Charge Mobility Research Articles

An analytical I-V model of SiC double-gate junctionless MOSFETs

Silicon carbide(SiC) double gate junctionless metal oxide semiconductor field-effect transistors(DG JL MOSFETs) have attracted significant attention due to their ideal high temperature characteristics and radiation resistance. Therefore, it is meaningful to exploit an I-V model for SiC DG JL MOSFETs. In this article, we make a linear approximation to describe the relationship between the surface mobile charge density and the surface electron concentration of the device. Based on this approximation and using the one-dimensional Poisson’s equation, we solve for the potential distribution of a SiC DG JL MOSFET in the subthreshold region. From this solution, we derived a functional relationship between the surface mobile charge density in the channel and the channel quasi-Fermi potential. Then we successfully developed a unified I-V model for the SiC DG JL MOSFETs. Based on the drain to source current calculation formula, the calculation expressions for the device’s transconductance and output conductance are derived. By comparing our model with the results from the two-dimensional numerical simulation software Silvaco Atlas, our model’s calculations closely match the two-dimensional numerical simulation results from the subthreshold region to the accumulation region. This model has reference significance for SiC DG JL MOSFETs in the high temperature electronic circuit application field.

Heterojunction Organic Solar Cells with Efficient Charge Mobility and Separation Capabilities Studied by DFT.

The properties of the active layer materials play a decisive role in determining the power conversion efficiency of organic solar cells (OSCs). Chlorophyll and its derivatives are abundant and environmentally friendly functional organic molecular materials. Using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), we have calculated the absorption spectra and their excited state properties based on optimized ground state structures. It was found that bacteriochlorin exhibits superior structural properties, a smaller energy gap and hole reorganization energy, redshifted absorption spectra, and higher hole mobility compared to the donor D18. This suggests that bacteriochlorin exhibits superior donor properties. Comparative studies between o-AT-2Cl and m-AT-2Cl showed that o-AT-2Cl had superior acceptor properties, implying that differences in substitution positions can influence the physicochemical properties of non-fullerene acceptors (NFAs). Subsequently, six bulk heterojunctions (BHJs) were constructed by combining three donors with nonfused ring electron acceptors, o-AT-2Cl and m-AT-2Cl. The bacteriochlorin-based BHJs performed well among them, with BChl3/o-AT-2Cl and BChl4/o-AT-2Cl having the largest interfacial charge separation rate. The results suggested that BHJs composed of bacteriochlorin and NFAs can improve OSCs' photovoltaic performance, providing a feasible scheme for designing efficient OSCs.

Fullerene-hybridized Fused-ring Electron Acceptor with High Dielectric Constant and Isotropic Charge Transport for Organic Solar Cells.

A novel isotropic fullerene-hybridized fused-ring electron acceptor, designated C60-Y, has been synthesized via a mild [4+2] Diels-Alder cycloaddition reaction with fullerene C60 to enhance the performance of organic solar cells (OSCs). Comparative analysis shows that C60-Y significantly outperforms the control acceptor Me-Y, with a notable increase in the relative dielectric constant from 2.79 to 3.95. This improvement enhances exciton dissociation and reduces non-radiative energy losses. Additionally, the isotropic molecular packing of C60-Y, similar to fullerene, facilitates efficient interface formation with donor polymers and improves charge mobility. As a result, incorporating C60-Y as an electron acceptor increases the power conversion efficiency (PCE) of binary OSCs to 15.02%, surpassing the 13.31% achieved with Me-Y. Moreover, when integrated into a ternary blend system, an impressive PCE of 19.22% is achieved, top-performing among reported ternary OSCs utilizing fullerene derivatives as the third component. These results suggest that fullerene-hybridized acceptors like C60-Y hold great potential for advancing high-efficiency OSCs by enhancing exciton dissociation, reducing energy losses, and improving charge mobility.

