSCs), it is important to optimize their porous TiO2 electrodes. This paper examines the surface and cross-sectional views of the electrodes using scanning electron micrography. Two types of samples for cross-sectional viewing were prepared by mechanically breaking the substrate and by using an Ar-ion etching beam. The former displays the surface of the TiO2 particles and the latter shows the cross-section of the TiO2 particles. We found interesting surface and cross-sectional structures in the scattering layer containing the 400 nm diameter particles, which have an angular and horned shape. The influence of TiO2 particle size and the thickness of the nanocrystalline-TiO2 electrode in DSCs using four kinds of sensitizing dyes (D 149, K 19, N 719 and Z 907) and two kinds of electrolytes (acetonitrile-based and ionic-liquid electrolytes) are discussed in regards to conversion efficiency, which this paper aims to optimize.
[en] We demonstrated a method to control the bandgap energy of GaN nanowires by forming GaNatInGaN core-shell hybrid structures using metal organic chemical vapor deposition (MOCVD). Furthermore, we show the growth of Au nanoparticles on the surface of GaN nanowires in solution at room temperature. The work shown here is a first step toward engineering properties that are crucial for the rational design and synthesis of a new class of photocatalytic materials. The hybrid structures were characterized by various techniques, including photoluminescence (PL), energy dispersive x-ray spectroscopy (EDS), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD).
[en] The Fenton and photo-Fenton detoxification of non-biodegradable chemical pollution in water was investigated under simulated UV light in the laboratory and under direct sunlight in Ouagadougou, Burkina Faso. The laboratory experiments enable one to make a systematic diagnosis among three types of wastewaters, identifying a bio recalcitrant wastewater containing the Chloro-hydroxy-Pryridine (CHYPR). The application of the photo-Fenton process on effluent containing the CHYPR showed not to stimulate the generation of biodegradable by-products. Optimal conditions for detoxification of effluent containing the CHYPR were found at ph=2.8, [Fe2+]=5.2 mM, initial [H2O2]=768 mM, for an effluent concentrated at 2.2 mM of CHYPR. The application of the photochemical process on a field pilot solar photo reactor for the detoxification of water polluted with a pesticide made with Endosulfan showed very promising results, with potential biodegradable effluents obtained at the end of the photochemical treatment. Optimal conditions of the applied study were found at ph=3. [H2O2]=8 mM and [Fe2+]=0.18 mM for an initial concentration of 0.36 mM of Endosulfan.
[en] Novel photo chromic spiro pyrans (SPPs) containing 6'-hydroxy group were synthesized and their spectral properties as well as abilities for complexation with metal ions studied. In solutions they exist as equilibrium mixture of spirocyclic (A) and merocyanine (B) isomers. The largest content of merocyanine form was found for the derivative with an electron-donating methyl group in position 5 of hetaryl fragment. The irradiation of SPPs in acetonitrile shifts the equilibrium to the B form. Similar effect causes the addition of metal cations due to formation of colored complexes with merocyanine isomers.
[en] TiO2-WO3 photo catalysts were prepared in a vacuum evaporator by impregnation of TiO2 with WO2 dissolved in an H2O2 solution (30%) and followed by calcination at 400 and 600 degree C. XRD analyses showed that at 400 degree C monoclinic phase of WO3 was dominated whereas at 600 degree C both monoclinic and regular phases of WO3 were present. Modification of TiO2 by WO3 caused increasing in the absorption of light to the visible range. TiO2 and photo catalysts modified with low amount of WO3 (15?wt.%) showed high adsorption of Acid Red (AR) on their surface and enhanced photo catalytic activity under UV irradiation. Under visible light irradiation, TiO2-WO3 photo catalysts prepared at 400 degree C were more active for AR decomposition than those prepared at 600 degree C suggesting that monoclinic phase of WO3 is more active under visible light than regular WO3. Although TiO2-WO3 photo catalysts appeared to be active under visible light for decomposition of AR, the UV irradiation was more efficient.
