Charge Injection Research Articles

Interfacial Engineering Using Covalent Organic Frameworks in Polymer Composites for High‐Temperature Electrostatic Energy Storage

AbstractThe use of inorganic nanofillers has been an effective method to improve high‐temperature capacitive performance of dielectric polymers, though there are unmet challenges such as undesirable organic–inorganic compatibility, and low efficiencies and energy densities. Herein, a surface functionalization strategy using covalent organic frameworks (COFs) is employed to address such challenges in realizing high‐performing polymer composites. Specifically, core–shell structured nanoparticles, where ZrO2 nanoparticles act as the core and a COF material forms the shell, are constructed and composited with the polyetherimide (PEI) matrix. The design leverages the high electron affinity (EA) of the outer COF shell to create energy traps, thereby capturing free charges and limiting electrical conduction. Concurrently, the low EA and wide bandgap of the ZrO2 core introduce energy barriers to impede charge injection and migration. This orchestrated “energy level cascade” results in a marked reduction of leakage current and energy loss. The resulting polymer composite showcases an impressive discharged energy density of 6.21 J cm−3 at an efficiency above 90%, with a maximum discharged energy density reaching 7.43 J cm−3 at 150 °C. These performance metrics position the PEI/ZrO2@COF polymer composite to surpass or be on par with state‐of‐the‐art high‐temperature PEI composites and other advanced polymer dielectrics.

Liquid-metal-based three-dimensional microelectrode arrays integrated with implantable ultrathin retinal prosthesis for vision restoration.

Electronic retinal prostheses for stimulating retinal neurons are promising for vision restoration. However, the rigid electrodes of conventional retinal implants can inflict damage on the soft retina tissue. They also have limited selectivity due to their poor proximity to target cells in the degenerative retina. Here we present a soft artificial retina (thickness, 10 μm) where flexible ultrathin photosensitive transistors are integrated with three-dimensional stimulation electrodes of eutectic gallium-indium alloy. Platinum nanoclusters locally coated only on the tip of these three-dimensional liquid-metal electrodes show advantages in reducing the impedance of the stimulation electrodes. These microelectrodes can enhance the proximity to the target retinal ganglion cells and provide effective charge injections (72.84 mC cm-2) to elicit neural responses in the retina. Their low Young's modulus (234 kPa), owing to their liquid form, can minimize damage to the retina. Furthermore, we used an unsupervised machine learning approach to effectively identify the evoked spikes to grade neural activities within the retinal ganglion cells. Results from in vivo experiments on a retinal degeneration mouse model reveal that the spatiotemporal distribution of neural responses on their retina can be mapped under selective localized illumination areas of light, suggesting the restoration of their vision.

Tuning of Interfacial Charge Transport in Organic Heterostructures via Aryl Electrografting for Efficient Gas Sensors.

Modulation of interfacial conductivity in organic heterostructures is a highly promising strategy to improve the performance of electronic devices. In this endeavor, the present work reports the fabrication of a bilayer heterojunction device, combining octafluoro copper phthalocyanine (CuF8Pc) and lutetium bis-phthalocyanine (LuPc2) and tunes the charge transport at the Cu(F8Pc)-(LuPc2) interface by aryl electrografting on the device electrode to improve the device NH3-sensing properties. Dimethoxybenzene (DMB) and tetrafluoro benzene (TFB) electrografted by an aryldiazonium electroreduction method form a few-nanometer-thick organic film on ITO. The conductivity of the heterojunction devices formed by coating a Cu(F8Pc)/LuPc2 bilayer over the aryl-grafted electrode strongly varies according to the electronic effects of the substituents in the aryl. Accordingly, DMB increases while TFB decreases the mobile charges accumulation at the Cu(F8Pc)-(LuPc2) interface. This is explained by the perfect alignment of the frontier molecular orbitals of DMB and Cu(F8Pc), facilitating charge injection into the Cu(F8Pc) layer. On the contrary, TFB behaves like a strong acceptor and reduces the mobile charges accumulation at the Cu(F8Pc)-(LuPc2) interface. Such interfacial conductivity variation influences the device NH3-sensing properties, which increase because of DMB grafting and decrease in the presence of TFB. DMB-based heterojunction devices contain four times higher active sites for NH3 adsorption and could detect NH3 down to 1 ppm with limited interference from humidity, making them suitable for real environment NH3 detection.

