Design Optimization Of Devices Research Articles

Efficient Nanocrystal Photovoltaics with PTAA as Hole Transport Layer.

The power conversion efficiency (PCE) of solution-processed CdTe nanocrystals (NCs) solar cells has been significantly promoted in recent years due to the optimization of device design by advanced interface engineering techniques. However, further development of CdTe NC solar cells is still limited by the low open-circuit voltage (Voc) (mostly in range of 0.5–0.7 V), which is mainly attributed to the charge recombination at the CdTe/electrode interface. Herein, we demonstrate a high-efficiency CdTe NCs solar cell by using organic polymer poly[bis(4–phenyl)(2,4,6–trimethylphenyl)amine] (PTAA) as the hole transport layer (HTL) to decrease the interface recombination and enhance the Voc. The solar cell with the architecture of ITO/ZnO/CdS/CdSe/CdTe/PTAA/Au was fabricated via a layer-by-layer solution process. Experimental results show that PTAA offers better back contact for reducing interface resistance than the device without HTL. It is found that a dipole layer is produced between the CdTe NC thin film and the back contact electrode; thus the built–in electric field (Vbi) is reinforced, allowing more efficient carrier separation. By introducing the PTAA HTL in the device, the open–circuit voltage, short-circuit current density and the fill factor are simultaneously improved, leading to a high PCE of 6.95%, which is increased by 30% compared to that of the control device without HTL (5.3%). This work suggests that the widely used PTAA is preferred as the excellent HTL for achieving highly efficient CdTe NC solar cells.

Study on the Discharge Process and Mechanism of Anti-Corrosion Pill Particles in the Oil and Gas Field Wellbore Casing Annulus Based on the Discrete Element Method

This research studies the discharge process and its mechanism using the discrete element method (DEM) with self-developed annular corrosion pill particles and the discharge device as an example in order to optimize the oil and gas field wellbore casing annular corrosion process. The object of study was chosen from four different grid numbers and four different grid widths, and EDEM software was utilized to simulate and assess the pill particle discharge process based on preliminary experimental research. Under five different pill wheel rotation speeds, the effects of the grid number and grid width on the filling amount, filling density, discharge variation coefficient, and compressive force of pill particles were investigated from macroscopic and microscopic viewpoints. The findings reveal that the grid number, grid width, and rotation speed all have a significant impact on pill filling and discharge performance. As a result, the discharge wheel’s structure and operating characteristics were optimized. The discharge wheel performs best when the grid number is 8, the grid width is 75 mm, and the rotation speed is 15 rpm; the pill filling density is 692.26 kg/m3, the discharge variation coefficient is 0.022, and the maximum compressive force is 188 N. This study establishes the groundwork for enhancing wellbore integrity management in oil and gas fields by providing a reference for the optimal design of wellbore casing annular corrosion prevention devices in oil and gas fields.

Impact of PODE3 on soot oxidation reactivity at different stages in n-heptane/toluene diffusion flames

PODE3, with the molecular formula of CH3O(CH2O)3CH3, is considered a highly competitive alternative fuel due to the absence of CC bond and its high oxygen content, and have been shown to significantly reduce soot emission when applied as a diesel fuel additive. However, the effect of PODE3 addition on the oxidation reactivity of soot generated in the flame remains unclear which is of great importance for the optimal design of the post-treatment devices during its application. In this work, the impact of PODE3 (0 %, 10 %, and 20 % by volumetric fraction) addition on the oxidation reactivity of soot at different maturity and oxidation degrees in n-heptane/toluene co-flow diffusion flames was specially investigated combining information on thermogravimetric analysis, high-resolution transmission electron microscope, and Raman spectroscopy. Results showed that PODE3 substitution significantly shrank soot generation region, and increased the flame temperatures before height above burner (HAB) < 45 mm. The addition of PODE3 improved the soot oxidation reactivity, which had a strong ability to hinder the growth of the microcrystalline carbon layers and resulted in a high content of amorphous carbon in soot particles. Specifically, it had more significant impacts on the soot in the oxidation stage than the surface growth stage. These can be explained that with PODE3 addition, on the one hand, the “reliable carbon atom” for soot formation is significantly reduced and the amount of oxidizing species is increased, resulting in a smaller particle size and a higher content of disordered and amorphous carbon in soot particles. On the other hand, the flame temperatures increased where HAB < 45 mm, which would promote the soot formation reactions. The combined effects of these factors make PODE3 have more significant inhibitory impacts in reactivity of soot sampled at oxidation stage than that at surface growth stage. Therefore, the impact of PODE3 addition on soot nanostructures and oxidation reactivity is not only reflected in its chemical effect but also in temperature effect.

