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Sustained thermoelectric efforts have concentrated on the enhancement of conversion efficiency of power generators, while simultaneously achieving high output power continues to lag. Specifically, the highest output power density of emerging Mg‐based modules reported so far is only half of that of commercial Bi2Te3‐based, mainly due to the low power factor of MgAgSb. Herein, homogenously distributed MgCuSb in situ nanoprecipitates in the MgAgSb matrix effectively optimized carrier concentration due to the effect of carrier injection from the metal–semiconductor Ohmic contact. As a result, a record‐high average power factor of 27.2 µW cm−1 K−2 is obtained in MgCu0.1Ag0.87Sb0.99 composite within the temperature range of 300–550 K, which is much higher than ever reported values of MgAgSb system. Benefiting from the combination of the optimized average power factor of p‐leg and low interface resistivity, a fabricated eight‐pair MgCu0.1Ag0.87Sb0.99/Mg3.2Bi1.5Sb0.5 module demonstrates an unprecedently high output power density of 2.9 W cm−2 under a temperature difference of 300 K, outperforming all low‐temperature advanced thermoelectric modules. Meanwhile, a competitive conversion efficiency of 7.65% is obtained simultaneously. The work significantly advances high‐power thermoelectric applications of Mg‐based modules in the field of low‐temperature sustainable energy harvesting. [ABSTRACT FROM AUTHOR]

The thermionic energy converter is a static thermoelectric conversion device, which is the core component of the thermionic nuclear reactor. To improve the conversion efficiency of thermionic energy converters, it is necessary to test its basic performance and conduct research on the optimization mechanism of its thermoelectric performance. At present, a basic experimental device of thermionic energy converter with the flat electrode pair has been developed in China, which can be used to achieve isothermal equipotential of electrodes during the power generation experiments. However, the corresponding analysis method of thermoelectric characteristic of electrodes has not yet been established, so it is urgent to set up a reasonable testing technology for the analysis of the basic thermionic performance. By drawing inspiration from the theory and empirical formula of thermionic energy conversion, and combining with the test data of voltammetry characteristics obtained in experiments, a specialized testing technology for the thermoelectric conversion characteristics of flat electrode pair was established. Then, the tests of thermoelectric conversion of W-Mo electrode pair with the basic experimental device was conducted. The established testing technology was validated and evaluated by comparing the values of the effective work function of the tungsten emitter tested in the experimental device with the theoretical and experimental values in the literature. And the results show that the measured values of the effective work function of the emitter in this study are consistent with those in the literature, indicating that the established testing technology was accurate and reasonable. Therefore, it can be asserted that this testing technology can be used to analyze the output electrical characteristics of a flat electrode type thermionic energy conversion device. What’s more, the thermoelectric conversion performance of W-Mo electrode pairs was further studied using this testing technique. The influence of power generation parameters, including emitter temperature and cesium pot temperature, on the output characteristics of W-Mo electrode pair were analyzed through a series of thermoelectric conversion experiments. The results show that the emitter temperature has a more significant impact on the output power density of the thermionic energy converter. As the emitter temperature increases, the output voltage correspondingly increases; and within the range of 1 600-1 900 K for the emitter temperature, the corresponding optimal cesium pot temperature is 577 K, with cesium pressure of 267.7 Pa. Moreover, the maximum output power density of the W-Mo electrode pair measured using the thermionic basic experimental device is 5.6 W/cm2, corresponding to the power generation parameters of the emitter temperature TE=1 800 K, cesium pot temperature TCs=577 K, and output voltage V=0.7 V. This result can provide parameter reference for the application of the W-Mo electrode pair in thermionic energy converters.

Bi(Te, Se)-based compounds have attracted lots of attention for nearly two centuries as one of the most successful commercial thermoelectric (TE) materials due to their high performance at near room temperature. Compared with 3D bulks, 2D thin films are more compatible with modern semiconductor technology and have unique advantages in the construction of micro- and nano-devices. For device applications, high average TE performance over the entire operating temperature range is critical. Herein, highly c-axis-oriented N-type Bi(Te, Se) epitaxial thin films have been successfully prepared using the pulsed laser deposition technology by adjusting the deposition temperature. The film deposited at ∼260 °C demonstrate a remarkable average power factor (PFave) of ∼24.4 μW·cm−1·K−2 over the temperature range of 305–470 K, higher than most of the state-of-the-art Bi(Te, Se)-based films. Moreover, the estimated average zT value of the film is as high as ∼0.81. We then constructed thin-film TE devices by using the above oriented Bi(Te, Se) films, and the maximum output power density of the device can reach up to ∼30.1 W/m2 under the temperature difference of 40 K. Predictably, the outstanding average TE performance of the highly oriented Bi(Te, Se) thin films will have an excellent panorama of applications in semiconductor cooling and power generation.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this letter, AlGaN/GaN HEMTs with tall-gate-stem structures were realized to improve the power performance of Ka-band devices, and a film thinning process is adopted in the fabrication process to reduce the parasitic capacitance caused by the thick silicon nitride film. According to the S-parameter measurement results, devices owning a tall-gate-stem structure and undergoing the film thinning process have higher cut-off frequency (fT) and maximum oscillation frequency (fmax) values with lower extracted parasitic capacitance. For the load-pull measurement result, the AlGaN/GaN HEMT with a tall gate stem has improved output power density (Pout) and power added efficiency (PAE) at Ka-band. The device with the elevated stem shows a steady-state current density of 883 mA/mm and a maximum transconductance of 323 mS/mm at 20 V bias, and it achieves ${\mathrm{ f}}_{\mathrm{ T}}$ of 39.5 GHz, ${\mathrm{ f}}_{\max }$ of 112.9 GHz with the maximum PAE of 24.6% and the maximum ${\mathrm{ P}}_{\mathrm{ out}}$ of 6.6 W/mm at 38 GHz.