Theoretical Designing of Atomically Precise MgO/TiO2(001) Quantum Dot-Sensitized Solar Cell for High Visible Light Absorption and Fast Charge Injection

Theoretical Designing of Atomically Precise MgO/TiO₂(001) Quantum Dot-Sensitized Solar Cell for High Visible Light Absorption and Fast Charge Injection

Nanoporous graphene-based thin-film microelectrodes for in vivo high-resolution neural recording and stimulation

One of the critical factors determining the performance of neural interfaces is the electrode material used to establish electrical communication with the neural tissue, which needs to meet strict electrical, electrochemical, mechanical, biological and microfabrication compatibility requirements. This work presents a nanoporous graphene-based thin-film technology and its engineering to form flexible neural interfaces. The developed technology allows the fabrication of small microelectrodes (25 µm diameter) while achieving low impedance (∼25 kΩ) and high charge injection (3–5 mC cm−2). In vivo brain recording performance assessed in rodents reveals high-fidelity recordings (signal-to-noise ratio >10 dB for local field potentials), while stimulation performance assessed with an intrafascicular implant demonstrates low current thresholds (<100 µA) and high selectivity (>0.8) for activating subsets of axons within the rat sciatic nerve innervating tibialis anterior and plantar interosseous muscles. Furthermore, the tissue biocompatibility of the devices was validated by chronic epicortical (12 week) and intraneural (8 week) implantation. This work describes a graphene-based thin-film microelectrode technology and demonstrates its potential for high-precision and high-resolution neural interfacing.

Effects of molecular assembly on heterogeneous interactions in electronic and photovoltaic devices

Heterogeneous junctions extensively exist in electronic and photovoltaic devices. Due to essential differences, the contacts of heterogeneous junctions are imperfect with structural discontinuity and chemical inconsistency, which have negative impacts on the mechanical, electrical, and thermal properties of devices. To improve the heterogeneous interactions, surface/interfacial modification approaches are developed in which molecular assembly engineering appears to be a promising strategy. Versatile functionalities can be accomplished by smart arrangement and design of the functional groups and geometry of the organic molecular layers. Specific functionality can also be maximized by well organization of the grafting orientation of molecules at the heterogeneous contacts. This article comprehensively reviews the approaches of molecular assembly engineering employed in the construction of the heterogeneous junctions to improve their mechanical, electrical, and thermal properties. Following the introduction of molecular assembly engineering at the target surface/interface, examples are introduced to show the efficacy of molecular assembly engineering on the interfacial adhesion, atomic interdiffusion, dielectric nature, charge injection and recombination, and thermoelectric property in electronic and photovoltaic devices.

Tailoring Electronic Properties of Colloidal Quantum Dots for Efficient Optoelectronics

Colloidal quantum dots (CQDs) are nanocrystals synthesized in solution, boasting remarkable optical properties and notable electronic characteristics, such as size‐tunable bandgaps and high photoluminescence quantum yield. These features, coupled with solution processability, position CQDs as potential candidates for cost‐effective and high‐performance optoelectronic devices. However, several technological challenges hinder the full exploitation of CQDs in optoelectronics. Among these is the need for long insulating organic ligands in liquid‐phase synthesis, which restrict efficient charge injection and transport in quantum dot (QD) films. Furthermore, the high surface‐to‐volume ratios and core–shell structures prompt complexities in terms of doping and modifying electronic properties. The colloidal nature of quantum dots (QDs) also raises challenges regarding controlled deposition and patterning, which are critical for device fabrication. In this review, the imperative is outlined to tailor CQDs for optoelectronic applications, the limitations that obstruct the implementation of desired modifications are elaborated on, and the specific hurdles confronting electronic coupling, targeted doping, and precision patterning of CQDs are focused on. Additionally, herein, a summary of the solutions proposed to date is offered, insights are shared on the discussed topics, and areas warranting future investigation are highlighted.

