Electrical Charge Transport Research Articles

Improved Electrical Ideality and Photoresponse in Near Infrared Phototransistors Realized by Incorporating a Bulk Heterojunction Channel

Simultaneous increase in electrical ideality and near infrared (NIR) response in the organic phototransistors (OPTs) is realized by applying a donor/acceptor bulk heterojunction (BHJ) channel layer. A comprehensive analysis has been carried out to understand the effects of the miscibility between the donor and acceptor in the BHJ channel, and the morphology of the channel layer on the electrical charge transport and optical response of the OPTs. The presence of the acceptors in the channel layer helps to trap the undesirable injected electrons, avoiding the accumulation of the electrons at the active channel/dielectric interface, and thereby improving the hole transporting in the p-type channel. The electrical stability is then improved with mitigated dependence of charge mobility on gate voltage in the saturation region. The use of a BHJ channel in the OPTs also offers an improved photoresponse through enhanced exciton dissociation at the donor/acceptor interface and the stable mobility in the saturation region, leading to more than one order of magnitude increase in responsivity than that in a conventional OPT with a single p-type semiconductor channel layer. The OPTs with a BHJ channel layer exhibit an excellent hole mobility of 1.0 cm2V-1s-1, a high photoresponsivity of the 104 A/W and a high specific detectivity of 1.2×1012 Jones in the NIR wavelength.

Variation of the electrocatalytic activity of isostructural oxides Sr2LaFeMnO7 and Sr2LaCoMnO7 for hydrogen and oxygen-evolution reactions.

The effect of the electronic configurations of transition metals on electrocatalytic activity, charge transport, and magnetic properties is demonstrated through the investigation of Sr2LaFeMnO7 and Sr2LaCoMnO7. The two compounds are isostructural and contain bilayer stacks of octahedrally coordinated transition metals. Despite their structural similarity, the magnetic transition temperature of Sr2LaCoMnO7 is significantly lower than that of Sr2LaFeMnO7. The electrical charge-transport properties are also different, where Sr2LaCoMnO7 shows considerably improved electrical conductivity. Importantly, the electrocatalytic activities for the two half-reactions of water-splitting, i.e., the hydrogen-evolution reaction (HER) and the oxygen-evolution reaction (OER), are improved in Sr2LaCoMnO7 compared to Sr2LaFeMnO7. In addition, better kinetics for the HER and OER are observed for Sr2LaCoMnO7, as evaluated by the Tafel method. Furthermore, the electrochemically active surface area (ECSA) shows an enhancement for Sr2LaCoMnO7. Therefore, the trends in electrical charge transport, the HER and OER activities, kinetics and ECSA are all similar, indicating the improved properties of Sr2LaCoMnO7. These changes are explained in the context of a greater bond covalency in this material due to the higher electronegativity of Co, which results in a better overlap between the transition metal d orbital and oxygen p orbital. The relation between the electrocatalytic performance and the optimum eg orbital occupancy in Sr2LaCoMnO7 is also discussed.

Electrochemiluminescent Transistors: A New Strategy toward Light-Emitting Switching Devices.

Light-emitting transistors (LETs) have attracted a significant amount of interest as multifunctional building blocks for next-generation electronics and optoelectronic devices. However, it is challenging to obtain LETs with a high carrier mobility and uniform light-emission because the semiconductor channel should provide both the electrical charge transport and optical light-emission, and typical emissive semiconductors have low, imbalanced carrier mobilities. In this work, a novel device platform that adapts the electrochemiluminescence (ECL) principle in LETs, referred to as an ECL transistor (ECLT) is proposed. ECL is a light-emission phenomenon from electrochemically excited luminophores generated by redox reactions. A solid-state ECL electrolyte consisting of a network-forming polymer, ionic liquid, luminophore, and co-reactant is employed as the light-emitting gate insulator of the ECLT. Based on this construction, high-performance LETs that make use of various conventional non-emissive semiconductors (e.g., poly(3-hexylthiophene), zinc oxide, and reduced graphene oxide) are successfully demonstrated. All the devices exhibit a high mobility (0.9-10 cm2 V-1 s-1 ) and a uniform light-emission. This innovative approach demonstrates a novel LET platform and provides a promising pathway to achieve significant breakthroughs to develop electronic circuits and optoelectronic applications.

