Charge Trapping Sites Research Articles

TIPS‐BDT Derivatives Based Charge Trapping Elements for Photoresponsive Organic Transistor Memories

Comprehensive SummaryOFET‐type optical memories using light bias as the fourth terminal enable low voltage electrical stresses to suffice in generating substantial memory window and photoassisted multibit storage. The undefined molecular structure and trapping mechanism of most storage media limit their practical applications. Herein, we report a series of charge trapping materials with the rigid and planar conjugated structure of benzo[1,2‐b:4,5‐b’]dithiophene (BDT) acting as the charge trapping site and photoresponsive group, while the insulated (triisopropylsilyl)acetylene (TIPS) unit is introduced to prevent the leakage path of the charge. The pentacene‐based OFET memory with solution‐processing TTIPS‐BDT shows fast trapping speed, tunable ambipolar memory, large memory window and reliable charge retention, which is obviously improved compare to the performance of BDT and DTIPS‐BDT devices. In addition, the charge trapping, memory characteristics and photoresponsive behaviors are also discussed in detail. The TTIPS‐BDT device shows a specific response to green light illumination. This study suggests that BDT derivatives serving as charge trapping elements possess potential applications in future photoresponsive memory and plastic electronics.

Achieving ultrahigh charge-discharge efficiency and energy storage in high-temperature polar polymeric dielectrics via restrained dipole interactions.

Advancements in microelectronics and electrical power systems require dielectric polymeric materials capable of maintaining high discharged energy density and charge-discharge efficiency over a wide temperature range. Intrinsic polar polymers with enhanced dielectric constants are crucial for achieving high energy density and are extensively utilized at room temperature. However, the compatibility of high energy density and efficiency remains a significant challenge. Most polar polymer dielectric films suffer a considerable drop in capacitive performance as the temperature rises, with efficiency falling below 50%, and the waste Joule heat generated from conduction loss may lead to a vicious cycle. Herein, a new strategy of restraining dipole interactions in polar polymers is proposed to achieve optimal molecular chain stacking configurations, significantly decreased conductivity, and deeper charge trap sites, thus exhibiting enhanced energy density with outstanding efficiency at elevated temperatures. Remarkably, an energy density of 4.61 J cm-3 at an ultra-high efficiency above 95% was achieved, as well as cycling stability exceeding 150 000 cycles with an energy density of 2.4 J cm-3 at 150 °C, surpassing current high polar polymers and most advanced polymer composites. This discovery presents a promising solution for preserving high capacitive performance in polar polymeric materials at elevated temperatures.

Role of a cyclopentadienyl ligand in Hf precursors using H2O or O3 as oxidant in atomic layer deposition

Reducing the gate dielectric thickness in semiconductor devices leads to an increase in leakage current due to tunneling. High-k materials, such as HfO2, are essential in countering this and ensure an adequate equivalent oxide thickness at reduced physical thicknesses. This study investigated atomic layer deposition (ALD) of HfO2 films using the heteroleptic precursor CpHf(NMe2)3 with two different oxidants, H2O and O3, to understand their effects on the growth characteristics, chemical compositional properties, structural properties, and electrical properties. Growth per cycle (GPC) analysis shows that O3 achieved a saturated GPC of 0.85 Å/cycle, whereas H2O exhibits a lower GPC of 0.6 Å/cycle owing to steric hindrance from incomplete Cp ligand removal, leading to higher carbon impurity. X-ray photoelectron spectroscopy revealed an increase in carbon impurity in the H2O-deposited films, supporting these findings. Density functional theory calculations indicated more efficient Cp ligand removal when O3 was used as the oxidant. Furthermore, x-ray diffraction analysis shows that the O3-deposited films had a dominant monoclinic phase after postannealing, whereas the H2O-deposited films exhibited an increase in orthorhombic/tetragonal phases owing to greater carbon concentrations and oxygen vacancy. Electrical characterization of metal-oxide-semiconductor capacitors revealed higher Not values and increased leakage current densities in the H2O-deposited films. These differences are attributed to the higher levels of impurity and oxygen vacancy, which create additional charge-trapping sites and leakage paths. This study underscores the importance of selecting appropriate reactants for ALD to optimize the HfO2 film properties in advanced semiconductor applications.