Critical Importance of Nonuniform Polarization and Fringe Field Effects for Scaled Ferroelectric FinFET Memory

The ferroelectric field-effect transistor (FEFET) is an emerging nonvolatile memory technology that can offer ultra-scalability, fast operation, and reduced power consumption. However, a limited understanding of FEFET physics poses challenges for optimum device design. In this article, we provide physical insights into the operation of FinFET-based FEFETs (FEFinFETs) using a phase-field framework built on time-dependent Landau–Ginzburg (TDGL) thermodynamic theory. We exploit the source–drain fringing field to stabilize a monodomain configuration in the OFF state of short channel FEFinFETs. Based on recent experiments, we first analyze the switching dynamics of FEFinFETs with low remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) and high coercive field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) hafnium zirconium oxide (HZO) FE. We find that the switching in these FEFinFETs occurs via domain nucleation and growth from the gate metal edges at the source–drain spacers. We also show that a non-zero drain bias can be used for dynamically modulating the memory window (MW) of FEFinFET to lower its power consumption. Furthermore, we find the spacer permittivity to be a crucial design parameter to control the MW and show that a lower spacer permittivity can significantly increase the MW. Finally, we show that the commonly held idea that a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> leads to a large MW is not always valid. For a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> , the formation of multiple domains in the FE layer can lead to a significant reduction in the MW. In addition, these devices can suffer from low write endurance due to exposure of the interfacial oxide layer to high electric fields.

Predicting the Optimal Performance of a Concentrated Solar Segmented Variable Leg Thermoelectric Generator Using Neural Networks

The production of high-performing thermoelectrics is limited by the high computational energy and time required by the current finite element method solvers that are used to analyze these devices. This paper introduces a new concentrating solar thermoelectric generator made of segmented materials that have non-uniform leg geometry to provide high efficiency. After this, the optimum performance of the device is obtained using the finite element method conducted using ANSYS software. Finally, to solve the high energy and time requirements of the conventional finite element method, the data generated by finite elements are used to train a regressive artificial neural network with 10 neurons in the hidden layer. Results are that the power and efficiency obtained from the optimized device design are 3× and 2× higher than the original unoptimized device design. Furthermore, the developed neural network has a high accuracy of 99.95% in learning the finite element data. Finally, the neural network predicts the modified device performance about 800× faster than the conventional finite element method. Overall, the paper provides insights into how thermoelectric manufacturing companies can harness the power of artificial intelligence to design very high-performing devices while saving time and cost.

Unveiling the influence of selective-area-regrowth interfaces on local electronic properties of GaN p-n junctions for efficient power devices

