Analysis Of Loss Mechanisms Research Articles

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Low-cost photoreactors for highly photon/energy-efficient solar-driven synthesis

Highly Efficient Silicon-Based Thin-Film Schottky Barrier Photodetectors

Internal photoemission (IPE) is a promising phenomenon for sub-bandgap photodetection at near-infrared wavelengths using large bandgap semiconductor materials. To improve the photon-to-electron conversion efficiency in silicon-based sub-bandgap Schottky barrier photodetectors (SBPDs), previous studies have mainly focused on subwavelength-scale nanostructures to enhance the electric fields and optical absorption. Here, in a different way from the previous approaches, we theoretically and experimentally demonstrate a rigorous quantum efficiency analysis framework that can quantitatively explain the hot carrier transport processes. Guided by the design principles from the hot carrier loss mechanism analysis, we experimentally demonstrate patternless thin-film SBPDs that can surpass the performance of conventional nanostructured SBPDs, exceeding the external quantum efficiency of 10–3. Our work shows that optical absorption and hot carrier generation are responsible for only a part of the entire IPE process and other transport mechanisms should be carefully considered in a wholistic manner, indicating the importance of quantitative quantum efficiency analysis.

Analysis of Loss Mechanisms in CZGSe Thin-Film Kesterite Solar Cells: A Statistical Distribution for Defects and Traps

Kesterite materials is popular for low cost photovoltaic and opto-electronic applications. Currently the achievable efficiency of kesterite based CZTSe material is only 12% due to poor quality of material. As an alternative, substituting Sn with Ge as Cu-Zn-Ge-Se (CZGSe) not only enhances the optical properties of materials but also improves the performance of solar cell. The carrier dynamics of the device is examined with variation of different parameters like doping. The worst-case behavior of the device is also examined by adding different loss mechanisms such as deep defects and traps. A remarkable efficiency of 19% and worst case efficiency across a range of 11 to 12% could achieved from the proposed device at a defect concentration of 1×1016 cm−3 eV−1.

Three-dimensional network FeNi/C composites with excellent microwave-absorbing properties

In this paper, the carbon coated iron nickel nanoparticles were obtained by calcining PVP crosslinked iron nickel oxalate. The morphology, structural composition and microwave-absorbing (MA) properties of the composites were analyzed by various characterization methods. The results show that FeNi/C composites have excellent impedance matching characteristics and MA performance in multiple frequency by virtue of their microscopic network structure. At the same time, through the analysis of loss mechanism, we found that the material has high dielectric loss and magnetic loss characteristics. Under the joint action of various loss mechanisms such as interface polarization and eddy current loss, the material has a high reflection loss (RL) value at different frequency. At a thickness of 3 mm, the sample FNC12 has a minimum RL of − 52.99 dB at 3.6 GHz. The effective absorption bandwidth (EAB) (RL ≤ −10 dB) is 1.81 GHz.

Lightweight and broadband 2D MoS2 nanosheets/3D carbon nanofibers hybrid aerogel for high-efficiency microwave absorption

Three-dimensional (3D) porous molybdenum disulfide nanosheets/carbon nanofibers (MoS2/CNF) hybrid aerogels were synthesized by using solvothermal method and following carbonization, where two-dimensional (2D) MoS2 nanosheets were homogenously in-situ grown on the interconnected CNF skeleton derived from bacterial cellulose, forming a hierarchical porous structure. This unique heterogeneous structure of the MoS2/CNF hybrid aerogels were conducive to electromagnetic loss, including conduction, polarization, multi-scatterings, and reflections, thus resulting in a balanced impedance matching and microwave attenuation capacity. It was found that the resulted MoS2/CNF hybrid aerogels demonstrate excellent microwave absorbing performance when the only 5.0 wt% fillers were loaded in paraffin. Particularly, MoS2/CNF-2–900 hybrid aerogel displayed an effective absorption bandwidth of 5.68 GHz and minimum reflection loss (RLmin) value of −36.19 dB at a thickness of 2.0 mm. As the thickness increases to 4.4 mm, the RLmin value of MoS2/CNF-2–900 hybrid aerogel reaches −48.53 dB. Electromagnetic loss mechanism analysis indicates that such improved microwave attenuation is attributed to proper component, multiple heterogenous interface and hierarchical porous structures. All the results in this work pave the avenue for the development of ultralight microwave absorber with high absorption capacity as well as broad effective absorption bandwidth.

