Mohamed Houcine Dhaou

This study focuses on the modeling and optimization of B_xGa_1−xAs/In_yGa_1−yAs double-junction photovoltaic cells and GaAs/B_xIn_yGa_1−x−yAs quantum well pin cells. It relies on Silvaco Atlas software 2.10.26R to simulate these structures, considering the desired number of QWs or the constant percentage of boron and indium in the III-V-based alloys of B_xGa_1−xAs, In_yGa_1−yAs, and B_xIn_yGa_1−x−yAs. The B_xIn_yGa_1−x−yAs material finds its application in the fabrication of quantum wells incorporated into the intrinsic GaAs-type absorber layer. This absorber layer is positioned between the heavily doped base and the emitting regions, in order to generate a uniform field that allows all photogenerated carriers to escape from the QWs. As part of the modeling, a comparison was made between a 40-layer GaAs/B_xIn_yGa_1−x−yAs quantum well solar cell and a standard GaAs solar cell. This analysis revealed an increase in the conversion efficiency of the simulation results from 22.66% to 31.73%. As a result, the integration of quantum wells into the structure of solar cells seems promising to optimize their performance. The optimized B_xGa_1−xAs/In_yGa_1−yAs tandem structure demonstrated a short-circuit current density of 17.50 mA/cm², an open-circuit voltage of 1.99 V, a fill factor of 87.29%, and a conversion efficiency of 30.40% under AM1.5G illumination at 300 K.

The compounds LiCo_1−xMn_xO₂ (x = 0.5, 0.7) were synthesized via the solid-state method and exhibited crystallization in the cubic spinel structure (space group Fd-3m). UV–Vis spectroscopy reveals strong visible-light absorption and a reduction in the indirect optical band gap from 1.85 eV (x = 0.5) to 1.60 eV (x = 0.7) with increasing Mn content, which is consistent with semiconducting behavior. This narrowing arises from Mn³⁺/Mn⁴⁺ mixed valence, which introduces mid-gap states and enhances Co/Mn 3d–O 2p orbital hybridization within the spinel framework. In contrast, the Urbach energy increases from 0.55 eV to 0.65 eV, indicating greater structural and energetic disorder in the Mn-rich composition which is attributed to the Jahn–Teller distortions and valence heterogeneity associated with Mn³⁺. Impedance and dielectric modulus analyses confirm two distinct non-Debye relaxation processes related to grains and grain boundaries. AC conductivity is governed by the Correlated Barrier Hopping (CBH) model, with bipolaron hopping identified as the dominant conduction mechanism. The x = 0.7 sample displays significantly enhanced conductivity due to increased Mn³⁺/Mn⁴⁺ mixed valence, lattice expansion, efficient 3D electronic connectivity of the spinel lattice, and reduced interfacial resistance. These findings highlight the potential of these two spinels compounds as narrow-gap semiconductors for optoelectronic applications including visible-light photodetectors, photocatalysts, and solar absorber layers extending their utility beyond conventional battery cathodes.

In the present study, the hydrogen-absorption properties of the LaNi₅ and the La_0.7Ce_0.1Ga_0.3Ni₅ compounds were determined and compared. This work is therefore divided into two parts: an experimental part that presents and discusses the kinetics and isotherms of hydrogen absorption in the two compounds at two different temperatures (298 K and 318 K). In addition, the temperature variations inside the hydride bed were determined. In the second section, the experimental isotherms were compared to a numerical model processed using statistical physics. Following that, thanks to the perfect agreement between the experimental data and the proposed model, the stereographic and energetic parameters associated with the hydrogen absorption reaction, such as the number of hydrogen atoms per receptor site (n₁, n₂), the densities of the sites (N_m1, N_m2), the half-saturation pressures (P₁, P₂) and the absorption energies (ΔE₁, ΔE₂) for each receptor site, were calculated. All of these parameters are acquired by making numerical adjustments to the experimental data. Thermodynamic functions, such as internal energy and Gibbs energy, which regulate the absorption process, were then identified using these parameters. For both compounds, all of the aforementioned were compared and discussed in relation to initial temperature and pressure. The results demonstrated that the hydrogen-storage properties in LaNi₅ are enhanced by more than 30% of stored mass and kinetics when Ce and Ga are substituted at the La sites.