We report correlated nanoscale mapping of the structure, composition, and properties of regrown GaN p-n junctions to identify how etching and non-planar regrowth processes limit diode performance via the introduction of unintentional dopants and defect states. p-GaN was selectively regrown in n-GaN trenches with SiO2 masks of variable mask-to-trench-width ratio. Dilute Al layers were periodically introduced during regrowth as markers of the growth interface. Correlated nanoscale mapping of doping, conductivity, and dopant complexes was achieved with atom probe tomography (APT), scanning spreading resistance microscopy (SSRM), and cathodoluminescence (CL) spectroscopy, respectively. The Al marker layers, detected by APT, enabled reconstruction of the faceted growth interface and correlation of the dopant concentration with position and time. The p-GaN growth rate is proportional to the mask-to-trench width ratio while the dopant incorporation rate is invariant. At trench edges, magnesium incorporation is suppressed, and oxygen incorporation enhanced, due to preferential incorporation on the semi-polar growth surface, leading to compensation and less abrupt p-n junctions; the SiO2 mask is a source of oxygen. Residual etch damage below the regrowth interface induces n-type and p-type conductivity, creating leakage pathways. The non-uniform Mg incorporation is driven by crystal anisotropy and is thus inherent to non-planar regrowth, but can be mitigated by engineering the regrowth interface and process parameters. The unprecedented integration of spatially resolved mapping of dopants, impurities, conductivity, and carrier type is a powerful approach to discriminating distinct factors that limit the performance of regrown diodes, enabling the rational optimization of process and device design.

Unified polarizable electrode models for open and closed circuits: Revisiting the effects of electrode polarization and different circuit conditions on electrode-electrolyte interfaces.

A precise understanding of the interfacial structure and dynamics is essential for the optimal design of various electrochemical devices. Herein, we propose a method for classical molecular dynamics simulations to deal with electrochemical interfaces with polarizable electrodes under the open circuit condition. Less attention has been given to electrochemical circuit conditions in computation despite being often essential for a proper assessment, especially comparison between different models. The present method is based on the chemical potential equalization principle, as is a method developed previously to deal with systems under the closed circuit condition. These two methods can be interconverted through the Legendre transformation so that the difference in the circuit conditions can be compared on the same footing. Furthermore, the electrode polarization effect can be correctly studied by comparing the present method with conventional simulations with the electrodes represented by fixed charges, since both of the methods describe systems under the open circuit condition. The method is applied to a parallel-plate capacitor composed of platinum electrodes and an aqueous electrolyte solution. The electrode polarization effects have an impact on the interfacial structure of the electrolyte solution. We found that the difference in circuit conditions significantly affects the dynamics of the electrolyte solution. The electric field at the charged electrode surface is poorly screened by the nonequilibrium solution structure in the open circuit condition, which accelerates the motion of the electrolyte solution.

A novel methodology for accurate estimation of magnetic permeability of magnetorheological elastomers

Identifying a reliable nonlinear B-H curve for magneto-rheological elastomers (MREs) is a fundamental necessity for modeling and optimal design of MRE-based devices, particularly in the initial design stages. The main contribution of this study is to propose a novel methodology for the accurate estimation of magnetic permeability and nonlinear B-H curve for MREs. The proposed method involved three series of simple experiments employing an air gap electromagnet, which required only a Gauss meter to measure air gap magnetic flux density, together with formulation of an equivalent magnetic circuit (EMC). The data acquired from the first two series of experiments were used to characterize the relative magnetic permeability of MREs, while that obtained from the third series of experiments permitted an accurate estimation of the nonlinear B-H curve. For this purpose, isotropic MRE samples with 30% particle volume fraction were fabricated. Results showed that the relative magnetic permeability of MREs decreases with increasing magnetic field. The effectiveness of the proposed methodology for estimating magnetic permeability was demonstrated by comparing with that obtained from a VSM device, which revealed relatively low prediction error of 4.1%. The proposed method could thus be utilized for characterization of nonlinear magnetic permeability of MREs with minimal complexity and cost. The proposed methodology, unlike the VSM devices, could predict magnetic properties of MRE under tension/compression loadings.

Finite element analysis of the magnetoelectric effect on hybrid magnetoelectric composites

The multi-component hybrid magnetoelectric (ME) composites obtained by using high molecular polymer as the first component and ferromagnetic or ferroelectric material as the second component by hierarchical compounding has the advantages of light weight, easy processing and flexibility. It has the characteristics of good performance and can also realize the conversion between magnetic energy and electric energy, which has potential applications in the fields of bionic robots and medical non-invasive detection. In this study, the finite element method is used to study its ME effect. Considering the distribution characteristics of the component materials and their nonlinear constitutive equations, as well as the dynamic equation and the corresponding mechanical and electrical boundary conditions, a finite element model of the ME effect of the ME composites is established. The distribution of elastic field, magnetic field and electric field of the hybrid ME composites were studied, and the influence of microstructural distribution characteristics, geometric parameters, external magnetic field, temperature and other factors on its magnetoelectric coefficient was analyzed. The calculated results can provide the theoretical guidance for the optimal design of high-performance magnetoelectric devices and render better support for the technological development in the field of magnetoelectricity.

