Charge Injection Research Articles

Low-Temperature Cross-Linked Hole Transport Layer for High-Performance Blue Quantum-Dot Light-Emitting Diodes.

Quantum-dot light-emitting diodes (QLEDs), a kind of promising optoelectronic device, demonstrate potential superiority in next-generation display technology. Thermal cross-linked hole transport materials (HTMs) have been employed in solution-processed QLEDs due to their excellent thermal stability and solvent resistance, whereas the unbalanced charge injection and high cross-linking temperature of cross-linked HTMs can inhibit the efficiency of QLEDs and limit their application. Herein, a low-temperature cross-linked HTM of 4,4'-bis(3-(((4-vinylbenzyl)oxy)methyl)-9H-carbazol-9-yl)-1,1'-biphenyl (DV-CBP) with a flexible styrene side chain is introduced, which reduces the cross-linking temperature to 150 °C and enhances the hole mobility up to 1.01 × 10-3 cm2 V-1 s-1. More importantly, the maximum external quantum efficiency of 21.35% is successfully obtained on the basis of the DV-CBP as a cross-linked hole transport layer (HTL) for blue QLEDs. The low-temperature cross-linked high-mobility HTL using flexible side chains could be an excellent alternative for future HTL development.

Capacitive Synaptor With Overturned Charge Injection for Compute-in-Memory

Capacitive Synaptor With Overturned Charge Injection for Compute-in-Memory

Controlled phase distribution of quasi-2D perovskite enables improved electroluminescence

Abstract Quasi-two-dimensional (quasi-2D) perovskites are increasingly explored for integration into light-emitting diodes (LEDs) as light-emissive layers. However, the quasi-2D perovskite films likely exhibit non-uniform dimensional phase distribution and irregular internal crystal structures. These characteristics are known to contribute to undesirable effects, including non-radiative recombination losses and radiative recombination in perovskites of various dimensions, impeding the realization of efficient electroluminescence and high color purity in LEDs. In this study, we present an investigation on the correlation between the dimensional distribution of quasi-2D perovskites and charge carrier behaviour by modulating anti-solvent dripping during the film fabrication processes. We provide a comprehensive analysis on the impact of controlled dimensional distribution on charge injection and recombination processes associated with performance of quasi-2D perovskite LEDs. Our work emphasizes the crucial role played by controlled dimensionality in quasi-2D perovskites in realizing efficient and stable perovskite-based LEDs.

Molecular Dynamics Simulations on Epoxy Resin Composite via Grafting Acryloyl-chloride to Inhibit Electron Transport and Improve Thermal-mechanical Properties

Abstract Electrical, thermal, and mechanical properties of cross-linked epoxy resin (EP) modified by the chemical grafting of acryloyl chloride (AC) were studied to explore the trapping mechanism of charge transport inhibition. The bound state traps deriving from grafted molecules were analyzed by first-principles calculations combined with electron transmission spectra to study the underlying mechanism of the electrical properties. In contrast to pure EP, the EP-graft-AC (EP-g-AC) represents significantly depressed conductivity due to the electron scattering from polar-groups of the grafted AC molecule. The substantial deep traps are generated in EP-g-AC molecules by the polar group of grafted AC and accordingly decrease charge mobility and raise the charge injection barrier, consequently suppressing space charge accumulation and charge carrier transport. EP-g-AC polymer acquires a significant amelioration in thermal and mechanical properties, as indicated by the higher cohesive energy density, glass transition temperature, and decomposition temperature in consistence with the lower thermal vibrations compared with pure EP polymer, except that the resulting higher fractional free volume is not preferable, which is attributed to the mixing incompatibility of the grafted AC molecules with EP molecular-chains.

