arXiv subjects

Fedwa El Mellouhi

Publications and source records attributed to Fedwa El Mellouhi.

4 recordsLinked to original sources

arXiv2024

Automated Model Training (AMT) GUI: An Opportunity for integrating AI in the Laboratory Experiment

In the field of materials science, comprehending material properties is often hindered by the complexity of datasets originating from various sources. This study introduces the Automated Model Training (AMT) Graphical User Interface (GUI), specifically crafted for the use of researchers and scientists without a programming background to design the next set of experiments either in a chemistry lab or on the computer. The GUI integrates diverse machine learning models, such as XG-Boost, Random Forest, Support Vector Regression, Linear Regression, Generalized Additive Model (GAM), and Stack Regressors, offering a robust toolkit for data analysis. It facilitates the exploration of complex relationships, non-linear patterns, and predictive accuracy optimization. To further enhance its utility, the GUI integrates the Particle Swarm Optimization (PSO) technique, allowing researchers to systematically explore vast parameter spaces and identify optimal experimental conditions. This synergy between machine learning and PSO empowers material scientists through a user-friendly platform for data-driven discovery. The AMT GUI bridges the gap between traditional experimentation and machine learning, enabling precise and efficient exploration of the materials research space.

cond-mat.mtrl-sci↗

arXiv2017

Reduced work function of graphene by metal adatoms

In this paper, the work function of graphene doped by different metal adatoms and at different concentrations is investigated. Density functional theory is used to maximize the reduction of the work function. In general, the work function drops significantly before reaching saturation. For example in the case of Cs doping, the work function saturates at 2.05 eV with a modest 8 % doping. The adsorption of different concentrations on metal adatoms on graphene is also studied. Our calculations show that the adatoms prefer to relax at hollow sites. The transfer of electron from metallic dopants to the graphene for all the studied systems shifts the Fermi energy levels above the Dirac-point and the doped graphenes become metallic. The value of Fermi energy shifts depends on the type of metallic dopants and its concentrations. A detail analysis of the electronic structure in terms of band structure and density of states, absorption energy, and charge transfer for each adatom-graphene system is presented.

cond-mat.mtrl-sci↗

arXiv2015

Charge carrier mobility in hybrid halide perovskites

The charge transport properties of hybrid halide perovskites are investigated with a combination of density functional theory including van der Waals interaction and the Boltzmann theory for diffusive transport in the relaxation time approximation. We find the mobility of electrons to be in the range 5-10 cm$^2$V$^{-1}$s$^{-1}$ and that for holes within 1-5 cm$^2$V$^{-1}$s$^{-1}$, where the variations depend on the crystal structure investigated and the level of doping. Such results, in good agreement with recent experiments, set the relaxation time to about 1 ps, which is the time-scale for the molecular rotation at room temperature. For the room temperature tetragonal phase we explore two possible orientations of the organic cations and find that the mobility has a significant asymmetry depending on the direction of the current with respect to the molecular axis. This is due mostly to the way the PbI$_3$ octahedral symmetry is broken. Interestingly we find that substituting I with Cl has minor effects on the mobilities. Our analysis suggests that the carrier mobility is probably not a key factor in determining the high solar-harvesting efficiency of this class of materials.

cond-mat.mtrl-sci↗

arXiv2015

Revealing the role of organic cations in hybrid halide perovskites CH3NH3PbI3

The hybrid halide perovskite CH$_{3}$NH$_{3}$PbI$_{3}$ has enabled solar cells to reach an efficiency of about 18\%, demonstrating a pace for improvements with no precedents in the solar energy arena. Despite such explosive progress, the microscopic origin behind the success of such material is still debated, with the role played by the organic cations in the light-harvesting process remaining unclear. Here van-der-Waals-corrected density functional theory calculations reveal that the orientation of the organic molecules plays a fundamental role in determining the material electronic properties. For instance, if CH$_{3}$NH$_{3}$ orients along a (011)-like direction, the PbI$_{6}$ octahedral cage will distort and the band gap will become indirect. Our results suggest that molecular rotations, with the consequent dynamical change of the band structure, might be at the origin of the slow carrier recombination and the superior conversion efficiency of CH$_{3}$NH$_{3}$PbI$_{3}$.

cond-mat.mtrl-sci↗