Charge Loss Research Articles

Superior Charge Density of Triboelectric Nanogenerator via Trap Engineering

AbstractTriboelectric nanogenerator (TENG) offers a novel approach for converting high‐entropy mechanical energy into electrical energy, yet achieving high charge density remains critical. Optimizations using dielectrics with high specific capacitance have mitigated air breakdown, but charge loss within dielectrics persists as a limiting factor. Here, based on poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF‐TrFE‐CFE)) with high specific capacitance, (P(VDF‐TrFE‐CFE)) composites’ trap density and energy are engineered using high‐polarity interfaces from barium titanate (BTO) nanoparticles and dense chain segment stacking induced by electrostatic interaction with polyetherimide (PEI) to enhance charge retention capability. With modified high interfacial traps, an ultrahigh charge density of 9.23 mC m−2 is achieved in external charge excitation (ECE) TENG using 0.2 vol% PEI/P(VDF‐TrFE‐CFE) film, marking the highest charge density reported for single‐unit TENGs. This work provides novel material strategies for high‐performance TENGs, paving the way for their large‐scale practical applications.

Comprehensive investigations on defects’ stability caused lateral charge loss in Ti-doped 3D NAND

The comprehensive investigations on defects’ stability caused lateral charge loss are investigated in Ti-doped 3D NAND. The detailed study shows that the Ti-doping strategy could reduce pre-existing shallow traps in pure Si3N4. The stability of TiSi and Tii defects are observed under program/erase stress, but unstable TiN defects with shallow-trap levels (0.41 eV) also occur. Based on unstable defects, the device simulations are carried out revealing its effects on lateral charge loss, which indicates that TiN defects should be reduced for reliability. Our results strongly suggest the stability of Ti-related defects could be key points for lateral charge loss.

Self-passivation of Halide Interstitial Defects by Organic Cations in Hybrid Lead-Halide Perovskites: Ab Initio Quantum Dynamics.

Halide interstitial defects severely hinder the optoelectronic performance of metal halide perovskites, making research on their passivation crucial. We demonstrate, using ab initio nonadiabatic molecular dynamics simulations, that hydrogen vacancies (Hv) at both N and C atoms of the methylammonium (MA) cation in MAPbI3 efficiently passivate iodine interstitials (Ii), providing a self-passivation strategy for dealing with the Hv and Ii defects simultaneously. Hv at the N site (Hv-N) introduces a defect state into the valence band, while the state contributed by Hv at the C site (Hv-C) evolves from a shallow level at 0 K to a deep midgap state at ambient temperature, exhibiting a high environmental activity. Both Hv-N and Hv-C are strong Lewis bases, capable of capturing and passivating Ii defects. Hv-C is a stronger Lewis base, bonds with Ii better, and exhibits a more pronounced passivation effect. The charge carrier lifetimes in the passivated systems are significantly longer than in those containing either Hv or Ii, and even in pristine MAPbI3. Our demonstration of the Hv and Ii defect self-passivation in MAPbI3 suggests that systematic control of the relative concentrations of Hv and Ii can simultaneously eliminate both types of defects, thereby minimizing charge and energy losses. The demonstrated defect self-passivation strategy provides a promising means for defect control in organic-inorganic halide perovskites and related materials and deepens our atomistic understanding of defect chemistry and charge carrier dynamics in solar energy and optoelectronic materials.

A Game Theory Based Scheduling Approach for Charging Coordination of Multiple Electric Vehicles Aggregators in Smart Cities

In this paper, a game theory-based coordination approach is presented to find the minimum operation cost of multiple electric vehicle (EV) aggregators that are connected to the upstream network. In order to provide a comprehensive study various EVs aggregators including residential, commercial, official, university, and industry parking lots have been considered and the proposed game theory is utilized to coordinate the charging power from/to different microgrids and/or upstream network. In addition of operation cost, a reliability index, service charge and power loss are included in the objective function. The proposed approach is applied on an electricity network with 7 connected microgrids and different scenarios have been investigated. The simulation results show the overall operation cost in the coalition operation mode is globally minimized in comparison with the non-coalition operation mode. In addition, the reliability index, service charge and power loss force the aggregators to buy their necessary power from the nearby microgrids. The average network loss in the coalition and non-coalition modes are 2.88% and 4.28%, respectively. Moreover, the average reliability cost in coalition and non-coalition modes are $2.65 and $4.25, respectively.