Charge interaction behaviors at interfacial domains in DC GIL insulators

Long-term operation of high voltage direct current at elevated temperatures can result in the accumulation of surface charges in DC gas-insulated transmission line (GIL) insulators. Such a phenomenon leads to localized electric field distortion, increasing the risk of surface discharge. The analysis of interaction behaviors between surface charge and space charge at interfacial domains of GIL insulators is a complex task, which requires a comprehensive understanding of physical mechanisms of the gas–solid interface charging. In this work, a two-dimensional bipolar charge transport and interaction (2D BCTI) model is established, with the consideration of both surface and space charge dynamics. Pulsed electroacoustic tests and surface potential measurements are conducted on DC GIL insulator materials under different electrical-thermal coupling conditions. Experimental results exhibit great consistency with the predictions from the 2D BCTI model. The local accumulation of space charge near interfaces has certain effects on surface potential distribution, which in turn influences charge injection behavior from electrodes. In comparison to traditional surface charge simulation models, the consideration of space charge–surface charge interaction behaviors proves to be essential for estimating the polarity and amplitude of surface potential distribution. This model holds promise for assessing charge characteristics in electrical equipment where direct measurement is challenging.

Ultrathin layer TAFC on BiVO4 with ligand-to-metal charge transfer enhances built-in electric field for boosting photoelectrochemical water oxidation

To reveal the mechanism of charge transfer between interfaces of BiVO4-based heterogeneous materials in photoelectrochemical water splitting system, the cocatalyst was grown in situ using tannic acid (TA) as a ligand and Fe and Co ions as metal centers (TAFC), and then uniformly and ultra-thinly coated on BiVO4 to form photoanodes. The results show that the BiVO4/TAFC achieves a superior photocurrent density (4.97 mA cm−2 at 1.23 VRHE). The charge separation and charge injection efficiencies were also significantly higher, 82.0 % and 78.9 %, respectively. From XPS, UPS, KPFM, and density functional theory calculations, Ligand-to-metal charge transfer (LMCT) acts as an electron transport highway in TAFC ultrathin layer to promote the concentration of electrons towards metal center, leading to an increase in the work function, which enhances the built-in electric field and further improves the charge transport. This study demonstrated that the LMCT pathway on TA-metal complexes enhances the built-in electric field in BiVO4/TAFC to promote charge transport and thus enhance water oxidation, providing a new understanding of the performance improvement mechanism for the surface-modified composite photoanodes.

A Novel Bootstrapped CMOS Switch with Minimized Sampling and Holding Error Using Sampling Window Error Analysis

This study proposes a novel 6-transistor bootstrapped switch with minimized sampling and holding error obtained through sampling window error analysis for SAR ADC design. The proposed switch design strategically mitigates channel charge injection and minimizes the input signal dependency of on-resistance by optimizing its sizing parameters. To counteract channel charge effects, dummy NMOS and PMOS components are judiciously employed, culminating in a substantial improvement in the effective number of bits (ENOB). The complete analysis of the proposed circuit is done using the Cadence Virtuoso SCL 0.18[Formula: see text][Formula: see text]m CMOS process. For a 51.514[Formula: see text]kHz sinusoidal 1[Formula: see text]V peak-to-peak differential input signal with a 1[Formula: see text]MSPs clock speed, the proposed circuit achieves 2.0141[Formula: see text]mV maximum sampling window error, 0.131[Formula: see text][Formula: see text]W power consumption, 84.67 dB signal-to-noise ratio (SNR), 84.67 signal-to-noise and distortion (SINAD) ratio and 86.02 dB spurious-free dynamic range (SFDR), which produces 13.77 bits ENOB. For the impacts of process variations and mismatch on switch performance, a comprehensive 500-point Monte Carlo (MC) simulation of the proposed bootstrap switch is conducted in this study. Post-layout results show that the proposed circuit is suitable for IoT applications.

Leakage current as a probe into the mechanics of carrier transport in insulating composite polymers

Amorphous composite polymers are widely used as insulators in microelectronics due to their high dielectric strength, mechanical robustness, and thermal stability. However, organic–inorganic composite systems suffer from undesirable performance and accelerated degradation due to leakage current (JTot). Unfortunately, the underlying mechanism of JTot and its components (e.g., ionic and electronic constituents) are inadequately understood, particularly in extreme use conditions (e.g., high humidity and temperature). In this study, we use numerical simulation and experimental JTot data (in amorphous epoxy polymer with silica fillers) to (i) unify the electrostatic model for JTot in composite polymers, (ii) illustrate that the early part of JTot (i.e., external current) is primarily due to the image charge associated with ion transport/ localization (Jion) near the metallic contacts, (iii) demonstrate that the accumulated counter-ions reduce the barrier for electronic charge injection (by band bending) and facilitate electronic injection from the metals (Jelec), and (iv) provide an algorithm for the in situ ion transport characterization of composite insulators by exploiting Jion. This work provides new insights regarding the leakage current mechanism and how it can be used as a probe into the complex transport mechanisms of the composite material.