Perovskite modules with 99% geometrical fill factor using point contact interconnections design

AbstractThin‐film photovoltaic technology, based on hybrid metal halide perovskites, has achieved 25.2% and 16.1% certified power conversion efficiencies for solar cell and solar module devices, respectively. Still, the gap between power conversion efficiency of small area solar cells and large area solar modules is greater than for any other photovoltaic technology. Analysis of loss mechanisms in n‐i‐p solution processed devices defined layer inhomogeneity loss and inactive area loss as the two most prominent loss mechanisms in upscaling. In this study, we focus on minimizing inactive area loss. We analyze the point contact interconnections design and demonstrate it on perovskite thin‐film solar modules to achieve a geometrical fill factor of up to 99%. Numerical and analytical simulations are utilized to optimize interconnections and solar module design and balance inactive area loss, series resistance loss, and contact resistance loss.

Groove Gap Waveguide in 3-D Printed Technology for Low Loss, Weight, and Cost Distribution Networks

This paper presents the design and fabrication of low loss, weight, and cost prototypes in groove gap waveguide technology at Ka-band, manufactured with a metallized 3-D printing technique. A wide analysis of loss mechanisms and printing imperfections has been conducted, as well as the effect of temperature on structural deformations. Metallized 3-D printed and CNC machined prototypes have been compared and characterized with simulations and measurements at a band from 28 to 30 GHz. The average measured losses for metallized plastic prototypes are 1.4 dB/m.

Analysis of loss mechanisms in InGaN solar cells using a semi-analytical model

InGaN semiconductors are promising candidates for high-efficiency next-generation thin film solar cells. In this work, we study the photovoltaic performance of single-junction and two-junction InGaN solar cells using a semi-analytical model. We analyze the major loss mechanisms in InGaN solar cell including transmission loss, thermalization loss, spatial relaxation loss, and recombination loss. We find that transmission loss plays a major role for InGaN solar cells due to the large bandgaps of III-nitride materials. Among the recombination losses, Shockley-Read-Hall recombination loss is the dominant process. Compared to other III-V photovoltaic materials, we discovered that the emittance of InGaN solar cells is strongly impacted by Urbach tail energy. For two- and multi-junction InGaN solar cells, we discover that the current matching condition results in a limited range of top-junction bandgaps. This theoretical work provides detailed guidance for the design of high-performance InGaN solar cells.

Optimal design and loss mechanism analysis of microwave absorbing unidirectional SiC fiber composites with broad absorption band and good polarization stability

A microwave-absorbing unidirectional SiC fiber composite with wide absorption and good polarization stability was designed by genetic algorithm. The anisotropic nature of unidirectional fiber composites was considered in the design by characterizing tensor permittivity. This special composite is composed of two kinds of SiC fibers that separately exhibit relatively high conductivity and low conductivity. The electromagnetic loss mechanism of this composite was examined for polarizations that differ in the electric field of the incident wave, applied either in the direction of the fiber or in the transverse direction, perpendicular to the fibers. For both polarizations, the absorption band of our composite can reach 6 GHz and the lowest microwave reflectivity was about −20 dB over a range of 8–18 GHz. When the electric field is polarized parallel to fibers, strong coupling among the high-conductivity fibers can induce a strong current and thus efficiently dissipate the electromagnetic energy. When the electric field is polarized perpendicular to fibers, the electromagnetic loss mechanism in the composite resembles the electric energy loss in capacitors and currents in the transverse direction are obstructed by the fibers resulting in attenuation of the electromagnetic energy in the matrix.

