Device Performance Stability Research Articles

Highly Flexible Electroluminescent Devices Based on Super Durable AlN‐Dispersed Ag Ultrathin Films

AbstractHigh performance and durable electrodes are prerequisites for the stable operation of various optoelectronic devices, such as alternating current electroluminescence (ACEL) applications. As for the flexible electrodes based on ultrathin metals, which have attracted much attention in recent years, stability problems as evidenced by optically lossy and electrical degradation of the silver (Ag) layer in the service environment are the key issues to be solved before its practical application. This work prepares ultrathin and stable doped silver films by introducing a small amount of AlN during the sputtering process. The Ag‐AlN thin films exhibit a comprehensive stability promotion in terms of high temperature (250 °C in the air) and damp‐heat (85 °C, 85% relative humidity (RH) for 12 h) test compared with pure Ag counterpart. In addition, flexible ACEL devices based on AZO/Ag‐AlN/AZO/polyethylene terephthalate (PET) films with a luminance of 176.1 cd m−2 at 300 V and 400 Hz and excellent luminescence performance and mechanical flexibility under operating conditions are developed. Such ACEL devices based on these ultrathin and durable Ag‐AlN films are up‐and‐coming in practical, flexible electronics applications.

Demonstration of a Double Flat-Roofed Sine Waveguide Slow Wave Structure With Low Loss for 220-GHz Traveling-Wave Tube

A double flat-roofed sine waveguide (DFRSWG) slow wave structure (SWS) with low loss for 220-GHz traveling-wave tube (TWT) has been demonstrated in this letter. Through the simulation method, it is inferred that this structure has a large coupling impedance and excellent transmission properties. Besides, the experimental results demonstrate that the transmission loss of the circuit is only 0.62–0.75 dB/cm and the return loss is more than 19.3 dB in the frequency band of 210–250 GHz. Eventually, a two-section DFRSWG interaction circuit is designed to achieve stable device performance. Based on the particle-in-cell (PIC) simulation results, it can be predicted that the DFRSWG TWT can generate the maximum output power of 235 W at 220 GHz, which corresponds to a gain of 36.72 dB and an electronic efficiency of 6.06%.

Densely Packed Fiber Electrodes Composed of Liquid Crystalline MXenes for High‐Areal‐Density Supercapacitors

Because electrode structure is a crucial determinant of supercapacitor performance, there are multiple studies of supercapacitor electrodes with various structures. Here, experimental observations of the diameter‐dependent supercapacitor performance of a liquid crystalline (LC)‐assisted MXene fiber‐based electrode produced through a wet‐spinning process is reported. It is shown that Ti3C2Tx nanosheets are highly dispersed in water and do not form aggregates or undergo phase separation. MXene dispersion exhibits the typical shear thinning behavior of liquid crystals above the critical mass fraction. Various MXene fibers derived from needles of different diameters can be produced using one method. LC‐assisted MXene fibers are characterized by a high electrical conductivity of up to 2012.27 S cm−1. Furthermore, the optimized MXene fiber‐based device has an areal capacitance of up to ≈6.82 F cm−2, indicating the utility of LC‐assisted MXene fibers in fiber‐shaped supercapacitor devices. The synthetic method has considerable advantages for applications in high‐performance supercapacitors with both stable device operation and high areal capacitance.

A study on improving shielding performance of shielded cable

AbstractWith the developments in power electronics equipment, the electromagnetic environment has become severe for electronic equipment. In the smart facility field, the stable operation of electronic devices is indispensable, and noise countermeasures must be improved. To suppress intrusive noise from cables, shielded cables are used in many cases. However, electromagnetic induction cannot be suppressed when the shield is grounded at one end, and when grounding both ends of the shield, current flows through the shield creating intrusive noise in the cable. That is, even if a shielded cable is used, a sufficient effect cannot be obtained. Therefore, as a countermeasure, this study prototypes and evaluates cables that combine double shielded cables with magnetic cores. Evaluations conducted using the copper pipe method, triaxial method, and impulse test confirm that the shielded performance improved by 10–30 dB compared with the conventional shielded cable.