Photo-crosslinking and layer-by-layer processed organic photodetectors with remarkably suppressed dark current

The effective reduction of dark (or noise) current presents a significant hurdle in enhancing the detectivity of organic photodetectors (OPDs). To address this challenge, a photo-crosslinkable donor polymer, PM6-Br50, is synthesized by introducing bromoalkyl side-chains onto the PM6 structure. This modification enables the formation of a pseudo planar heterojunction (p-PHJ) structure of crosslinked donor/acceptor through a layer-by-layer (LbL) sequential process without the necessity for an semi-orthogonal solvent. This innovation effectively overcomes solvent-related limitations in the LbL process. Additionally, we replace the semi-metallic hole-transport layer (HTL), PEDOT:PSS, with a semiconducting conjugated polyelectrolyte (TPAFS-TMA) with a high conduction band. The p-PHJ configuration, featuring pure donor/anode and pure acceptor/cathode contacts, enhances the charge injection barrier for electrons (holes) from the anode (cathode) in the dark under reverse bias, effectively minimizing dark current. Furthermore, the TPAFS-TMA HTL serves to impede electron injection from the anode. Through the synergistic combination of these two strategies, a significantly reduced dark current density (4.03 × 10−10 A cm−2) is measured by four orders of magnitude, compared to the bulk heterojunction OPDs with PEDOT:PSS. Furthermore, we measure remarkably high shot noise-based and total noise current-based specific detectivities of 4.27 × 1013 and 6.97 × 1012 cm Hz1/2 W−1 (with linear dynamic range of 73.7 dB), respectively.

High-Efficiency and Stable Colloidal One-Dimensional Core/Shell Nanorod Light-Emitting Diodes.

Anisotropic nanocrystals such as nanorods (NRs) display unique linearly polarized emission, which is expected to break the external quantum efficiency (EQE) limit of quantum dot-based light-emitting diodes (LEDs). However, the progress in achieving a higher EQE using NRs encounters several challenges, primarily involving a low photoluminescence quantum yield (PLQY) of NRs and imbalanced charge injection in NR-LEDs. In this work, we investigated NR-LEDs based on CdSe/CdZnS/ZnS rod-in-rod NRs with a high PLQY and higher linear polarization compared to those of dot-in-rod NRs. The balanced charge injection is achieved using ZnMgO nanoparticles as the electron transport layer and poly-TPD {poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine]} as the hole transport layer. Therefore, the NR-LEDs exhibit a maximum EQE of 21.5% and a maximum luminance of >120 000 cd/m2 owing to the high level of in-plane transitions with a dipole moment of 90%. The NR-LEDs also have greatly inhibited droop in EQE under a high current density as well as outstanding operation lifetime and cycle stability.

Autonomous self-healing supramolecular polymer transistors for skin electronics

Skin-like field-effect transistors are key elements of bio-integrated devices for future user-interactive electronic-skin applications. Despite recent rapid developments in skin-like stretchable transistors, imparting self-healing ability while maintaining necessary electrical performance to these transistors remains a challenge. Herein, we describe a stretchable polymer transistor capable of autonomous self-healing. The active material consists of a blend of an electrically insulating supramolecular polymer with either semiconducting polymers or vapor-deposited metal nanoclusters. A key feature is to employ the same supramolecular self-healing polymer matrix for all active layers, i.e., conductor/semiconductor/dielectric layers, in the skin-like transistor. This provides adhesion and intimate contact between layers, which facilitates effective charge injection and transport under strain after self-healing. Finally, we fabricate skin-like self-healing circuits, including NAND and NOR gates and inverters, both of which are critical components of arithmetic logic units. This work greatly advances practical self-healing skin electronics.