An investigation into the optimal device design for selenium solar cells

Despite a resurgence in recent years, the optimal device design for selenium solar cells is still not known with individual studies using significantly different window layers, hole transport layers and selenium absorber thicknesses. In this work we present results comparing the effect of each of these on device performance and propose that the ideal absorber thickness is influenced by the specific device structure being utilized. A TiO2 window layer and P3HT hole transport layer with a 200 nm Se absorber layer was found to produce the best performance of 2.1% from materials investigated in this study, however performance remains limited due to the presence of an interfacial charge extraction barrier apparent from current–voltage analysis.

Large-Area, High-Specific-Power Schottky-Junction Photovoltaics from CVD-Grown Monolayer MoS2.

The deployment of two-dimensional (2D) materials for solar energy conversion requires scalable large-area devices. Here, we present the design, modeling, fabrication, and characterization of monolayer MoS2-based lateral Schottky-junction photovoltaic (PV) devices grown by using chemical vapor deposition (CVD). The device design consists of asymmetric Ti and Pt metal contacts with a work function offset to enable charge separation. These early stage devices show repeatable performance under 1 sun illumination, with VOC of 160 mV, JSC of 0.01 mA/cm2, power conversion efficiency of 0.0005%, and specific power of 1.58 kW/kg. An optoelectronic model for this device is developed and validated with experimental results. This model is used to understand loss mechanisms and project optimized device designs. The model predicts that a 2D PV device with ∼70 kW/kg of specific power can be achieved with minimum optimization to the current devices. By increasing the thickness of the absorber layer, we can achieve even higher performance devices. Finally, a 25 mm2 area solar cell made with a 0.65 nm thick MoS2 monolayer is demonstrated, showing VOC of 210 mV under 1 sun illumination. This is the first demonstration of a large-area PV device made with CVD-grown scalable 2D materials.

Optimal Design of a Novel Magnetic Twisting Device based on NSGA-II Algorithm

Abstract This paper presents a novel magnetic twisting device with a coaxial double rotor based on non-contact transmission characteristics of magnetic drive technology. When the twisting device rotates one cycle, the yarn can get triple twists. This means the new device can twist three times more than what the traditional single twist does. The structure of the magnetic twisting device is designed according to the twisting principle. The influence of main structural parameters on the magnetic torque is analyzed. To optimize the maximum transmission torque and the minimum magnet volume, the multi-objective optimization design model for the twisting device is established. Main parameters such as the relative angle of active disc assembly and passive disc assembly, the thickness of magnet, and the average radius of the magnet distribution are optimized by NSGA-II algorithm. Optimization results show that the proposed structural optimization design of a twisting device based on the magnetic drive has excellent performance and is effective for industrial application.

ВЫБОР ОПТИМАЛЬНОЙ КОНСТРУКЦИИ ПЕРЕМЕШИВАЮЩЕГО УСТРОЙСТВА

The paper discusses the features of the choice of a mixing device for boiler-type apparatuses. In particular, the hydrodynamic calculation of the mixing device of the apparatus for the preparation of commercial oils was carried out and, based on the results of calculations, the most optimal design of the mixing device was selected

Multi-objective optimisation of a sloped-motion, multibody wave energy converter concept

