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Inorganic metallic halide perovskites and cesium lead triiodide, CsPbI3, in particular, have gained enormous attention recently due to their unique photovoltaic properties and low processing temperatures. However, their structural stability and phase transition still need an in-depth investigation to better optimize their optoelectronic properties. For sake of time and cost, Classical Molecular Dynamics (CMD) and first principles calculations are being used to predict the structure stability and phase transition of CsPbI3. The major challenge of CMD is the choice of proper interatomic potential functions. In this paper, a new hybrid force field is being introduced, which integrates the embedded atomic potentials of Cs–Cs and Pb–Pb with Buckingham–Coulomb potentials. The Buckingham–Coulomb interatomic potential was solely employed as well. The outputs from both force fields were reported and compared to the experimental values. In fact, the new Hybrid Embedded Atomic Buckingham–Coulomb (EABC) potential reproduces, with a great degree of accuracy (within 2.5%), the structural properties, such as the radial distribution functions, interatomic separation distances, and the density. Also, it detects the phase transformation from an orthorhombic into a cubic crystal structure and the melting temperature at 594 K and 750 K respectively which agrees with the experimental values to within 1%. The new proposed hybrid potential proved to be accurate so it could potentially be used to infer the structure stability and the mechanical and thermal properties of the pure inorganic halide perovskites and the mixed halide perovskites as well which are used in various applications.

Lead-free halide perovskites are of great importance as prospective materials for efficient solar cells. Germanium is a very promising non-toxic alternative to lead. In this study, the crystal configuration, projected density of states and band structure of the trigonal CsGeI 3 , the yellow and the quenched black orthorhombic CsPbI 3 , and the cubic CsPbI 3 were investigated using the density functional theory with Perdew-Burke-Ernzerhof functional. Our calculations showed that for the CsGeI 3 , the valence band maximum is mainly contributed by the I 5p and Ge 4s orbitals whereas the conduction band minimum is mainly contributed by the Ge 4p orbitals. The replacement of Pb with Ge results in a narrower bandgap.

Inorganic metallic halide perovskites and cesium lead triiodide, CsPbI

With the increasing demand for small and portable electronic devices, new energy conversion systems that can harvest energy from body motion and ambient environment are needed. Triboelectricity has recently become promising among the various energy conversion mechanisms because triboelectric devices can be small, flexible, and portable. The triboelectric output performance is closely related to the materials ‘properties employed. In this study, the effect of electrical conductivity on the electrical output of a triboelectric device is investigated experimentally. Experiments are conducted using a vertical contact/separation mode with polydimethylsiloxane (PDMS) based material as one of the contacting materials. The electrical conductivity of PDMS is tuned by adding two different weight percent of multiwall carbon nanotube (CNT): 10wt% CNT and 20wt% CNT. The relationship between electrical conductivity and the triboelectric output performance is obtained by correlating the open circuit voltage (Voc) and short circuit current (Isc) with the different weight percent CNT-PDMS materials. A maximum Voc of 98V and a maximum Isc of 3.2μA were obtained with the 20wt% CNT-PDMS and Teflon pair; this increase is likely due to the combination of enhanced triboelectric polarity difference and electrical conductivity. The optimum external resistance was also measured for the different CNT-PDMS weight percent materials. The maximum triboelectric output power reached 180μW at 80MΩ for the 20wt% CNT-PDMS and Teflon pair.

In this study, numerical simulations were utilized to model the optical performance of the perovskite intermediate band solar cells with dispersed quantum dots. Two quantum dots materials were investigated: PbS and Ge. In addition, three volumetric concentrations of the quantum dots were modeled and analyzed. It was concluded that PbS outperformed Ge. Additionally, as the volumetric concentration of the QDs increased, the absorption increased as well.

The optical absorption and the short circuit current of CdTe thin film solar cells have been improved by incorporating arrays of nanostructures in the gold back contact/reflector layer. In this study, three different nano pillar heights, 100, 200 nm, and 300 nm with two periodicities, were investigated. ANSYS HFSS wave optics simulation software was utilized. An increase of 10% in short circuit current density is achieved comparing to the planar cell of an equivalent thickness. Further enhanced performance of CdTe solar cells is expected by incorporating such optimized nanostructure arrays of different sizes and shapes.