In this work, novel microporous layers (MPLs) were developed based on fluorinated ethylene propylene (FEP), as a hydrophobic agent, and carboxymethylcellulose (CMC), as a wettability modulator and rheology controller for the inks, which were deposited onto pre-hydrophobized macroporous gas diffusion layers (GDLs). Higher CMC amounts led to higher dynamic viscosities of the inks, which induced the formation of a more compact and less cracked MPL surface. Different concentrations of CMC were tested and the experimental measurements showed a threshold limit pointing out an optimal composition that positively affected the electrochemical performances at medium-low relative humidity (RH), which is important to mitigate the need of saturating inlet gases. Durability of the best performing samples was assessed by means of an ad hoc developed accelerated stress test (AST) and compared to one of the conventional FEP-based GDMs. It was found that a lower decrement of both the output power density and the overall cell efficiency can be obtained upon the ASTs with the novel samples. [ABSTRACT FROM AUTHOR]

In this paper, we report on an enhancement of mm-wave power performances with a vertically scaled AlN/GaN heterostructure. An AlGaN back barrier is introduced underneath a non-intentionally doped GaN channel layer, enabling the prevention of punch-through effects and related drain leakage current under a high electric field while using a moderate carbon concentration into the buffer. By carefully tuning the Al concentration into the back barrier layer, the optimized heterostructure offers a unique combination of electron confinement and low trapping effects up to high drain bias for a gate length as short as 100 nm. Consequently, pulsed (CW) Load-Pull measurements at 40 GHz revealed outstanding performances with a record power-added efficiency of 70% (66%) under high output power density at VDS = 20 V. These results demonstrate the interest of this approach for future millimeter-wave applications. [ABSTRACT FROM AUTHOR]

Significant advances in the performance of organic photovoltaic (OPV) devices can facilitate their use in internet of things applications. However, achieving excellent photostability and high efficiency using stable, efficient OPV devices in indoor settings is considerably difficult. To address this issue, a zinc oxide (ZnO) electron transport layer (ETL) was modified with a self-assembled monolayer of 4-aminobenzoic acid (ABA) in the present study, and the impact of this modification was correlated with the indoor performance of an OPV device with the PM6:L8-BO photoactive layer. The ABA-treated ZnO ETL exhibited a significant reduction in the work function (from 4.51 to 4.04 eV), surface roughness (from 0.201 to 0.177 nm), and hydrophilicity of an indium-tin-oxide electrode; this aided in selectively extracting charge carriers from the device and minimizing trap-assisted recombination losses. Additionally, the ABA treatment of the ZnO ETL considerably enhanced the electron mobility and recombination resistance. It reduced the trap density, thereby enabling the ZnO/ABA-based device to achieve improved performance. Consequently, the ZnO/ABA-based device exhibited a noteworthy 14.68% higher maximum power output than that of the device without any ZnO surface modification under 1000 lx halogen (HLG) illumination ( P _out, max = 354.48 and 309 µ A cm ^−2 , respectively). Moreover, under thermal illumination conditions (1000 lx HLG lighting), the ZnO/ABA-based device sustained ∼74% of its initial power conversion efficiency over 120 h, significantly higher than its ABA-free equivalent (∼55%).