2D Ti3C2Tx-MXene and its superstructures as dual-function electrodes for triboelectric nanogenerators for self-powered electronics

Selecting distinct materials to design a tribopositive and tribonegative electrode pair for a triboelectric nanogenerator (TENG) device is a challenging task, as the interfacial electric field causes surface charges to diffuse into the air or within the material itself, leads to charge deterioration. To address these challenges, there is a strong demand for engineered materials and electrode designs that enable effective charge accumulation and trapping to regulate their performance optimally. Herein, we introduce a unique electrode design for a contact-separation (CS) mode triboelectric nanogenerator TENG featuring multilayered Ti3C2Tx MXene/Kapton as tribonegative electrodes. For the tribopositive electrode, we developed an innovative synthesis strategy to create MXene-seeded layered TiO2 superstructures/PVA-based tribopositive electrodes. After optimization of both triboelectric layers, the optimized TENG showed an open-circuit voltage (Voc) ∼ 120 V, short-circuit current (Isc) ∼ 25 μA, and power density of 5.66 W·m−2. The surface terminations groups in highly conductive black MXene nanosheets and the oxygen vacancies in TiO2-layered superstructures provide abundant charge accumulation and trapping sites due to organized multilayered structures at both ends. Moreover, the induced polarization in the tribopositive layer due to the hybrid film could further hinder the free electrons’ drift to the bottom electrode, preventing charge recombination. The optimized TENG was tested as a pressure sensor to monitor different sensitive physiological movements of the human body. Further application of the designed TENG has been revealed by humidity sensing characteristics, powering LEDs, stopwatches, pedometers, and swiftly charging micro-capacitors by utilizing direct output power. By employing a controlled synthesis strategy, our approach leverages the unique properties of MXenes to function as both tribo-positive and tribonegative electrodes within the same device. This dual-function capability simplifies material selection and enhances overall device performance, presenting a transformative solution for next-generation TENG applications.

Synergistic Passivation of Bulk and Interfacial Defects Improves Efficiency and Stability of Inverted Perovskite Solar Cells

Defects both in bulk and at the interfaces serve as charge trapping sites for nonradiative recombination and as ion migration pathways, resulting in degradation of perovskite solar cell efficiency and stability. In this work, a strategy for simultaneous passivation of both bulk and interfacial defects is reported. For bulk passivation polystyrene (PS) is used as an additive in the perovskite precursor which reduces the structural defects by forming larger defect‐free grains. While the F‐PEAI cation is used to passivate the interfacial defects, present at both perovskite HTL/ETL interfaces. Furthermore, by conducting control measurements with just bulk modification (PS), just interface modification (F‐PEAI), and a combination of both, the role of individual defect passivation strategies is decoupled. As a result of simultaneous bulk as well as interfacial passivation, the modified perovskite solar cell shows the highest efficiency of 22.32% with a high Voc of 1.14 V and fill factor of 80%. Moreover, the cells have excellent stability retaining 92% and 99% of their initial efficiency after 1008 h and 560 h under ISOS‐ D1 and D2 storage conditions. These results highlight the importance of simultaneous bulk and interfacial passivation for improving solar cell efficiency and stability.

A novel simulation of space charge decay dynamics after removing the voltage in epoxy resin composites

