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Numéro 01

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Simulation study of InGaN/GaN multiple quantum well solar cells

It’s known that indium gallium nitride InGaN alloys has a direct band gap varying from 0.7 to 3.4 eV which covers nearly the whole solar spectrum making it material of choice to make tandem solar cells. In other hand, it’s experimentally known that uses of InGaN/GaN multiple quantum well MQW structures in GaN based devices decreases surface recombination and, thus, enhances devices performance. Here, we present a simulation study of multiple quantum well MQW InGaN/GaN solar cells, where cell’s active region is formed by a number of InGaN quantum wells (QWs) separated byGaN quantum barriers (QBs). We will present indium element content of InxGa1-xN wells and number of InGaN/GaN periods impacts on solar cell parameters.

Nanostructured metallic oxides coating

This project has been focused on structural, morphological, optical and photoluminescence properties of pure ZnO thin film. Here, zinc oxide thin films are grown on glass via facile and low cost sol gel spin coating process @ fixed spinning speed of 1000 RPM. The X-ray patterns, the transmittance, the particle size by the atomic force microscope are investigated. The particle size is equal to 120 nm and the surface roughness is found to be 23.33 nm. The photoluminescence analysis reveals near band emission and strong visible emission 2.11 and 2.80 eV.
Keywords : Spin coated ZnO films ; X-rays pattern ; transmittance ; photoluminescence ; SEM ; TEM ; Electron diffraction ; AFM.

Electronic and structural properties of NaZnAs compound ; an ab-initio study in the tetragonal and cubic α phases

A theoretical study of structural, and electronic properties of NaZnAs compound is presented by performing ab initio calculations based on density-functional theory using the full-potential linear augmented plane wave (FP-LAPW). The generalized-gradient approximation (GGA) and the local density approximation LDA) are chosen
for the exchange–correlation energy. The Engel-Vosko (EVGGA) formalism is applied for electronic properties The calculated structural parameters, such as the lattice constant, bulk modulus and pressure derivative, the electronic band structures and the related total density of states and charge density are presented. The high-pressure α phase of the NaZnAs is investigated and phase transition pressure from tetragonal to high-pressure phase is determined. We have found that the Nowotny–Juza compounds NaZnAs is direct gap semiconductor at ambient pressure. The bonding character and the phase stability of NaZnAs compound are discussed. The nature and the size of the band gap of NaZnAs compound are associated with the bonding character of two Kinds of bonds, namely, Na–As and Zn–As bonds.

Photocatalytic degradation of Methylene blue by modified porous silicon nanowires

In this paper, the effect of the time deposition of metal nanoparticles on the photodegradation of methylene blue is studied. The modified silicon nanowires were used as heterogeneous photocatalysts for the decomposition of methylene blue under UV light irradiation. The above reactions were monitored by UV–Vis spectrophotometer which shows the positive effect of the time deposition of metal nanoparticles on the photodegradation of methylene blue. 91% of the degradation was observed with the hydrogen terminated porous silicon nanowires and the degradation is about 95% for the modified porous silicon nanowires with Au (80min) and the same degree was obtained with Pt (120min) at 200 minutes of irradiation. The rate of the degradation reaches 100% at 90min of illumination with the decorated porous silicon nanowires with Pd nanoparticles.

Design and simulation of a valveless piezoelectric micropump for fuel delivery in fuel cell devices

Micro- and nano-electromechanical systems (MEMS or NEMS)-based fuel delivery in direct methanol fuel cell (DMFC) devices offer opportunities to address unmet fuel cells related to fuel delivery. By applying an alternating electrical field across the actuator, the resultant reciprocating movement of the pump diaphragm can be converted into pumping effect. Nozzle/diffuser elements are used to direct the flow. To make the power system applicable for portable electronic devices, the micropump needs to meet some specific requirements : low power consumption but sufficient fuel flow rate. In this study, a theoretical method have been used to investigate the effects of materials properties, actuator dimensions, driving voltage, driving frequency, nozzle/diffuser dimension, and other factors on the performance of the whole system. As a result, a viable design of micropump system for fuel delivery in DMFC devices has been achieved and some further improvements are suggested. A mathematical model was used to simulate the behaviour of the micropump. The results of mechanical calculations and simulations show good agreement with the actual behaviour of the pumps.

