Carrier Conduction Research Articles

Nanostructure-Dependent Electrical Conductivity Model Within the Framework of the Generalized Effective Medium Theory Applied to Poly(3-hexyl)thiophene Thin Films.

One of the key parameters characterizing the microstructure of a layer is its degree of order. It can be determined from optical studies or X-ray diffraction. However, both of these methods applied to the same layer may give different results because, for example, aggregates may contribute to the amorphous background in XRD studies, while in optical studies, they may already show order. Because we are usually interested in the optical and/or electrical properties of the layers, which in turn are closely related to their dielectric properties, determining the optical order of the layers is particularly important. In this work, the microstructure, optical properties and electrical conductivity of poly(3-hexyl)thiophene layers were investigated, and a model describing the electrical conductivity of these layers was proposed. The model is based on the generalized theory of the effective medium and uses the equation from the percolation theory of electrical conductivity for the effective medium of a mixture of two materials. The results indicate a key role of the aggregate size and limited conductivity of charge carriers, mainly due to structural imperfections that manifest themselves as an increase in the number of localized states visible in the subgap absorption near the optical absorption edge. The critical value of the order parameter and the corresponding values of the Urbach energy, excitonic linewidth and band gap energy are determined.

Comparing the Efficacies of Electrospun ZnO and TiO2 Nanofibrous Interlayers for Electron Transport in Perovskite Solar Cells

ZnO and TiO2 are both well-known electron transport materials. Their comparison of performance is considered advantageous and novel. Therefore, a viable electrospinning route was considered for the development of highly polycrystalline TiO2 and ZnO nanofibers as an electron transport material (ETM) for perovskite solar cells. The materials were well-characterized in terms of different analytical techniques. The X-ray diffraction detected polycrystalline structural properties corresponding to TiO2 and ZnO. Morphological analysis by scanning electron microscopy revealed that the nanofibers are long, uniform, and polycrystalline, having a diameter in the nanometer range. Optoelectronic properties showed that TiO2 and ZnO exhibit absorption values in the ultraviolet and visible ranges, and band gap values for TiO2 and ZnO were 3.3 and 3.2 eV, respectively. TiO2 bandgap and semiconductor nature were more compatible with Electron Transport Layer (ETL) compared to ZnO. Electrical studies revealed that TiO2 nanofibers have enhanced values of conductivity and sheet carrier mobility compared to ZnO nanofibers. Therefore, higher photovoltaic conversion efficiency was achieved for TiO2 nanofibers (10.4%) compared to ZnO (8.5%).

Localized Transformation of 2D Perovskite by Protonated Metformin for Efficient Carbon‐Based Perovskite Photovoltaic and Photo‐Charging Applications

AbstractDimensional engineering is promising for achieving a high power conversion efficiency (PCE) and long‐term stability of perovskite solar cells (PSCs). However, insulated organic spacers in 2D perovskites often severely hinder carrier transport between the internal layers of devices. Herein, the “protonation‐induced localized transformation of 2D perovskites” is proposed to overcome the low carrier transport and conductivity of 2D/3D perovskite heterojunctions. Metformin, with its multiple amine groups and a substantial difference between its pKa value and perovskites, is protonated in an acidic environment or directly converted into the hydrochloride salt for the surface passivation of methylammonium lead iodide. This leads to the transformation of disorderedly oriented layered 2D perovskite into vertically oriented ones at grain boundaries. Consequently, the PCE of a carbon‐based PSC treated by protonated metformin increased considerably, reaching an optimal level of 14.13%. Additionally, applying this passivation strategy to a planar device (ITO/4PADCP/perovskite/PCBM/BCP/Ag) increased PCE from 20.82% to 22.09%, confirming the applicability of the strategy. To demonstrate the practical stability, an integrated PSC–supercapacitor device is assembled, which shows good cycling stability. This article introduces a novel method to improve carrier transport in 2D/3D perovskite heterojunctions, promoting the extensive utilization of dimensional engineering.