Abstract Epoxy resin serves as a critical insulating component in ultra-high voltage dry direct current bushings. However, the accumulation of space charges within the epoxy resin, a byproduct of charge mobility, poses a significant risk to the reliability and operational safety of bushings. Conventional space charge attenuation models, especially after voltage removal, have limited use in simulations aimed at understanding this phenomenon. This study introduces an improved model integrating the bipolar charge transport mechanism with space charge decay based on the hopping conduction mechanism and Schottky’s theorem, establishes a theoretical framework for predicting the space charge behavior following voltage removal, and conducts a simulation to investigate the decay process within the internal structure of epoxy resin and measure the residual charges after voltage removal using the pulsed electro-acoustic method. The experimental data validate the accuracy of the proposed model and theoretical assumptions. The findings show that the remaining negative charges after voltage removal are not enhanced by the field enhancement; the anodic positive and cathodic positive charges are distributed in two-segment discontinuous traps, whereas the negative charges are distributed in one-segment traps. The model identifies two distinct trapping sites for anodic and cathodic positive charges, and one trapping site for negative charges. After voltage removal, when the field strength exceeded 40 kV mm−1, positive charges exist near the upper and lower electrodes, and negative charges exist near the center of the specimen. The consistency between the simulated predictions and experimental data proves the effectiveness of the proposed model in accurately simulating the space charge decay in epoxy materials after voltage removal.

Polymer Coating Enabled Carrier Modulation for Single-Walled Carbon Nanotube Network Inverters and Antiambipolar Transistors.

The control of the performance of single-walled carbon nanotube (SWCNT) random network-based transistors is of critical importance for their applications in electronic devices, such as complementary metal oxide semiconducting (CMOS)-based logics. In ambient conditions, SWCNTs are heavily p-doped by the H2O/O2 redox couple, and most doping processes have to counteract this effect, which usually leads to broadened hysteresis and poor stability. In this work, we coated an SWCNT network with various common polymers and compared their thin-film transistors' (TFTs') performance in a nitrogen-filled glove box. It was found that all polymer coatings will decrease the hysteresis of these transistors due to the partial removal of charge trapping sites and also provide the stable control of the doping level of the SWCNT network. Counter-intuitively, polymers with electron-withdrawing functional groups lead to a dramatically enhanced n-branch in their transfer curve. Specifically, SWCNT TFTs with poly (vinylidene fluoride) coating show an n-type mobility up to 61 cm2/Vs, with a decent on/off ratio and small hysteresis. The inverters constructed by connecting two ambipolar TFTs demonstrate high gain but with certain voltage loss. P-type or n-type doping from polymer coating layers could suppress unnecessary n- or p-branches, shift the threshold voltage and optimize the performance of these inverters to realize rail-to-rail switching. Similar devices also demonstrate interesting antiambipolar performance with tunable on and off voltage when tested in a different configuration.

A Mechanism of Resistance Switching in CNT Based Memory Devices

Carbon nanotubes (CNTs) show promise for high energy efficiency electronic devices due to their high electrical conductivity. One possible application is in the fabrication of resistance-change computer memory, where the application of an external electrical bias can use a CNT layer as the switching element in a RAM cell. Memory cells of this type have been extensively demonstrated, where the electrical resistance of a switching layer of CNTs can be reversibly controlled by the application of external bias [1].To better understand these devices, we have developed a nanoscale model of their electrical switching. Towards this end, first-principles calculations of the electrical conductivity of CNT-CNT junctions were performed using the Density Functional Tight Binding (DFTB) in combination with the Non-Equilibrium Greens functions (NEGF) approach, enabling an improved understanding of the tunnelling of electrons across a range of CNT junctions [2]. These results demonstrate that the conductivity of CNT contacts depends on the overlap area between nanotubes and exponentially on the distances between the carbon atoms of the interacting CNTs. Secondly, we employed coarse-grained molecular dynamics [3,4] to produce nanoscale dense CNT film models like those used in the devices. We devise a set of metrics for characterising the structural properties of CNT films, and apply them to a set of model films designed to mimic those used in microelectronics devices. In order to understand how the geometrical properties of CNTs affect the film structure, we analyse films with different CNT chirality and length distributions. Unlike previous studies that focused on relatively low-density systems below ∼0.4 g/cm3, we also consider films with density of ∼0.6 g/cm3, as employed in experimentally fabricated CNT-based NRAM devices. By adding amorphous carbon to the film models, in varying amounts, we are then able to assess its effects. Finally, these two elements were combined to produce electrical simulations of the conductivity of the CNT films connected to TiN electrodes. These electrodes are shown to be partially oxidized during the device fabrication. The electrical conductivity in a device is characterized by formation of conduction paths formed by CNTs between the electrodes and connected via the CNT junctions. The conductivity is modulated by charging of CNTs and amorphous carbon present in the film.Using these simulations, we propose a resistance switching mechanism in TiN/CNT/TiN devices based on the physical movement of CNTs. During the initial operation of the device, oxygen is released from the oxidized bottom electrode and this readily reacts with individual CNTs to form charge trapping sites. Once these sites have become charged, they enable controllable movement of CNTs at the bottom electrode under the application of electric field. By reversibly connecting and disconnecting such CNTs from the bottom electrode, the electrical conductivity through the CNT film as a whole can be controlled.