A comprehensive simulation study of methylammonium-free perovskite solar cells

The power conversion efficiency (PCE) of thin-film solar cells (TFSCs) has drastically increased in the last few years. In this regard, perovskite solar cells (PSCs) come on the top thanks to their bandgap tunability, lower fabrication cost, and high absorption coefficient. In this work, a comprehensive simulation study is presented in which methylammonium-free PSCs are analyzed and designed. Also, the design of the presented solar cell structure is based on using a hole transport layer (HTL)-free. So, the design is carried out in such a way as to prevent the instability and cost issues associated with the organic materials, usually incorporated in HTLs, as well as methylammonium (MA) which limits the device operation stability. Next, the conduction band offset between the perovskite as an absorber and the electron transport layer (ETL) is controlled to provide a spike-like band offset that is more desirable by selecting appropriate materials serving as ETLs. The work function of the back contact is also investigated, and it is found that using Carbon, which has a lower cost than gold, is beneficial to get high efficiency. An enhanced performance has been achieved by combining the different steps of the design. This is reflected in the PCE which performs 25.35% instead of the initial calibrated cell which shows a PCE of 20.7%. The PCE could further be boosted to 27.8% if reduced absorber and interface defects are included. The calibration and simulation of the presented PSCs were done by utilizing SCAPS one-dimensional simulator, based on practical material parameters, at AM1.5 illumination.

Polymer‐Based n‐Type Yarn for Organic Thermoelectric Textiles

AbstractA conjugated‐polymer‐based n‐type yarn for thermoelectric textiles is presented. Thermoelectric textile devices are intriguing power sources for wearable electronic devices. The use of yarns comprising conjugated polymers is desirable because of their potentially superior mechanical properties compared to other thermoelectric materials. While several examples of p‐type conducting yarns exist, there is a lack of polymer‐based n‐type yarns. Here, a regenerated cellulose yarn is spray‐coated with an n‐type conducting‐polymer‐based ink composed of poly(benzimidazobenzophenanthroline) (BBL) and poly(ethyleneimine) (PEI). The n‐type yarns display a bulk electrical conductivity of 8 × 10−3 S cm−1 and Seebeck coefficient of −79 µV K−1. A promising level of air‐stability for at least 13 days can be achieved by applying an additional thermoplastic elastomer coating. A prototype in‐plane thermoelectric textile, produced with the developed n‐type yarns and p‐type yarns, composed of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)‐coated regenerated cellulose, displays a stable device performance in air for at least 4 days with an open‐circuit voltage per temperature difference of 1 mV °C−1. Evidently, polymer‐based n‐type yarns are a viable component for the construction of thermoelectric textile devices.

Improvement in current drivability and stability in nanoscale vertical channel thin-film transistors via band-gap engineering in In–Ga–Zn–O bilayer channel configuration

Vertical channel thin film transistors (VTFTs) have been expected to be exploited as one of the promising three-dimensional devices demanding a higher integration density owing to their structural advantages such as small device footprints. However, the VTFTs have suffered from the back-channel effects induced by the pattering process of vertical sidewalls, which critically deteriorate the device reliability. Therefore, to reduce the detrimental back-channel effects has been one of the most urgent issues for enhancing the device performance of VTFTs. Here we show a novel strategy to introduce an In–Ga–Zn–O (IGZO) bilayer channel configuration, which was prepared by atomic-layer deposition (ALD), in terms of structural and electrical passivation against the back-channel effects. Two-dimensional electron gas was effectively employed for improving the operational reliability of the VTFTs by inducing strong confinement of conduction electrons at heterojunction interfaces. The IGZO bilayer channel structure was composed of 3 nm-thick In-rich prompt (In/Ga = 4.1) and 12 nm-thick prime (In/Ga = 0.7) layers. The VTFTs using bilayer IGZO channel showed high on/off ratio (4.8 × 109), low SS value (180 mV dec−1), and high current drivability (13.6 μA μm−1). Interestingly, the strategic employment of bilayer channel configurations has secured excellent device operational stability representing the immunity against the bias-dependent hysteretic drain current and the threshold voltage instability of the fabricated VTFTs. Moreover, the threshold voltage shifts of the VTFTs could be suppressed from +5.3 to +2.6 V under a gate bias stress of +3 MV cm−1 for 104 s at 60 °C, when the single layer channel was replaced with the bilayer channel. As a result, ALD IGZO bilayer configuration could be suggested as a useful strategy to improve the device characteristics and operational reliability of VTFTs.