Winding Loss Mechanism Analysis of Magnetic Valve Controlled Reactor

With the increase of the magnetic valve controlled reactor capacity, winding loss brings more and more harm. Based on the physical model and mathematical model of magnetic valve controlled reactor, this paper proposes a valid method for calculating the winding loss .The proposed method calculates winding current harmonic content under different saturation, and obtains the leakage magnetic field distribution of magnetic distributed-valve reactor by using ANSYS. According to the leakage magnetic field distribution, winding loss can be calculated, and the loss curve can be deduced, which is only related to the saturation degree. The error between the ANSYS simulation results and the proposed method results is very small.

<formula formulatype="inline"><tex Notation="TeX">$W$</tex></formula>-Band Dual-Polarization Phased-Array Transceiver Front-End in SiGe BiCMOS

This paper discusses the design and implementation of a 94-GHz phased-array transceiver front-end in SiGe BiCMOS that is capable of receiving concurrently in both vertical (V) and horizontal (H) polarizations and time-duplexed transmission in either polarization. The compact front-end is implemented in $\hbox{1.3 mm}\times \hbox{ 1.45 mm}$ of silicon area to ensure compatibility with a scalable phased-array tile approach with $\lambda/2~(\sim \hbox{1.6 mm})$ spacing between elements. Each transceiver front-end includes variable transmitter (TX) and receiver (RX) gain and 360 $^{\circ}$ variable phase shift in TX and RX. Co-integration of the transmit-receive (T/R) switch with the power amplifier (PA) and low-noise amplifier (LNA) matching network minimizes switch impact on RX noise figure (NF). A varactor-based passive reflection-type phase shifter (RTPS) is shared between the TX and RX to reduce area. Analysis of loss mechanisms in on-chip RTPS leads to a novel RTPS load that minimizes RTPS loss while ensuring that the amplitude variation across phase shift is $ . In RX mode, the front-end achieves 30-dB RX gain, bandwidth of 15 GHz (84–99 GHz) with $ 10-dB NF in the high-gain mode. In TX mode, the front-end achieves $> $ 2-dBm saturated output power and $> $ 0-dBm output-referred 1-dB compression point (OP1dB) in V and H polarizations (time-duplexed), 30-dB gain, and 8-GHz bandwidth (89–97 GHz). The 94-GHz phase shifters achieve full 360 $^{\circ}$ variable phase shift with 5-bit phase resolution (11.25 $^{\circ}$ resolution) and $ error and $ 1-dB rms gain error at 94 GHz. The front-end consumes 160 mW in RX mode for dual-polarization concurrent reception/phase-shifting and 116 mW in TX mode for time-duplexed V and H output in the $W$ -band.

Power balance and loss mechanism analysis in RF transmit coil arrays.

To establish a framework for transmit array power balance calculations based on power correlation matrices to accurately quantify the loss contributions from different mechanisms such as coupling, lumped components, and radiation. Starting from Poynting's theorem, power correlation matrices are derived for all terms in the power balance, which is formulated as a matrix equation. Finite-difference time-domain simulations of two 7 T eight-channel head array coils at 297.2 MHz are used to verify the theoretical considerations and demonstrate their application. Care is taken to accurately incorporate all loss mechanisms. The power balance for static B1 phase shims as well as two-dimensional spatially selective transmit SENSE pulses is shown. The simulated power balance shows an excellent agreement with theory, with a maximum power imbalance of less than 0.11%. Power loss contributions from the different loss mechanisms vary significantly between the investigated setups, and depending on the excitation mode imposed on the coil. The presented approach enables a straightforward loss evaluation for an arbitrary excitation of transmit coil arrays. Worst-case power imbalance and losses are calculated in a straightforward manner. This allows for deeper insight into transmit array loss mechanisms, incorporation of radiated power components in specific absorption rate calculations and verification of electromagnetic simulations.

