Rate Of Charge Transport Research Articles

Charge Transport through Self‐Assembled Monolayers of Monoterpenoids

AbstractThe nature of the processes at the origin of life that selected specific classes of molecules for broad incorporation into cells is controversial. Among those classes selected were polyisoprenoids and their derivatives. This paper tests the hypothesis that polyisoprenoids were early contributors to membranes in part because they (or their derivatives) could facilitate charge transport by quantum tunneling. It measures charge transport across self‐assembled monolayers (SAMs) of carboxyl‐terminated monoterpenoids (O2C(C9HX)) and alkanoates (O2C(C7HX)) with different degrees of unsaturation, supported on silver (AgTS) bottom electrodes, with Ga2O3/EGaIn top electrodes. Measurements of current density of SAMs of linear length‐matched hydrocarbons—both saturated and unsaturated—show that completely unsaturated molecules transport charge faster than those that are completely saturated by approximately a factor of ten. This increase in relative rates of charge transport correlates with the number of carbon–carbon double bonds, but not with the extent of conjugation. These results suggest that polyisoprenoids—even fully unsaturated—are not sufficiently good tunneling conductors for their conductivity to have favored them as building blocks in the prebiotic world.

All-electrodeposited amorphous MoSx@ZnO core-shell nanorod arrays for self-powered visible-light-activated photoelectrochemical tobramycin aptasensing

The design and construction of high-performance photoelectrode with efficient visible-light absorption and fast charge transport rate are crucial to developing photoelectrochemical (PEC) sensor. Herein, a well-aligned amorphous MoSx (a-MoSx)@ZnO core-shell nanorod arrays was uniformly grown on indium tin oxide (ITO) via a facile all-electrochemical strategy. Simultaneous boosted PEC performance and stability in the visible region were obtained. Those could be attributed to the collaboration effect of fast electron transfer path within the oriented ZnO nanorod and extended visible-light absorption upon combining a-MoSx, as well as favorable energy-band alignment between the two PEC materials. By employing tobramycin-binding aptamer as recognition element, a self-powered PEC aptasensor for tobramycin was successfully fabricated for the first time. The sensor exhibited a rapid response in a wide linear range of 0.010–50 ng/mL with good stability and reproducibility. The detection limit was as low as 5.7 pg/mL. Ultrasensitive and high-affinitive determination of tobramycin in serum samples was realized at 0 V (vs.SCE) with desired accuracy and satisfactory recovery. This work reveals the promising application of all-electrodeposited a-MoSx@ZnO NR arrays-based photoanode for self-powered PEC bioassay in the tobramycin-related disease diagnosis.

Short‐Chain Ligand‐Passivated Stable α‐CsPbI3 Quantum Dot for All‐Inorganic Perovskite Solar Cells

AbstractCubic phase CsPbI3 (α‐CsPbI3) perovskite quantum dots (QDs) have received extensive attention due to their all‐inorganic composition and suitable band gap (1.73 eV). However, α‐CsPbI3 QDs might convert to δ‐CsPbI3 (orthorhombic phase with indirect band gap of 2.82 eV) due to easy loss of surface ligands. In addition, commonly used long‐chain ligands (oleic acid, OA, and oleylamine, OLA) hinder efficient charge transport in optoelectronic devices. In order to relieve these drawbacks, OA, OLA, octanoic acid, and octylamine are used as capping ligands for synthesizing high‐quality α‐CsPbI3 QDs. The results indicate that these QDs exhibit excellent optical properties and long‐term stability compared to QDs capped only with OA and OLA. Moreover, QDs with shorter ligands exhibit an enhanced charge transport rate, which improves the power conversion efficiency of photovoltaic devices from 7.76% to 11.87%.

Boosting the Oxygen Evolution Reaction Activity of NiFe2O4 Nanosheets by Phosphate Ion Functionalization.

Here, we demonstrate an effective strategy to constitutionally increase the conductivity and electrocatalytic property of NiFe2O4 by phosphate ion functionalization. The phosphate-ion-modified NiFe2O4 (P-NiFe2O4) nanosheets are readily grown on a carbon cloth by a simple hydrothermal method and followed by a phosphating process. The introduction of phosphate ions on the NiFe2O4 surface is highly beneficial for increasing the charge transport rate and electrocatalytic active sites. As a result, the as-prepared P-NiFe2O4 nanosheets show outstanding electrocatalytic activity toward oxygen evolution reaction (OER), with a low overpotential (231 mV at 10 mA/cm2) and Tafel slope (49 mV/dec). Furthermore, the P-NiFe2O4 electrode has a remarkable stability with no activity fading after 50 h. In addition, the as-fabricated water electrocatalysts exhibit excellent flexibility at the foldable state. These features make the phosphate-ion-functionalized NiFe2O4 electrodes open a new way to develop OER electrocatalysts with high electrochemical property.