Insight into formaldehyde decomposition over MOFs-derived CeO2-MnOx bimetallic oxides

The ubiquitous presence of formaldehyde as a pollutant has aroused significant environmental and health concerns. The design and performance of (OR: transition metal oxide) catalysts in the catalytic oxidation method continue to face a myriad of challenges. Herein, a series of CeO2-x-MnOx catalysts are synthesized using manganous nitrate impregnated Ce-metal–organic-frameworks as the precursor, followed by a traditional calcination step. Interestingly, we found that the gases released during the pyrolysis of metal–organic-frameworks significantly affect the valence states of Ce and Mn, which are key factors responsible for catalytic activity. Characterizations results show that the CeO2-x-MnOx-2.5 sample contains a large amount of Ce3+, a high Mn3+/Mn4+ ratio, and an abundance of reactive oxygen species on its surface. Density functional theory results demonstrate that oxygen vacancies not only effectively suppress charge loss of Mn and Ce atoms but also significantly enhance the adsorption strength of CeO2-x-MnOx-2.5 for both formaldehyde and O2. These structural features jointly influence the adsorption as well as the rapid oxidation of formaldehyde molecules, leading to the excellent catalytic performance towards formaldehyde oxidation. This study provides a promising platform for designing straightforward, cost-effective, and highly efficient bimetallic catalysts suitable for low-temperature formaldehyde oxidation.

Decomposition of Charge Loss Mechanisms in 3-D Nand Flash Memory: Impact of Cell Dimension via High-Temperature Long-Term Retention Characteristics

Decomposition of Charge Loss Mechanisms in 3-D Nand Flash Memory: Impact of Cell Dimension via High-Temperature Long-Term Retention Characteristics

Evidence of Widely Distributed Time Constants in the Vertical Charge Loss of 3-D Charge-Trap NAND Flash Memories

Evidence of Widely Distributed Time Constants in the Vertical Charge Loss of 3-D Charge-Trap NAND Flash Memories

Assessing pristine and metal doped C2N monolayer as a nanocarriers for anticancer drug

Theoretical research has introduced two-dimensional structures of thin sheets known as the pristine C2N monolayer and the Zn-doped C2N monolayer. These sheets show promise as nanocarriers for delivering the anticancer drug purinethol (PU). Through calculations of binding energy (Eb), it was observed that both the pristine C2N monolayer (−0.505 eV) and the Zn-decorated C2N monolayer (−0.762 eV) exhibit favorable characteristics for drug delivery. Eb values fall within range of physisorption, indicating their suitability as candidates for transporting drugs. An observed charge transfer (CT) of 0.035 e occurs in the Zn-decorated C2N monolayer, leading to a depletion of charge in the Zn-doped C2N monolayer system. The primary contributor to this charge loss is the Zn atom, which experiences a charge reduction of 0.035 e. To understand the phenomenon of drug release, the binding energy was recalculated under biological conditions, specifically in an acidic environment. The results indicate a decline in Eb (−0.218 eV) as well as a short recovery time, suggesting successful release of PU within body. The theoretical predictions we have made are expected to serve as inspiration for experimental researchers in their efforts to design drug delivery systems (DDSs) based on C2N monolayers.

Enhanced Design of Kesterite Solar Cells through High-Throughput Screening and Machine Learning Approaches.