C-Si Solar Cells based on Laser-processed Dielectric Films

This paper shows an innovative and low temperature fabrication technology for crystalline silicon (c-Si) solar cells where the highly-doped regions are punctually defined through laser processed dielectric films. Phosphorus-doped silicon carbide stacks (SiCx(n)) and aluminium oxide/silicon carbide (Al2O3/SiCx) stacks are used for the creation of n+ and p+ regions respectively. These films provide excellent surface passivation on both n- and p-type substrates with effective surface recombination velocity below 20cm/s. Moreover, a wide laser parameter window for laser processing them leads to low recombination highly-doped regions that show emitter saturation current densities of 21 and 113 fA/cm2 for n+ and p+ emitters respectively. All this is combined in the DopLa (Doped by Laser) cell structure whose fabrication process can be reduced to wafer cleaning, film depositions, laser processing and metallization. As a proof of concept, 1×1 cm2 solar cells were finished on both p- and n-type substrates with promising results. The analysis of loss mechanisms shows that optical losses and technological issues in the translation of surface passivation from the solar cell precursors to the final device are limiting efficiency. Both are not inherent to DopLa structure and suggest room for improvement in these devices. On the other hand, the crucial role played by ohmic losses in the proposed structure is identified. These ohmic losses arise from the fact that both base contacts and emitter regions are defined in point-like patterns. Firstly, base contacts are defined in a 1mm pitch square matrix introducing additional series resistance that can be reduced by using low resistivity substrates. Secondly, the emitter consists of laser processed local diffusions with an inversion layer emitter in-between characterized by very high sheet resistances. The ohmic losses introduced by this induced emitter are closely linked to the fixed charge density located at the dielectric/c-Si interface. As a result, we conclude that low resistivity n-type substrates fit better to DopLa cell concept because emitters are based on Al2O3/SiCx stacks which have higher fixed charge density, i.e. inversion layer emitters with lower sheet resistances, than their SiCx(n) counterparts.

Prediction method of impeller performance and analysis of loss mechanism for mixed-flow pump

A loss model for the mixed-flow pump impellers was developed by summarizing a variety of loss calculation formulas systematically. The internal flow field of the impeller was obtained by employing the iterative calculation for S1 and S2 stream surfaces to solve the continuity and motion equations of fluid. Based on the calculation method of the flow field and the loss model, it is achieved to predict the impeller performance of the mixed-flow pump and the performance curves of a mixed-flow pump model with adjustable blades. Compared with the test data, the loss model of the mixed-flow pump based on the iterative calculation can predict the impeller performance quickly and accurately, which has a high value on the engineering applications. Based on the test verification, curves of various kinds of losses varied for the flow rate were analyzed under different blade angles. In addition, the mechanisms of various kinds of losses inside the mixed-flow pump impeller were discussed in-depth.

Silicon nanocrystals on bottle resonators: Mode structure, loss mechanisms and emission dynamics

Bottle resonators can support high Q-factor whispering gallery modes (WGMs) and demonstrate a rich mode spectrum. Resonators were fabricated using a fiber tapering apparatus and were coated with a thin, smooth layer of luminescent silicon nanocrystals. The photoluminescence spectrum showed WGM peaks with Q-factors near 2,500; however, evanescent measurements showed that these modes are a composite of many modes with Q-factors exceeding 106, the highest yet seen for a silicon-nanocrystalcoated microresonators. The mode structure showed strong polarization and sensitivity to position within the bottle resonator. An analysis of loss mechanisms establishes surface roughness scattering as the limiting factor in these nanocrystal-coated bottle resonators in the absence of excited carriers.