Effect of Nuclear Motion on Charge Transport in Fullerenes: A Combined Density Functional Tight Binding—Density Functional Theory Investigation

Fullerene-based materials are widely used as acceptor and electron transport layer materials in organic and planar perovskite solar cells. Modeling of electronic properties such as band alignment and charge transport for these applications is typically done using optimized geometries. Here, we estimate the effects of nuclear motions on band structure and electron and hole transport in two prototypical fullerenes, C60 and C70. We model the dynamics in solid fullerenes using Density Functional Tight Binding and we use the Density Functional Theory based Projection of Monomer Orbitals on Dimer Orbitals (DIPRO) approach to estimate effects on charge transfer integral in the Marcus approximation. We show that room-temperature molecular dynamics cause a shift and spread of frontier orbital energies on the order of 0.1 eV which leads to an increase by more than a factor of two in the Marcus exponent, and can cause a decrease by up to orders of magnitude in the overlap integral, leading in most cases to an overall decrease in the charge transport rate.

In situ growth of a P-type CuSCN/Cu2O heterojunction to enhance charge transport and suppress charge recombination

In situ growth CuSCN/Cu2O heterojunction using a simple alkali treatment technique, to promote charge transport and suppress interface recombination.

Solution-processed aggregation-induced delayed fluorescence (AIDF) emitters based on strong π-accepting triazine cores for highly efficient nondoped OLEDs with low efficiency roll-off

Abstract Currently, aggregation-induced delayed fluorescence (AIDF) is the most potential method that overcomes the limitations of thermally activated delayed fluorescence (TADF) emitters. Herein, to develop high efficient AIDF emitters, a novel strategy of introducing carbazole dendrites to a strengthen electron acceptor to construct D−π−A structure has been presented. Two emitters, namely diphenyl(4-(4-phenyl-6-(4-(3,3″,6,6″-tetra-tert-butyl-9′H-[9,3':6′,9″-tercarbazol]-9′-yl)phen yl)-1,3,5-triazin-2-yl)phenyl) phosphine oxide (CzTAZPO) and diphenyl(4-(4-phenyl-6-(4-(3,3″,6,6″-tetra-tert-butyl-9′H-[9,3':6′,9″-tercarbazol]-9′-yl)phenyl)-1,3,5-triazin-2-yl)phenyl)phosphine oxide (sCzTAZPO) with a twisted carbazole dendrites structure are synthesized and investigated theoretically and experimentally. Both compounds show aggregation-induced emission, a prominent TADF and bipolar properties. The reasonable molecular design strategy allows CzTAZPO to exhibit high oscillator strengths (f) and small singlet–triplet energy gap (ΔEST) at the same time, which signifcantly increase the rate of reverse intersystem crossing process and fluorescence quantum efficiency. High-performance nondoped OLEDs are fabricated with CzTAZPO neat films as the emission layers, providing excellent maximum current efficiency (CEmax) and maximum external quantum efficiency (EQEmax) of 29.1 cd A−1 and 12.8%, respectively. More importantly, nondoped OLEDs provided negligible EQE roll-off of 1.6% from the maximum values to those at 1000 cd m−2. The AIDF emitters with small ΔEST, high photoluminescence quantum yields (ΦPL), bipolar charge transport and high rate constant of reverse intersystem crossing process are promising candidates for OLEDs that are roll-off-free and possess high efficiency.