CdTe solar cells have become a competitive player in the commercial photovoltaic market competing with CIGS and Si wafers. Considerable research attention has been devoted to increasing the overall conversion efficiency of CdTe which reached 22%. Among the challenges facing this technology is the scarcity of Te. In this paper, we investigated the use of an ultra-thin CdTe layer, which would result in a substantial decrease in Te consumption by almost 90%. However, this substantial decrease in the absorber thickness must be accompanied by some embedded nano-light-trapping structures. The purpose of these nanostructures is to increase the light absorption of the UV-VIS and NIR wavelengths which leads to an increase in the generated photo-current. Also, an electron reflector layer must be added between the metallic contact and the thin absorber layer to mitigate the high recombination rate. Additionally, three different metallic contacts were explored: Au, Ag, and Al. The absorption in the CdTe layer which is responsible for the photo-generated current and the parasitic absorption in the metallic back contact, as well as the short circuit current densities, were determined and analyzed. The numerical Wave optics finite element method and the analytical transmission line theory were utilized. It was noted that these nanostructures showed a substantial increase in the absorption in the CdTe absorber layer in the visible and NIR ranges. A net increase in the short circuit current density of 36% has been realized with the top nano-structured CdTe layer comparing to the flat reference cell of the same absorber volume. Furthermore, the Ag metallic back-contact outperforms both Al and Au and achieved the highest short circuit current density and the lowest parasitic absorption. These findings would open a new route to integrate optimized light trapping nano-structures into the commercial CdTe solar cells to further enhance their material utilization and efficiency.

The thin film solar cells (TFSCs) are becoming more widely implemented due to their light weight, lower cost, and flexibility when compared to the conventional monocrystalline silicon wafer solar cells. Common materials used in the TFSCs today are amorphous silicon (a-Si) and microcrystalline silicon due to their abundance. However, these materials suffer from decreased absorption efficiency especially in the infrared range due to the sub-micron thickness of the absorber. Cadmium Telluride/Cadmium Sulfide (CdTe/CdS) is a promising candidate for TFSC material due to the near ideal, direct band gap of the CdTe, which allows it to be implemented without suffering greatly from decreased absorption efficiency. Nano-texturing is a widely researched and implemented way to increase the absorption of TFSCs. In this project, the wave optical analyses for the wavelength range of 300–1100 nm were executed using ANSYS High Frequency Structural Simulator (HFSS) to study the interaction of the geometric parameters of the nano-structures in CdS/CdTe TFSCs. A 3X3 factorial design of experiments was implemented to investigate 3 different levels of the height (H), diameter (D), and period (Pd) for a conical shaped nano-texture pattern and to study their effect on the absorption and the short circuit current (Jsc). A total of 27 different combinations were investigated. It was found that the model with H = 1000 nm, D = 1000 nm, and P/D = 1 had the highest Jsc of 26.66 mA/cm2, a 29.14 % increase from the planar control cell. In addition, it was noted that when the P/D ratio is 1, an increase in both height and diameter will increase Jsc. Finally, when the height was 200 nm, an increase in the diameter has little to no effect on Jsc. These findings are important to TFSCs manufactures to better design the nano-texturing implemented in TFSCs.

The newly developed airplanes are using composite laminates to replace the metal alloys for different components, such as the fuselage and the wings. The major advantage of the composite materials is to reduce structural weight which results in reducing the fuel consumption. The aim of this project is to investigate the structural integrity of an airplane fuselage, which uses various types of carbon composite laminates under the static loading of the cabin pressurization. The research is performed using the finite element method and the HYPERMESH commercial software with a composite tool to change the thickness and the orientation of carbon fiber laminates used in the facesheet of the sandwich structure. Three different orientations/stacking sequence of the HexPly 8552 AS4 carbon fibers with two honeycomb cores: Hexagonal Al and Nomex. The results show that the composite material using the HexPly 8552 carbon fiber oriented at angle 30 and angle 45 and the Nomex Honeycomb core of a total laminate thickness of 15.875mm outperform all other thicknesses and orientations in regards to the static loading failure.

This paper presents a new modeling approach called Progressive Modeling (PM) and demonstrates it by solving the Cell Formation Problem (CFP). In this paper, the Progressive Modeling (PM), a component-based optimization technique, is used to solve the cell formation problem (CFP). This novel solution algorithm is utilized to find optimal or near-optimal solutions. A user-friendly Windows application is presented to capture the problem data, demonstrate the solution process, and display the results. A benchmark problem in the literature is solved and presented in this paper. The paper concludes by demonstrating the efficiency of the new modeling approach and its future extension.