Electrical characteristics of Organic Light Emitting Diode “OLED” finite difference modeling

In this paper, a finite difference modeling of single layer organic light emitting diode “OLED” based on MEH-PPV [Poly (2-Methoxy, 5-(2’-Ethyl-Hexoxy)-1, 4-Phenylene-Vinylene)] and DP-PPV [Poly (2, 3-DiPhenyl-Phenylene-Vinylene)] is presented through the simulation of the basic equations i.e. the time independent continuity equations, with a drift diffusion form for current density, coupled to Poisson’s equation. Thus, several parameters are extracted from this model ; J (V) characteristics for the two devices which are compared to the experimental results and the spatial distributions of the potential, the electric field and the carrier concentrations.

The Effect of Ground albedo on the Performance GaInP and (a-Si : H) of Solar Cells

Solar radiation incident on vertical and inclined surfaces consists of beam, sky diffuse and ground reflected components. The ground reflected component may be significant, particularly in the northern latitudes due to low elevations of the sun and, at times, due to the presence of highly reflecting snow cover. Accurate estimation of ground reflected radiation would require knowledge of the foreground type and geometry, its reflectivity and the condition of the sky. The electrical current generated by the solar cells is very sensitive to the incident spectral distribution and intensity. This distribution varies greatly during the day due to changes in the sun’s position or weather conditions. This work investigates the feasibility of using a solar spectral radiation model SMARTS2 to estimate the global solar irradiance on two different sites in Algeria (Setif and Bejaia) and assess the influence of varying ground albedo on the conversion efficiency of GaInP and amorphous (a-Si : H) solar cells. The results show an augmentation in the short circuit current of amorphous (a-Si : H) solar cell due to increasing albedo. It is 6.25% and 9.84% under global radiation and for Setif and Bejaia sites respectively. However for GaInP solar cell, the augmentation of the short circuit current is 6.97% and 10.93% for Setif and Bejaia sites respectively. Nevertheless, the efficiency increases with increasing albedo for GaInP and amorphous (a-Si : H) solar cells.

Thickness optimization of various layers of CZTS solar cell

Thin film solar cells based on Cu2ZnSnS4 (CZTS) absorbers are proposed with the structure glass/Mo/CZTS/buffer/ZnO. In this work we have simulated CZTS thin film solar cell using solar cell capacitance simulator (SCAPS). The influences of thickness of (CZTS) absorber, thickness of (CdS) buffer layer and Zinc oxide window Layer (ZnO) on the photovoltaic cell parameters are studied. It can be seen after reviewing the results, that for high conversion efficiency, the cell should have a thin buffer layer and a thick absorber layer. In addition, the effect of operating temperature on the cell performance shows that the efficiency will be strongly affected by the increased temperature.

Synthesis, characterization and cytotoxic effect of ZnO nanoparticles obtained by mechanical alloying

ZnO nanoparticles with different grain sizes have been obtained by mechanical milling, after different treatment times : 3, 6, 12and 24 hours.
The final products have been characterized by different analytical techniques, such as X Ray Diffraction, Photoluminescence,Fourier transform infrared (FTIR) and UV-Visible spectroscopies.The cytotoxic effect of one selected concentration ZnO nanoparticles have been evaluated for paramecium growth kinetics and the mortality rate have been recorded as a function of time.Findings demonstrated that the evolution of the paramecium cell number is clearly affected by ZnO Nps presence.

The effect of bath temperature on the electrodeposition of zinc oxide nanostructures via nitrates solution

Zinc oxide (ZnO) nanostructures were electrodeposited onto ITO coated glass substrates from nitrate medium at different temperatures. The electrochemical deposition process was analyzed and the characteristics of the nanostructures were discussed. The electrochemical results showed that the deposition temperature had an important effect on the current density and the film morphology. From the Mott-Schottky measurements, the flat-band potential and the donor density for the ZnO
nanostructure are determined. The morphological, structural and optical properties were studied by scanning electron microscopy (SEM), x-ray diffraction techniques (XRD) and spectrophotometer in the ultraviolet UV–visible region. SEM images demonstrated that the morphology of ZnO nanostructures depend greatly on the bath temperature. The XRD patterns revealed the formation of phase-pure ZnO nanostructure with hexagonal wurtzite phase. The optical transmittance spectrum gave a high transmittance of 82 % at low temperatures, and the optical band-gap (Eg) of the ZnO nanostructures was between 3.253.49 eV.

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