Sol-gel synthesized hexagonal boron nitride/titania nanocomposites with enhanced photocatalytic activity

Hexagonal boron nitride (H-BN)/titania (TiO2) nanocomposites photocatalysts were synthesized by a facile sol-gel method. The structure was verified by comprehensive analysis from X-ray diffraction, Raman, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscope and transmission electron microscope. The degradation of organic dyes such as rhodamine B (RhB) and methylene blue (MB) under UV light irradiation was used to measure the photocatalytic activity of the h-BN/TiO2 nanocomposites. The photocatalytic performance and the stability of H-BN/TiO2 nanocomposites in the degradation of dyes (MB and RhB) significantly outperformed pure TiO2 nanoparticles. The formed BOTi bond in H-BN/TiO2 gave rise to a strong link between h-BN sheets and TiO2 nanoparticles, and thus the charge transportation rate was improved and the recombination of electrons and holes was suppressed in the photocatalytic processes. The degradation percentage for RhB and MB reached 98% and 92% within 50 min irradiation. The degradation rate (k) of first-order linear value of h-BN/TiO2 nanocomposites (0.05952 and 0.0498) for RhB and MB degradation was 3.64 and 4.22 times higher than that of pure TiO2 (0.01637 and 0.0118). The enhanced photocatalytic property of the nanocomposites was attributed to the reduction in charge recombination and the adsorption interaction between organic dyes and h-BN. Consequently, h-BN sheets hold a great promise to enhance the photocatalytic activity of semiconductive materials.

Flexible supercapacitor electrodes fabricated by dealloying nanocrystallized Al-Ni-Co-Y-Cu metallic glasses

Nanoporous oxides of transition metals are of great potential for applications as super-capacitor electrodes because of their variable valence. However, the low conductance of electrons in oxides and slow transportation of ions in nanopores limit their performance. In this work, NiCo-contained metal/metal-oxide nanoporous composites are fabricated by one-step dealloying nanocrystallized Al82Ni6Co3Y6Cu3 (at.%) metallic glass ribbons in KOH solutions. The capacitance of the dealloyed nanoporous composites reaches 3.35 F cm−2 (about 1522 F cm−3), which is 3–10 times higher than that dealloyed from as-spun metallic glass and crystalline precursors. The large capacitance is attributed to the combination of efficient charge transportation rate and high loading amount of active materials. These results demonstrate for the first time that the nanocrystallized metallic glasses are promising easy-processing precursors for fabricating flexible free-standing nanoporous electrodes.

Charge Diffusion Variations in Pan-STARRS1 CCDs

Thick back-illuminated deep-depletion CCDs have superior quantum efficiency over previous generations of thinned and traditional thick CCDs. As a result, they are being used for wide-field imaging cameras in several major projects. We use observations from the Pan-STARRS 3π survey to characterize the behavior of the deep-depletion devices used in the Pan-STARRS 1 Gigapixel Camera. We have identified systematic spatial variations in the photometric measurements and stellar profiles that are similar in pattern to the so-called “tree rings” identified in devices used by other wide-field cameras (e.g., DECam and Hypersuprime Camera). The tree-ring features identified in these other cameras result from lateral electric fields that displace the electrons as they are transported in the silicon to the pixel location. In contrast, we show that the photometric and morphological modifications observed in the GPC1 detectors are caused by variations in the vertical charge transportation rate and resulting charge diffusion variations.

Insight into Metal-Organic Framework Reactivity: Chemical Water Oxidation Catalyzed by a [Ru(tpy)(dcbpy)(OH2 )]2+ -Modified UiO-67.

Investigation of chemical water oxidation was conducted on [Ru(tpy)(dcbpy)(OH2 )]2+ (tpy=2,2':6',2''-terpyridine, dcbpy=5,5'-dicarboxy-2,2'-bipyridine)-doped UiO-67 metal-organic framework (MOF). The MOF catalyst exhibited a single-site reaction pathway with kinetic behavior similar to that of a homogeneous Ru complex. The reaction was first order with respect to both the concentration of the Ru catalyst and ceric ammonium nitrate (CAN), with kcat =3(±2)×10-3 m-1 s-1 in HNO3 (pH 0.5). The common degradation pathways of ligand dissociation and dimerization were precluded by MOF incorporation, which led to sustained catalysis and greater reusability as opposed to the molecular catalyst in homogeneous solution. Lastly, at the same loading (ca. 97 nmol mg-1 ), samples of different particle sizes generated the same amount of oxygen (ca. 100 nmol), indicative of in-MOF reactivity. The results suggest that the rate of redox-hopping charge transport is sufficient to promote chemistry throughout the MOF particulates.

The effect of polymer molecular weight on the performance of PTB7-Th:O-IDTBR non-fullerene organic solar cells

Activation energy for charge transport, carrier concentration and recombination rate are identified to strongly affect the device characteristics.