Evolution laws of charge mobility of transformer oil and pressboard material with temperature and electric field strength

Abstract Charge mobility, a pivotal parameter in the space charge analysis model for oil-pressboard insulation of converter transformer under DC electric fields, predominantly relies on theoretical or empirical data. The prevalent omission of empirical, measurement-based evaluations, combined with the neglect of temperature and electric field intensity effects, introduces uncertainties in the calculation of electric field and charge dynamics. Grounded on the principles of the electroacoustic pulse technique for space charge measurements, our investigation established a temperature-controlled platform to determine the charge-charge mobility in oil and pressboard insulation mediums. Utilizing diverse oil-pressboard insulation systems, this study identified the temporal patterns of both positive and negative charge mobilities and unravelled the mechanisms modulated by temperature and electric field intensity: (1) with increasing temperatures (from 20 °C to 80 °C) and intensifying electric field strengths (from 5kV mm−1 to 25kV mm−1), the charge mobility within transformer oil and pressboard exhibits a rising trend. Notably, temperature variations exert the most significant influence, yielding amplifications up to 24.8 times. (2) The intrinsic properties of different transformer oils and oil-impregnated pressboards result in pronounced differences in their charge transport behaviors. Specifically, naphthenic-based oil demonstrates enhanced charge mobility relative to its paraffin-based counterpart. In contrast, transformer oils with higher kinematic viscosities exhibit diminished charge mobility compared to those with lower viscosities. (3) A linear relationship is observed between the oil absorption rate and electrical conductivity, aligning closely with the insulating pressboard’s charge mobility. The evaluation of electric field and interface charge dynamics in oil-pressboard insulation under both DC and polarity-reversed conditions revealed that the electric field decay in naphthenic-based oil is more rapid than in paraffin-based oils. Moreover, both the magnitude and rate of interface charge accumulation in naphthenic-based oils exceed those in paraffin-based variants, further validating the accuracy of our charge mobility measurements and ensuing analysis.

Morphology and structural properties of thin rubrene crystallites grown on graphite

Abstract Crystallization of rubrene, progressing from an amorphous phase to a triclinic meta-stable and ultimately to the orthorhombic stable phase, offers broad applications not only in organic electronic devices but also for in-depth studies of optical and electronic properties, including exciton distribution and dynamics. We investigate the crystallization of rubrene on highly oriented pyrolytic graphite (HOPG), aiming at the growth of the preferred rubrene orthorhombic phase, which has been reported to have one of the highest charge mobilities in organic semiconductors. This is achieved through controlled heating and enhanced partial pressure. Through precise control of the initial deposition on the substrate, we investigate the growth habit of rubrene crystals by high-rate heat treatment beyond the second crystallization temperature. Furthermore, this work addresses thermal stability and photodegradation across various morphologies.

Origin of Oxidation Variations in Ambient-Stable β-InSe.

Understanding and controlling the oxidation of layered materials remain critical issues in the final stages of their practical application in devices. Layered materials achieve a band gap by removing inversion symmetry. However, the oxidation process becomes complex, and the oxidation of these materials is not yet fully understood. As a representative example, InSe has attracted considerable attention due to its high charge mobility and Si-like band gap. However, conflicting observations such as oxidation by Se and In have been reported, including contrasting assessments of the oxidation susceptibility. In this study, we report in situ spectroscopy results detailing the origins of various oxidation pathways. We observed that at low defect densities the reduced reaction barrier of InSe due to Se vacancies leads to oxygen adsorption, while as defects increase, the lower electronegativity of In rises as a new pathway for oxidation. At low defect density, the bulk layer was more energetically favored for oxygen adsorption, allowing oxygen to diffuse to a depth sufficient to form pseudoheterojunctions and making the surface layer seemingly resistant to oxidation. Our results provide an answer to why the resulting diversity of optical responses is expected to increase as well as strategies to achieve gas stability.

Structurally Compact Penta(N,N‐diphenylamino)corannulene as Dopant‐free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells

AbstractHole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor‐(DPA)5, characterized by a bowl‐shaped core with symmetric five diphenylamine groups. Compared to already‐known HTMs, the bowl‐shaped and relatively compact structure of cor‐(DPA)5 facilitates intermolecular π–π interactions, promotes film formations, and enhances charge transport. Consequently, the cor‐[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro‐OMeTAD and cor‐OMePTPA, our newly synthesized cor‐(DPA)5 HTM is free from any ionic dopants. As a result, the dopant‐free cor‐[DPA(2)]5‐based PSC demonstrates an impressive efficiency of 24.01 %, and exhibits outstanding operational stability. It retains 96 % after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Structurally Compact Penta(N,N-diphenylamino)corannulene as Dopant-free Hole Transport Materials for Stable and Efficient Perovskite Solar Cells.