Turbulence intensity in offshore environments has significant effects on the performance of offshore wind turbines. To maximize output power of offshore wind turbines within a limited space, i.e., achieving maximum output power density, it is essential to investigate the influences of incoming turbulence intensity and turbine spacing on output power density. The Large Eddy Simulation coupled Actuator Line Method (LES-ALM) is used in this study to simulate two utility-scale NREL-5 MW wind turbines in different turbulent environments and turbine spacings. The optimal incoming turbulence intensity and turbine spacing are identified using an active learning method. The determined optimal parameters act as a benchmark for the impact analysis. The findings indicate that the increase of turbine spacing initially results in a considerable rise in the output power density of the two NREL-5 MW wind turbines, followed by a slight downward trend across various turbulent environments. The increase of the incoming turbulence leads to a steady rise of the output power density when the turbine spacing is less than 5.1 D (D is the rotor diameter), while a rise followed by a decrease in the output power density is observed for the turbine spacing exceeding 5.1 D. Notably, when the turbine spacing is 5.9 D and the reference value of turbulence intensity is 15.2%, the output power density reaches its global maximum. • Emphasis on output power density to assess power generation efficiency. • Quantitative analysis of incoming turbulence and turbine spacing effects. • Identification of the optimal turbulence intensity for wind farm site selection. • Determination of optimal turbine spacing to fit various turbulent environments. • Application of active learning to effectively identify optimal variable combinations. [ABSTRACT FROM AUTHOR]

For the first time, we report achieving a considerable output power density in metal-semiconductor field-effect transistors according to silicon-on-insulator technology (SOI MESFETs). Our main idea is to improve the breakdown voltage and the saturation current simultaneously and, therefore, the output power density of SOI MESFET devices by silicon dioxide engineering. Our silicon dioxide engineering consists of a step-shaped buried oxide (BOX) and an extra layer of silicon dioxide under the gate (SB-LO-SOI) in this work. A step-shaped in the channel area results in a more significant drain current due to increasing total carrier concentrations. Also, by omitting a part of the BOX and substituting it with n-doped silicon, the depletion layer changes, and the channel charges increase. Besides, the distribution of the electric field improves by the additional rectangular silicon dioxide layer under the gate as a result of extending the depletion layer. By having a premier electric field distribution, the breakdown voltage will enhance. According to the results, the breakdown voltage and the saturation current of the considered device improve by 130 % and 33 %, respectively, compared to the traditional one. As well as, the output power density of the considered device rises by 212 %. Thereupon, the SB-LO-SOI MESFET device outperforms the conventional SOI MESFET device in terms of electrical properties. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shenzhen University Science & Engineering is the property of Editorial Department of Journal of Shenzhen University Science & Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A solar thermoelectric generator (STEG) that harvests solar energy and converts it into electricity based on the fundamentals of the Seebeck effect is a promising alternative to photovoltaic technologies. The combination of a phase change material (PCM) with STEG further enables stable and durable energy output despite the variations of solar radiation flux. However, the widespread promotion of STEG is still impeded by its restricted output electricity (<50 W m−2), attributed to the undesirable thermal management in PCMs. Herein, an ingenious phase change composite, with the typical conformation of circular truncated cone and embedded with the actinomorphic arrangement of polybenzobisoxazole fibers, is tailored by a mold processing strategy. The fibrous crystals in organic fibers offer temperature‐resistance thermal highways during the charging/discharging processes, while their actinomorphic configuration facilitates a controllable thermo‐conductive behavior. These structural features render concentrated thermal energy to be efficiently stored in the PCM and maximally discharged into the thermoelectric system. A record‐breaking power density as high as 198.70 W m−2 can be achieved in this powerful STEG via real‐environment solar‐thermal‐electric conversion, a value comparable to that of some commercial photovoltaic devices. This work opens up opportunities for durable and giant electricity supply from clean solar energy during real‐time STEG applications. [ABSTRACT FROM AUTHOR]

In this work, a new structure of 4H-SiC MESFET with un-doped and recessed region under the gate (UR-MESFET) is reported. Channel of the proposed device is recessed into the p-buffer layer. The length and thickness of the un-doped area is equal to those of the recessed section. The un-doped section reduces peak electric field in the channel and then postpones breakdown phenomena. This can enhance breakdown voltage. Maximum breakdown voltage of the suggested transistor is about 138 V. This value is about 19% larger than that in the conventional (116 V). Recessed channel to the p-buffer increases saturated drain current significantly. Obtained results illustrate that saturated drain current of UR-MESFET is about 50% higher than that of the conventional device. Also, increasing breakdown voltage and drain current in the proposed device improves output power density about 90% compared to that in the conventional device. The suggested structure also reduces the gate-source and gate-drain capacitors significantly. The proposed transistor at best reduces the gate-source capacitor by 55% and reduces the gate-drain capacitor by 20% compared to the conventional structure. This makes the transistor perform better at high frequencies. As a result, it can be said that the proposed structure has better performance at high power and frequency than that of the conventional transistor. [ABSTRACT FROM AUTHOR]

Osmotic energy, as a renewable clean energy with huge energy density and stable yield, has received widespread attention over the past decades. Reverse electrodialysis (RED) based on ion-exchange membranes is an important method of obtaining osmotic energy from salinity gradients. The preparation of ion-exchange membranes with both high ion selectivity and ion permeability is in constant exploration. In this work, metal hydroxide-organic framework (MHOF) membranes are successfully prepared onto porous anodic aluminum oxide (AAO) membranes by a facile hydrothermal method to form Ni 2 (OH) 2 @AAO composite membranes, used for osmotic energy conversion. The surface is negatively charged with cation selectivity, and the asymmetric structure and extreme hydrophilicity enhance the ionic flux for effective capture of osmotic energy. The maximum output power density of 5.65 W m -2 at a 50-fold KCl concentration gradient is achieved, which exceeds the commercial benchmark of 5 W m -2 . Meanwhile, the composite membrane can also show good performance in different electrolyte solutions and acid-base environments. This work provides a new avenue for the construction and application of MHOF membranes in efficient osmotic energy conversion., (© 2024 Wiley‐VCH GmbH.)

