Device Performance Stability Research Articles

Improved magnetic and thermal conductivity performance of FeSi soft magnetic composites by adding h-BN

Low heat generation and high thermal conductivity are the basic guarantees for stable operation of magnetic devices. In this paper, h-BN nano-sheet were coated on FeSi particles to prepare FeSi/h-BN magnetic cores with a low loss and high thermal conductivity. The surface modified h-BN evenly coated on FeSi particles improved the insulation between magnetic particles. Appropriate amount of h-BN sheet addition effectively reduced the eddy current loss and improved thermal conductivity of FeSi soft magnetic composites (SMCs), which can be attributed to the high resistivity and high planar thermal conductivity of h-BN nano-sheet. The FeSi SMCs with 3 wt% h-BN has the optimum comprehensive properties, effective permeability of 57, saturation magnetization of 172.2 A.m2/kg, low core loss of 601.6 mW/cm3 at 60 mT and 100 kHz, and its thermal conductivity increased by 62 % to 11.03 W m-1K−1, which is useful for the stable operation of devices.

Water-Borne Fluorinated Polyimide Dielectric for Large-Area IGZO Transistors and Logic Gates.

Thin-film transistors offer excellent and uniform electrical properties over large areas, making them a promising option for various future electronic devices. Polyimide dielectrics are already widely used in various electronic devices because of their exceptional dielectric properties, thermal stability, and desirable mechanical flexibility, which make them suitable for harsh environments. However, the current research on polyimide dielectric materials has certain limitations, such as the use of toxic solvents, high-temperature processes, and deficient coating properties. Herein, we introduce an aromatic polyimide dielectric, which exhibits excellent electrical properties even when processed at a low temperature of 250 °C using environmentally friendly water-based "one-step" polymerization. Despite its thin thickness of <200 nm, the water-borne fluorinated polyimide dielectric material demonstrates stable insulating properties over a wide range of electric fields and achieves a high breakdown voltage of over 4.5 MV cm-1. Furthermore, we successfully achieved a large-area coating of uniform dielectric layers with no pinholes using only water as a solvent and a simple solution process without any additional processing steps. These results demonstrate that the water-borne polyimide gated indium-gallium-zinc oxide transistor exhibits excellent and stable device performance. Moreover, we used the transistor to successfully demonstrate various logic gates (NOT, NAND, and NOR). Overall, this study provides guidelines for the eco-friendly and sustainable use of water-borne polyimide dielectric materials with high electrical performance and large-processing window advantages.

Real-time plasma boundary shape reconstruction using visible camera on EAST tokamak

Abstract Accurate plasma shape reconstruction is crucial for the stable operation of tokamak devices. In this study, a plasma optical boundary reconstruction system is constructed on the Experimental Advanced Superconducting Tokamak (EAST), and real-time shape reconstruction based on an optical method is realized for the first time on EAST. First, a boundary extraction algorithm based on gray features is designed to extract the optical boundary from plasma optical images. Then, to reconstruct the optical boundary in the tokamak coordinate system, a camera calibration algorithm is developed based on feature point matching, and a coordinate mapping algorithm is designed based on plasma geometric features. Then, the system reconstructs the plasma boundary shape based on images acquired by a camera. Finally, the system is deployed in real-time on EAST, and its reconstruction rate meets the requirement of the EAST plasma shape control system. This study validates the feasibility of using an optical boundary shape reconstruction method on a tokamak device for real-time plasma shape reconstruction, providing a new shape reconstruction approach during steady-state discharge in future fusion devices.

Chemical Synergic Stabilization of High Br‐Content Mixed‐Halide Wide‐Bandgap Perovskites for Durable Multi‐Terminal Tandem Solar Cells with Minimized Pb Leakage