Molecular Break Junction: A Stage for Redox Transformations

AbstractAn exceptionally brilliant strategy to miniaturize electronic devices is to employ a single‐molecule between two electrodes for carrier conduction at single‐molecule break junctions (SMBJ). To understand the intrinsic mechanisms of operation at these junctions, extremely crucial is to study physical, chemical, and electrochemical properties employing single‐molecules at SMBJs. Further, redox‐based transformations at the nano‐junction could be achieved electrochemically to allow efficient switching between different redox states of a single‐molecule, showcasing the possibility of maneuvering transport properties with on‐off states of the molecule. Herein, are presented the fundamentals of SMBJs, and the electrochemically influenced transformations or switching of organic molecules pursued at SMBJs. Such an understanding of electrochemical phenomena at the nanoscale dimension could bridge the knowledge gap between macroscopic electronic circuits and single‐molecule electronic circuits, whereby the feasibility of switching between the states could maneuver the electronic properties as well as other photophysical parameters.

Quantifying Heterogeneous Interface Effect of Fe3O4(111)/C for Enhanced Low-Frequency Electromagnetic Wave Absorption

How to tailor electromagnetic parameters of multi-component materials is the fundamental issues for low-frequency electromagnetic wave absorbers (EMA). However, there remains a challenge to accurately elucidate the impact of respective components at heterogeneous interfaces on the EMAs, not to mentioning the further quantitative contribution of the interfacial effect to the electromagnetic loss. In this paper, we for the first time separated the Fe3O4(111)/C heterogeneous interface of Fe3O4@C via a controllable interfacial separation strategy, meanwhile ensuring the consistent microstructure and the ratio of each component, as well as the unchanged macroscopic structure of the particles. Once all potential influences on electromagnetic parameters have been independently studied, the unique difference in heterogeneous interfaces enabled us to quantitatively evaluate the effect of them on electromagnetic parameters. Both experimental and density functional theory (DFT) calculation results consistently demonstrate that the Fe3O4(111)/C heterointerface increases carrier concentration and conductivity, thereby enhancing the imaginary part of the dielectric constant. Very distinguished from traditional interfacial polarisation mechanism presented in previous publications, this study introduces a novel interfacial loss mechanism primarily characterized by conductivity loss, which is rigorously investigated in a quantitative way. This discovery offers a novel approach for designing controllable heterogeneous interfaces and manipulating electromagnetic parameters in multicomponent EMAs.

Enhancing hole-transport efficiency in (CH3NH3)2CuClxBr4-x perovskite solar cells through functionalization of multi-walled carbon nanotubes

This study addresses the conductivity limitation of conventional hole-transporting layers (HTLs) like Spiro-OMeTAD in perovskite solar cells. We integrate functionalized multi-walled carbon nanotubes (MWCNTs) into Spiro-OMeTAD and examine the impact of chemical oxidation/functionalization of MWCNTs on their application in perovskite solar cells. Various ratios of H2SO4/HNO3 mixture were employed to functionalize MWCNTs, with FTIR analysis confirming functional group attachments on the nanotube walls. Raman spectroscopy was utilized to analyze defect formation in the MWCNTs, while FESEM images displayed both the tubular structure and morphological alterations resulting from functionalization. XRD analysis was conducted to examine the structural variances resulting from different functionalization ratios. A lead-free copper-based perovskite (CH3NH3)2CuBr4-xClx (x = 0.5), synthesized via a straightforward solution method, served as the active material for solar cells. The XRD assessment of the active material confirmed perovskite formation, with morphological analysis revealing a layered structure. Diffuse Reflectance Spectroscopy (DRS) measurements yielded a bandgap of approximately 1.86 eV for the perovskite. Dark I–V measurements were executed for Spiro-OMeTAD films incorporated with pure and functionalized MWCNTs, showcasing improved conductivity attributed to charge carrier conduction via defect passivation. Hybrid solar cells were fabricated with structures such as TiO2/(CH3NH3)2CuBr4-xClx (x = 0.5)/Spiro-OMeTAD/Ag, and TiO2/(CH3NH3)2CuBr4-xClx (x = 0.5)/functionalized MWCNTs/Spiro-OMeTAD/Ag. These cells demonstrated enhanced stability, retaining over 65 % of their initial efficiency after 10 days of storage, attributed to improved moisture permeability inferred from contact angle measurements and XRD analysis. Photovoltaic characterization revealed significant improvements in fill factor (∼70 %), short-circuit current density (2.94 mA), open-circuit voltage (0.70 V), and power conversion efficiency (PCE) (1.6 %) for the FTO/TiO2/(CH3NH3)2CuCl0·5Br3.5/Spiro-MWCNT-1/Ag device.