Numerical modelling of self-potential in subsurface reservoirs

We report a new, open-source, MATLAB-based 3D code for numerically simulating the self-potential (SP) in subsurface reservoirs. The code works as a post-processor, using outputs from existing reservoir flow and transport simulators at a selected timestep to calculate the SP throughout the reservoir model. The material properties required to calculate the SP are user defined and may be constant or vary in each cell. The code solves the equations governing flow and transport of electrical charge and global charge conservation using a control-volume-finite-difference scheme. Electrical currents associated with the SP may spread beyond the reservoir model domain, and the code allows for the domain to be extended vertically and laterally to account for this. Here, we present the governing equations and the numerical method used and demonstrate application of the code using an example in which we predict the SP signals associated with oil production from a subsurface reservoir supported by water injection.

Growth of films with seven-coordinated diorganotin(IV) complexes and PEDOT:PSS structurally modified for electronic applications

This work refers to the manufacture and characterization of organic electronic devices made from seven-coordinated diorganotin(IV) complexes and the polymer poly(3,4-ethylenedyoxithiophene)-poly(styrene sulfonate) (PEDOT:PSS). In order to obtain the best electronic behavior, the devices were manufactured by spin-coating with seven-coordinated diorganotin(IV) complexes, synthetized with different peripheral substituents. The modification of the polarity in the molecule, from the presence of the different functional groups, is used as a way to enhance the charge transport inside the devices. Additionally, the devices received a post-treatment with isopropyl alcohol, in order to change the structure of PEDOT:PSS from benzoid form to quinoid form. The electric charge transport was evaluated from the current density–voltage characteristics, under dark and illuminated conditions. The devices present a mobility of ∼10−9 cm2/Vs decreasing to values of ∼10−11–10−10 cm2/Vs. They display a photocurrent of ∼10−7–10−8 A cm−2 and a reduction is observed after the treatment. It is mainly the presence of the peripheral substituents in the diorganotin(IV) complexes, and not the polymer structure, that causes the electrical behavior of the device. The films made from seven-coordinated diorganotin(IV) complex particles deposited on the PEDOT:PSS, as well as their post-treatment, were characterized by Raman, ultraviolet-vis spectroscopy, scanning electronic microscopy and atomic force microscopy.

Modelling of the mean electric charge transport equation in a mono-dispersed gas–particle flow

Abstract

Electrical Characterization and Charge Transport in Chemically Exfoliated 2D LixCoO2 Nanoflakes

Transition metal oxides often possess complex interactions between charge, spin, lattice, and orbital degrees of freedom, resulting in correlated electronic and magnetic phases. LixCoO2, one of the...

Polymer/molecular semiconductor all-organic composites for high-temperature dielectric energy storage

Dielectric polymers for electrostatic energy storage suffer from low energy density and poor efficiency at elevated temperatures, which constrains their use in the harsh-environment electronic devices, circuits, and systems. Although incorporating insulating, inorganic nanostructures into dielectric polymers promotes the temperature capability, scalable fabrication of high-quality nanocomposite films remains a formidable challenge. Here, we report an all-organic composite comprising dielectric polymers blended with high-electron-affinity molecular semiconductors that exhibits concurrent high energy density (3.0 J cm−3) and high discharge efficiency (90%) up to 200 °C, far outperforming the existing dielectric polymers and polymer nanocomposites. We demonstrate that molecular semiconductors immobilize free electrons via strong electrostatic attraction and impede electric charge injection and transport in dielectric polymers, which leads to the substantial performance improvements. The all-organic composites can be fabricated into large-area and high-quality films with uniform dielectric and capacitive performance, which is crucially important for their successful commercialization and practical application in high-temperature electronics and energy storage devices.