Non-Faradaic optoelectrodes for safe electrical neuromodulation

Nanoscale optoelectrodes hold the potential to stimulate optically individual neurons and intracellular organelles, a challenge that demands both a high-density of photoelectron storage and significant charge injection. Here, we report that zinc porphyrin, commonly used in dye-sensitized solar cells, can be self-assembled into nanorods and then coated by TiO2. The J-aggregated zinc porphyrin array enables long-range exciton diffusion and allows for fast electron transfer into TiO2. The formation of TiO2(e−) attracts positive charges around the neuron membrane, contributing to the induction of action potentials. Far-field cranial irradiation of the motor cortex using a 670 nm laser or an 850 nm femtosecond laser can modulate local neuronal firing and trigger motor responses in the hind limb of mice. The pulsed photoelectrical stimulation of neurons in the subthalamic nucleus alleviates parkinsonian symptoms in mice, improving abnormal stepping and enhancing the activity of dopaminergic neurons. Our results suggest injectable nanoscopic optoelectrodes for optical neuromodulation with high efficiency and negligible side effects.

Lateral Migration‐based Flash‐like Synaptic Device for Hybrid Off‐chip/On‐chip Training

AbstractAn increase in the demand for artificial intelligence is leading to advanced research in the field of neuromorphic systems, which imitate human brain functions with the hope of increasing computational speed and lowering power consumption. Especially, the development of energy‐efficient and reliable synaptic devices is critical as synapses are fundamental building blocks of neuromorphic systems. In this study, by adjusting the charge injection pathway of conventional flash memory devices, a lateral migration‐based synaptic device is proposed. Using the efficient program/erase method, the proposed device is operable at a significantly low voltage while maintaining formidable retention and endurance characteristics. Furthermore, an efficient hybrid off‐chip/on‐chip training method using the proposed device is presented. The results demonstrate a variation‐robust neuromorphic system, indicating the superiority of the proposed device.

Engineering of Molecular Bridge on Buried Interface via Ferrocene Carboxylic Acid for High Performance Perovskite Light‐Emitting Devices

AbstractQuasi‐two‐dimensional (Quasi2D) perovskite materials gained widespread attention due to whose unique and highly desirable luminescence properties. However, the behavior of perovskite lightemitting diodes (PeLEDs) is prejudiced by inefficient cascading energy transfer of perovskite film and unbalanced charges injection. Here, ferrocene carboxylic acid (FcAd) is employed between hole transport layer (HTL) and perovskite layer as a molecular bridge to solve the current problems of PeLEDs. Ferrocene units can bond with [PbBr6]4−, forming one‐dimensional (1D) intermediate phases of FcPbBr3 at the interface, which can manipulate the growth kinetics of perovskite and reconstruct the phase distribution. Therefore, due to the suppression of low dimensional phase content, not only is the cascaded energy transfer of PEA2(CsPbBr3)2PbBr4 films effectively achieved, but also the quasi‐2D perovskite's work function is reduced. Additionally, Pb2+ coordinated with the carboxyl group of FcAd, inducing an electric dipole effect that leads to an further upward shift of the perovskite energy level. Eventually, the synergy achieves a significant tailoring between the perovskite and HTL energy exhibits the most excellent external quantum efficiency (EQE) exceeds 27% and optimal brightness exceeds 240000 cd m−2. Therefore, the preparation method will provide an effective strategy to widen the color gamut of next‐generation displays.