Fast Impedance Spectroscopy Method for Insulating Layers with Very High Impedance

This paper presents the fast impedance spectroscopy method for objects with a very high impedance |Zx| ≥ 1GΩ modeled by RC networks. The method is suitable for predicting the lifetime and reliability of insulating materials. The fast impedance spectroscopy method was tested on insulating layers which were part of the system metalinsulator-metal (MIM). The method is based on measurements of the power loss and phase shift in the AC voltage divider, which consists of the measured system MIM and of the known impedance. Computer controlled instruments measure the gain and phase shift between the two outputs of alternating electrical circuit and a computer program calculates the parameters of the impedance spectroscopy from these values. The output is the graphical and tabular impedance characteristics of the MIM system, namely: the dielectric loss of the insulating film, imaginary part of impedance, loss factor, parallel resistance Rp and the capacity Cp of the MIM system, all frequency dependent. Frequency characteristics provide an analysis of loss mechanisms that may affect the quality and reliability of the insulating layers.

Winding loss mechanism analysis and design for new structure high-frequency gapped inductor

An inductor with air-gap used in high-frequency switch-mode power supply has high extra eddy current winding losses due to the air-gap, resulting in low efficiency and high temperature rise in the inductor. In order to reduce the extra winding losses, many techniques are proposed. But all these techniques make the winding and core structures much more complicated. In this work, by 2D eddy current finite element analysis (FEA) field simulation, eddy current winding loss mechanism in the inductor with air-gap was deeply investigated and then a new simple inductor structure was proposed to reduce the winding losses greatly. Moreover, analysis and design for the new structure was also performed.

Investigation of On-Board Hybrid Pulse Tube Cryocooler for High Temperature Superconducting Rotor

This paper discusses the practical realization of an advanced cooling method for superconducting rotor; on-board cryocooler. A hybrid pulse tube cryocooler was designed and tested in the rotating system. A Stirling cryocooler precooled the regenerator of the pulse tube cryocooler to produce lower temperature at the cold end of the pulse tube cryocooler. Based on adiabatic model and loss mechanism analysis, the pulse tube cryocooler was designed and fabricated. The hybrid cryocooler was aligned in the test rotor to have a concentric centerline with the rotation axis. Even if the performance of the rotating hybrid pulse tube cryocooler was not satisfactory, achieving 55 K, the feasibility of on-board cryocooler method for superconducting rotor was confirmed.

Loss mechanism analysis in single-crystal and polycrystalline silicon MIS solar cells to produce 13% efficiency

Current mechanism studies have revealed band-to-band tunneling and surface state currents to control chromium MIS solar cell behavior. This information, together with intrinsic and design-related loss analysis, was used to optimize the design of the chromium MIS solar cell. It is shown that a high efficiency can be produced when the interface and grain boundary state densities are below 10 12 cm −2 eV −1, the interface oxide thickness is 12 – 18 Å, the grain size is above 40 μm and the doping density is 10 16 – 10 17 cm −3. This computer-aided design was used to fabricate a 13.2% experimental solar cell in agreement with the predicted performance.

Visible photoabsorption by noble-gas trimer ions

A study of the electronic structure and photoabsorption characteristics of noble-gas trimer ions has been carried out using quantum mechanical methods. This study includes detailed density functional calculations of the potential energy surfaces for a prototype system, Ar+3, an analysis of the spectroscopic properties of the ground state of this ion, and prediction of the strong absorption bands. Studies in D3h, C2v, and D∞h symmetries were carried out. The lowest state of Ar+3 corresponds to the degenerate 2E′ symmetry with an indicated dissociation energy of 0.17 eV relative to Ar+2 (A 2Σ+u)+Ar (1S0). This trimer ion exhibits a small Jahn-Teller distortion which does not significantly alter our conclusions concerning the ground-state stability or absorption characteristics. A strong and very broad photoabsorption band (λ=480–670 nm) is predicted for the 2E′→2A′1 transition of this trimer ion. This suggests that such species may be important in the analysis of loss mechanisms in visible excimer lasers operating under high-pressure conditions with mixtures containing the noble gases.