Thin film solar cells (TFSC) differ from the conventional wafer solar cell panels in that they are a fraction of the thickness, hence they boast reduced material costs, lighter weight, and possible flexibility. To improve their light-trapping and absorption efficiency, manufacturers currently use nanometer scale texturing. When manufacturing nano textured thin film solar cells in the substrate configuration, the back reflector is also textured. It has been observed that a textured back reflector leads to parasitic light absorption in silicon solar cells. This occurrence reduces the back reflector effectiveness, and thus reduces absorption in the absorber layer and overall efficiency. However, there is little to no similar research done for thin film (CdTe/CdS) solar cells devices. In this work, wave optical analyses of thin film CdTe/CdS solar cells with and without nano texturing on the metal back reflectors were simulated using ANSYS ANSOFT High Frequency Structural Simulator (HFSS). The optical analyses yielded percentage absorptions for unit cells with four absorber thicknesses range between 250- to 1000 nm, with and without a textured back reflector over six wavelengths range from 360nm to 860 nm, and with 3 different back contact metals (Au, Ag, and Al). It was noted that the textured back contacts show a substantial increase in the absorption in the active CdTe layer in the infrared range. Additionally, back reflector texturing increases the parasitic absorption in the metal back reflector layer as well, especially with ultrathin absorber layer. It was also found that additional parasitic absorption due to a textured back reflector has less of an impact on absorption as the active absorber thickness increases to 500 nm, 750 nm, or 1000 nm. Finally, silver (Ag) as back contact outperforms both aluminum (Al) and gold (Au). This finding might be crucial to solar cell manufacturers because it could possibly be an overlooked factor in achieving higher efficiencies for relatively thin cells.

In recent years, micro surface texturing for friction and adhesion control has gained momentum in a wide range of applications, such as MEMS devices, punches, and tools used metal forming processes, and injection molding machines. In this study, air hardened tool steel, A2, with micro hexagonal dimples of different sizes and densities but constant depth, have been modeled and tested under dry sliding contact. Three-dimensional finite element models depict sliding dry contact between a rigid indenter and elastic-plastic textured surfaces are simulated. Coefficients of friction have been determined and compared for different texturing sizes and densities. In addition, these hexagonal patterns were fabricated on tool steel (A2) samples using photolithography. Coefficients of friction were experimentally measured using micro scratch tribometer. Both simulation and experimental results show there is a strong correlation between micro-texturing parameters and coefficient of friction. The results demonstrate that under dry sliding contact, coefficient of friction can be controlled through optimization of micro texturing parameters, specifically the spatial texture density (D/L) which is equal to the ratio of the size of the dimple (D) to the distance between the centers of two consecutive dimples (L). A minimum coefficient of friction exits at values of spatial texture densities (D/L) that range between 0.25 and 0.5 for this specific material.

This paper presents a new modeling approach called Progressive Modeling (PM) and demonstrates it by solving the Assembly Line Balancing Type I Problem. PM introduces some new concepts that make the modeling process of large-scale complex industrial problems more systematic and their solution algorithms much faster and easily maintained. In the context of SALBP-I, PM introduces a component model to deploy the problem logic and its solution algorithm into several interacting components. The problem is represented as an object-oriented graph G (V, E, W) of vertices, edges, and workstations which enables problem solutions to start anywhere. The novel representation relaxes the only forward and backward tracking approach used in the assembly line balancing literature. A set of well-reported problems in the literature are reported and solved. The paper concludes by demonstrating the efficiency of the new modeling approach and future extensions.

Al/Si alloys are considered to be one of the most promising light weight alloys that can be used extensively in aerospace and automotive industry except for the poor tribological behaviour. However, with advancement and precision of the surface coating depositing techniques, new coating design which significantly enhances the tribological properties of the light weight alloys becomes attainable. In this paper, an innovative coating design is presented and thoroughly analyzed using finite elements method. The proposed model consists of Al/Si 319 as a matrix within which the geometrically defined hard Si particles are dispersed on the surface, and a hard coating layer then deposited in between the Si particles so that the lateral movement of the Si particles is constrained. ABAQUS is utilized to model and address the effects of different parameters, such as coating material, the hard coating thickness, and geometrical shape of the Si particles on the fracture and deboning of the entire structure. Two Si particles shapes are studied: circular and elliptical. Three coating materials are investigated: DLC, CrN and Al2O3. Besides, four coating thicknesses of 4 µm , 8µm, 15µm and 20µm are tested. It is found out that there is no single significant parameter which affects the fracture and deboning of Si particles, yet it is the combination of different parameters. The Si particle geometry plays a major role in determining the critical fracture stress with a circular shape outperforms the elliptical shape. The combination the circular Si particles and the CrN as coating material gives the highest critical fracture stress. Finally, DLC does not perform well with the circular Si Particle and it show the highest possible fracture stress with elliptical Si particle