Nanoscale single-electron box with a floating lead for quantum sensing: Modeling and device characterization

We present an in-depth analysis of a single-electron box (SEB) biased through a floating node technique that is common in charge-coupled devices. The device is analyzed and characterized in the context of single-electron charge sensing techniques for integrated silicon quantum dots (QD). The unique aspect of our SEB design is the incorporation of a metallic floating node, strategically employed for sensing and precise injection of electrons into an electrostatically formed QD. To analyze the SEB, we propose an extended multi-orbital Anderson impurity model (MOAIM), adapted to our nanoscale SEB system, that is used to predict theoretically the behavior of the SEB in the context of a charge sensing application. The validation of the model and the sensing technique has been carried out on a QD fabricated in a fully depleted silicon on insulator process (FD-SOI) on a 22-nm CMOS technology node. We demonstrate the MOAIM's efficacy in predicting the observed electronic behavior and elucidating the complex electron dynamics and correlations in the SEB. The results of our study reinforce the versatility and precision of the model in the realm of nanoelectronics and highlight the practical utility of the metallic floating node as a mechanism for charge injection and detection in integrated QDs. Finally, we identify the limitations of our model in capturing higher order effects observed in our measurements and propose future outlooks to reconcile some of these discrepancies.

Charge Carrier Regulation for Efficient Blue Quantum-Dot Light-Emitting Diodes Via a High-Mobility Coplanar Cyclopentane[b]thiopyran Derivative.

The performance of blue quantum dot light-emitting diodes (QLEDs) is limited by unbalanced charge injection, resulting from insufficient holes caused by low mobility or significant energy barriers. Here, we introduce an angular-shaped heteroarene based on cyclopentane[b]thiopyran (C8-SS) to modify the hole transport layer poly-N-vinylcarbazole (PVK), in blue QLEDs. C8-SS exhibits high hole mobility and conductivity due to the π···π and S···π interactions. Introducing C8-SS to PVK significantly enhanced hole mobility, increasing it by 2 orders of magnitude from 2.44 × 10-6 to 1.73 × 10-4 cm2 V-1 s-1. Benefiting from high mobility and conductivity, PVK:C8-SS-based QLEDs exhibit a low turn-on voltage (Von) of 3.2 V. More importantly, the optimized QLEDs achieve a high peak power efficiency (PE) of 7.13 lm/W, which is 2.65 times that of the control QLEDs. The as-proposed interface engineering provides a novel and effective strategy for achieving high-performance blue QLEDs in low-energy consumption lighting applications.

Exploring the influence of the contact resistance on perovskite phototransistors

Organic–inorganic hybrid perovskites are widely used in photodetection owing to their high optical absorption coefficients. A variety of research has been conducted on perovskite phototransistors and their optoelectronic properties, but the exploration of the influence of contact resistance remains limited. In this work, we employed the transmission-line method to separate the contact resistance Rc × W (ranging from 4.81 × 104 to 4.77 × 103 Ω cm) and the channel resistance Rch × W (ranging from 1.93 × 104 to 1.16 × 104 Ω cm) of (PEA)2SnI4 perovskite phototransistors at different light intensities (520 nm, ranging from 0 to 2550 μW/cm2). Further analysis reveals that illumination-induced accumulation of charge carriers at the metal/semiconductor interface reduces the Schottky barrier. Approximately 90% of the observed increase in photocurrent can be attributed to the reduction in the contact resistance. Our finding underscores the crucial role of charge injection in influencing perovskite-based phototransistors.

Metal-Graphene Hybrid Terahertz Metasurfaces for Circulating Tumor DNA Detection Based on Dual Signal Amplification.