This article reports on the high operation voltage large-signal performance of two-dimensional hole gas diamond metal–oxide semiconductor field-effect transistors (MOSFETs) with thick atomic-layer-deposition (ALD)-Al2O3 formed on high purity polycrystalline diamond with a (110) preferential orientation. MOSFETs with a 1- $\mu \text{m}$ gate-length having a gate oxide layer of 200-nm-thick Al2O3, formed by ALD and asymmetric structures, to withstand high-voltage operations. The large-signal performances were evaluated at a quiescent drain voltage of greater than −60 V for the first time in diamond field-effect transistor (FET). As a result, an output power density of 2.5 W/mm under class-A operation at 1 GHz, which is higher than that of diamond FETs fabricated by a self-aligned gate process, was obtained. Moreover, an output power density of 1.5 W/mm was exhibited by the MOSFET when biased at a quiescent drain voltage of −40 V under class-AB operation at 3.6 GHz using an active load-pull system. This is the highest recorded value for diamond FETs at a frequency greater than 2 GHz, owing to the high-voltage operation. These results indicate that diamond p-FETs under high-voltage operations are the most suitable for high-power amplifiers with complementary circuits. [ABSTRACT FROM AUTHOR]

Energy harvesters (EHs) are widely used to transform ambient energy sources into electrical energy, and have tremendous potential to power wearables electronics and biomedical devices by eliminating, or at least increasing, the battery life. Nevertheless, the use of EHs for a specific application depends on various aspects including the form of energy source, the structural configuration of the device, and the properties of materials. This paper presents a comprehensive review of the classification of EHs, notably thermoelectric generators (TEGs), triboelectric nanogenerators (TENGs), and piezoelectric generators (PEGs) that allows a wide variety of devices to be operated. The EHs are discussed in terms of their operating principles, optimization factors, state‐of‐the‐art materials, and device structure, that directly influence their operational efficiency. Besides, the breakthrough performance of each of the EHs listed above is highlighted. From the review and analysis, the maximum output power density of 9.2 mW cm−2, 50 mW cm−2, and 64.9 µW cm−2, respectively, are obtained from the TEG, TENG, and PEG, respectively. Furthermore, recent applications relevant to a specific EH and their output performance, are also enlightened. Eventually, the essential outcomes and future direction from this review are discussed and encapsulated. [ABSTRACT FROM AUTHOR]

Differing estimates have emerged about how much land or water area is used by existing wind farms and how much power can be obtained from that area. Whereas, no single unique method exists to define wind farm spacing area, the spacing area (thus installed and output power densities) of a wind farm can be determined in a way to meet specific logical criteria, This study proposes a new, intuitive, data based, automatized method of estimating spacing areas occupied by existing onshore and offshore wind farms worldwide. The method eliminates the erroneous counting of space outside of wind farm boundaries, space between clusters of turbines, and overlapping space that results when assuming a large fixed area around each turbine. At least one of three types of extra space has incorrectly been included in all calculations of wind farm areas to date. Unlike most previous methods, this method also ensures that the addition of a wind turbine to a farm increases the overall required spacing area of the farm. The study then uses data from over 1600 operating wind turbines in 16 onshore and 7 offshore wind farms in 13 countries across 5 continents during the period 2016–2018 to quantify installed and output power densities of these farms. Finally, it compares results with estimates from other studies. Results indicate that the mean (range) installed and output power densities of onshore wind farms in Europe are 19.8 (6.2–46.9) MW/km2 and 6.64 (2.3–8.2) W/m2, respectively; of onshore wind farms outside of Europe are similarly 20.5 (16.5–48) MW/km2 and 6.84 (4.81–11.2) W/m2, respectively; and of offshore wind farms in Europe are 7.2 (3.3–20.2) MW/km2 and 2.94 (1.15–6.32) W/m2, respectively. The mean capacity factors in each case are thus 33.5%, 33.4%, and 40.8%, respectively. These results indicate substantially higher installed and output power densities than previously reported, based simply on different definitions of land area, with no impact on capacity factor. Thus, existing wind turbines may extract more wind power over less land or water than previously thought. • A new method of estimating onshore and offshore wind turbine installed and output power densities has been developed. • The mean of installed power densities of onshore turbines are 19.8 (6.2-46.9) and 20.5 (16.5-48) MW/km2. • Offshore turbines are spaced further apart within farms with a mean installed power density of 7.2 (3.3-20.2) MW/km2. • The mean capacity factors of the three categories of wind farms are 33.5%, 33.4%, and 40.8%, respectively. [ABSTRACT FROM AUTHOR]