Preparation of high temperature proton exchange membrane through covalent organic framework doped polyvinylidene fluoride nanofibers

Covalent organic framework (COF) exhibits the great potential to promote proton conduction under low relative humidity for proton exchange membranes (PEMs). In this research, quick and stable proton conduction has been achieved since the prepared COF and polyvinylidene fluoride (PVDF) nanofibers are believed to constitute successive proton conduction channels. The PVDF-COF nanofibers membrane is prepared through the in-situ growth of COF along PVDF nanofibers. The fine compatibility can drive the stable combination of COF with the PVDF nanofibers in PVDF-COF nanofibers. Most importantly, the fibrous PVDF nanofibers accelerate proton conduction through confining the proton conduction pathways. Additionally, ionic liquids of 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-butyl-3-methylimidazole hexafluorophosphate (BmimPF6) as proton conduction carriers have been introduced to accelerate proton conduction in the prepared PVDF-COF/BmimCl/PA and PVDF-COF/BmimPF6/PA membranes. Phosphoric acid (PA) molecules are combined by COF and ionic liquid cations with the formation of intermolecular hydrogen bonds. As a result, the PVDF-COF/BmimPF6/PA membrane exhibits the proton conductivity of (1.81 ± 0.07) × 10−1 S/cm at 160 °C. The long-term proton conductivity stability is determined, deriving from the proton conductivities of 1.77×10−2 S/cm at 80 °C and 1.42×10−2 S/cm at 110 °C in the 400 h non-stop measurement. The single fuel cell equipped with the PVDF-COF/BmimPF6/PA membrane represents the open circuit voltage of 0.927 V and the peak power density of 178.8 mW/cm2 at 100 °C, 0.907 V and 326.5 mW/cm2 at 120 °C.

Uniform Diffusion of Cooper Pairing Mediated by Hole Carriers in Topological Sb2Te3/Nb.

Spin-helical Dirac Fermions at a doped topological insulator's boundaries can support Majorana quasiparticles when coupled with s-wave superconductors, but in n-doped systems, the requisite induced Cooper pairing in topological states is often buried at heterointerfaces or complicated by degenerate coupling with bulk conduction carriers. Rarely probed are p-doped topological structures with nondegenerate Dirac and bulk valence bands at the Fermi level, which may foster long-range superconductivity without sacrificing Majorana physics. Using ultrahigh-resolution photoemission, we report proximity pairing with a large decay length in p-doped topological Sb2Te3 on superconducting Nb. Despite no momentum-space degeneracy, the topological and bulk states of Sb2Te3/Nb exhibit the same isotropic superconducting gaps at low temperatures. Our results unify principles for realizing accessible pairing in Dirac Fermions relevant to topological superconductivity.

Thermoelectric performance of Cu2SnSe3-AgInSe2 solid solutions with Sn vacancy

Diamond-like compound Cu2SnSe3 has garnered widespread attentions in the field of thermoelectricity due to its considerable performance and non-toxic/earth-abundant characters. However, the high lattice thermal conductivity and low carrier concentration of pristine Cu2SnSe3 pose a significant barrier for further thermoelectric performance optimization. In this study, we make a series of Cu2SnSe3 based solid solutions with AgInSe2 to reduce the lattice thermal conductivity, while simultaneously modulating the carrier concentration by introducing Sn vacancies. This approach leads to a significant enhancement in thermoelectric performance of Cu2SnSe3, finally achieving a maximum zT value of 1.02 in the (Cu2Sn0.99Se3)0.8 (AgInSe2)0.2 sample at 773 K.

Selective Control of Electric Charge of Weyl Fermions in Pyrochlore Iridates.