Kesterite Cu2ZnSnS4 (CZTS) is regarded as one of the most promising materials for thin-film solar cells due to its high light absorption capability, composition of earth-abundant and nontoxic elements, and ease of low-cost mass production. Although the certified power conversion efficiency (PCE) of kesterite solar cells has exceeded 14%, this efficiency remains significantly below the Shockley-Queisser limit. In this study, we generated a Perdew-Burke-Ernzerhof (PBE) band gap data set encompassing 263 64-atom species for high-throughput screening by substituting elements at different sites in A2BCX4 quaternary kesterite materials. Additionally, we utilized a symbolic regression method based on genetic programming to explore the functional relationship among the oxidation state, ionic radius, and electronegativity of kesterites with PBE band gaps. Simultaneously, we employed decision tree models (XGBoost, LightGBM, CatBoost, and random forest) and convolutional neural network (CNN) models (CustomCNN, VGG16, DenseNet121, Xception, and EfficientNetV2B0) to predict band gaps, achieving a coefficient of determination (R2) of up to 0.93. Furthermore, we selected 54 kesterite materials with PBE band gaps ranging from 0.4 to 1.5 eV for detailed electronic structure calculations with Heyd-Scuseria-Ernzerhof (HSE06) functional and investigated the effects of B-site atomic substitutions on the performance of solar cell materials. Compared to Ag2CaSnSe4, Ag2SrSnSe4 exhibits fewer deep defects and richer shallow defects, which contribute to an increased carrier concentration and reduced charge and energy losses, making it a superior candidate for solar cell applications.

Achieving 11.23 % efficiency in CZTSSe solar cells via defect control and interface contact optimization

The high open-circuit voltage deficit (VOC, def) caused by structural imperfections in the absorber layer and charge loss during carrier transport is a critical barrier affecting the performance of Cu2ZnSn(S,Se)4 (CZTSSe) devices. In this work, Ag was added to the DMF-based Cu+-Sn4+ system, which significantly improved the crystal morphology and electrical properties of the absorber layer. Additionally, optimizing the selenization process not only reduced surface roughness and eliminated voids at the bottom of the absorber layer but also resulted in the formation of a MoSe2 back interface layer with a more suitable thickness. These measures collectively enhanced the overall quality of the absorber layer, reducing the formation of deep-level defect clusters and effectively boosting carrier transport efficiency. Consequently, the concentration of bulk and interfacial defects decreased, and the impact of potential barriers on carrier movement was minimized. With these comprehensive improvements, the power conversion efficiency of CZTSSe solar cells increased from 8.48 % to 11.23 %. Our research demonstrates that optimizing the structure of the absorber layer can effectively enhance the performance of CZTSSe solar cells, providing valuable insights for the fabrication of high-efficiency devices in the future.

Breaking the size limitation of nonadiabatic molecular dynamics in condensed matter systems with local descriptor machine learning

Nonadiabatic molecular dynamics (NA-MD) is a powerful tool to model far-from-equilibrium processes, such as photochemical reactions and charge transport. NA-MD application to condensed phase has drawn tremendous attention recently for development of next-generation energy and optoelectronic materials. Studies of condensed matter allow one to employ efficient computational tools, such as density functional theory (DFT) and classical path approximation (CPA). Still, system size and simulation timescale are strongly limited by costly ab initio calculations of electronic energies, forces, and NA couplings. We resolve the limitations by developing a fully machine learning (ML) approach in which all the above properties are obtained using neural networks based on local descriptors. The ML models correlate the target properties for NA-MD, implemented with DFT and CPA, directly to the system structure. Trained on small systems, the neural networks are applied to large systems and long timescales, extending NA-MD capabilities by orders of magnitude. We demonstrate the approach with dependence of charge trapping and recombination on defect concentration in MoS2. Defects provide the main mechanism of charge losses, resulting in performance degradation. Charge trapping slows with decreasing defect concentration; however, recombination exhibits complex dependence, conditional on whether it occurs between free or trapped charges, and relative concentrations of carriers and defects. Delocalized shallow traps can become localized with increasing temperature, changing trapping and recombination behavior. Completely based on ML, the approach bridges the gap between theoretical models and realistic experimental conditions and enables NA-MD on thousand-atom systems and many nanoseconds.