Summary: In this work, we designed and optimized a gallium nitride (GaN)‐based betavoltaic (BV) cell using an AlGaN back‐barrier layer and finger structure for improving the output power density. A short‐circuit current density (JSC) and an open‐circuit voltage (VOC) of the BV cells associated with an output power density were investigated by using electron‐beam (e‐beam) irradiation. The device with the Al0.25Ga0.75N back‐barrier layer exhibited an enhanced JSC because the potential barrier with a high height reduced excess carriers moving to the substrate region. The finger structure of the proposed BV cells was optimized by changing parameters such as the width of the intrinsic GaN region (Wi‐GaN) and heights of the p‐GaN and n‐GaN regions (Hp‐GaN and Hn‐GaN). The optimized BV cell with a Wi‐GaN of 100 nm, a Hn‐GaN of 100 nm, and a Hp‐GaN of 200 nm obtained a higher JSC compared to that of the conventional p‐i‐n BV cell because an optimum structure resulted in a wide depletion area, which was involved in the improved charge collection. As a result, the output power density of the proposed BV cell was enhanced by 14.8% than that of the conventional BV because of the improved JSC. The proposed structure shows a high potential for BV cells with a high‐power conversion efficiency. [ABSTRACT FROM AUTHOR]

• A new solar powered electricity and cooling cogeneration system is proposed. • Various irreversible losses within the proposed system are described. • Parameters evaluating the proposed system performance are mathematically formulated. • Absorption refrigerators are effective to improve the DSSC performance. • Effects of some designing parameters and operating conditions are revealed. To improve the energy conversion efficiency of a dye-sensitized solar cell (DSSC), a novel hybrid system representatively consisting of a DSSC and an absorption refrigerator (APR) is put forward, in which the APR is used to thermally harness the part of high wavelength sunlight that not converted by the DSSC. The amount of heat from the DSSC is calculated, and mathematical formula for energy conversion efficiencies and output powers of the DSSC, APR and hybrid system are derived. Numerical calculations show that the maximum output power density and maximum energy conversion efficiency of hybrid system are enhanced by 9.93% and 9.92% in comparison with that of the single DSSC, respectively. Integration of APR to DSSC is a feasible route to effectively improve the energy conversion efficiency. Comprehensive sensitivity analyses are conducted to explore how the whole hybrid system performance depends on various working conditions and designing parameters, including porous nano-TiO 2 film thickness, photoelectron absorption coefficient, internal irreversibility factor, heat transfer coefficient and various temperatures. The research results can provide some new understandings for further enhancing the DSSC performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • 0-D models for a tiny thermoelectric harvester at matched or constant loads are built. • New theoretical formulas are deduced to gauge the needed thermoelectric materials. • The TEG's optimal configurations are directly predicted for the highest power output. • A designed harvester exhibits areal power density nearly 100 times of commercial one. Thermoelectric (TE) generators (TEGs) have recently attracted significant attention for harvesting ubiquitous heat energy to power industrial sensor nodes or wearable and implantable electronics. Such applications require that a small, fitted heat sink be incorporated into a tiny harvester to ensure conformal deployment and ease of use. Since the small heat sink will exhibit very poor heat rejection performance, the optimal structural design of the TEG device and the proper selection of its constituent TE materials are extremely important to ensure that sufficient electric power is provided to the connected post-stage circuits. Regrettably, the traditional forward design strategies, i.e. , material-to-device and device-to-harvester, are often disconnected from one another and fail to form a complete chain, thereby presenting a fundamental challenge in achieving ultrahigh-power-density harvesters. Here we present a zero-dimensional model for a tiny harvester to establish a set of new metrics (not limited to the figure of merit zT) that can be used to determine the optimal TE material and to directly deduce the optimal configuration of the TEG for guaranteeing the maximum output power at various load conditions, making backward design strategy possible. Two tiny harvesters are accordingly fabricated and exhibit areal power densities 52 and 94 times that of a harvester incorporating a commercial TEG, with identical amounts of TE material used for each. [ABSTRACT FROM AUTHOR]

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm2 was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications.