AbstractHigh Br‐content lead mixed‐halide perovskites with wide‐bandgap (WBG) of 1.6–2.0 eV have showcased vast potential to be used in tandem solar cells. However, WBG perovskites often suffer from severe halide segregation, phase separation and ion migration under the stress of light, heat, moisture and electric bias, which would accelerate the decomposition of perovskite films and thus deteriorate the photovoltaic performance and even aggravate the lead leakage from damaged devices. Here, we report a novel chemical synergic interaction strategy to mitigate the abovementioned issues in WBG perovskites. To achieve that, a small amount of cationic β‐cyclodextrin, composed of multiple ammonium cations, chlorine ions and abundant hydroxyl functional groups, was introduced into WBG perovskites, which effectively stabilized the halide ions and homogenized the phase distribution, comprehensively passivated the crystallographic defects, as well as efficiently immobilized the Pb2+ ions. Encouragingly, the cationic β‐cyclodextrin was universal and useful for different WBG perovskite compositions (i.e. 1.68 eV, 1.79 eV and 1.99 eV), which favorably boosted the efficiencies by 10 %–36 % and extended the operational stability of resultant devices to 2680 h. The four‐terminal all‐perovskite tandem and six‐terminal all‐perovskite tandem solar cells integrated with different WBG perovskite sub‐cells exhibited efficiencies up to 24.39 % and 22.42 %, respectively. More importantly, we demonstrated the cationic β‐cyclodextrin‐assisted internal chemical encapsulation effectively prevented the Pb leakage when the devices were severely damaged and immersed in water. Surprisingly, there was only 5.63 ppb Pb leaching out for the single‐junction devices, far below than the U.S. standard for safe drinking water (&lt;15 ppb). The target tandem solar cells with cationic β‐cyclodextrin modification also realized a Pb sequestration efficiency of 93.4 % under the most adverse environment.

Chemical Synergic Stabilization of High Br-Content Mixed-Halide Wide-Bandgap Perovskites for Durable Multi-Terminal Tandem Solar Cells with Minimized Pb Leakage.

High Br-content lead mixed-halide perovskites with wide-bandgap (WBG) of 1.6-2.0 eV have showcased vast potential to be used in tandem solar cells. However, WBG perovskites often suffer from severe halide segregation, phase separation and ion migration under the stress of light, heat, moisture and electric bias, which would accelerate the decomposition of perovskite films and thus deteriorate the photovoltaic performance and even aggravate the lead leakage from damaged devices. Here, we report a novel chemical synergic interaction strategy to mitigate the abovementioned issues in WBG perovskites. To achieve that, a small amount of cationic β-cyclodextrin, composed of multiple ammonium cations, chlorine ions and abundant hydroxyl functional groups, was introduced into WBG perovskites, which effectively stabilized the halide ions and homogenized the phase distribution, comprehensively passivated the crystallographic defects, as well as efficiently immobilized the Pb2+ ions. Encouragingly, the cationic β-cyclodextrin was universal and useful for different WBG perovskite compositions (i.e. 1.68 eV, 1.79 eV and 1.99 eV), which favorably boosted the efficiencies by 10 %-36 % and extended the operational stability of resultant devices to 2680 h. The four-terminal all-perovskite tandem and six-terminal all-perovskite tandem solar cells integrated with different WBG perovskite sub-cells exhibited efficiencies up to 24.39 % and 22.42 %, respectively. More importantly, we demonstrated the cationic β-cyclodextrin-assisted internal chemical encapsulation effectively prevented the Pb leakage when the devices were severely damaged and immersed in water. Surprisingly, there was only 5.63 ppb Pb leaching out for the single-junction devices, far below than the U.S. standard for safe drinking water (<15 ppb). The target tandem solar cells with cationic β-cyclodextrin modification also realized a Pb sequestration efficiency of 93.4 % under the most adverse environment.

Further Application Of Automatic Control Based On Servo Motor In Smart Grid

The paper summarize the advantages and applications of servo motor. As a kind of equipment that can replace manual long-distance inspection, the intelligent inspection device for overhead transmission lines can significantly improve inspection efficiency and reduce labor intensity. The servo motor with high power density and low torque ripple can guarantee the high precision and stable operation of the intelligent inspection device in line inspection, which provides a certain practical intelligent application significance for transmission line inspection.