Hole transport materials (HTMs) are essential for improving the stability and efficiency of perovskite solar cells (PSCs). In this study, we have designed and synthesized a novel organic small molecule HTM, cor-(DPA)5, characterized by a bowl-shaped core with symmetric five diphenylamine groups. Compared to already-known HTMs, the bowl-shaped and relatively compact structure of cor-(DPA)5 facilitates intermolecular π-π interactions, promotes film formations, and enhances charge transport. Consequently, the cor-[DPA(2)]5 HTM exhibits high charge mobility, exceptional hydrophobicity, and a significantly elevated glass transition temperature. Superior to previously reported HTMs such as spiro-OMeTAD and cor-OMePTPA, our newly synthesized cor-(DPA)5 HTM is free from any ionic dopants. As a result, the dopant-free cor-[DPA(2)]5-based PSC demonstrates an impressive efficiency of 24.01 %, and exhibits outstanding operational stability. It retains 96 % after continuous exposure to 1 sun irradiation for 800 hours under MPP (maximum power point) tracking in ambient air. These findings present a structurally compact novel HTM and exemplify a new approach to the molecular design of HTM for the development of stable and effective PSCs.

Carbon dots modified hydrange-shaped ZnCo(OH)F used as a flexible electrode for sensitive detection of dopamine and uric acid

Dopamine (DA), widely recognized as the most prevalent catecholamine neurotransmitter in the brain, functions as a vital regulator of various physiological processes within the central nervous system. Meanwhile, uric acid (UA) serves as the terminal product of purine metabolism, and hyperuricemia emerges as a significant risk factor for gout, with a steep escalation in risk as blood uric acid levels surge. Consequently, monitoring the concentrations of DA and UA in biological fluids is crucial not only for the treatment of related disorders but also for enhancing disease prevention strategies. In this work, the blooming hydrangea shaped ZnCo(OH)F/carbon dots (CDs) composite was grown on carbon cloth (CC) substrate by a simple hydrothermal method, which was used as a flexible sensor for the detection of DA and UA. The unique open structure and morphologic adjustment strategy of ZnCo(OH)F/CDs/CC provided a large surface area and highly exposed active site. After screening the experimental variables that affect the sensor performance, the optimal ZnCo(OH)F/CDs/CC flexible electrode achieved individual and simultaneous detection for DA and UA in the concentration ranges of 1.0220.0 µM and 1.0500.0 µM, the detection limits (LOD) of DA and UA were 0.0129 and 0.044 μM, respectively (S/N=3). In addition, the sensor exhibited good repeatability, stability and selectivity, realizing the detection of DA and UA in human serum with recovery rate of 95.20 % 105.3 %. Also, the density functional theory (DFT) calculations were used to explore the interaction between electrode material and detected substrate. A simple hydrothermal method was utilized to grow the ZnCo(OH)F/CDs composite onto the CC substrate. The presence of F− in ZnCo(OH)F can increase the charge mobility and improve the conductivity. ZnCo(OH)F/CDs/CC as flexible electrode material can determine DA and UA simultaneously in human serum with a satisfactory recovery rate. This flexible sensor has a broad application prospect in the manufacture of wearable devices.

Electrostatic-elastic coupling in colloidal crystals

Abstract Electrostatic-elastic coupling in colloidal crystals, composed of a mobile Coulomb gas permeating a fixed background crystalline lattice of charged colloids, is studied on the continuum level in order to analyze the lattice-mediated interactions between mobile charges. The linearized, Debye-H{" u}ckel-like mean-field equations incorporating a minimal coupling between electrostatic and displacement fields imply an additional effective attractive interaction between mobile charges. For small screening lengths, the interactions between like mobile charges exhibit colloid lattice-mediated effective interaction, ranging from weak to strong attraction, while for large screening lengths the lattice mediated interaction is purely attractive. Continuum theory incorporating the standard lattice elasticity and electrostatics of mobile charges, augmented by the minimal electrostatic-elastic coupling terms, can serve as a baseline for more detailed microscopic models.

Synergistic Effects of Solid and Solvent Additives on Film Morphology Enable Binary Organic Solar Cells with Efficiency of Over 19%

AbstractRegulating the film morphology features of the photoactive layer is critically important for developing high‐performance organic solar cells (OSCs). Adding solvent or solid additives is widely used to realize fine‐tuned film morphology. However, most high‐performance OSCs are processed only using single component additive, either solvent additive or solid additive. Herein, two structurally similar analogs of 1‐benzothiophene (BT) and benzo[1,2‐b:4,5‐b']dithiophene (BDT) are applied as volatilizable solid additives and are used with the well‐known solvent additive 1‐chloronaphthalene (CN), respectively. Comprehensive morphology analysis revealed that the addition of BT with better volatilization can promote the formation of stronger molecular packing and desirable phase separation, resulting in higher charge mobility and more efficient charge separation. However, the insufficient volatilization of BDT caused excessive aggregation, leading to severe recombination. Consequently, the PMZ‐10:Y6 based binary OSCs treated with the hybrid additives of CN and BT delivered a notable efficiency of 19.03%, which is one of the best values of the Y6‐based binary devices reported so far. Overall, this work highlights the importance of hybrid additive strategy and the reasonable combination of solid and solvent additives in further advancing the development of OSCs field.