The effect of Li(Ni0.9Co0.05Mn0.05)O2 on improving electrical properties of semi-conductive LDPE/EVA/CB composites

The conductive mechanism of the semiconductor shielding layer between the conductive core and the insulation layer of high-voltage direct current (HVDC) cables includes tunneling and over-diffusion theories; however, the ethylene vinyl acetate copolymer (EVA) matrix in the semi-conductive composite material expands when heated, leading to a break in the carbon black (CB) conductive networks, which results in an increase in resistivity and the formation of the positive temperature coefficient (PTC) effect. The addition of materials with negative temperature coefficient (NTC) properties can weaken the PTC effect while absorbing some free electrons to enhance the suppression of space charge injection into the insulating layer. Li(Ni0.9Co0.05Mn0.05)O2 (NCM) was prepared by sol–gel method, which was melted and mixed with low-density polyethylene (LDPE), EVA, and CB, and pressed and molded to obtain modified semi-conductive composites. The semiconducting composites were measured by resistivity, thermal stimulation depolarizing current method (TSDC), and pulsed electroacoustic method (PEA). The results showed that the composites had the best performance when the NCM doping was 2 wt%.

Buried‐Contact Organic Field‐Effect Transistor: The Way of Alleviating Drawbacks from Interfacial Charge Transfer

AbstractFacile charge transfer between source/drain (S/D) electrodes and organic semiconductor (OSC) channel is crucial for high‐mobility organic field‐effect transistors (OFETs). Herein, a novel OFET geometry is developed by modifying a top‐contact bottom‐gate device structure, termed a buried‐contact OFET, enabling close proximity between the S/D‐OSC interface and conducting channel, consequently decreasing the access contact resistance (RC,acc) and overall contact resistance (RC). Conventional post‐thermal annealing is combined with a burying pressure (pressure‐thermal annealing (PTA)). The synergistic effect of thermal and pressure annealings leads to the softened OSC layer enabling metal electrodes to bury inward by applied pressure. This process induces structural transitions from a top‐contact to buried‐contact configuration, as verified by atomic force microscopy and finite element simulations. Transfer line method and 4‐probe measurements revealed that PTA reduces the contact by 1/3 (65 kΩ cm) and the source‐to‐drain voltage waste due to charge injection from 52% to 31%. Consequently, the field‐effect mobility is four times higher than that of a conventional thermally annealed top‐contact OFET. The density of deep traps (Ntr) is mainly distributed in the OSC bulk responsible for charge injection. Remarkably, the Ntr decreased 30‐fold using PTA, resulting in a shallow sub‐threshold region and a threshold voltage close to zero.

Co-regulation strategy dominated by double short molecules permitting the regrowth of quantum dots for efficient deep-blue perovskite light-emitting diodes

Recently, blue perovskite quantum dots (PeQDs) have garnered considerable attention for use in full-color optoelectronic displays. However, the large specific surface area caused by the small particle size of blue PeQDs results in high defect state density, which severely limits their optical pursuit. To address this issue, a co-regulation strategy using double short-chain molecules of tetraoctylammonium fluoride and tetraethylammonium perfluorooctanesulfonate is proposed to enhance the regrowth of blue CsxRb1−xPb(ClyBr1−y)3 PeQDs. Long-chain insulated oleylamine and oleic acid ligands, which restrict the growth of PeQDs, are substantially replaced using short-chain ligands with higher adsorption energy. This replacement promotes PeQDs to regrow considerably from ∼8 to ∼18 nm, and the defect-state density decreases by 3–5 times. Consequently, highly efficient blue PeQDs with a photoluminescent quantum yield of unity are obtained. Moreover, the PeQDs exhibit lower insulating ligand density and improved charge injection property. As a result, the synthesized deep-blue PeQD light-emitting diodes (PeQLEDs) exhibit a maximum external quantum efficiency of 5.7% at the CIE coordinate of (0.148, 0.032). According to the International Telecommunication Union Radiocommunication Sector television standard (Rec. 2100), the obtained PeQLEDs are state-of-the-art among colloidal deep-blue PeQDs. This study provides a novel strategy to improve the optical performance of deep-blue PeQLEDs and paves the way for developing high-end wide color-gamut displays.