The results of an experimental and mathematical study into the MmNi_4.2Mn_0.8 compound’s hydrogen storage properties are presented in the present research. Plotting and discussion of the experimental isotherms (P-C-T) for different starting temperatures (288 K, 298 K, 308 K, and 318 K) were carried out first. Then, the enthalpy and entropy of formation (ΔH₀, ΔS₀) were deduced from the plot of van’t Hoff. Following that, the P-C-T were contrasted with a mathematical model developed via statistical physics modeling. The steric and energetic parameters, such as the number of the receiving sites (n₁, n₂), their densities (N_m1, N_m2), and the energy parameters (P₁, P₂) of the system, were calculated thanks to the excellent agreement between the numerical and experimental results. Therefore, plotting and discussing these parameters in relation to temperature preceded their application in determining the amount of hydrogen in each type of site per unit of metal ([H/M]₁, [H/M]₂) as well as for the entire system [H/M] versus temperature and pressure besides the absorption energies associated with each kind of site (ΔE¹, ΔE²) and the thermodynamic functions (free energy, Gibbs energy, and entropy) that control the absorption reaction.

In recent years, there has been a growing replacement of synthetic fibers by natural ones, particularly by autochthonous materials. In the case of Algeria, the most abundant plant resources are the PALF (Pineapple leaf fiber), the date palm, and the Alfa fibers. In this work, the development and use of analytical and numerical methods are proposed to predict the mechanical properties of layers based on natural fibers that will be applied to manufacture skins of the sandwich cylinder. To achieve these predictions, four analytical models were used, namely the Halpin–Tsai, the Chamis, the Hashin vs. Rosen, and the ROM. The analytical results were compared with the numerical simulations and experimental data. The prediction of the elastic properties of the three fiber-based eco-composites showed an important dispersion in terms of stiffness.

The objective of this manuscript is to study the possibility of improving the thermal performance of an Evacuated Tube Solar Collector (ETSC) with the integration of a Phase Change Material (PCM) incorporated into metallic foam and fitted with plate fins. A 2D mathematical model has been proposed. Two types of metal foams (copper and nickel) were inserted. In addition, the effect of metal foam pore size of on heat transfer was studied. The results were acquired through numerical simulations of four different cases; namely, Case 1: pure PCM, Case 2: with metal foam, Case 3: with fins and Case 4: with metal foam and fins. The evaluation procedure involved observing the total change in Heat Transfer Fluid (HTF) temperature and melted PCM fraction during a single day. The results proved that the thermal performance of ETSC is improved considerably by inserting metal foam and fins simultaneously. The time required for the whole process is improved by almost 9% compared to the case of pure PCM, and 2% compared to the case of inserting only plate fins. Results revealed that the pore size of the metal foams slightly affects the dynamic process of heat storage/release in the ETSC/PCM system.

The Ag_2−xNa_xZnP₂O₇ (x = 0, 1, and 2) materials are prepared using the solid–solid method followed by heat treatment. The investigated samples are characterized by combining X‐ray powder diffraction and electrical impedance spectroscopy techniques. The Rietveld refinement of the X‐ray diffraction (XRD) pattern revealed that these Ag₂ZnP₂O₇, AgNaZnP₂O₇, and Na₂ZnP₂O₇ compounds are indexed in the tetragonal system with the P4₂/n space group. Their dielectric properties are measured in the frequency and temperature ranges of 200–10⁷ Hz and 419–518 K, respectively. In these compounds, the dielectric relaxation can be described by a Cole–Cole model. The frequency dependence of the conductivity is interpreted in terms of Jonscher's law. For the three compounds, the activation energy for conduction has a different value compared to the activation energy for the relaxation process. This indicates that the conduction in the compound is not predicted by the simple hopping model. Then, the temperature dependence of the power‐law exponent(s) suggests that the non‐overlapping small polaron tunneling model is the dominant transport process in these materials. Moreover, the values of defect states N(EF) and the tunnel distance R_W show the electrical performance of the Ag₂ZnP₂O₇ compound.