Aqueous fibrous membrane electrolyte for ultrathin flexible Zinc-air batteries

Membrane electrolytes are key to constructing planar energy storage devices of low thickness and high flexibility, requesting simultaneous optimization of ionic conductivity and mechanical stability. Herein, aqueous phase electrospinning (APE) was implemented to co-spin polyvinyl alcohol and pullulan polysaccharide for fabricating crosslinked fibrous membrane electrolytes. While the hydroxyl-rich polymeric backbone grafted with quaternary ammonium endows a strong hydrogen-bonding network affording a large ionic conductivity of 30.2 mS cm−1, the cellulose-braced fibrous structure manifests a high tensile strength of 4.6 MPa. What’s more, the porous structure of the membrane electrolyte with enhanced charge mobility and uniformity helps to guide homogeneous Zn plating/stripping with suppressed dendrite growth. As a result, the assembled ultrathin flexible ZAB delivers a superb round-trip energy efficiency of 59.8 %, a maximum power density of 102 mW cm−2 and a long-term cycling stability over 100 h at 5 mA cm−2. By innovating the concept and methodology of aqueous fibrous membrane electrolytes, this study opens up a new chapter on the development of solid electrolytes in aqueous battery systems for powering wearable electronics.

Security-Economic Driven Coordinated Operation of the Mobile Charging Robots Cluster and Active Distribution Networks

Security-Economic Driven Coordinated Operation of the Mobile Charging Robots Cluster and Active Distribution Networks

Multi-Agent Deep Reinforcement Learning for Blockchain-Based Energy Trading in Decentralized Electric Vehicle Charger-Sharing Networks

With The integration of renewable energy sources into smart grids and electric vehicle (EV) charger-sharing networks is essential for achieving the goal of environmental sustainability. However, the uneven distribution of distributed energy trading among EVs, fixed charging stations (FCSs), and mobile charging stations (MCSs) introduces challenges such as inadequate supply at FCSs and prolonged latencies at MCSs. In this paper, we propose a multi-agent deep reinforcement learning (MADRL)-based auction algorithm for energy trading that effectively balances charger supply with energy demand in distributed EV charging markets, while also reducing total charging latency. Specifically, this involves a MADRL-based hierarchical auction that dynamically adapts to real-time conditions, optimizing the balance of supply and demand. During energy trading, each EV, acting as a learning agent, can refine its bidding strategy to participate in various local energy trading markets, thus enhancing both individual utility and global social welfare. Furthermore, we design a cross-chain scheme to securely record and verify transaction results of energy trading in decentralized EV charger-sharing networks to ensure integrity and transparency. Finally, experimental results show that the proposed algorithm significantly outperforms both the second-price and double auctions in increasing global social welfare and reducing total charging latency.

Transient Exciton-Charge Interconversion in Single-Crystal Hybrid Perovskites.

Ultrafast oscillatory transient absorption (TA) dynamics are observed in single crystals of hybrid organic-inorganic perovskite (CH3NH3)PbX3 with X = I, Br, Cl. High-density photoinduced charges, low binding energy of the excitons, efficient generation and high mobility of charges, and long diffusion length of both excitons and charges led to transient interconversion between excitons and charges with high efficiency, which is responsible for the oscillatory TA dynamics at re-excitation by the probe pulses. The pump pulses initiated a quasi-equilibrium scheme of coexisting excitons and charges with high densities, the probe pulse triggered a perturbation through interconversion between these two kinds of excited "particles," which was overlapped on the intrinsic exciton relaxation dynamics, producing an oscillatory modulation with time delay. This not only reveals important photoelectronic processes with determined time scales, but also supplies physics for applications of this group of materials.