Microscopic analysis of low but stable perovskite solar cell device performance using electron spin resonance

Perovskite solar cells have attracted much attention as next-generation solar cells. However, a typical hole-transport material, spiro-OMeTAD, has associated difficulties including tedious synthesis and high cost. To overcome these shortcomings, an easily synthesized and low-cost hole-transport material has been developed: HND-2NOMe. Although HND-2NOMe has high local charge mobility because of the quasi-planar structure, its lower device performance is a weak point, the cause of which has not yet been clarified. Here, we analyse the source of the lower performance by clarifying the internal states from a microscopic viewpoint using electron spin resonance. We observe hole diffusion from perovskite to HND-2NOMe under dark conditions, indicating hole barrier formation at the perovskite/HND-2NOMe interface, leading to lower performance. Although such a barrier is formed, less hole accumulation for the HND-2NOMe-based cells under solar irradiation occurs, which is related to the stable performance. The sources of the lower but stable performance are crucially important for providing guidelines for improving the device performance.

Lead-Free Perovskite Light-Emitting Diodes.

Metal halide perovskites have been identified as a promising class of materials for light-emitting applications. The development of lead-based perovskite light-emitting diodes (PeLEDs) has led to substantial improvements, with external quantum efficiencies (EQEs) now surpassing 30% and operational lifetimes comparable to those of organic LEDs (OLEDs). However, the concern over the potential toxicity of lead has motivated a search for alternative materials that are both eco-friendly and possess excellent optoelectronic properties, with lead-free perovskites emerging as a strong contender. In this review, the properties of various lead-free perovskite emitters are analyzed, with a particular emphasis on the more well-reported tin-based variants. Recent progress in enhancing device efficiencies through refined crystallization processes and the optimization of device configurations is also discussed. Additionally, the remaining challenges are examined, and propose strategies that may lead to stable device operation. Looking forward, the potential future developments for lead-free PeLEDs are considered, including the extension of spectral range, the adoption of more eco-friendly deposition techniques, and the exploration of alternative materials.

Transient Leakage Electroluminescence of Quantum-Dot Light-Emitting Diodes.

Parasitic emission or leakage emission caused by electron leakage to a hole transport layer in quantum-dot light-emitting diodes (QLEDs) critically impacts device efficiency and operational stability. The buildup dynamics of such emission channels, however, was insufficiently researched. Herein, we investigate transient electroluminescence dynamics of leakage emission in red/green/blue (R/G/B) QLEDs and reveal notable contrast for R and G. In RQLEDs, leakage emission exhibits delayed turning-on than primary emission, which is attributed to much slower filling up from lower-energy electron states and the initial quenching by nonradiative recombination with trapped holes. For GQLEDs, leakage emission turns on much more concurrently, and emission preferably starts from higher energy states. For R/G QLEDs, under varied offset voltage modulation, the current efficiency of primary emission is invert-correlated to leakage emission, reconfirming leakage emission as a loss indicator.

Unveiled mechanism of prolonged stability of Zn anode coated with two‐dimensional nanomaterial protective layers toward high‐performance aqueous Zn ion batteries

AbstractRechargeable aqueous zinc (Zn) ion batteries (AZIBs) are gaining popularity in large‐scale energy storage due to their low cost, high safety, and environmental friendliness; however, dendrite growth and side reactions in Zn metal anodes limit their practical applications. Additionally, the difficulty of developing successful passivation of Zn anodes, combined with large‐area coating of protective layers, remains a major limitation to the commercialization of AZIBs. Here, we introduce two‐dimensional (2D) nanomaterials including MoS2, h‐BN, and Ti3C2Tx MXene as protective layers for Zn anodes, created on a Zn surface using a scalable, large‐area spray‐coating process. Examinations of electrochemical performance‐related material characterizations revealed that a specific type of 2D material with an optimal thickness prevents vertical growth of Zn dendrites, as well as side reactions including hydrogen evolution and corrosion, resulting in stable device operation with minimal overpotential and extended life, even under harsh measurement conditions. The highly stable MoS2@Zn anode allowed the MoS2@Zn//MnO2 full cell to achieve significantly more stable capacity retention, compared with the bare Zn//MnO2 cell. Our versatile and scalable solution‐based coating technique for easily forming large‐area 2D protective layers on Zn anodes offers new insights concerning improvements to AZIB reliability and performance.image

Hydrophobic Multilayered PEG@PAN/MXene/PVDF@SiO2 Composite Film with Excellent Thermal Management and Electromagnetic Interference Shielding for Electronic Devices.