Research progress of flexible energy storage dielectric materials with sandwiched structure

&lt;sec&gt;Polymer dielectric materials show wide applications in smart power grids, new energy vehicles, aerospace, and national defense technologies due to the ultra-high power density, large breakdown strength, flexibility, easy processing, and self-healing characteristics. With the rapid development of integration, miniaturization and lightweight production of electronic devices, it is required to develop such a storage and transportation dielectric system with larger energy storage density, higher charge and discharge efficiency, good thermostability and being environmentally friendly. However, the contradiction between dielectric constant and breakdown strength of dielectric materials is the key factor and bottleneck to obtain a high performance dielectric material. It is accepted that controlling charge distribution and inhibiting charge carrier injection are important to improve the energy storage characteristics of polymer dielectrics. In recent years, the materials with sandwiched or stacking structures have demonstrated outstanding advantages in inhibiting charge injection and promoting polarization, allowing polymer dielectrics to have increased permittivity and breakdown strength at the same time. Therefore, from the perspectives of material composition, structural design, and preparation methods, this study reviews the research progress of polymer dielectric films with sandwiched structure in improving the energy storage performance. The influence of dielectric polarization, charge distribution, charge injection, interfacial barrier and electrical dendrite growth on the energy storage performance and the synergistic enhancement mechanisms in such sandwich-structured dielectric materials are systematically summarized, showing good development and vast application prospects.&lt;/sec&gt;&lt;sec&gt;In brief, introducing easy polarization, wide-gap and deep-trap nanofillers has greater designability and regulation in the dielectric and breakdown properties. In addition, using the hard layer as the outer layer can reduce charge injection more effectively, resulting in a high breakdown resistance performance that is easy to achieve. The sandwiched structure design also possesses advantages over other methods in maintaining good flexibility and dielectric stability of dielectric materials, thus having become a hot-topic research area in recent years. In the future, it is necessary to combine low conductivity and high thermal conductivity of dielectric polymers to realize high temperature energy storage and efficiency. Researches on recyclable, self-repairing sandwiched insulating films are good for the service life and safety of electronic components and will further expand the application scope of dielectric polymers. Finally, effective evaluation of dielectric with sandwiched structure and energy storage performances through simulation and theoretical modeling is very helpful in revealing the breakdown mechanism and thermal failure mechanism, and also in theoretically guiding the design of polymer dielectric materials.&lt;/sec&gt;

Phase transition in WSe2-xTex monolayers driven by charge injection and pressure: a first-principles study.

Alloying strategies permit new probes for governing structural stability and semiconductor-semimetal phase transition of transition metal dichalcogenides (TMDs). However, the possible structure and phase transition mechanism of the alloy TMDs, and the effect of an external field, have been still unclear. Here, the enrichment of the Te content in WSe2-xTex monolayers allows for coherent structural transition from the H phase to the T' phase. The crystal orbital Hamiltonian population (COHP) uncovers that the bonding state of the H phase approaches the high-energy domain near the Fermi level as the Te concentration increases, posing a source of structural instability followed by a weakened energy barrier for the phase transition. In addition, the structural phase transition driven by charge injection opens up new possibilities for the development of phase-change devices based on atomic thin films. For WSe2-xTex monolayers with the H phase as the stable phase, the critical value of electron concentration triggering the phase transition decreases with an increase in the x value. Furthermore, the energy barrier from the H phase to the T' phase can be effectively reduced by applying tensile strain, which could favor the phase switching in electronic devices. This work provides a critical reference for controllable modulation of phase-sensitive devices from alloy materials with rich phase characteristics.