The WaveTrain device is a wave energy converter concept designed to extend the high performance of buoys that undergo sloped motion into a deep water environment. It achieves this by mechanically interconnecting a series of sloped modules, amongst which restorative forces can be exchanged in order to prevent detrimental pitching motion, whilst sufficiently free motion along the inclined axis is retained. Importantly, this circumvents the requirement of a rigid seabed connection, but introduces a potential vulnerability of operational failure of the rotational joints that link each connecting strut to the adjacent module. In this paper, the impact of considering the fatigue damage accumulating at the joints, in addition to the power extraction, is investigated with regards to the optimal design of the WaveTrain device. A specially-tailored multi-objective genetic algorithm is used to explore the optimal design candidates with two variants of the pair of conflicting objectives (power extraction and fatigue damage). Some key design criteria are then presented, with reference and comparison to the design criteria that are considered optimal when only power extraction is considered.

Risk-Based Optimal Design of Seismic Protective Devices for a Multicomponent Bridge System Using Parameterized Annual Repair Cost Ratio

Base isolators and fluid viscous dampers are viable protective devices that have been commonly considered in the seismic protection of civil engineering structures. However, the optimal design of these devices remains a tedious and iterative undertaking due to the uncertainty of ground motions, the nonlinear behavior of the structure, and its change of dynamic characteristics (i.e., effective stiffness and damping ratio) under each new design. The optimal design problem becomes more challenging concerning a multiresponse bridge system where conflicting damage potential is often expected among multiple bridge components (e.g., column, bearing, shear key, deck unseating, foundation). In this respect, this study develops a risk-based optimization strategy that directly links the expected annual repair cost ratio (ARCR) of the bridge to the design parameters of base isolators and fluid dampers. This strategy is achieved by devising a multistep workflow that integrates a seismic hazard model, a design of experiment for bearings and dampers, a logistic regression towards parameterized component-level fragility models, and a bridge system-level seismic loss assessment. The developed ARCR is parameterized as a convex function of the influential parameters of seismic protective devices. As such, optimal bearing and damper designs can be pinpointed by directly visualizing the global minimum of the parameterized ARCR surface. The optimal design is carried out against a typical reinforced concrete highway bridge in California that is installed with the fluid dampers and three types of widely-used isolation bearings—the elastomeric bearing, lead-rubber bearing, and friction pendulum system. It is shown that optimal design parameters can be obtained to significantly reduce the expected ARCR of the bridge, whereas combining optimally designed bearings and dampers can provide the minimum seismic risk.

Robust Design Optimization of Electrical Machines and Devices

This article introduces a Special Issue (SI) that contains fourteen chosen articles from robust design optimization of electrical machines and devices [...]

Reprint of: Triboelectric nanogenerator-based wearable electronic devices and systems: Toward informatization and intelligence

Nowadays, wearable electronic devices with rich functions have significantly facilitated individual combat in the military and daily lives of people. To achieve implanting and sustainable wearable electronic systems, it is necessary to develop self-powered sensors utilizing environmental energy harvesting with superior mechanical stretchability and flexibility. Triboelectric nanogenerators (TENGs) can capture the low-frequency mechanical energy in human motion and convert it into electricity, which is expected to be a potential solution for this urgent need. In this review, based on advanced applications, the rich functions of TENG-based wearable devices are thoroughly discussed, including human body perception and human-machine interaction, personnel identification, as well as generation and recognition of coded information. Then, we elaborate on three crucial strategies for achieving an optimal design of TENG-based wearable devices, including selection and optimization of flexible materials, structural design and optimization, and synergistic information acquisition using multiple sensors. The representative signal processing methods are investigated to exploit the potential information behind the output signals, including basic qualitative waveform features and quantization thresholds, anti-interference processing and joint processing of multiple signals, and implementation of complex functions based on artificial intelligence. The review concludes with an overview of the remaining key challenges and potential technologies that can achieve the ultimate goal of a “fully self-powered wearable microsystem”.