Weyl fermions can exhibit exotic phenomena due to their magnetic charge in momentum space, while Weyl nodes are usually located away from Fermi energy, which forms electron or hole pockets as the electric charges. Previous studies have mostly focused on the magnetic charge, however, the electric charges are rarely explored. Here, the intriguing Hall responses arising from the interplay between magnetic and electric charges of Weyl fermions in pyrochlore iridates are reported. Explicitly, unexpected linear scaling is observed between the anomalous Hall conductivity and Hall carrier density in strained Nd2Ir2O7 thin films, and its slope shows a sign change approaching the Néel temperature of Nd. Theoretical calculations unveil that the cluster magnetic multipoles induce local energy inversion of Weyl nodes, which alters the electric charge of Weyl fermions and accounts for the observed nontrivial Hall responses. Moreover, the correlation between the magnetic and electric charges is further probed by voltage-controlled hydrogenation, which leads to the suppression of the anomalous Hall effect through electron filling. This work not only reveals the essential role of the both magnetic and electric charges of Weyl fermions, but also demonstrates the hydrogenation as an effective tuning knob in exploring correlated topological properties.

Integrating the independent granular charge carriers into microbial fuel cell: From performance to mechanism analysis

The mutual benefits between electroactive bacteria (EAB) and non-EAB promote bioenergy recovery in microbial fuel cell (MFC), while competition between functional and non-functional bacteria on electrodes hinders further performance improvement. Introducing non-electrode conductive carriers into MFC may reduce contact resistance and alleviate interspecies competition. In this study, three-dimensional spherical biochar (BC) granules as independent microbial and charge carriers are introduced into anode chamber of an MFC without direct contact with the electrode (carbon cloth, CC) creating CC-BC-MFC. CC-BC-MFC achieves superior power density of 15 ± 1.4 W m−3 compared to CC-MFC (12 ± 1.4 W m−3) and CC/BC-MFC (10 ± 1.2 W m−3, where BC directly contacts CC). Higher effluent quality highlights the outstanding contribution of adequate biomass in effective containment treatment. Smaller internal resistance and higher coulombic efficiency are obtained in CC-BC-MFC by relieving microbial competition at anode. Syntrophic growth between Geobacter (69.4 %) and Methanosarcina (98 %) is established on BC in CC-BC-MFC, with high expression of Geobacter-associated pili genes and acetotrophic and CO2-reducing methanogenic genes associated with methanogens. Therefore, incorporating BC as flexible and independent charge carriers can reduce internal resistance, provide adequate habitat, alleviate microbial competition at anode, and offer a feasible strategy for MFC in wastewater treatment.

Effect of micromechanical properties of commercial grade electrolytic copper foils on lithium-ion batteries

As the carrier and electrical conduction component of positive and negative electrode materials, current collector plays an important role in lithium-ion batteries(LIBs). With the industrial application of silicon-doped anode materials with higher gram capacity, the huge volume change of silicon-doped anode materials puts forward higher requirements for the mechanical properties of copper foils(CFs). It is of great significance to study the effect of micromechanical properties on LIBs for the application screening of CFs. In this article, the effects of micromechanical properties of conventional tensile strength(CTS), high tensile strength(HTS) and ultra-high tensile strength(UHTS) commercial grade electrolytic CFs on LIBs were studied. The tensile strength of CTS, HTS and UHTS was 316.88 MPa, 464.74 MPa and 673.43 MPa, respectively; the elongation were 6.49 %, 5.38 % and 4.47 %, respectively. The surface morphology and XRD tests show that the microstructure such as grain size and dislocation density are the key factors affecting the mechanical properties of CFs. And under the same conditions, the main factors affecting bonding strength of electrode are microstrain and residual stress of CFs rather than surface roughness. The larger the microstrain and residual stress of CFs, the worse the interface bonding strength between CFs and coating materials, and the larger the corresponding interface charge transfer impedance, which is well confirmed by DCR and EIS. The charge-discharge test results show that the mutual stress between CFs and coating materials also have a great influence. The lower elastic modulus and microscopic stress of CFs can better eliminate the expansion pressure and contraction tension of coating materials, thereby reducing the resistance and overpotential in the process of lithium-ion diffusion, and achieving higher capacity under high rate system. The retention rates of three CFs after 500 cycles at 25℃ and 45℃ were 25-CTS(92.64 %), 25-HTS(90.63 %) 25-UHTS(89.11 %), and 45-CTS(82.17 %), 45-HTS(82.14 %), 45-UHTS(80.77 %), respectively, which indicates that the difference in mechanical properties of CFs have an important influence on long-term application of LIBs. The primary cause of the variation in electrochemical performance, aside from copper foil’s conductivity, is the phase interface shift brought on by the microstress of the material; and the overpotential caused by the phase interface force cannot be ignored.