With the rapid development of electronic industry, it's pressing to develop multifunctional electromagnetic interference (EMI) shielding materials to ensure the stable operation of electronic devices. Herein, multilayered flexible PEG@PAN/MXene (Ti3C2Tx)/PVDF@SiO2 (PMF) composite film has been constructed from the level of microstructure design via coaxial electrospinning, coating spraying, and uniaxial electrospinning strategies. Benefiting from the effective encapsulation for PEG and high conductivity of MXene coating, PEG@PAN/MXene composite film with MXene coating loading density of 0.70mg cm-2 exhibits high thermal energy storage density of 120.77 J g-1 and great EMI shielding performance (EMI SE of 34.409dB and SSE of 49.086dB cm3 g-1) in X-band (8-12GHz). Therefore, this advanced composite film can not only help electronic devices prevent the influence of electromagnetic pollution in the X-band but also play an important role in electronic device thermal management. Additionally, the deposition of nano PVDF@SiO2 fibers (289±128nm) endowed the PMF composite film with great hydrophobic properties (water contact angle of 126.5°) to ensure the stable working of hydrophilic MXene coating, thereby breaks the limitation of humid application environments. The finding paves a new way for the development of novel multifunctional EMI shielding composite films for electronic devices.

Novel identification algorithm for plasma boundary gap based on visible endoscope diagnostic on EAST tokamak

The precise plasma boundary gap identification at the midplane is a prerequisite for achieving controlled plasma positioning and holds a significant importance for the stable operation of tokamak devices. This study proposes a plasma boundary gap at the midplane recognition algorithm based on visual endoscopy diagnostic. The model is an end-to-end one that uses a convolutional neural network that does not require manual data labeling. The model performance is improved by experimentally comparing different convolutional layers and input image sizes. The model is validated using a testing dataset comprising 400 plasma discharge moments. The model has average errors of 3.7 and 4 mm for gap-in and -out, respectively, when compared to those obtained by equilibrium fitting. The proposed approach offers a convenient and effective means of obtaining the boundary gap value and is particularly suited for future fusion experimental devices, such as BEST and ITER tokamak.

NiOx Passivation in Perovskite Solar Cells: From Surface Reactivity to Device Performance.

Nonstoichiometric nickel oxide (NiOx) is one of the very few metal oxides successfully used as hole extraction layer in p-i-n type perovskite solar cells (PSCs). Its favorable optoelectronic properties and facile large-scale preparation methods are potentially relevant for future commercialization of PSCs, though currently low operational stability of PSCs is reported when a NiOx hole extraction layer is used in direct contact with the perovskite absorber. Poorly understood degradation reactions at this interface are seen as cause for the inferior stability, and a variety of interface passivation approaches have been shown to be effective in improving the overall solar cell performance. To gain a better understanding of the processes happening at this interface, we systematically passivated specific defects on NiOx with three different categories of organic/inorganic compounds. The effects on NiOx and the perovskite (MAPbI3) deposited on top were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Here, we find that the perovskite's structural stability and film formation can be significantly affected by the passivation treatment of the NiOx surface. In combination with density functional theory (DFT) calculations, a likely origin of NiOx-perovskite degradation interactions is proposed. The surface passivated NiOx layers were incorporated into MAPbI3-based PSCs, and the influence on device performance and operational stability was investigated by current-voltage (J-V) characterization, impedance spectroscopy (IS), and open circuit voltage decay (OCVD) measurements. Interestingly, we find that a superior structural stability due to interface passivation must not relate to high operational stability. The discrepancy comes from the formation of excess ions at the interface, which negatively impacts all solar cell parameters.