The electroviscous effect in nanochannels with overlapping electric double layers considering the height size effect on surface charge

The electroviscous effect has been extensively investigated in micro/nano scale ions transport, fluidic flow and heat transfer, etc. Previous researches often used constant surface charge in theoretic calculation and numerical simulations. However, for thick overlapping electric double layer (EDL) nanochannels, the channel height size effect on surface charge cannot be neglected. In this work, we consider the channel height size effect on surface charge to investigate the related ions transport, fluidic flow and heat transfer in nanochannels. The corresponding results show that the deviation considering the height effect or not is significant, especially in the situation of boundary slip. The relative errors of local ionic concentration and potential can reach 50% and 8%, respectively. The maximum relative errors of induced electrical field strength and the ratio of apparent viscosity to fluidic viscosity reach 10% and 9%, respectively, indicating strong height size effect on the fluidic flow. The deviation of Nu is relatively small and almost not affected by the surface charge. These deviations will decrease to zero when the channel height is large enough or the solution concentration is high enough to reach a non-overlapping EDL situation. The results of this work are meaningful to further understand the electroviscous effect in nanochannels, which may provide useful guidelines for the design and performance optimization of nanofluidic devices.

Resonance Analysis of Piezoelectric Bulk Acoustic Wave Devices Based on YCOB Crystals with Monoclinic Symmetry Excited by Lateral Electric Fields

The monoclinic YCOB crystal still maintains good piezoelectric properties at 800 °C; thus, it has a good application prospect in high-temperature piezoelectric acoustic wave sensors. However, due to the lower symmetry compared crystals in trigonal and tetragonal systems, the exciting characteristics of piezoelectric plates based on monoclinic YCOB crystals are more complicated. The vibration analysis model of lateral-field-excitation (LFE) devices based on monoclinic crystals is scarce; thus, the coupling relationships between different vibration modes and energy-trapping characteristics of the devices are unclear, which hinders the optimal design of devices. In this paper, by using Mindlin plate theory, the high-frequency vibrations of piezoelectric resonators based on monoclinic YCOB crystal plates excited by a lateral electric field are modeled and analyzed. The coupling relationships between the vibration modes of the device are clarified. The influences of the electrode width, electrode/plate mass ratio and electrode gap value on resonances and energy-trapping characteristics of the device are achieved. In addition, the effects of the structure parameters on the mass sensitivity of the monoclinic YCOB LFE devices are investigated, which are further verified by FEM simulations. The results are crucial to obtaining good resonance and sensing characteristics for LFE high-temperature piezoelectric sensors based on crystals with monoclinic symmetry.

Brillouin Light Scattering of Halide Double Perovskite

Cs2Ag1−x Na x In1−y Bi y Cl6 with high photoluminescence quantum yield (PLQY) and broadband emission due to self‐trapped excitons (STEs) is one of the promising candidates for single‐emitter‐based white light–emitting materials and devices. Considering fundamental physical mechanisms, structure design and performance optimization of devices, comprehensive knowledge of the elasticity, and thermal properties are imperative to understand the formation of STEs in Cs2Ag1−x Na x In1−y Bi y Cl6 and minimize thermomechanical stresses induced device failure, respectively. However, its elastic and thermal properties are still poorly understood. Herein, the first angle‐resolved Brillouin light scattering (BLS) measurements study for a bulk Cs2Ag0.4Na0.6InCl6:0.04%Bi3+ crystal is reported, and the first‐principles calculations of phonon dispersions are used to further validate our experimental results. Using the measured Brillouin frequency shifts, we evaluate the low elasticity of Cs2Ag0.4Na0.6InCl6:0.04%Bi3+: C 11 = 38.63, C 12 = 16.11, and C 44 = 10.20 GPa, which supports the thesis that STEs exist in semiconductors with excitons and a soft lattice. Additionally, an ultralow‐acoustic Debye temperature (87 K) and lattice thermal conductivity (1.03 W m−1 K−1) along the [111] direction of Cs2Ag0.4Na0.6InCl6:0.04%Bi3+, which indicates the weak interatomic interactions and elasticity are estimated. Furthermore, a general approach is also provided to investigate the elastic and thermal properties of materials with different crystal structures utilizing angle‐resolved BLS spectroscopy.