Versatile Use of 1,12-Diaminododecane as an Efficient Charge Balancer for High-Performance Quantum-Dot Light-Emitting Diodes

Balancing the charge injection rates in the emissive layer (EML) is a key factor in achieving high-performance quantum-dot light-emitting diodes (QD-LEDs). This has mostly been pursued by controlling the injection rate of one type of charge carrier (typically electrons). Simultaneous engineering of both types of charge carriers, however, would be more efficient in achieving the desired charge balance within a device. Herein, the versatile use of 1,12-diaminododecane (DAD) ligands is proposed to achieve balanced charge injection rates into the QD EML, thereby enhancing QD-LED performance. By utilizing the dipole moment and short chain lengths, DAD ligands function as efficient electron retarders and hole boosters. Specifically, DAD treatment on the surface of zinc oxide generates an electronic barrier to QDs. Meanwhile, DAD treatment on the surface of the QDs reduces the potential difference between the organic hole transport layers and QDs. Consequently, the QD-LEDs with the adoption of DAD at the two different positions exhibit balanced charge injection rates into the QDs, enhancing device efficiency and operational stability. The present study proposes a simple yet efficient chemical method that controls both electron and hole injection properties to achieve high-performance QD-LEDs.

Impulse power detection for fusion power supply based on cascaded quasi-proportion resonance

Megawatt power impact frequently occurs during experiments on magnetic confinement fusion devices. This power impact, which shows the features of high amplitude, rapid change, and strong randomness, threats to the stable operation of fusion devices when achieving long-pulse high temperature conditions. To more effectively handle such power impact, the precise and real-time detection of impulse power is indispensable. Aiming at the issue, the quasi-proportion resonance (QPR) algorithm based on adjustable damping factor is developed, which realizes good extraction and high-speed response performance. Combined with the reference phase angle of grid voltage, the active and reactive power can be further divided. Considering the harmonic power with various frequencies included in impulse power, the cascaded quasi-proportion resonance (CQPR) detection strategy is proposed, which compensates for the deficiency that QPR is unable to handle multi-frequency impulse power. Finally, the validity and stability of CQPR algorithm are proved by MATLAB and experiments with Digital Signal Processing (DSP) platform.

Research on plasma vertical displacement calculation based on neural network

Plasma vertical displacement control is essential for the stable operation of tokamak devices. The traditional plasma vertical displacement calculation method is not suitable for balancing speed and accuracy simultaneously, which is necessary for real-time feedback control. In this study, neural networks are used to rapidly detect vertical displacement recognition. Based on a fully connected neural network, the vertical displacement calculation model is trained and tested using magnetic data of approximately 2000 shots. To compare the effects of different inputs on vertical displacement calculation, different magnetic measurement diagnostic signals are used to train and test the model. Compared with a full magnetic measurement dataset, 39 magnetic measurement signals (38 magnetic probes and plasma current) show better accuracy with mean square error <0.0005. The model is tested using historical experimental data, and it demonstrates accurate vertical displacement calculation even in the case of a vertical displacement event. In general, neural network algorithm has great application potential in vertical displacement calculation.