Effect of Terminal Phosphate Groups on Collisional Dissociation of RNA Oligonucleotide Anions.

The increasing need for mass spectrometric analysis of RNA molecules calls for a better understanding of their gas-phase fragmentation behaviors. In this study, we investigate the effect of terminal phosphate groups on the fragmentation spectra of RNA oligonucleotides (oligos) using high-resolution mass spectrometry (MS). Negative-ion mode collision-induced dissociation (CID) and higher-energy collisional dissociation (HCD) were carried out on RNA oligos containing a terminal phosphate group on either end, both ends, or neither end. We find that terminal phosphate groups affect the fragmentation behavior of RNA oligos in a way that is dependent on the precursor charge state and the oligo length. Specifically, for precursor ions of RNA oligos of the same sequence, those with 5'- or 3'-phosphate, or both, have a higher charge state distribution and lose the phosphate group(s) in the form of a neutral (H3PO4 or HPO3) or an anion ([H2PO4]- or [PO3]-) upon CID or HCD. Such a neutral or charged loss is most conspicuous for precursor ions of an intermediate charge state, e.g., 3- for 4-nt oligos or 4- and 5- for 8-nt oligos. This decreases the intensity of sequencing ions (a-, a-B, b-, c-, d-, w-, x-, y-, z-ions) and hence is unfavorable for sequencing by CID or HCD. Removal of terminal phosphate groups by calf intestinal alkaline phosphatase improved MS analysis of RNA oligos. Additionally, the intensity of a fragment ion at m/z 158.925, which we identified as a dehydrated pyrophosphate anion ([HP2O6]-), is markedly increased by the presence of a terminal phosphate group. These findings expand the knowledge base necessary for software development for MS analysis of RNA.

Tracking surface charge dynamics on single nanoparticles.

Surface charges play a fundamental role in physics and chemistry, in particular in shaping the catalytic properties of nanomaterials. However, tracking nanoscale surface charge dynamics remains challenging due to the involved length and time scales. Here, we demonstrate time-resolved access to the nanoscale charge dynamics on dielectric nanoparticles using reaction nanoscopy. We present a four-dimensional visualization of the spatiotemporal evolution of the charge density on individual SiO2 nanoparticles under strong-field irradiation with femtosecond-nanometer resolution. The initially localized surface charges exhibit a biexponential redistribution over time. Our findings reveal the influence of surface charges on surface molecular bonding through quantum dynamical simulations. We performed semi-classical simulations to uncover the roles of diffusion and charge loss in the surface charge redistribution process. Understanding nanoscale surface charge dynamics and its influence on chemical bonding on a single-nanoparticle level unlocks an increased ability to address global needs in renewable energy and advanced health care.

Efficient energy conversion mechanism and energy storage strategy for triboelectric nanogenerators

Energy management strategy is the essential approach for achieving high energy utilization efficiency of triboelectric nanogenerators (TENGs) due to their ultra-high intrinsic impedance. However, the proven management efficiency in practical applications remains low, and the output regulation functionality is still lacking. Herein, we propose a detailed energy transfer and extraction mechanism addressing voltage and charge losses caused by the crucial switches in energy management circuits. The energy conversion efficiency is increased by 8.5 times through synergistical optimization of TENG and switch configurations. Furthermore, a TENG-based power supply with energy storage and regularization functions is realized through system circuit design, demonstrating the stable powering electronic devices under irregular mechanical stimuli. A rotating TENG that only works for 21 s can make a hygrothermograph work stably for 417 s. Even under hand driving, various types of TENGs can consistently provide stable power to electronic devices such as calculators and mini-game consoles. This work provides an in-depth energy transfer and conversion mechanism between TENGs and energy management circuits, and also addresses the technical challenge in converting unstable mechanical energy into stable and usable electricity in the TENG field.