Terahertz (THz) spectroscopy has impressive capability for label-free biosensing, but its utility in clinical laboratories is rarely reported due to often unsatisfactory detection performances. Here, we fabricated metal-graphene hybrid THz metasurfaces (MSs) for the sensitive and enzyme-free detection of circulating tumor DNA (ctDNA) in pancreatic cancer plasma samples. The feasibility and mechanism of the enhanced effects of a graphene bridge across the MS and amplified by gold nanoparticles (AuNPs) were investigated experimentally and theoretically. The AuNPs serve to boost charge injection in the graphene film and result in producing a remarkable change in the graded transmissivity index to THz radiation of the MS resonators. Assay design utilizes this feature and a cascade hybridization chain reaction initiated on magnetic beads in the presence of target ctDNA to achieve dual signal amplification (chemical and optical). In addition to demonstrating subfemtomolar detection sensitivity and single-nucleotide mismatch selectivity, the proposed method showed remarkable capability to discriminate between pancreatic cancer patients and healthy individuals by recognizing and quantifying targeted ctDNAs. The introduction of graphene to the metasurface produces an improved sensitivity of 2 orders of magnitude for ctDNA detection. This is the first study to report the combined application of graphene and AuNPs in biosensing by THz spectroscopic resonators and provides a combined identification scheme to detect and discriminate different biological analytes, including nucleic acids, proteins, and various biomarkers.

Multifunctional Photodetector with Tunable Response Bandwidth and Polarization Sensitivity

AbstractMultifunctional organic photodetectors (MFOPDs) have garnered significant attention due to their remarkable potential for integrating diverse device functionalities. In contrast to previous MFOPDs that have primarily emphasized the integration of various response bands, a pioneering multifunctional photodetector is introduced based on the P3HT:PC61BM system capable of selectively responding to both wavelength and polarization. Under positive bias, the device operates in a wide‐band, polarization‐insensitive mode, achieving an external quantum efficiency (EQE) of up to 7.01 × 104%. The EQE dichroic ratio (DR) of the device remains <1.01 (at 650 nm). Conversely, under negative bias, the device transitions into a narrow‐band, polarization‐sensitive mode, achieving an EQE of up to 4.82 × 104% with a narrow full width at half maximum (FWHM) of only 25 nm at 650 nm. The EQE DR exceeds 10 in this mode, marking it as one of the highest values within the field of polarization‐sensitive organic photodetectors. This versatile operation is made possible through the strategic use of double‐sided barriers, an oriented light harvesting layer, and a charge injection narrowing (CIN) approach. This work represents a significant advancement toward the realization of multifunctional photodetectors capable of selecting response bands and polarization sensitivity.

Nickel Oxide Hole Injection Layers for Balanced Charge Injection in Quantum Dot Light-Emitting Diodes.

Quantum dot (QD) light-emitting diodes (QLEDs) are promising for next-generation displays, but suffer from carrier imbalance arising from lower hole injection compared to electron injection. A defect engineering strategy is reported to tackle transport limitations in nickel oxide-based inorganic hole-injection layers (HILs) and find that hole injection is able to enhance in high-performance InP QLEDs using the newly designed material. Through optoelectronic simulations, how the electronic properties of NiOx affect hole injection efficiency into an InP QD layer, finding that efficient hole injection depends on lowering the hole injection barrier and enhancing the acceptor density of NiOx is explored. Li doping and oxygen enriching are identified as effective strategies to control intrinsic and extrinsic defects in NiOx, thereby increasing acceptor density, as evidenced by density functional theory calculations and experimental validation. With fine-tuned inorganic HIL, InP QLEDs exhibit a luminance of 45200cdm-2 and an external quantum efficiency of 19.9%, surpassing previous inorganic HIL-based QLEDs. This study provides a path to designing inorganic materials for more efficient and sustainable lighting and display technologies.

An ultrahigh input impedance low noise analog front‐end design for epilepsy brain recording system