Enhancing photoluminescence of monolayer MoS2 on h-BN substrate through plasmonic resonance for high-power optoelectronic devices

Abstract Hexagonal boron nitride (h-BN) is an excellent substrate material due to its superb thermal conductivity, excellent thermal stability and smooth surface qualities. In this study, a silicon-based h-BN substrate was prepared using the magnetron sputtering technique. Subsequently, monolayer MoS2 obtained by the CVD method was transferred onto the h-BN substrate. Then, Au-core-Ag-shell nanoparticles with a diameter of 80 nm were prepared by a self-assembly method and uniformly dispersed and spin-coated on the MoS2 surface. Applying a laser with a wavelength of 532 nm can effectively excite the plasma resonance effect of the system. Under the intense thermal effect induced by the high laser power and plasma effect, the h-BN substrate ensures that MoS2 exhibits less red-shift and higher photoluminescence intensity compared with SiO2 substrate due to its excellent thermal conductivity. This means that h-BN substrates are particularly suitable for optoelectronic applications under high laser power environments, and can maintain excellent optoelectronic device performance while effectively curbing overheating to ensure long-term stable device operation.

Overcoming stability challenges in perovskite solar cells: Addressing Li ions movement in Spiro-OMeTAD layer through nano-graphdiyne incorporation

The most used hole transport material in high-performance perovskite solar cells (PSCs) is the lithium compounds-doped 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD). However, PSCs based on the Spiro-OMeTAD suffer from serious instability induced by Li+ migration and aggregation. Herein, nano-graphdiyne (nano-GDY) was incorporated into the Spiro-OMeTAD to retard such free Li+ movement and reduce its impact on device operation stability. We verify that the nano-GDY-modified HTL efficiently enhances carrier transport and promotes favorable energy level alignment compared to that of the control HTL, contributing to improved device performance. Furthermore, the coordination interaction between the nano-GDY and Li+ significantly retrains the Li+ migration into the perovskite and SnO2 layers, and meanwhile, eliminates their aggregation with HTLs under elevated temperature and prolonged light soaking. Consequently, the nano-GDY incorporated PSCs exhibit a champion power-conversion efficiency (PCE) of 24.16 % with negligible hysteresis. Encouragingly, the devices also exhibit robust stability, retaining 97 % and 80 % of peak PCE at maxima power point tracking for 6000 s and continuous illumination for 1080 h, respectively.

Deuterated Multiple‐Resonance Thermally Activated Delayed Fluorescence Emitter and Their Application in Vacuum‐Deposited Organic Light‐Emitting Diodes

AbstractMultiple‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters have garnered significant attention in recent years due to their remarkable properties, such as high luminescent quantum yield, robustness, and their compliance with the Broadcast Television 2020 standard for the new generation of ultrahigh‐definition. Despite these advancements, the operational lifetimes of organic light‐emitting diodes (OLEDs) relying on MR‐TADF emitters still fall short for practical application. It is believed that the enhancement of the intrinsic molecular stability of tBu‐DABNA, a fundamental backbone of MR‐TADF emitters, holds great promise to be a universal strategy for all MR‐TADF emitters improving the operational lifetimes of OLEDs. Herein, the design and synthesis of targeted deuteration are reported on donor and/or backbone of MR‐TADF emitters, where the structure‐property relationship between intrinsic molecular stability upon isotopic effect and device operational stability are examined. The isotopic analogs show a gradual increase in the device operational stability and achieve long‐lifetime LT80 (80% of the initial luminance of 1000 cd m−2) of 24.3 h for TADF‐sensitized fluorescence OLED, representing a sevenfold enhancement when compared with the undeuterated counterpart. This strategic deuteration approach underlines the importance of structural modification on materials toward device operational stability.

Regulating Water Adsorption Sites of Keto-Enamine COF by Base Exfoliation and Deprotonation for Enhanced Humidity Response.

Covalentorganic framework (COF) has received much attention owing to its unique framework structure formed by diverse organic units. However, challenges, including low conductivity, structure instability, and limited control of adsorption and desorption processes, stimulate the modification of COF in electronic sensors. Herein, inspired by the alterable structure of COF in different solvents, a facile base exfoliation and deprotonation method is proposed to regulate the water adsorption sites and improve the intrinsic conductivity of TpPa-1 COF. TpPa-1 COF powders are exfoliated to nanosheets to increase water adsorption, while the deprotonation is utilized to adjust the affinity of water molecules on TpPa-1 COF framework, contributing to water accumulation in the 1D pores. The as-fabricated TpPa-1 COF sensor exhibits a decreased recovery time from 419 to 49s, forming a linear relation between relative humidity (RH)value and humidity response. The excellent chemical stability of the covalent bond of TpPa-1 COF contributes to the excellent stable device performance in 30 days, promoting further integration and data analysis in respiration monitoring.