SnIn4S8/FeNi2P Z-scheme heterojunction hollow nanorods for photocatalytic hydrogen production

Climate change and natural disasters have stimulated the exploration of renewable energy, photocatalytic hydrogen production utilizing solar energy is considered an effective way. In this study, hollow FeNi2-MIL-88 nanorods were synthesized by the hydrothermal method, and then FeNi2P was obtained by gas phase phosphorization. Finally, SnIn4S8 was utilized to coat the surface of FeNi2P through an in-situ growth method to obtain rod-like SnIn4S8/FeNi2P. The results showed that the hydrogen production of SnIn4S8/FeNi2P reached 18083.93 μmol/g within 3 h. And SnIn4S8/FeNi2P showed good stability. The photocurrent response spectra and electrochemical impedance spectra confirmed that SnIn4S8/FeNi2P had good carrier conductivity and effectively inhibited the reorganization of photogenerated carriers. The modification of SnIn4S8 enabled the construction of a Z-scheme heterojunction between SnIn4S8 and FeNi2P. It provided more active sites and promoted the separation of photogenerated carriers, ultimately improving the hydrogen production performance of the SnIn4S8/FeNi2P photocatalyst. It would offer essential insights into the design and development of efficient MOFs-derived photocatalysts.

Characterization of ZnSe Thin Film Electrodeposited at Room Temperature in Aqueous Medium without Complexing Agents

This study includes a simple electrodeposition technique for the fabrication of ZnSe thin film at room temperature and in an aqueous medium without additional complexing agents. Comprehensive analysis of the optical, structural, and morphological characteristics of the ZnSe thin film electrodeposited onto an ITO substrate was conducted using UV-Vis spectrometry, X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and field emission–scanning electron microscopy (FE–SEM). Furthermore, the photoelectrochemical properties were evaluated through current-time (I-t) measurements and electrochemical impedance spectroscopy (EIS) under light on/off conditions. Mott-Schottky analysis was also performed to determine the conductivity type, carrier concentration, and flat band potential of the ZnSe thin film. Structural investigations revealed that the ZnSe thin film has a hexagonal structure, the longitudinal optical (LO) phonon mode, stretching and bending vibration modes of Zn-Se. The carrier type of the ZnSe thin film was identified as n- type semiconductor and photoelectrochemical measurements exhibited a photoresponse under the light illumination

Structural, electrical, leakage current, and magnetic characteristics of double perovskite Nd2NiTiO6

AbstractThis study investigates the structural, electrical, leakage current, and magnetic characteristics of the double perovskite material Nd2NiTiO6 synthesized through the sol–gel citrate auto‐ignition method. The Rietveld refinement of the X‐ray diffraction patterns confirmed a monoclinic symmetry (space group P21/n) with an ordered arrangement of alternate NiO6 and TiO6 octahedra. Impedance spectroscopic analysis exhibited the material's non–Debye‐type relaxation mechanism and semi‐conductive nature. AC conduction analysis revealed that the conduction of charge carriers occurs via the nonoverlapping small polaron hopping mechanism, consistent with Mott's variable range hopping model. Temperature‐ and frequency‐dependent dielectric measurements were interpreted using the Maxwell–Wagner interfacial polarization model. The analysis of thermal‐ and field‐dependent leakage currents established that conduction is ohmic, which the Schottky barrier model explains. Studies on magnetization ruled out the presence of magnetic ordering connected to indirect interaction between Ni2+ ions via Ti4+ ions and the rare‐earth cation (Nd3+) moment.