Small sized of anion doping effect on semiconducting single-walled carbon nanotube network for field-effect transistors

Carbon nanotubes have shown great promise for high-performance, large-area, solution processable field-effect transistors due to their exceptional charge transport properties. In this study, we utilize the spin-coating method to form networks from selectively sorted semiconducting single-walled carbon nanotubes (s-SWNTs), aiming for scalable electronic device fabrication. The one-dimensional nature of s-SWNTs, however, introduces significant roughness and charge trap sites, hindering charge transport due to the van der Waals gap (∼0.32 nm) between nanotubes. Addressing this, we explored the effects of anion doping on the spin-coated s-SWNT random network, with a focus on the influence of the small size of halogen anions (0.13–0.22 nm) on these electronic properties. Raman and ultraviolet–visible–near-infrared optical spectroscopy results indicate that smaller anions significantly enhance doping effects through strong non-covalent anion–π interactions, improving charge transport and carrier injection efficiency in s-SWNTs, especially for n-type operation. This improvement is inversely proportional to the size of the halogen anions, with the smallest anion (fluorine) effectively transitioning the electrical characteristics of the s-SWNT network from ambipolar to n-type by reducing both junction and contact resistances through anion doping, based on anion–π interaction.

Artificial nociceptor based on interface engineered ferroelectric volatile memristor

Artificial nociceptor based on interface engineered ferroelectric volatile memristor

Harnessing Persistent Photocurrent in a 2D Semiconductor-Polymer Hybrid Structure: Electron Trapping and Fermi Level Modulation for Optoelectronic Memory.

Recently, 2D semiconductor-based optoelectronic memory has been explored to overcome the limitations of conventional von Neumann architectures by integrating optical sensing and data storage into one device. Persistent photocurrent (PPC), essential for optoelectronic memory, originates from charge carrier trapping according to the Shockley-Read-Hall (SRH) model in 2D semiconductors. The quasi-Fermi level position influences the activation of charge-trapping sites. However, the correlation between quasi-Fermi level modulations and PPC in 2D semiconductors has not been extensively studied. In this study, we demonstrate optoelectronic memory based on a 2D semiconductor-polymer hybrid structure and confirm that the underlying mechanism is charge trapping, as the SRH model explains. Under light illumination, electrons transfer from polyvinylpyrrolidone to p-type tungsten diselenide, resulting in high-level injection and majority carrier-type transitions. The quasi-Fermi level shifts upward with increasing temperature, improving PPC and enabling optoelectronic memory at 433 K. Our findings offer valuable insights into optimizing 2D semiconductor-based optoelectronic memory.

Highly sensitive and selective detection of dopamine using atomic layer deposited HfO2 ultra-thin films

Highly sensitive and selective detection of dopamine using atomic layer deposited HfO2 ultra-thin films

Electrical Double-Layer Transistors Comprising Block Copolymer Electrolytes for Low-Power-Consumption Photodetectors.