Multi-Objective Optimization Scheduling of Microgrids Considering Single Use Cost of Energy Storage and Unit Combination Startup and Shutdown Cost

Abstract Microgrids typically consist of various energy resources such as thermal power, solar energy, wind energy, energy storage, and so on. These energy resources have different characteristics and fluctuations. By utilizing the characteristics of different energy resources in a complementary and synergistic manner, their energy utilization efficiency can be promoted and the system stability can be improved. This paper considers the energy storage device in the completion of a single charge and discharge loss, that is, the single-use cost. Special attention to the impact of start-stop costs of unit combinations on microgrid operations. It proposes that in the daily dispatch and operation of microgrids, sinking costs can be reasonably reduced within a reasonable range, and power supply reliability can be appropriately lowered to improve the economic performance of power systems. Using the single-use cost of energy storage devices and the start-stop costs of unit combinations as variables, their impact on the economic operation of isolated microgrids is analyzed. For grid-connected microgrids with the objectives of minimizing operating costs and achieving optimal environmental protection, an optimal balance between economic and environmental performance is achieved through solving by Anti-Entropy weight method and Particle Swarm Optimization combination.

Low‐Power Charge Trap Flash Memory with MoS2 Channel for High‐Density In‐Memory Computing

AbstractWith the rise of on‐device artificial intelligence (AI) technology, the demand for in‐memory comptuing has surged for data‐intensive tasks on edge devices. However, on‐device AI requires high‐density, low‐power memory‐based computing to efficiently handle large data volumes. Here, this study proposes a reliable multilevel, high gate‐coupling ratio memory device with MoS2 channel tailored for high‐density 3D NAND Flash‐based in‐memory computing. The MoS2 channel, featured by its small bandgap and high‐mobility, facilitates reliable memory window of approximately 8 V thanks to erase operation through hole injection. This not only suppresses vertical charge loss but also alleviates the burden on voltage generator circuits, indicating the suitability of MoS2 as channel material for 3D NAND Flash architecture. Additionally, a low‐k (≈2.2) tunneling layer deposited via initiated chemical vapor deposition increases the gate‐coupling ratio, thereby reducing the operating voltage. Utilizing Au nanoparticles as the charge storage layer, MoS2 memory devices show synaptic plasticity with 6‐bit, endurance (104 cycles), read disturbance (105 cycles), and retention times (105 s). Furthermore, device‐to‐system simulations for neural networks based on MoS2‐memory devices have successfully achieved a fingerprint recognition of 95.8%. These results provide the foundation to develop multi‐bit MoS2‐memory devices for AI accelerators and 3D NAND Flash memory.

Suppressing charge recombination by synergistic effect of ferromagnetic dual-tribolayer for high output triboelectric nanogenerator

Charge recombination occurring inside the tribolayer limits the further improvement of triboelectric nanogenerator (TENG) output. While the doping of ferromagnetic medium in triboelectric materials has been proven effective in boosting the TENG output, its working mechanism in the tribolayer remains to be investigated. Herein, the dual tribolayer synergistic effect is demonstrated as a means of suppressing surface charge recombination, thus achieving a high peak power density of TENG based on a composite film of polymer/nickel nanoparticles. A dual tribolayer model is proposed to reveal the working mechanism of the ferromagnetic medium for suppressing charge recombination in the positive and negative tribolayer. The charge recombination ratio as a standardized assessment method is defined to quantify the surface charge loss. Owing to the dual tribolayer synergistic effect, the optimal TENG exhibits a record-high peak power density of 15.2 W m-2 Hz-1 with the ultra-low charge recombination ratio of 2.1%, representing a remarkable 3100% increase in comparison to pristine TENG in the atmospheric environment. A self-powered sitting posture monitoring system is developed based on the woven structured DT-TENGs benefiting from the dual-tribolayer synergistic effect. This work demonstrates the superior behavior of TENG in generating ultra-high-power output and provides a significant guidance in materials selection.