Research on improving the insulation properties of epoxy filled with surface fluorinated polystyrene nanospheres

Epoxy resin nanocomposites are widely used in the field of electronic packaging. It is of great significance to regulate the dielectric and insulation properties of composite materials by introducing nano-filler to meet special application requirements. This paper proposes a chemical copolymerization method, fluorinated polystyrene nanospheres were synthesized through an addition reaction as filler, and finally the epoxy nanocomposites were prepared. The polystyrene nanospheres have a uniform size and good compatibility with the epoxy resin. The introducing of nanospheres reduces the dielectric constant of the epoxy resin composite material and increases the breakdown strength simultaneously. Although the dielectric loss increases, the composites’ imaginary part remains below 0.04 within 1MHz frequency. In particular, the 2wt% fluorinated polystyrene/epoxy composite exhibits a decrease in dielectric constant and DC conductivity, while the AC and DC breakdown strengths increase by 12.6% and 6%, respectively.&lt;br&gt;The results of the Pulse Electro-acoustic method indicate that the charge injection of the epoxy resin filled with non-fluorinated polystyrene nanospheres is evident, while the introducing of fluorinated nanospheres significantly reduces the charge injection level. Calculations based on the depolarization process reveal that the introducing of fillers leads to an increase in trap density and depth of energy levels in the composites. Notably, the epoxy resin filled with fluorinated fillers has the deepest trap levels, providing an explanation for the improved insulation breakdown performance. The research can provide guidance for the regulation of dielectric properties of epoxy composites and material synthesis for the application of electronic insulation packaging.

Numerical Analysis of Ion Flow in One-Bipole HVDC Transmission Line Using Revised Charge Injection Methods

Numerical Analysis of Ion Flow in One-Bipole HVDC Transmission Line Using Revised Charge Injection Methods

Programmable particle assembly in composite through controlled charge injection

Programmable particle assembly in composite through controlled charge injection

Optimizing the gradient of electric field distribution and inhibiting charge injection in multilayer dielectric films for high capacitive performance

Nanocomposite films obtain superior energy storage density, which is by far the most energy storage performance reported to date.

Sonochemical regulation of oxygen vacancies for Bi2WO6 nanosheet-based photoanodes to promote photoelectrochemical performance.

Integration of oxygen vacancies (Vo) into nanostructured semiconductor-based photocatalysts has been recognized as a promising strategy for enhancing the performance of photoelectrochemical (PEC) water splitting. However, precisely controlling the Vo concentration in photocatalysts via an effective and tunable approach remains challenging. Herein, a series of optimized bismuth tungstate (Bi2WO6) nanosheet-based photoanodes with varying concentrations of Vo were prepared by a sonochemical method with in situ cavitation detection, which enables accurate manipulation of the acoustic cavitation intensity applied to the surface of Bi2WO6 photoanodes in alkaline solution. Based on the analysis of the Vo concentration and sound field characteristics, the mechanism of sonochemical regulation of Vo in Bi2WO6 nanosheets was interpreted. Specifically, the increase in Vo concentration can be attributed to the enhancement of Bi-O bond dissociation. This enhancement is influenced not only by the intensified impact of shear force and the generation of active radicals by transient cavitation, but also by the accelerated diffusion of the reactant, a result of stable cavitation. By optimizing the transient and stable cavitation intensity, a Vo-rich Bi2WO6 photoanode was obtained without altering the microstructure of Bi2WO6 nanosheets. The presence of high concentration Vo facilitates the interfacial chemical reactivity and the transmission of photogenerated carriers, leading to the drastic promotion of the PEC water splitting performance. The transient photocurrent density of the Vo-rich Bi2WO6 photoanode reaches 69.2 μA cm-2 (1.23 V vs. RHE), 7.86 times that of the untreated Bi2WO6 photoanode. Additionally, the charge injection efficiency increases to 35.4%. This work provides a controllable and effective method for defect engineering of nanostructured semiconductor-based electrodes.