Electrical double-layer transistors (EDLTs) have received extensive research attention owing to their exciting advantages of low working voltage, high biocompatibility, and sensitive interfacial properties in ultrasensitive portable sensing applications. Therefore, it is of great interest to reduce photodetectors' operating voltage and power consumption by utilizing photo-EDLT. In this study, a series of block copolymers (BCPs) of poly(4-vinylpyridine)-block-poly(ethylene oxide) (P4VP-b-PEO) with different compositions were applied to formulate polyelectrolyte with indigo carmine salt in EDLT. Accordingly, PEO conduces ion conduction in the BCP electrolyte and enhances the carrier transport capability in the semiconducting channel; P4VP boosts the photocurrent by providing charge-trapping sites during light illumination. In addition, the severe aggregation of PEO is mitigated by forming a BCP structure with P4VP, enhancing the stability and photoresponse of the photo-EDLT. By optimizing the BCP composition, EDLT comprising P4VP16k-b-PEO5k and indigo carmine provides the highest specific detectivity of 2.1 × 107 Jones, along with ultralow power consumptions of 0.59 nW under 450 nm light illumination and 0.32 pW under dark state. The results indicate that photo-EDLT comprising the BCP electrolyte is a practical approach to reducing phototransistors' operating voltage and power consumption.

Tailoring the Molecular Planarity of Perylene Diimide-Based Third Component toward Efficient Ternary Organic Solar Cells.

Incorporating a third component into binary organic solar cells (b-OSCs) has provided a potential platform to boost power conversion efficiency (PCEs). However, gaining control over the non-equilibrium blend morphology via the molecular design of the perylene diimide (PDI)-based third component toward efficient ternary organic solar cells (t-OSCs) still remains challenging. Herein, two novel PDI derivatives are developed with tailored molecular planarity, namely ufBTz-2PDI and fBTz-2PDI, as the third component for t-OSCs. Notably, after performing a cyclization reaction, the twisted ufBTz-2PDI with an amorphous character transferred to the highly planar fBTz-2PDI followed by a semi-crystalline character. When incorporating the semi-crystalline fBTz-2PDI into the D18:L8-BO system, the resultant t-OSC achieved an impressive PCE of 18.56%, surpassing the 17.88% attained in b-OSCs. In comparison, the addition of amorphous ufBTz-2PDI into the binary system facilitates additional charge trap sites and results in a deteriorative PCE of 14.37%. Additionally, The third component fBTz-2PDI possesses a good generality in optimizing the PCEs of several b-OSCs systems are demonstrated. The results not only provided a novel A-DA'D-A motif for further designing efficient third component but also demonstrated the crucial role of modulated crystallinity of the PDI-based third component in optimizing PCEs of t-OSCs.

Electronic and optical properties of pyrochlore Re2Ti2O7 (Re = Sm and Eu) from first-principles

Rare-earth titanate oxides are believed to be prospective functional materials for photocatalytic and photoluminescent applications because of their excellent optical properties and thermal stability of their physical properties. However, the relationships between optical properties and photoelectron trapping mechanisms are unclear. Herein, the structure, electronic, and optical properties of pyrochlore-structure Re2Ti2O7 (Re = Sm and Eu) were investigated using the first-principles approach with the Hubbard parameter U (GGA + U). The calculated bandgap is 2.5 eV for Sm2Ti2O7 and 2.4 eV for Eu2Ti2O7, which is in good agreement with the experimental observation. The results indicate that the strongly localized f states at the top of valence band are charge-trapping sites for photoexcitation of Re2Ti2O7, where electrons can absorb photon energy and transfer from the valence band to the conduction band, resulting in the photocatalytic and/or fluorescent effects in the visible and early UV regions. The important optical parameters, dielectric function ε(ω), refractive index n(ω), extinction coefficient k(ω), reflectivity R(ω), absorption coefficient I(ω), optical conductivity σ(ω), and electron energy-loss L(ω) were studied in detail, indicating that these optical parameters of Sm2Ti2O7 and Eu2Ti2O7 are insensitive to the ultra-violet (UV) radiation, but both Sm2Ti2O7 and Eu2Ti2O7 exhibit excellent optical properties in the visible and early UV regions. This work provides a clear understanding on the photoelectron trapping mechanism of pyrochlore-structure Re2Ti2O7, which will help to improve the photocatalytic and photoluminescent performance of Re2Ti2O7 and broaden their applications.

Low-frequency noise behaviors of quasi-two-dimensional electron systems based on complex oxide heterostructures

Low-frequency noise behaviors of quasi-two-dimensional electron systems based on complex oxide heterostructures

Unifying and Suppressing Conduction Losses of Polymer Dielectrics for Superior High-Temperature Capacitive Energy Storage.