We report enhanced thermoelectric performance of SnTe by further increasing its intrinsic high carrier concentration caused by Sn vacancies in contrast to the traditional method. Along with In2Te3 alloying, which results in an enhanced Seebeck coefficient, Li2Te is added to further increase the carrier concentration in order to maintain high electrical conductivity. Finally, a relatively high PFave of ~28 µW cm-1 K-2 in the range between 300 and 873 K is obtained in an optimized SnTe-based compound. Furthermore, nanoprecipitates with extremely high density are constructed to scatter phonons strongly, resulting in an ultralow lattice thermal conductivity of ~0.45 W m-1 K-1 at 873 K. Given that the Z value is temperature dependent, the (ZT)eng and (PF)eng values are adopted to accurately predict the performance of this material. Taking into account the Joule and Thomson heat, output power density of ~5.53 W cm-2 and leg efficiency of ~9.6% are calculated for (SnTe)2.94(In2Te3)0.02-(Li2Te)0.045 with a leg length of 4 mm and cold- and hot-side temperatures of 300 and 870 K, respectively. [ABSTRACT FROM AUTHOR]

It is an urgent need to develop lead-free piezoelectric energy harvesters (PEHs) to address the energy dilemma and meet environmental protection requirements. However, the low output power densities limit further promotion of lead-free PEHs for use in daily life. Here, an entropy-increasing strategy is proposed to achieve an increased output power density of 819 μW/cm 3 in lead-free potassium sodium niobate (KNN)-based piezoceramics by increasing the configuration entropy and realizing nearly two times the growth compared with low-entropy counterparts. Evolution of the energy-harvesting performance with increasing configuration entropy is demonstrated systematically, and the excellent energy-harvesting properties achieved are attributed to the enhanced lattice distortion, the flexible polarization configuration, and the high-density randomly distributed nanodomains with the entropy-increasing effect. Moreover, excellent vibration fatigue resistance and variable temperature output power characteristics were also realized in the PEH prepared by the proposed entropy-increasing material. The significant enhancement of the comprehensive energy-harvesting performance demonstrates that the construction of KNN-based ceramics with high configuration entropy represents an effective and convenient strategy to enable design of high-performance piezoceramics and thus promotes the development of advanced PEHs.

A type of multipolar linear permanent magnet generator (MLPMG) was developed in order to harvest human lower-limb motion energy to meet the increasing power supply needs of portable electronic devices. A large acceleration of the foot, particularly at the heel, was noted when analyzing human lower-limb motion during walking, so an energy harvester was placed on the heel. A series of MLPMGs were then designed and the static magnetic induction intensity vector diagram was obtained from each. A key parameter of MLMPG efficiency was found to be the gap between the stator and mover. Another important factor is the thickness of the mover spacers between magnet pieces. Finally, a number of experiments were conducted, which supported the conclusion that the output power of harvesters have negative relation with length of gap and thickness of spacers. It was found that a subject, walking at a speed of 5 km/h with a matched resistor load, can produce an output power of 20 mW. [ABSTRACT FROM AUTHOR]

In this study, state-of-the-art thermoelectric (TE) materials working between 300 K and 1000 K are cautiously selected, including materials in categories of Chalcogenides, SiGe alloy, Skutterudites and Half-Heuslers. The selection principle is an overall reflection of the figure of merit ( ZT ), compatibility factors and power factors of TE materials. These chosen TE materials are divided into four groups for construction of two kinds of segmented p-type TEG legs and two kinds of segmented n-type TEG legs. Built on different combinations of these segmented TE groups, thermoelectric generators (TEGs) have been systematically modelled to find out the best cost-performance ratios and the corresponding efficiencies, output power densities and TEG geometries as well. All the TE material properties input in the simulation are temperature-dependent and the electrical & thermal contact resistances have been taken into account for every TE-TE and TE-electrode interfaces. The results demonstrate that the successful segmentation of high- ZT TE materials rather than their counterparts with large power factors can offer a cost-performance ratio of ∼0.86 $ W −1 , less than the commercially desired cost-effectiveness of 1 $ W −1 , while maintaining an efficiency of 17.8% and delivering a power density over 3 Watt cm −2 . These results not only confirm ZT as indeed the top criterion for choosing TE materials, but also predict the commercial feasibility and competitiveness of segmented TEGs in the same dollar per watt metrics as other renewable energy sources. [ABSTRACT FROM AUTHOR]

New AlGaN/GaN high electron mobility transistors (HEMTs) that their barrier layers under the gate are divided into two regions horizontally are presented in this work. Upper region is Si 3 N 4 (SI-HEMT) or un-doped AlGaN (UN-HEMT) and lower region is AlGaN with heavier doping compared to barrier layer. Upper region in SI-HEMT and UN-HEMT reduces peak electric field in the channel and then improves breakdown voltage considerably. Lower region increases electron density in the two dimensional electron gas (2-DEG) and enhances drain current significantly. For instance, saturated drain current in SI-HEMT is about 100% larger than that in the conventional one. Moreover, the maximum breakdown voltage in the proposed structures is 65 V. This value is about 30% larger than that in the conventional transistor (50 V). Also, suggested structure reduces short channel effect such as DIBL. The maximum g m is obtained in UN-HEMT and conventional devices. Proposed structures improve breakdown voltage and saturated drain current and then enhance maximum output power density. Maximum output power density in the new structures is about 150% higher than that in the conventional. [ABSTRACT FROM AUTHOR]