Assessment of the Contribution of Minority Carriers to the Thermo-electromotive Force of Thermoelectric Generators in the Case Where the Electrical Conductivity of the Majority Carriers Remains Very Large Compared to that of the Minority Carriers

Assessment of the Contribution of Minority Carriers to the Thermo-electromotive Force of Thermoelectric Generators in the Case Where the Electrical Conductivity of the Majority Carriers Remains Very Large Compared to that of the Minority Carriers

Upper limit of mobility and concentration of charge carriers in fluoride superionic conductors with fluorite and tysonite structures

Within the framework of a crystal-physical model, the maximum values of mobility and concentration of charge carriers in fluoride superionic conductors belonging to the structural types of fluorite (CaF2, SrF2, BaF2, PbF2) and tysonite (LaF3) were calculated. It has been shown that the upper limit of ionic conductivity, mobility and charge carrier concentration in the crystalline state of fluoride superionics is 4 ± 1 S/cm, (5 ± 1) × 10–3 cm2/(сВ) и (5 ± 2) × 1021 cm–3 (10 ± 4% of the total fluoride ions), respectively.

Junction-Controlled-Diode-Embedded SiC-MOSFET for Improving Third Quadrant and Turn-On Characteristics

In this paper, we propose a novel 1200V SiC MOSFET featuring the embedded junction-controlled-diode (JCD-MOSFET) and demonstrate its static and dynamic characteristics through TCAD simulations. Without sacrificing blocking and conduction performance, the adoption of JCD can effectively reduce knee voltage to 1.7V based on unipolar carrier conduction mode. Due to the reduced peak reverse recovery current and reverse recovery charge, the JCD-MOSFET achieves 30.8% lower turn-on losses than conventional MOSFET. Meanwhile, the fabrication process for the JCD-MOSFET is the same as conventional MOSFET without an extra mask. This proposed JCD-MOSFET prototype shows great potential in target applications in the near future.

Carbon-based conductive carriers promote coupled Fe(II)-driven autotrophic and heterotrophic denitrification of wastewater with low C/N ratios

Denitrification of wastewater with a low organic carbon to NO3--N ratio (C/N ratio) faces challenges due to slow rates and low efficiency. This study reported that carbon-based conductive carriers are able to enhance the removal of nitrogen from wastewater with low C/N ratio by coupling Fe(II)-driven autotrophic and heterotrophic bioelectrochemical denitrification. When Fe(II) was the sole electron donor, the bioreactor using conductive carrier achieved a denitrification rate constant (kDN) of 0.016 h−1, 1.7 times of that with non-conductive materials. This enhancement was due to the conductive carrier boosting direct electron transfer and supporting the growth of electroactive microorganisms. For wastewater with a low C/N ratio of 0.76, the bioreactor featuring both Fe(II) and the conductive carrier reached a kDN of 0.095 h−1, five times higher than without Fe(II). The presence of Fe(II) promoted denitrification by enhancing electron transfer and serving as a mediator. Microbial analysis showed that adding Fe(II) enriched electroactive bacteria like Comamonas and denitrifiers such as Chryseobacterium. Our findings suggest a promising strategy to enhance denitrification in wastewater treatment systems with low C/N ratios.

Dopant Activation Comparison in Phosphorus and Nitrogen Implanted 4H-Silicon Carbide

Bulk mobility and dopant activation of implanted species into 4H-SiC plays a crucial role in the carrier conduction, blocking behavior, and channel properties of a 4H-SiC vertical power MOSFET. Nitrogen and phosphorus ion implantation became the norm as n-type dopants for 4H-SiC. Therefore, the doping and temperature behavior of both species in 4H-SiC needs to be well characterized. In this study, we report a comparison in electrical characteristics between nitrogen and phosphorus implanted 4H-SiC as a function of temperature for various doping levels. For this purpose, 4-point van der Pauw samples are prepared, resistivity and Hall measurements are conducted. We found that resistivities drop as temperature increases from 140 K with phosphorus having higher resistivities at all implanted doping concentrations. The carrier concentrations increase with increase of temperature, indicating incomplete ionization of dopants. Mobilities drop at low temperature due to increased impurity scattering, reaches a peak near 300 K and drops at higher temperature due to increased phonon scattering. From the obtained data, using a two-level charge neutrality equation, the activation percentage and ionization energies of dopants in hexagonal and cubic sites for both species are extracted and compared.