Diminish charge loss by mica incorporation into nylon nanofibers for performance enhancement of triboelectric nanogenerators operating in harsh ambient

The triboelectric nanogenerator (TENG) is a fascinating energy-harvesting device that utilizes the triboelectric effect caused by contact electrification and electrostatic induction. Nylon 66 is used widely in TENG applications because it is a representative tribo-positive polymer with excellent biocompatibility. On the other hand, the generated charges are vulnerable to discharge due to moisture in the air, which impedes the TENG performance in harsh environments. Moreover, the dielectric loss, which generates heat by consuming the considerable electric charge in triboelectric materials, significantly degrades the TENG performances. This study fabricated the composite nanofiber (NF) structure of nylon 66 and mica, which has excellent electrical insulation, low dielectric loss, high thermal conductivity, and enhanced tribo-positive properties, to circumvent these problems. Embedding the mica into the nylon NFs enhanced the TENG performance and prevented performance degradation even in harsh environments at a relative humidity of 70%. Furthermore, after 100,000 cycles of friction, the nylon/mica composite NFs showed smaller temperature increments than the pristine nylon NF because of the low dielectric loss and efficient heat dissipation of the mica. The nylon/mica composite NFs were applied to a sustainable and wearable power generator operating in a humid and hot environment by attaching the device to the forearm and soles of the feet. The generators were efficient enough to turn on 80 light-emitting diodes.

Pd(II)/Pd(IV) redox shuttle to suppress vacancy defects at grain boundaries for efficient kesterite solar cells

Charge loss at grain boundaries of kesterite Cu2ZnSn(S, Se)4 polycrystalline absorbers is an important cause limiting the performance of this emerging thin-film solar cell. Herein, we report a Pd element assisted reaction strategy to suppress atomic vacancy defects in GB regions. The Pd, on one hand in the form of PdSex compounds, can heterogeneously cover the GBs of the absorber film, suppressing Sn and Se volatilization loss and the formation of their vacancy defects (i.e. VSn and VSe), and on the other hand, in the form of Pd(II)/Pd(IV) redox shuttle, can assist the capture and exchange of Se atoms, thus contributing to eliminating the already-existing VSe defects within GBs. These collective effects have effectively reduced charge recombination loss and enhanced p-type characteristics of the kesterite absorber. As a result, high-performance kesterite solar cells with a total-area efficiency of 14.5% (certified at 14.3%) have been achieved.

Self-discharge in flowless Zn-Br2 batteries and its mitigation

Several decades after the invention of the flow Zn-Br2 systems, persistent attempts have been made to develop stationary Zn-Br2 batteries. Such development should increase the energy density of the system simultaneously significantly reducing their cost and opening new challenges associated with the cell design and its performance. One of the major concerns is the rapid self-discharge of stationary systems leading to spontaneous charge loss during battery storage time. While self-discharge in flow cells is generally attributed to the chemical oxidation of the Zn anode, we show that the origin of self-discharge in a static configuration is completely different. By systematic investigations of activated carbon with different surface areas under varied charging conditions, mechanistic insights into this phenomenon were provided. Based on this understanding, we proposed herein an effective way to suppress the cathode's self-discharge by encapsulation of a bromine complexing agent inside the electrode's pore matrix. The modified electrodes unveil unique chemical kinetics of deaggregation of the stable fuse salt phase composed of bromine complexing agent and Br3− anions upon discharging. To the best of our knowledge, such a phenomenon has not been reported yet. The proposed system demonstrates high capacity (up to 300 mAh/g) and impressive long-term stability.