Highly stable Mo/Al bilayer electrode for stretchable electronics

Highly-stable molybdenum/aluminum (Mo/Al) bilayered electrodes have been demonstrated as promising candidates for use in stretchable electronics. The serpentine-shaped Mo/Al bilayer electrode is shown to be operable with up to 220% elongation and no significant change in resistance. In Al-only electrodes, Al penetrates into the polyimide (PI) because of its high chemical reactivity with PI. This issue can be overcome by inserting Mo underneath the Al layer, blocking the reaction between Al and PI and enabling the formation of robust and highly conductive stretchable electrodes. With the proposed bilayer electrodes, stretchable thin-film transistor arrays that can be operated even when elongated up to 220% are realized. The fabricated devices exhibit very stable device performance under highly stretched conditions.

HIGH-SPEED COMPUTER POLARIMETER BASED ON CMOS MATRIX

Under the conditions of the COVID-19 pandemic and a full-scale war in Ukraine, the lack of computer equipment for conducting online chemical experiments is experienced. In connection with the implementation of the New Ukrainian School and the development of STEM education, there was an urgent need to develop domestic educational computer equipment. The Department of Physics and Chemistry of H.S. Skivoroda’s Kharkiv National Pedagogical University is developing the SchoolKit software-methodological complex (PMK), which is based on three universal software tools: ColorKit, ChemKit, SoundCardScientificKit. When creating applications, only free software is used, which ensures low cost and, accordingly, accessibility for a wide range of users. A computer polarimeter was developed based on the ColorKit software. A new principle of polarimeter operation is proposed, which is based on computer processing of the image that occurs when optically polarized light is passed sequentially through an optically active solution, a transparent plate with internal tension, and an analyzer. A high-speed computer polarimeter based on a CMOS matrix was developed, a working model was manufactured and tested. The device differs from others since it uses a fundamentally new way of processing visual data and does not contain any mechanical components and polarization modulators. It is also easy to manufacture, and quite reliable. The polarimeter software allows data to be accumulated in the form of tables and displayed in real-time graphical form. The computer polarimeter was used for two years during laboratory classes in the “Mechanisms of Organic Reactions” subject, including online mode. In particular, it was used to experimentally determine the constants of acid hydrolysis of sucrose at different temperatures, concentrations of acid and sucrose. Visual display of measurement results, stability of device operation and good reproducibility of experimentally obtained data allow intensification and/or optimisation of the education process due to the automation of polarimetric measurements. After some improvements and validation, the device is planned to be used in scientific research.

Microwave-Irradiated Metal-Oxide Thin-Film Transistors With Recessed Gate Structure and Their Applications in Logic Circuits

The effects of a recessed gate structure on the device performance of sol-gel-based metal-oxide thin-film transistors (oxide-TFTs) consisting of aluminum oxide dielectric and indium-gallium-zinc oxide semiconducting films fabricated through effective microwave irradiation are investigated, as compared with elevated and non-patterned gate structures. Low-voltage operating oxide-TFTs with an optimized recessed gate structure exhibited improved device performance including OFF-state current of approximately <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-{11}}$ </tex-math></inline-formula> A and field-effect mobility of 3.4 cm2/V-s in the linear regime, compared with those with elevated (~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-{9}}$ </tex-math></inline-formula> A and 1.9 cm2/V-s) and non-patterned (~ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10^{-{10}}$ </tex-math></inline-formula> A and 2.8 cm2/V-s) gate structures. Furthermore, the charge transport mechanism responsible for improved device performance and operational stability against prolonged positive and negative gate bias stresses in the oxide-TFTs with the recessed gate structure is investigated through activation energy and velocity distribution that are determined from direct-current and time-domain non-quasi-static transient analyses, respectively. Finally, enhancement-load-type nMOS inverters operating at 5 V are developed for logic circuits, which exhibit a relatively high dc gain of 32.2 in the recessed gate structure, compared with that of 17.1 and 27.1 in the elevated and the non-patterned gate structures, respectively.