Influence of the Contact Area on the Current Density across Molecular Tunneling Junctions Measured with EGaIn Top-Electrodes

This paper describes the relationship between the rates of charge transport (by tunneling) across self-assembled monolayers (SAMs) in a metal/SAM//Ga2O3/EGaIn junction and the geometric contact area (Ag) between the conical Ga2O3/EGaIn top-electrode and the bottom-electrode. Measurements of current density, J(V), across SAMs of decanethiolate on silver demonstrate that J(V) increases with Ag when the contact area is small (Ag < 1000 μm2), but reaches a plateau between 1000 and 4000 μm2, where J(0.5 V) ≈ 10–0.52±0.10 A/cm2. The method used to fabricate Ga2O3/EGaIn electrodes generates a tip whose apex is thicker and rougher than its thin, smoother sides. When Ag is small, the Ga2O3/EGaIn electrode contacts the bottom-electrode principally over this rough apex and forms irreproducible areas of electrical contact. When Ag is large, the contact is through the smoother regions peripheral to the apex and is much more reproducible. Measurements of contact pressure between conical EGaIn electrodes and atomic forc...

Charge transport and dipolar relaxations in phosphonium-based ionic liquids.

The role of anions in charge transport and localized dipolar relaxations in tributyloctylphosphonium ionic liquids is investigated by broadband dielectric spectroscopy and rheology. The dielectric spectra are quantitatively described by a combination of the random barrier model which accounts for ion transport and empirical Havriliak-Negami functions to characterize dipolar relaxations. Two secondary relaxations are observed at temperatures below the calorimetric glass transition temperature, where the primary structural relaxation is essentially frozen at the relevant experimental time scales. The faster process has an anion independent activation energy of 30 kJ/mol and is attributed to libration motion of the phosphonium cation. The slower relaxation is similar to a process previously assigned to a Johari-Goldstein relaxation in imidazolium-based ionic liquids; however, the activation energy is significantly higher in the phosphonium systems. For the charge transport dominated regime, it is observed that variation of the anion results in differences in the dc ionic conductivity and characteristic charge transport rates by ∼2.5 decades. Upon scaling by the calorimetric glass transition temperature, both transport quantities are observed to coincide. From these results, a picture of glass transition assisted hopping emerges as the underlying microscopic mechanism of ion conduction, in agreement with recent results obtained for other classes of aprotic ionic liquids.

Virtual Design in Organic Electronics: Screening of a Large Set of 1,4-Bis(phenylethynyl)benzene Derivatives as Molecular Semiconductors

In this work, we have theoretically studied the electronic properties of a large series of 1,4-bis(phenylethynyl)benzene derivatives, with the chemical formula Y–C≡C–X–C≡C–Y, with X and Y being aromatic rings and chosen to act as donor and acceptor moieties. Employing state-of-the-art DFT calculations, we analyzed a set of relevant electronic properties related to the optoelectronic and semiconductor character of these systems, namely, molecular and energy levels, electron affinity, ionization potential, reorganization energy, and electronic coupling between neighboring molecules forming dimers, obtained after evaluation of binding energy landscapes. The latter energy magnitude is needed to disclose first the favored intermolecular interactions (i.e., the lowest binding energy) to concomitantly estimate next the charge transport rates. The systematic screening performed allowed us to anticipate the possible use of some of these derivatives as p-type, n-type, or even ambipolar organic molecular semiconductors.

Charge Transport and Entropy Production Rate in Magnetically Active Molecular Dimer

We consider charge and thermal transport properties of magnetically active paramagnetic molecular dimer. Generic properties for both transport quantities are reduced currents in the ferro- and antiferromagnetic regimes compared to the paramagnetic and efficient current blockade in the antiferromagnetic regime. In contrast, while the charge current is about an order of magnitude larger in the ferromagnetic regime, compared to the antiferromagnetic, the thermal current is efficiently blockaded there as well. This disparate behavior of the thermal current is attributed to current resonances in the ferromagnetic regime, which counteract the thermal flow. The temperature difference strongly reduces the exchange interaction and tends to destroy the magnetic control of the transport properties. The weakened exchange interaction opens up a possibility to tune the system into thermal rectification, for both the charge and thermal currents.