SummaryThis paper presents an ultrahigh input impedance, low noise, and wide bandwidth four‐channels analog front‐end (AFE) for low‐power neural recording systems. To achieve high input impedance, the buffer channels are placed between the electrodes and the main amplifier stage of the AFE. The buffer is designed with low noise and low power consumption to obtain high input impedance of overall AFE while maintaining low input‐referred noise and low power consumption. A chopper capacitively coupled chopper instrumentation amplifier (CCIA) is placed after the buffer as the main amplifier stage of the AFE to improve the common mode rejection ratio (CMRR) and the input‐referred noise of the overall AFE design. A new chopper stabilization control technique is proposed and used in the CCIA stage to reduce the charge injection and clock feedthrough and consequently the high‐frequency ripple of the AFE output signal. A programmable gain amplifier (PGA) is designed as the third stage to adjust the overall gain of the AFE. Benefiting from PGA, the AFE can adapt its gain with both action potential and local field potential signals. To reduce the number of the electrode to be implanted and reduce the impedance mismatch that causes the degradation on overall CMRR performance, two AFE channels shared a reference electrode followed by a reference buffer. The proposed AFE is designed and simulated using a standard 180 nm CMOS process and operates in a wide frequency band of 2.1 to 2500 Hz with low input‐referred noise of 1.6 μVrms and a CMRR over 80 dB at 2.1 Hz. The total power consumption is lower than 4.3 μW per channel. With the proposed structure of AFE, the input impedance is 35 GΩ @ 21 Hz and the minimum impedance over operational bandwidth is 75 MΩ @ 2.5 kHz.

Extending the understanding of Shannon's safe stimulation limit for platinum electrodes: biphasic charge-balanced pulse trains in unbuffered saline at pH = 1 to pH = 12.

In neural electrical stimulation, safe stimulation guidelines are essential to deliver efficient treatment by avoiding neural damage and electrode degradation. The widely used Shannon's limit, k, gives conditions on the stimulation parameters to avoid neural damage, however, underlying damage mechanisms are not fully understood. Moreover, the translation from bench testing to in vivo experiments still presents some challenges, including the increased polarisation observed, which may influence charge-injection mechanisms. In this work, we studied the influence on damage mechanisms of two electrolyte parameters that are different in vivo compared to usual bench tests: solution pH and electrolyte gelation. The potential of a platinum macroelectrode was monitored in a three-electrode setup during current-controlled biphasic charge-balanced cathodic-first pulse trains. Maximum anodic and cathodic potential excursions during pulse trains were projected on cyclic voltammograms to infer possible electrochemical reactions. In unbuffered saline of pH ranging from 1 to 12, the maximum anodic potential was systematically located in the oxide formation region, while the cathodic potential was located the molecular oxygen and oxide reduction region when k approached Shannon's damage limit, independent of solution pH. The results support the hypothesis that Shannon's limit corresponds to the beginning of platinum dissolution following repeated cycles of platinum oxidation and reduction, for which the cathodic excursion is a key tipping point. Despite similar potential excursions between solution and gel electrolytes, we found a joint influence of pH and gelation on the cathodic potential alone, while we observed no effect on the anodic potential. We hypothesise that gelation creates a positive feedback loop exacerbating the effects of pH ; however, the extent of that influence needs to be examined further. This work supports the hypothesis of charge injection mechanisms associated with stimulation-induced damage at platinum electrodes. The validity of a major hypothesis explaining stimulation-induced damage was tested and supported on a range of electrolytes representing potential electrode environments, calling for further characterisation of platinum dissolution during electrical stimulation in various testing conditions.

Gradient Alloy Shell Enabling Colloidal Quantum Wells Light-Emitting Diodes with Efficiency Exceeding 22.

Colloidal quantum well (CQW) based light emitting diodes (LEDs) possess extra-high theoretical efficiency, but their performance still lags far behind conventional LEDs due to severe exciton quenching and unbalanced charge injection. Herein, we devised a gradient composition CdxZn1-xS shell to address these issues. The epitaxial shell with gradient composition was achieved through controlling competition between Cd2+ and Zn2+ cations to preferentially bind to the anions S2-. Thus, exciton quenching was suppressed greatly by passivating defects and reducing nonradiative recombination, thereby achieving near-unity photoluminescence quantum yield (PLQY). The gradient energy level of the shell reduced the hole injection barriers and increased the hole injection efficiency to balance the charge injection of LEDs. As a result, the LEDs achieved a high external quantum efficiency (EQE) of 22.83%, luminance of 111,319 cd/m2 and a long operational lifetime (T95@100 cd/m2) over 6,500 h, demonstrating the state-of-the-art performance for the CQW based LEDs.