Interfacial engineering to modulate surface dipoles, work functions and dielectric confinement of halide perovskites.

The interfacial properties between perovskite photoactive and charge transport layers are critical for device performance and operational stability. Therefore, an accurate theoretical description of the link between surface dipoles and work functions is of scientific and practical interest. We show that for a CsPbBr3 perovskite surface functionalized by dipolar ligand molecules, the interplay between surface dipoles, charge transfers, and local strain effects leads to upward or downward shifts of the valence level. We further demonstrate that the contribution of individual molecular entities to the surface dipoles and electric susceptibilities are essentially additive. Finally, we compare our results to those predicted from conventional classical approaches based on a capacitor model that links the induced vacuum level shift and the molecular dipole moment. Our findings identify recipes to fine-tune materials work functions that provide valuable insights into the interfacial engineering of this family of semiconductors.

Anti-corrosion strategy to improve the stability of perovskite solar cells.

In recent years, perovskite solar cells (PSCs) have been considered as one of the most promising photovoltaic technologies due to their solution processing, cost effectiveness, and excellent performance. The highest certified power conversion efficiency (PCE) achieved to date is 25.8%, which is approaching the best PCE of 26.81% achieved for silicon-based cells. However, perovskite materials are susceptible to various aging stressors, such as humidity, oxygen, temperature, and electrical bias, which hinder the industrialization of perovskite photovoltaic technologies. In this review, we discuss the lifetime of PSCs from the perspective of corrosion science. On one hand, benefiting from a series of anti-corrosion strategies (passivation, surface coating, machining etc.) used in corrosion science, the stability of perovskite devices is remarkably enhanced; on the other hand, given that perovskites are soft crystal lattices, which are different from traditional metals, the revealed degradation processes and specific methods to improve device operation stability can be applied to the field of corrosion, which can enrich and expand corrosion science.

Compositional texture engineering for highly stable wide-bandgap perovskite solar cells

The development of highly stable and efficient wide-bandgap (WBG) perovskite solar cells (PSCs) based on bromine-iodine (Br-I) mixed-halide perovskite (with Br greater than 20%) is critical to create tandem solar cells. However, issues with Br-I phase segregation under solar cell operational conditions (such as light and heat) limit the device voltage and operational stability. This challenge is often exacerbated by the ready defect formation associated with the rapid crystallization of Br-rich perovskite chemistry with antisolvent processes. We combined the rapid Br crystallization with a gentle gas-quench method to prepare highly textured columnar 1.75-electron volt Br-I mixed WBG perovskite films with reduced defect density. With this approach, we obtained 1.75-electron volt WBG PSCs with greater than 20% power conversion efficiency, approximately 1.33-volt open-circuit voltage (Voc), and excellent operational stability (less than 5% degradation over 1100 hours of operation under 1.2 sun at 65°C). When further integrated with 1.25-electron volt narrow-bandgap PSC, we obtained a 27.1% efficient, all-perovskite, two-terminal tandem device with a high Voc of 2.2 volts.

A Study on Improving Shielding Performance of Shielded Cable

With the developments in power electronics equipment, the electromagnetic environment has become severe for electronic equipment. In the smart facility field, the stable operation of electronic devices is indispensable, and noise countermeasures must to be improved. To suppress intrusive noise from cables, shielded cables are used in many cases. However, electromagnetic induction cannot be suppressed when the shield is grounded at one end, and when grounding both ends of the shield, current flows through the shield creating intrusive noise in the cable. That is, even if a shielded cable is used, a sufficient effect cannot be obtained. Therefore, as a countermeasure, this study prototypes and evaluates cables that combine double shielded cables with magnetic cores. Evaluations conducted using the copper pipe method, triaxial method, and impulse test confirm that the shielded performance improved by 10 to 30dB compared with the conventional shielded cable.