Needle‐Leaf‐Like Cu2Mo6S8 Films for Highly Efficient Visible‐Light Photocatalysis

AbstractTernary sulfide Cu2Mo6S8 films with needle‐leaf‐like structures are grown on copper plates via a facile two‐step route. The needle‐leaf‐like Cu2Mo6S8 structures are directly converted from pregrown Cu(OH)2 nanowires on copper plates via a hydrothermal process. Interestingly, under visible light the hierarchically structured Cu2Mo6S8 films exhibit significantly improved photocatalytic performance in the degradation of methylene blue dye when compared to Cu(OH)2 nanowires. This result is attributed to the larger surface area from the dendritic Cu2Mo6S8 structures and the inherently faster charge transport rate of Cu2Mo6S8 as compared to Cu(OH)2.

Theoretical research on the charge transport properties of imidazoles axial-coordinated with protoheme molecule

The charge transport properties and the stability of imidazoles with axial-coordinated protoheme molecules have been investigated by the density functional theory (DFT) at B3LYP/6-31[Formula: see text]G(d) level. With energy of each compound, we find that all heme Fe[Formula: see text] and Fe[Formula: see text] complex compounds axially coordinate the imidazoles by strong field in low-spin state. Meanwhile, binding energies were calculated, the structure feature and the frontier orbital distribution of complex compounds were also analyzed. On the basis of Marcus theory, the reorganization energy, matrix element and charge transport rate constant were calculated. The results show that the charge transport rate of the complex compound coordinated imidazole is greater than that of the complex compound coordinated 2-methyl imidazole, which indicates that the charge transfer between the imidazole and the heme iron is more favorable to the heme iron than the 2-methyl imidazole. The results are in good agreement with the experimental ones obtained by Battistuzzi.

Preparation of 2D/2D g-C3N4 nanosheet@ZnIn2S4 nanoleaf heterojunctions with well-designed high-speed charge transfer nanochannels towards high-efficiency photocatalytic hydrogen evolution

In this work, we design and construct a novel 2D/2D g-C3N4 nanosheet@ZnIn2S4 nanoleaf via a simple one-step surfactant-assisted solvothermal method for photocatalytic H2 generation. Its unusual 2D/2D heterojunction structure provides far more contact areas and much faster charge transport rate than the 2D/0D heterojunction structure of g-C3N4 nanosheet@ZnIn2S4 microsphere. More importantly, this unique 2D/2D heterojunction leads the g-C3N4 nanosheet@ZnIn2S4 nanoleaf composite to generate numerous intimate high-speed charge transfer nanochannels in the interfacial junctions, and which could considerably enhance the photogenerated charge separation and migration efficiency, thus yielding a remarkable visible-light-driven H2 evolution rate without the additive Pt cocatalyst (HER=2.78mmolh−1g−1), nearly 69.5, 15.4, 8.2 and 1.9 times higher than that of pure g-C3N4 nanosheet, pure ZnIn2S4 microsphere, 2D/0D g-C3N4 nanosheet@ZnIn2S4 microsphere and pure ZnIn2S4 nanoleaf, respectively. Additionally, the 2D/2D g-C3N4 nanosheet@ZnIn2S4 nanoleaf exhibits an outstanding stability and recyclability, manifesting a promising potential application in sustainable energy conversion. This work would provide a platform for the design and synthesis of binary heterojunction composite system with highly-efficient charge separation and transfer.

Tracking Hole Transport in DNA Hairpins Using a Phenylethynylguanine Nucleobase

The hole transport dynamics of DNA hairpins possessing a stilbene electron acceptor and donor along with a modified guanine (G) nucleobase, specifically 8-(4'-phenylethynyl)deoxyguanosine, or EG, have been investigated. The nearly indistinguishable oxidation potentials of EG and G and unique spectroscopic characteristics of EG+• make it well-suited for directly observing transient hole occupation during charge transport between a stilbene electron donor and acceptor. In contrast to the cation radical G+•, EG+• possesses a strong absorption near 460 nm and has a distinct Raman-active ethynyl stretch. Both spectroscopic characteristics are easily distinguished from those of the stilbene donor/acceptor radical ion chromophores. Employing EG, we observe its role as a shallow hole trap, or as an intermediate hole transport site when a deeper trap state is present. Using a combination of ultrafast absorption and stimulated Raman spectroscopies, the hole-transport dynamics are observed to be similar in systems having EG vs G bases, with small perturbations to the charge transport rates and yields. These results show EG can be deployed at specified locations throughout the sequence to report on hole occupancy, thereby enabling detailed monitoring of the hole transport dynamics with base-site specificity.