Thermal transport in a weakly magnetized hot QCD medium

The thermal transport coefficients in a weakly magnetized quark-gluon plasma have been investigated within the ambit of a quasiparticle model to encode the effects of the realistic equation of state. The presence of a weak magnetic field leads to the Hall-type conductivity associated with thermal transport in the medium. An effective covariant kinetic theory has been employed to quantify the thermal dissipation while incorporating the mean field contributions in the medium. The interplay of thermal transport and electric charge transport in the weakly magnetized medium has been explored in terms of the Wiedemann-Franz law. Strong violation of the Wiedemann-Franz law has been observed in temperature regimes near to the transition temperature. The behaviour of thermal conductivity in the strong magnetic field limit has also been studied. It is observed that both the magnetic field and equation of state have a significant impact on the thermal dissipation in the medium.

Tip-enhanced electric field-driven efficient charge injection and transport in organic material-based resistive memories

Organic materials show promise as switching layers for resistive random access memory (RRAM). However, practical application has been limited by inefficient charge injection and transport in typical organic materials. This study proves that local enhancement of electric fields through structured electrodes can improve charge injection and transport in organic RRAM. Specifically, pyramid-structured electrodes with an extremely sharp tip are introduced into RRAM with a polyimide (PI) switching layer. The electric field in the pyramid-structured RRAM can be significantly enhanced only at the tip, thereby facilitating charge injection at the electrode/PI interface and charge transport through the PI switching layer. Indeed, the resulting RRAM exhibits low and reliable operating voltages (SET: 1.76 V ± 0.41 V / RESET: −0.49 V ± 0.15 V) compared with conventional PI-based RRAMs with planar electrodes. The conductive path formed in the tip region is observed directly using conductive atomic force microscopy, demonstrating that resistive switching occurs by tip-enhanced electric fields. Also, the charge transport mechanism follows the space charge-limiting current model modified by the Poole–Frenkel effect. These results provide an effective strategy to control the charge concentration, injection, and transport in organic RRAM, for realization of low-cost, large-area, shape-deformable data storage devices.

Exciton Quenching due to Hole Trap Formation in Aged Polymer Light‐Emitting Diodes

AbstractPolymer light‐emitting diodes based on two poly(p‐phenylene vinylene) derivatives are aged at a constant current density, leading to the formation of hole traps. Time‐resolved photoluminescence spectroscopy (TRPL) measurements show that the degraded polymer light‐emitting diodes (PLEDs) also demonstrate a decrease in exciton lifetime. The amount of nonradiative exciton quenching sites in the aged devices is quantified by Monte Carlo simulations. It is found that the number of hole traps obtained from electrical charge transport measurements matches the number of newly formed nonradiative quenching sites determined from the TRPL experiments. The results reveal the origin for the apparent different behavior of the electroluminescence and photoluminescence upon PLED degradation. The decrease of the electroluminescence is governed by recombination of free electrons with trapped holes, whereas the photoluminescence is reduced by nonradiative quenching processes between excitons and hole traps.

Field-induced polarization effect on space charge limited current in the charge transport of poly(-3octylthiophene) thin films

Herein, the effects of field-induced polarization on electrical charge transport of poly(3-octylthiophene) (P3OT) thin films are elucidated. The current-density versus voltage (J-V) characteristics of P3OT thin films were studied as a function of temperature (110–290 ​K), thickness (120–800 ​nm), and field-induced polarization in the hole-merely device setup. The data, so-obtained, were examined in terms of space charge limited conduction (SCLC) theory with the inclusion of shallow traps. The logJ-logV curves reveal explicitly two conduction regions, (i) Ohmic at low fields, and (ii) non–Ohmic at higher fields. The charge transport at higher-fields is credited to SCLC phenomena in the presence of shallow hole traps. The trap-density of 200 ​nm thick P3OT films is evaluated to be 8.04 ​× ​1023 ​m−3, which decreased with the increase of film thickness. The hole mobility is estimated to be 1.65 ​× ​10−6 ​cm2/V⋅s from the quadratic part of the SCLC region.