Abstract: A free‐standing high‐output power density polymeric thermoelectric (TE) device is realized based on a highly conductive (≈2500 S cm−1) structure‐ordered poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate film (denoted as FS‐PEDOT:PSS) with a Seebeck coefficient of 20.6 µV K−1, an in‐plane thermal conductivity of 0.64 W m−1 K−1, and a peak power factor of 107 µW K−2 m−1 at room temperature. Under a small temperature gradient of 29 K, the TE device demonstrates a maximum output power density of 99 ± 18.7 µW cm−2, which is the highest value achieved in pristine PEDOT:PSS based TE devices. In addition, a fivefold output power is demonstrated by series connecting five devices into a flexible thermoelectric module. The simplicity of assembling the films into flexible thermoelectric modules, the low out‐of‐plane thermal conductivity of 0.27 W m−1 K−1, and free‐standing feature indicates the potential to integrate the FS‐PEDOT:PSS TE modules with textiles to power wearable electronics by harvesting human body's heat. In addition to the high power factor, the high thermal stability of the FS‐PEDOT:PSS films up to 250 °C is confirmed by in situ temperature‐dependent X‐ray diffraction and grazing incident wide angle X‐ray scattering, which makes the FS‐PEDOT:PSS films promising candidates for thermoelectric applications. [ABSTRACT FROM AUTHOR]

In this letter, we have proposed a novel AlGaN/GaN FinFET featuring T-shaped gate and extremely linearity of transconductance characteristics ( \textG\mathrm {m}) . The formation of AlGaN/GaN nano-fins only in the gate opening region is enabled by a developed fabrication process, which is simple and well compatible with the conventional one. When normalized to effective channel width, the fabricated FinFET delivers a 1.45 times higher current density and a 1.66 times higher output power density as high as 11.3 W/mm at 8 GHz compared with the planar HEMTs, along with clearly improved linearity characteristics thanks to a flatter \textG\mathrm {m} response afforded by much lower source access resistance. To the best of our knowledge, this is the first demonstration of superior power performance of high-linearity GaN FinFETs, indicating significant advantages of tri-gate configuration over planar HEMTs for microwave power applications. [ABSTRACT FROM AUTHOR]

In this study, a gallium nitride (GaN) high electron mobility transistor (HEMT) with recessed insulator and barrier is reported. In the proposed structure, insulator is recessed into the barrier at the drain side and barrier is recessed into the buffer layer at the source side. We study important device characteristics such as electric field, breakdown voltage, drain current, maximum output power density, gate-drain capacitance, short channel effects and DC transconductance using two-dimensional and two-carrier device simulator. Recessed insulator in the drain side of the proposed structure reduces maximum electric field in the channel and therefore increases the breakdown voltage and maximum output power density compared to the conventional counterpart. Also, gate-drain capacitance value in the proposed structure is less than that of the conventional structure. Overall, the proposed structure reduces short channel effects. Because of the recessed regions at both the source and the drain sides, the average barrier thickness of the proposed structure is not changed. Thus, the drain current of the proposed structure is almost equivalent to that of the conventional transistor. In this work, length ( L ) and thickness ( T ) of the recessed region of the barrier at the source side are the same as those of the insulator at the drain side. [ABSTRACT FROM AUTHOR]

Improvements in thermoelectric material performance over the past two decades have largely been based on decreasing the phonon thermal conductivity. Enhancing the power factor has been less successful in comparison. In this work, a peak power factor of ~106 µW⋅cm-1⋅K-2 is achieved by increasing the hot pressing temperature up to 1,373 K in the p-type half-Heusler Nb0.95Ti0.05FeSb. The high power factor subsequently yields a record output power density of ~22 W⋅cm-2 based on a single-leg device operating at between 293 K and 868 K. Such a high-output power density can be beneficial for large-scale power generation applications. [ABSTRACT FROM AUTHOR]

A series of Nb doped (Hf 0.25 Zr 0.75 ) 1– x Nb x NiSn ( x = 0–0.03) samples were synthesized and studied by arc-melting the elements to first form ingots, then ball-milling the ingots to obtain fine powders, and finally hot-pressing the fine powder to form bulk samples. Instead of the conventional Sb doping on the Sn site of the n-type half-Heusler, it was found that Nb is also an effective dopant. When the carrier concentration is optimized at 2.2% Nb, a power factor of ∼47 μW cm −1 K −2 is achieved at and above 600 °C, and a peak ZT ∼0.9 is achieved at 700 °C with Nb doping from 1.8 at% to 2.2 at%. An output power density of ∼22 W cm −2 and a leg efficiency of ∼12% are calculated for the Nb doped samples. [ABSTRACT FROM AUTHOR]