Non‐Electron Withdrawing Unit Copolymerization to Enhance Photo‐Stability of Thiophene‐Based Organic Solar Cells

The impact of non‐electron withdrawing unit copolymerization on photostability of fullerene‐based organic solar cells is investigated using two donor polymers namely: benzodithiophene‐4,8‐dione (BDD) unit copolymerized with α‐quaterthiophene (4 T) unit (PBDD4T) and poly‐3‐hexyl‐thiophene (P3HT). The optical and electrochemical properties of the polymers reveal a deeper highest occupied molecular orbital (HOMO) and broader absorption in PBDD4T in comparison to P3HT owing to the BDD copolymerization. The copolymer achieves a higher power conversion efficiency (PCE) compared to the P3HT‐based device due to its higher VOC and Jsc that resulted from its deeper HOMO level and broader absorption. The photostability study reveals that PBDD4T‐based devices lost 14% of its initial PCE relative to the 48% reduction in PCE for P3HT‐based devices after 7 h of irradiation. Further investigation into the reasons behind the difference in the photostability suggests that photooxidation and recombination induced by irradiation in PBDD4T‐based devcie are suppressed by BDD‐copolymerization, maintaining better stability. In contrast, P3HT:PC71BM‐based solar absorber shows bimolecular recombination due to photoaging processes, which have negatively impacted the device stability. The reduction in stability of both devices is evident by lower photogenerated current attributed to reduced charge mobility and increased surface roughness.

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.

Isolation and characterisation of monolayer phosphorene analogues

Atomically thin group IV monochalcogenides or phosphorene analogues are a promising family of materials. Theoretical calculations predict that monolayers (MLs) should be semiconducting, ferroelectric and ferroelastic at room temperature, exhibit large charge mobilities and large non-linear optical response. Yet, experimental studies of these systems are scarce because of the difficulty to produce such MLs. Here we focus on two members of this family: GeSe and SnS. We demonstrate a simple mechanical exfoliation method to produce ML samples on gold substrates. We observe the evolution of the Raman scattering as a function of layers and the anisotropic optical response from reflectance contrast measurements. To the best of our knowledge this is the first report of mechanical exfoliation down to the ML of these materials and the first realisation of ML GeSe.

Influence of terminal moiety on PCE of DSSCs: An In Silico study based on triazatruxene-benzothiadiazole dye

Our study utilized an experimentally synthesized dye as a reference molecule, employing a donor-π linker-acceptor (D-π-A) framework for organic solar cells. The molecule featured a triazatruxene group linked with alkyl branches as the donor and ethynyl benzoic acid as the acceptor, connected through a derivative of benzothiadiazole as the π linker. To improve optoelectronic and photovoltaic properties, ten theoretically designed dyes (ZA1–ZA10) are proposed, differing from the reference (R) by modifying the terminal acceptor moiety. Various quantum analyses, including frontier molecular orbitals, optical properties, reorganization energies, binding energies, transition density matrices (TDM), molecular electrostatic potential (MEP), dipole moment, and density of states were carried out at DFT/B3LYP/6-31G(d,p). Ground state geometries revealed a co-planar morphology in ZA1–ZA10, facilitating efficient charge transportation. TDM and MEP illustrated improved electronic transitions in the excited states. Computational analyses revealed superior photovoltaic properties of ZA1–ZA10. Notably, ZA5 exhibited the most significant redshift (1021 nm) in absorption, lowest bandgap (1.44 eV), smallest transition energy (1.21 eV), least binding energy (0.23 eV), and improved charge mobilities. Results from the adsorption of ZA1-ZA10 on the TiO2 layer confirmed their anchoring potential and effective injection of electrons to anatase (TiO2)9. These significant outcomes promise the potential and novelty of our designed dyes for higher power conversion efficiencies (PCE) in dye-sensitized solar cells (DSSCs).

Microscopic analysis of low but stable perovskite solar cell device performance using electron spin resonance

Perovskite solar cells have attracted much attention as next-generation solar cells. However, a typical hole-transport material, spiro-OMeTAD, has associated difficulties including tedious synthesis and high cost. To overcome these shortcomings, an easily synthesized and low-cost hole-transport material has been developed: HND-2NOMe. Although HND-2NOMe has high local charge mobility because of the quasi-planar structure, its lower device performance is a weak point, the cause of which has not yet been clarified. Here, we analyse the source of the lower performance by clarifying the internal states from a microscopic viewpoint using electron spin resonance. We observe hole diffusion from perovskite to HND-2NOMe under dark conditions, indicating hole barrier formation at the perovskite/HND-2NOMe interface, leading to lower performance. Although such a barrier is formed, less hole accumulation for the HND-2NOMe-based cells under solar irradiation occurs, which is related to the stable performance. The sources of the lower but stable performance are crucially important for providing guidelines for improving the device performance.