Topological properties and direct current electrical charge transport mechanism of plasma polymerized cyclohexane thin films

High-performance plasma polymerized organic thin films have been synthesized by employing a capacitively coupled glow discharge technique and cyclohexane is used as a precursor material. The surface of the plasma polymerized cyclohexane (PPCHex) thin films observed to be smooth, pinhole free and uniform. It is observed from thermal analysis that the rate of loss of mass is very low in air atmosphere below 510 K and the films are thermally stable. Above 510 K weight loss takes place in different stages in air. The current density of the PPCHex thin films is increased when the thicknesses is decreased and that is increased with increasing temperatures. The conduction mechanism of carrier transport operative in these PPCHex thin film is dominated by Schottky type conduction mechanism. The activation energy of the PPCHex thin films for applied voltage 10 V is found 0.14 ± 0.05 eV near room temperature region and that in the higher temperature region is 0.57 ± 0.04 eV. The activation energy in the Schottky region for the applied voltage 50 V is about 0.16 ± 0.06 eV near the room temperature region and that is 0.83 ± 0.05 eV at the higher temperature region.

In-situ synthesis of three-dimensionally flower-like Ni3V2O8@carbon nanotubes composite through self-assembling for high performance asymmetric supercapacitors

To develop a high-performance positive electrode for asymmetric supercapacitor (ASC), a novel Ni3V2O8@carbon nanotubes (CNTs) composite with three-dimensionally (3D) flower-like structure is designed and prepared through an in-situ hydrothermal method. The particularly open architecture self-assembled by interlacement of Ni3V2O8 nano-petals with a high surface area provides interconnected ion diffusion channels and highly exposed active centers for ion absorption. The electrical conductivity and charge transport are greatly improved by anchoring CNTs on Ni3V2O8. The synergistic effect between Ni3V2O8 and CNTs gives rise to an improved electrochemical performance with high specific capacitance (1054 F g−1 at 1 A g−1), good rate capability and excellent cycling stability (89% capacitance retention after 10,000 cycles). An ASC equipped with a Ni3V2O8@CNTs positive electrode and an activated rice husk carbon (ARHC) negative electrode achieves a remarkable energy density of 45.5 Wh kg−1 at 795 W kg−1 and outstanding cycling stability after 10,000 cycles in a wide operating voltage window of 1.6 V. The impressive performance of the Ni3V2O8@CNTs composite makes it a promising candidate for commercial application.

Contemplating charge transport by modeling of DNA nucleobases based nano structures

Electrical charge transport through two basic strands Thymine and Adenine of DNA has been analyzed using jellium model approach. The FFT-2D computations have been performed for semi empirical Extended Huckel Theory using Atomistix Tool kit to contemplate the charge transport metrics like current and conductance. We have scrutinized the behavior of the devices in the range of -2 V–2 V for a step size of 0.2 V. A prominent observation is the drop in HLGs of Adenine and Thymine, when working as device as compared to their intrinsic values and this is comparative more visible in case of Adenine. The current in the thymine based device exhibit linear increase with voltage in spite of having low conductance. Further the broader transmission peaks represent the strong coupling of electrodes to the scattering molecule (Thymine). The NDR effect of Adenine based device for higher bias can be utilized in various future electronics applications.

Dimension transcendence and anomalous charge transport in magnets with moving multiple- Q spin textures

Multiple-$Q$ spin textures, such as magnetic bubble and skyrmion lattices, can be driven into motion by external stimuli. The motion of spin textures affects the electronic states. Here we show that to describe correctly the electronic dynamics, the momentum space needs to be transcended to higher dimensions by including the ancillary dimensions associated with phason modes of the translational motion of the spin textures. The electronic states have non-trivial topology characterized by the first and second Chern numbers in the high dimensional hybrid momentum space. This gives rise to an anomalous electric charge transport due to the motion of spin textures. By deforming the spin textures, a nonlinear response associated with the second Chern number can be induced. The charge transport is derived from the semi-classical equation of motion of electrons that depends on the Berry curvature in the hybrid momentum space. Our results suggest that the motion of multiple-$Q$ spin textures has significant effects on the electronic dynamics and provides a new platform to explore high dimensional topological physics.