We have fabricated a flexible, environment friendly piezoelectric nanogenerator (PENG) based on the ferroelectric Polyvinylidene fluoride (PVDF) composite incorporated with Barium titanate (BaTiO 3 ) nanowires (NWs) of piezoelectric coefficient d 33 . The single-layered PENG can deliver output power density of 10 -1 . The single-layered PENG can deliver output power density of 10 μ W cm -2 and an output voltage of 2 V with a nominal mechanical load of 1 kPa. BaTiO 3 (BTO) NWs of different concentrations were incorporated into PVDF to tune the polar phase content, internal resistance, and optimize the output power. We show that there exists a critical value of BTO NWs loading of 15 wt%, beyond which the piezoelectric energy harvesting characteristics of the PVDF nanocomposites decrease. The oxygen vacancies present in the BTO NWs surface attract the fluorine ions of PVDF chain and favour the formation of β phase. The enhanced value of dielectric constant and dielectric loss of BTO-PVDF samples in the low frequency region suggest strong interfacial polarization in the composite system. The fabricated PENG can charge a super-capacitor up to 4 V within 35 s. The origin of the high power output from the BTO (15 wt%)-PVDF composite is attributed to the combined effect of enhanced polar phase content, strong interfacial polarization, and reduced internal resistance. This study provides an effective pathway in enhancing the performance of BTO-PVDF based piezoelectric energy harvesters., (© 2022 IOP Publishing Ltd.)

Abstract: The experimental U–I characteristics of a single GaSb cell, a single Si cell and their modules in a TPV system using a SiC radiator were investigated. The influence of the radiator temperature and the radiator–cell distance on the output performances of a single cell and its module was analyzed. The results demonstrate that increasing the radiator temperature or decreasing the radiator–cell distance both lead to the increasing the short-circuit current density and the output power density, but the open-circuit voltage decreases because of the rise of the cell temperature. The maximum output power densities of a single GaSb cell and the corresponding module are 0.26 and 0.28W/cm2, respectively, which are approximately 4.3 and 6.0 times that of a single Si cell and its module for a combustion power of 4.2kW and a radiator–cell distance of 1.1cm. Furthermore, a mathematical physical model was constructed to analyze the influence of the cell temperature on the output performance of the cells. For a given radiator temperature and radiator–cell distance, the theoretical results indicate that the output power density decreases with cell temperature because of attenuation of the open-circuit voltage. [Copyright &y& Elsevier]

Abstract: This paper shows the possibility to improve DC and RF electrical performances of AlGaAs/InGaAs PHEMTs by using low gamma radiation dose. The drain–source saturation current and the DC transconductance increase when the devices are irradiated with a gamma dose of 42.8krad(GaAs) and then remain constant up to 0.85Mrad(GaAs). This improvement is attributed to a reduction of access resistances. In the same time, the Schottky diode and the current-gain cut-off frequency of these components are not degraded by the gamma irradiation. Moreover, the maximum output power density is improved by 18%. This paper demonstrates that it is possible to improve the component electrical performances by using an original method. [ABSTRACT FROM AUTHOR]

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm2 was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications. [ABSTRACT FROM AUTHOR]

The high potential at microwave frequencies of AlGaN/GaN high electron mobility transistors (HEMTs) on high resistive silicon [111] substrate for power applications has been demonstrated in this letter. For the first time, an output power density close to 1.8 W/mm and an associated power added efficiency of 32% have been measured on a 2 × 50 × 0.5 μm2 HEMT with a linear power gain of 16 dB. These results constitute the state of the art. [ABSTRACT FROM PUBLISHER]

A solar thermoelectric generator (STEG) that generates electricity from sunlight is expected to be a promising technology for harvesting and conversion of clean solar energy. The integration of a phase-change material (PCM) with the STEG even more enables engines to durably generate power in spite of solar radiation flux. However, its photothermal conversion and output electricity is still limited (<15 W/m 2 ) by the PCM's deficient thermal management performance, i . e ., restricted thermal conductivity and nonuniform heat-transfer behavior under concentrated sunlight radiation. In this study, a biomimetic phase-change composite, with centrosymmetric and a multidirectionally aligned boron nitride network embedded in polyethylene glycol, is tailored for the STEG via a radial ice-template assembly and infiltration strategy, which behaves in a highly and multidirectionally thermoconductive way and enables a rapid transfer of heat flux and uniform temperature distribution with respect to even a spot-like heat source. As a consequence, a powerful STEG is tactfully designed via the integration of this high-thermal-management characteristic and maximum collection of solar beams, for durable and real-environment solar-thermal-electric conversion, with its photothermal energy conversion efficiency of up to 85.1% and a high peak power density of 40.28 W/m 2 .