M. Y. Feteha

The effects of temperature and light concentration on the GaInP/GaAs multijunction solar cell’s performance

Monolithic Ga0.49In0.51P/GaAs cascade solar cells with a p+/n+ GaAs tunnel junction were grown by MOCVD technique. The variation of the photovoltage, photocurrent, fill factor, efficiency, I–V characteristics and spectral response under different temperatures (25–75 °C), and light intensity values (1–40 sun), were investigated experimentally.

Metal-insulator-semiconductor solar cell under gamma irradiation

The performance of a home made MIS–p-Si solar cell was experimentally studied under various gamma irradiation doses (up to 500 Mrad). The effect of radiation dose on the I−V and C−V characteristics was investigated in this work. The obtained results showed that all the output parameters of the cells under investigation were degraded with gamma radiation exposure. In addition, the effects of fabrication conditions (metal thickness and adding of antireflection coating) on the cell output parameters were also investigated.

Synthesis and characterization of core–shell–shell magnetic (CoFe2O4–SiO2–TiO2) nanocomposites and TiO2 nanoparticles for the evaluation of photocatalytic activity under UV and visible irradiation

Magnetic TiO2–SiO2–CoFe2O4 (TSC) composite photocatalytic particles with a core–shell structure and a high crystalline anatase TiO2 shell were synthesized via controlled hydrolysis and condensation of titanium isopropoxide. Nano-sized TiO2 powders were synthesized by a sol–gel/hydrothermal route. The prepared TiO2 and its composites were characterized by XRD, SEM, TEM, FT-IR, VSM, and UV-Vis. The results show that the obtained TSC composite particles were composed of spherical nanoparticles, about 5–8 nm in diameter, with several CoFe2O4 fine particles as cores and silica as coatings and barrier layers between the magnetic cores and anatase titania shells. The average crystallite size of TiO2 nanoparticles with an anatase structure is 6 nm. The photocatalytic activities of the samples were evaluated by the photocatalytic degradation of dichlorophenol-indophenol (DCPIP) dye. The maximum level reached for the degradation of the dye molecule was 95.32 and 87.27% for 3 minutes under UV and visible light respectively for mesoporous TiO2 nanoparticles.

Photocatalytic parameters and kinetic study for degradation of dichlorophenol-indophenol (DCPIP) dye using highly active mesoporous TiO2 nanoparticles.

Highly active mesoporous TiO2 of about 6nm crystal size and 280.7m(2)/g specific surface areas has been successfully synthesized via controlled hydrolysis of titanium butoxide at acidic medium. It was characterized by means of XRD (X-ray diffraction), SEM (scanning electron microscopy), TEM (transmission electron microscopy), FT-IR (Fourier transform infrared spectroscopy), TGA (thermogravimetric analysis), DSC (differential scanning calorimetry) and BET (Brunauer-Emmett-Teller) surface area. The degradation of dichlorophenol-indophenol (DCPIP) under ultraviolet (UV) light was studied to evaluate the photocatalytic activity of samples. The effects of different parameters and kinetics were investigated. Accordingly, a complete degradation of DCPIP dye was achieved by applying the optimal operational conditions of 1g/L of catalyst, 10mg/L of DCPIP, pH of 3 and the temperature at 25±3°C after 3min under UV irradiation. Meanwhile, the Langmuir-Hinshelwood kinetic model described the variations in pure photocatalytic branch in consistent with a first order power law model. The results proved that the prepared TiO2 nanoparticle has a photocatalytic activity significantly better than Degussa P-25.

Optimum design for bifacial silicon solar cells

In this paper, an optimization technique is used to achieve maximum efficiency for the bifacial buried emitter silicon solar cell (BBESC). The optimum thicknesses of the sub-cells of the BBESC are function of the level of back illumination through its dependence on the degree of the electrical mismatching between the different sub-cells.

Study on synthesis of superparamagnetic spinel cobalt ferrite nanoparticles as layered double hydroxides by co-precipitation method

Cobalt ferrite layered double hydroxide (LDH) nanoparticles with cubic structure were synthesized by the co-precipitation method: addition of NaOH solution to a solution of Co2+ and Fe3+. Formation of nanoparticles was confirmed by XRD, SEM, TEM, PSA, FT-IR, TGA, DSC, and magnetic characteristics were measured using VSM. Crystals produced by calcination at 900°C possessed high coercivity and pronounced physical and chemical stability. Nanoparticles of CoFe2O4 formed outer layers with poor crystallization on the surface of cobalt ferrite nanocrystals.

Gamma irradiated CdS(In)/p-Si heterojunction solar cell

An n-CdS(In)/p-Si heterojunction solar cell was fabricated by vacuum evaporation of a single source of a stoichiometric mixture of CdS and In on a p-Si single crystal wafer at a low temperature of 120°C. The open circuit voltage, short circuit current density, fill factor and conversion efficiency under AM1 were 0.47 V, 20 mA/cm2, 0.74 and 7%, respectively. The physical and photoelectric characteristics were measured and discussed. In addition, the cell was irradiated by gamma radiation of 1.25 MeV and its effect on the cell performance was studied. Various preparation parameters such as composition and CdS layer thickness affecting the cell characteristics were investigated before and after exposure to the radiation.

Organic field effect transistor based on polyaniline - dodecylbenzene sulphonic acid for humidity sensor

Humidity sensor based on organic field-effect transistor (OFET) was created using P-channel organic semiconductor polyaniline doped with dodecylbenzene sulfonic acid (DBSA)(1∶2.5) as an active layer and gate insulator polymethyl methacrylate (PMMA) layer on n-type silicon gate. The performance of OFET was evaluated using current-voltage characteristics (I–V) under exposure to humidity. The p-type OFETs operating in an enhancement mode with the current saturation (ISat) was 2.6 µA and the threshold voltage VT was found to be 2.4V. The OFET sensors exhibited a change in the electric characteristic such as the threshold voltage, the saturation current, and the field-effect charge carrier mobility when the sensors were exposed to Relative humidity (RH). Meanwhile, the favourable and rapid change in humidity response characteristics of the OFET sensors was observed from the change in the drain-source current as a function of time. After exposed to relative humidity, the drain current of sensor was enhanced due to the decrease of the channel resistance. When the sensors were exposed to 93.4 % RH the drain current was saturated.

Influence of calcination temperature on the physical properties of nano-titania prepared by sol-gel/hydrothermal method

Nano-sized TiO2 powders were synthesized by a modified hydrolysis reaction using titanium butoxide as a precursor, water as a solvent, acetylacetone to slowdown the hydrolysis and the condensation reactions and ammonia as a base catalyst. Phase transformation and particle size of the calcined powders were investigated as a function of the calcination temperature by room-temperature X-ray diffraction; scanning electron microscopy and Fourier transform infrared spectroscopy techniques. Thermal gravimetric analysis (TGA) was used to examine the thermal properties of the produced TiO2 nanoparticles. The XRD showed that the uncalcined sample was mostly the anatase phase with some rutile content. It was indicated that the thermal annealing resulted in increasing the average crystallite size from 8.2 to 53.5 nm. As the calcination temperature increased, the particle size, the rutile phase, the crystallization of the anatase phase, and the agglomeration were increased. The increase in the rutile content and grain growth are caused by the calcination at higher temperatures even calcination at 800°C for 2 h.