Effect of sintering pressure on electrical transport and thermoelectric properties of polycrystalline SnSe

Tin selenide (SnSe), which has high thermoelectric (TE) performance due to its low thermal conductivity, is considered as a promising TE material. It is good that TE properties were reported in single crystal form because polycrystalline SnSe exhibits low electrical conductivity compared to that of single crystal SnSe. To improve the electrical conductivity of polycrystalline SnSe, the effects of the pressure applied during spark plasma sintering (SPS) on the electrical charge transport and the TE properties of the polycrystalline SnSe were investigated. Degree of texture was enhanced with increasing sintering pressure from 30 to 120 MPa during SPS, which lead to the increase in carrier mobility, which resulted in the increase in electrical conductivity. Increase in pressure led to a significant increase in thermal conductivity due to an increase in the lattice thermal conductivity, which can be attributed to the decrease in phonon scattering at the grain boundary. A ZT of $${\sim }0.7$$ was obtained at 823 K from the polycrystalline SnSe sintered with a pressure of 60 MPa, which can result from large increase in electrical conductivity with very small increase in the thermal conductivity. This study shows that the TE properties of the polycrystalline SnSe can be enhanced by controlling the degree of texture which can be accomplished by changing the pressure applied during SPS.

Corrosion Resistance of Electrodeposited Layers using a Zn-Ni Electrolyte Impregnated with Tri-, Tetra-, and Pentavalent Elements

This paper describes the obtaining of an electrodeposited composite layer by enriching the Zn-Ni alkaline electrolyte with tri-, tetra- and pentavalent elements. The aim was to obtain a system of oxides of type n and p on the surface of a sample, after exposing to a corrosive environment that would block the electric charge transport. Measurements of the open-circuit potential, potentiodynamic polarization and the electrochemical impedance spectrum, shown that for a certain proportion of the enriching elements, the corrosion current is much lowered.

Tuning Thin Film Properties by Structural Modulations in Red Fluorescent Protein Chromophore Analogues

AbstractThe study of the role of substituents present in molecules is extremely important for designing new functional materials. In the present study, we have designed and synthesized four analogues (AR1‐AR4) of the red fluorescence protein (rfp) chromophore by varying the substituents and have studied their thin film properties by fabricating opto‐electronic devices with them. Molecules AR1 and AR2 were designed with improved donor‐acceptor (D−A) properties. Molecule AR3 was synthesized with an increased vinyl conjugation and molecule AR4 had an extra fluorescent moiety in the conjugation. The orbital levels and optical energy gap were estimated theoretically by density function theory. The optical absorption in solution/thin films, quality of film formation and the electrical charge transport mobility in films were studied. Photovoltaic parameters of bulk heterojunction solar cell devices formed with the four molecules were then determined. Interestingly, molecule AR3 with the extra vinyl conjugation was found to be the best of the four molecules reported here for application in organic electronics. The extra vinyl conjugation improved the π‐π stacking and helps to form smoother films with increased optical absorption and a desirable hole mobility.

Hole and Protonic Polarons in Perovskites.

Electric charge transport is an essential process for all electrical and electrochemical energy systems, including inanimate and animate matter. In this issue on materials for energy conversion, we compare and discuss the role of electron holes and protons as charge carriers in solids. Specifically we outline how the temperature or thermal bath affect the charge carrier concentration and mobility for some metal oxides with the perovskite structure. The frequent observation that the conductivity becomes independent of the activation energy at the isokinetic temperature, known as the Meyer-Neldel rule, is an important aspect of our interpretation of the physical mechanism of conduction by polaron hopping.