Pd(II)‐TADF Emitters Featuring Multiple Intramolecular Noncovalent Interactions: Toward Organic Light‐Emitting Diodes with EQEs up to 31.5% and Operational Half‐Lifetimes Exceeding 1600 h at 3000 cd m−2

AbstractThe second‐row transition metal complexes have been much less exploited as emitters for organic light‐emitting diodes (OLEDs). Despite the considerable efforts to develop phosphorescent Pd(II) complexes by ligand design, the triplet excited states of Pd(II) complexes usually have very long lifetimes because of their ligand‐centered nature. Hereina panel of sandwich‐type mononuclear Pd(II) complexes is reported, namely PdDDBPZ, PdDTRZ, and PdDPYR, which exhibit strong yellow to red thermally activated delayed fluorescence (TADF) with photoluminescence quantum yields (PLQYs) of 87–94% in doped films. The metal ion plays a perturbing role in the intraligand charge transfer excited state dynamics, giving rise to accelerated reverse intersystem crossing (RISC). Owing to the space‐confined sandwich configuration, there are multiple noncovalent interactions within the molecules, which are qualitatively and quantitatively analyzed by theoretical calculations. The Pd(II) complexes show high device efficiencies with external quantum efficiencies (EQEs) up to 31.5%. The ultralow efficiency roll‐off is as low as 1% at 1000 cd m−2. The device operational stability test for PdDTRZ reveals a half‐lifetime (LT50) of 1615 h at an initial luminance of 3000 cd m−2. The leverage of metal‐promoted TADF mechanism together with intramolecular noncovalent interactions proves feasible for developing practical Pd(II)‐TADF emitters toward OLEDs.

Dissecting the Role of the Hole-Transport Layer in Cu2 AgBiI6 Solar Cells: An Integrated Experimental and Theoretical Study.

Perovskite-inspired materials (PIMs) provide low-toxicity and air-stable photo-absorbers for several possible optoelectronic devices. In this context, the pnictogen-based halides Cu2AgBiI6 (CABI) are receiving increasing attention in photovoltaics. Despite extensive studies on power conversion efficiency and shelf-life stability, nearly no attention has been given to the physicochemical properties of the interface between CABI and the hole transport layer (HTL), which can strongly impact overall cell operations. Here, we address this specific interface with three polymeric HTLs: poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (poly-TPD), thiophene-(poly(3-hexylthiophene)) (P3HT), and poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA). Our findings reveal that devices fabricated with poly-TPD and P3HT outperform the commonly used Spiro-OMeTAD in terms of device operational stability, while PTAA exhibits worse performances. Density functional theory calculations unveil the electronic and chemical interactions at the CABI-HTL interfaces, providing new insights into observed experimental behaviors. Our study highlights the importance of addressing the buried interfaces in PIM-based devices to enhance their overall performance and stability.

Stable Pentagonal Layered Palladium Diselenide Enables Rapid Electrosynthesis of Hydrogen Peroxide.

Electrosynthesis of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e- ORR) is promising for various practical applications, such as wastewater treatment. However, few electrocatalysts are active and selective for 2e- ORR yet are also resistant to catalyst leaching under realistic operating conditions. Here, a joint experimental and computational study reveals active and stable 2e- ORR catalysis in neutral media over layered PdSe2 with a unique pentagonal puckered ring structure type. Computations predict active and selective 2e- ORR on the basal plane and edge of PdSe2, but with distinct kinetic behaviors. Electrochemical measurements of hydrothermally synthesized PdSe2 nanoplates show a higher 2e- ORR activity than other Pd-Se compounds (Pd4Se and Pd17Se15). PdSe2 on a gas diffusion electrode can rapidly accumulate H2O2 in buffered neutral solution under a high current density. The electrochemical stability of PdSe2 is further confirmed by long device operational stability, elemental analysis of the catalyst and electrolyte, and synchrotron X-ray absorption spectroscopy. This work establishes a new efficient and stable 2e- ORR catalyst at practical current densities and opens catalyst designs utilizing the unique layered pentagonal structure motif.