Superior high-temperature capacitive performance of polymer dielectrics is critical for the modern film capacitor demanded in the harsh-environment electronic and electrical systems. Unfortunately, the capacitive performance degrades rapidly at elevated temperatures owing to the exponential growth of conduction loss. The conduction loss is mainly composed of electrode and bulk-limited conduction. Herein, the contribution of surface and bulk factors is unified to conduction loss, and the loss is thoroughly suppressed. The experimental results demonstrate that the polar oxygen-containing groups on the surface of polymer dielectrics can act as the charge trap sites to immobilize the injected charges from electrode, which can in turn establish a built-in field to weaken the external electric field and augment the injection barrier height. Wide bandgap aluminum oxide (Al2O3) nanoparticle fillers can serve as deep traps to constrain the transport of injected or thermally activated charges in the bulk phase. From this, at 200 °C, the discharged energy density with a discharge-charge efficiency of 90% increases by 1058.06% from 0.31 J cm-3 for pristine polyetherimide to 3.59 J cm-3 for irradiated composite film. The principle of simultaneously inhibiting the electrode and bulk-limited conduction losses could be easily extended to other polymer dielectrics for high-temperature capacitive performance.

Enhancement of dielectric properties of the La2NiO4-CuO terpolymer nanocomposites by modified SiC nanofiller

Enhancement of dielectric properties of the La2NiO4-CuO terpolymer nanocomposites by modified SiC nanofiller

Enhanced Charge Separation in Nanoporous BiVO4 by External Electron Transport Layer Boosts Solar Water Splitting.

The optimization of charge transport with electron-hole separation directed toward specific redox reactions is a crucial mission for artificial photosynthesis. Bismuth vanadate (BiVO4 , BVO) is a popular photoanode material for solar water splitting, but it faces tricky challenges in poor charge separation due to its modest charge transport properties. Here, a concept of the external electron transport layer (ETL) is first proposed and demonstrated its effectiveness in suppressing the charge recombination both in bulk and at surface. Specifically, a conformal carbon capsulation applied on BVO enables a remarkable increase in the charge separation efficiency, thanks to its critical roles in passivating surface charge-trapping sites and building external conductance channels. Through decorated with an oxygen evolution catalyst to accelerate surface charge transfer, the carbon-encased BVO (BVO@C) photoanode manifests durable water splitting over 120h with a high current density of 5.9mAcm-2 at 1.23V versus the reversible hydrogen electrode (RHE) under 1sun irradiation (100mWcm-2 , AM 1.5G), which is an activity-stability trade-off record for single BVO light absorber. This work opens up a new avenue to steer charge separation via external ETL for solar fuel conversion.

Over- and Undercoordinated Atoms as a Source of Electron and Hole Traps in Amorphous Silicon Nitride (a-Si3N4).

Silicon nitride films are widely used as the charge storage layer of charge trap flash (CTF) devices due to their high charge trap densities. The nature of the charge trapping sites in these materials responsible for the memory effect in CTF devices is still unclear. Most prominently, the Si dangling bond or K-center has been identified as an amphoteric trap center. Nevertheless, experiments have shown that these dangling bonds only make up a small portion of the total density of electrical active defects, motivating the search for other charge trapping sites. Here, we use a machine-learned force field to create model structures of amorphous Si3N4 by simulating a melt-and-quench procedure with a molecular dynamics algorithm. Subsequently, we employ density functional theory in conjunction with a hybrid functional to investigate the structural properties and electronic states of our model structures. We show that electrons and holes can localize near over- and under-coordinated atoms, thereby introducing defect states in the band gap after structural relaxation. We analyze these trapping sites within a nonradiative multi-phonon model by calculating relaxation energies and thermodynamic charge transition levels. The resulting defect parameters are used to model the potential energy curves of the defect systems in different charge states and to extract the classical energy barrier for charge transfer. The high energy barriers for charge emission compared to the vanishing barriers for charge capture at the defect sites show that intrinsic electron traps can contribute to the memory effect in charge trap flash devices.