[en] The membranes 55 wt.% chitosan-45 wt.% NH4I, 33 wt.% chitosan-27 wt.% NH4I-40 wt.% EC, and 27.5 wt.% chitosan-22.5 wt.%?NH4I-50 wt.% buthyl-methyl-imidazolium-iodide (BMII) exhibit conductivity of 3.73 x 10-7, 7.34x10-6, and 3.43x10-5 S cm-1, respectively, at room temperature. These membranes have been used in the fabrication of solid-state solar cells with configuration ITO/TiO2/polymer electrolyte membrane/ITO. It is observed that the short-circuit current density increases with conductivity of the electrolyte. The use of anthocyanin pigment obtained by solvent extraction from black rice and betalain from the callus of Celosia plumosa also helps to increase the short-circuit current.
[en] This paper reviews recent investigations of the influence of dopants on the optical properties of TiO2 polymorph. The common undoped polymorph of TiO2 are discussed and compared. The results of recent doping efforts are tabulated, and discussed in the context of doping by elements of the same chemical group. Dopant effects on the band gap and photo catalytic activity are interpreted with reference to a simple qualitative picture of the TiO2 electronic structure, which is supported with first-principles calculations.
[en] Use of a solar cell in concentrator PV technology requires reduction in its series resistance in order to minimize the resistive power losses. The present paper discusses a methodology of reducing the series resistance of a commercial c-Si solar cell for concentrator applications, in the range of 2 to 10 suns. Step by step optimization of commercial cell in terms of grid geometry, junction depth, and electroplating of the front metal contacts is proposed. A model of resistance network of solar cell is developed and used for the optimization. Efficiency of un optimized commercial cell at 10 suns drops by 30% of its 1 sun value corresponding to resistive power loss of about 42%. The optimized cell with grid optimization, junction optimization, electroplating, and junction optimized with electroplated contacts cell gives resistive power loss of 20%, 16%, 11%, and 8%, respectively. An efficiency gain of 3% at 10 suns for fully optimized cell is estimated
[en] The present commercial photovoltaic solar cells (PV) converts solar energy into electricity with a relatively low efficiency, less than 20%. More than 80% of the absorbed solar energy is dumped to the surroundings again after photovoltaic conversion. Hybrid PV/T systems consist of PV modules coupled with the heat extraction devices. The PV/T collectors generate electric power and heat simultaneously. Stabilizing temperature of photovoltaic modules at low level is highly desirable to obtain efficiency increase. The total efficiency of 60-80% can be achieved with the whole PV/T system provided that the T system is operated near ambient temperature. The value of the low-T heat energy is typically much smaller than the value of the PV electricity. The PV/T systems can exist in many designs, but the most common models are with the use of water or air as a working fuid. Efficiency is the most valuable parameter for the economic analysis. It has substantial meaning in the case of installations with great nominal power, as air-cooled Building Integrated Photovoltaic Systems (BIPV). In this paper the performance analysis of a hybrid PV/T system is presented: an energetic analysis as well as an exergetic analysis. Exergy is always destroyed when a process involves a temperature change. This destruction is proportional to the entropy increase of the system together with its surroundings the destroyed exergy has been called energy. Exergy analysis identifies the location, the magnitude, and the sources of thermodynamic inefficiencies in a system. This information, which cannot be provided by other means (e.g., an energy analysis), is very useful for the improvement and cost-effectiveness of the system. Calculations were carried out for the tested water-cooled ASE-100-DGL-SM Solar watt module.
[en] The performances of a gas-solid two-dimensional fluidized bed reactor in photo catalytic selective oxidation reactions, irradiated with traditional UV lamps or with a microscale illumination system based on UV emitting diodes (UV A-LEDs), have been compared. In the photo catalytic oxidative dehydrogenation of cyclohexane to benzene on MoOx/TiO2-A12O3 catalyst the use of UV A-LEDs modules allowed to achieve a cyclohexane conversion and benzene yield higher than those obtained with traditional UV lamps. The better performances with UV A-LEDs are due to the UV A-LEDs small dimensions and small-angle emittance, which allow photons beam be directed towards the photo reactor windows, reducing the dispersion outside of photo reactor or the optical path length. As a consequence, the effectively illuminated mass of catalyst is greater. We have found that this illumination system is efficient for photo-oxidative dehydrogenation of cyclohexane to cyclohexene on sulphated MoOx-A12O3 and ethanol to acetaldehyde on VOx/TiO2.