Elucidating degradation mechanisms of mixed cation formamidinium-based perovskite solar cells under device operation conditions

Organic cation-based metal halide perovskites suffer from volatile material decomposition, and the approach to ensure stability under device operation conditions is still far from commercialization. Formamidinium (FA)-based perovskite solar cells (PeSCs) have been widely used, showing efficient power conversion efficiencies (PCEs). Despite the high PCE, FA-based perovskites lack stability, but the related degradation mechanisms are quite indefinite. In this study, we compared two different systems by introduction of inorganic and organic cations to increase FA-based perovskite stability. To relate the device operational stability, we exposed the mixed cation perovskite films under 1 sun illumination at 60 °C in ambient air and investigated the difference in the phase transition of inorganic-mixed and organic-mixed FA perovskites. Morphological and structural characterizations were collected to confirm that the type of the secondary cation plays a major role in determining whether perovskite degradation is triggered at the grain boundary or perovskite grain surfaces. Although the PCEs of the two device systems are similar, the degradation mechanisms varied significantly depending on the chemical properties of perovskite components.

Brine Refrigerants for Low‐cost, Safe Aqueous Supercapacitors with Ultra‐long Stable Operation at Low Temperatures

AbstractTraditional aqueous energy storage devices are difficult to operate at low temperatures owing to the poor ionic conductivity and sluggish interfacial dynamics in frozen electrolytes. Herein, the low‐cost brine refrigerants for food freezing and preservation as electrolytes, and unexpectedly realize high ionic conductivity and stable operation of an aqueous storage device at low temperatures are demonstrated. A CaCl2 brine refrigerant electrolyte (BRE) with a low freezing point −55 °C and high ionic conductivity (10.1 mS cm−1 at −50 °C) is developed for supercapacitors (SCs), which retains 80% of the room temperature capacity at −50 °C and exhibits ultra‐long cycle life with excellent capacity retention of 92% over 98,500 cycles, outperforming the other SCs which can be operated below −40 °C in literature. Moreover, the SCs with MgCl2 and NaCl BREs can also be operated successfully with excellent cycle stability and high‐capacity retention at low temperatures of −30 and −20 °C, respectively. Fundamental correlation between various cations and their effect on the freezing point reduction of aqueous electrolytes is revealed via Raman investigation and molecular dynamics simulations. This study provides a rational design strategy for green, inexpensive, and safe low‐temperature aqueous electrolytes for energy storage devices.

Stretchable printed circuit board integrated with Ag-nanowire-based electrodes and organic transistors toward imperceptible electrophysiological sensing

Wearable devices with excellent mechanical stretchability, comparable to that of human skin, are highly desirable for preventing discomfort and dermatitis. Composite material systems that use metal particles and elastomers are promising for realizing intrinsic stretchable electrodes with high conductivity and enhancing mechanical flexibility of wearable devices. However, it is challenging to achieve stable device performance under mechanical deformation using stretchable electrodes. In this study, stretchable electrodes with enhanced conductivity and stretchability are developed and integrated with organic transistors to fabricate a stretchable printed circuit board (PCB) that acts as a voltage amplifier under large strains. The stretchable electrodes are composed of silver microparticles, a small quantity of silver nanowires (AgNWs), and an elastomer matrix, which demonstrated a conductivity of 8.5 × 103 S cm−1 at a curing temperature of 100 °C. The observed conductivity was 3.6 times higher than that of electrodes without AgNWs. Owing to the addition of AgNWs, the durability strain in cyclic stretching increased from 10% to 75%; the increment can be attributed to the suppression of microcrack propagation. Moreover, the proposed stretchable PCB was applied to fabricate a voltage amplifier, which enabled stable amplification by 14 times under 0% and 75% strain owing to a mechanical rigid-soft patterning designed into the substrate according to the rigidness of the mounted components. The stabilization technologies in the proposed stretchable PCB can contribute to the development of wearable devices for long-term usage to assist the early detection of diseases.