One-dimensional Charge Transport Research Articles

Ethylenedioxythiophene-Based Small Molecular Donor with Multiple Conformation Locks for Organic Solar Cells with Efficiency of 19.3 .

Ternary organic solar cells (T-OSCs) represent an efficient strategy for enhancing the performance of OSCs. Presently, the majority of high-performance T-OSCs incorporates well-established Y-acceptors or donor polymers as the third component. In this study, a novel class of conjugated small molecules has been introduced as the third component, demonstrating exceptional photovoltaic performance in T-OSCs. This innovative molecule comprises ethylenedioxythiophene (EDOT) bridge and 3-ethylrhodanine as the end group, with the EDOT unit facilitating the creation of multiple conformation locks. Consequently, the EDOT-based molecule exhibits two-dimensional charge transport, distinguishing it from the thiophene-bridged small molecule, which displays fewer conformation locks and provides one-dimensional charge transport. Furthermore, the robust electron-donating nature of EDOT imparts the small molecule with cascade energy levels relative to the electron donor and acceptor. As a result, OSCs incorporating the EDOT-based small molecule as the third component demonstrate enhanced mobilities, yielding a remarkable efficiency of 19.3 %, surpassing the efficiency of 18.7 % observed for OSCs incorporating thiophene-based small molecule as the third component. The investigations in this study underscore the excellence of EDOT as a building block for constructing conjugated materials with multiple conformation locks and high charge carrier mobilities, thereby contributing to elevated photovoltaic performance in OSCs.

Edge mode percolation and equilibration in the topological insulator cadmium arsenide

Two-dimensional topological insulators can feature one-dimensional charge transport via edge modes, which offer a rich ground for studying exotic quasi-particles and for quantum materials applications. In this work, we use lateral junction devices, defined by nanoscale finger gates, to study edge mode transport in the two-dimensional topological insulator Cd3As2. The finger gate can be tuned to transmit an integer number of quantum Hall edge modes and exhibits full equilibration in the bipolar regime. When the Fermi level of the channel crosses a Landau level, reflected modes percolate through the channel, resulting in an anomalous conductance peak. The device does not fully pinch off when the channel is tuned into the topological gap, which is a sign of remnant modes in the channel. These modes are expected from band inversion, while residual bulk conduction associated with the disorder potential may also play a role.

Electrochemical detection of methyl parathion using zirconium dioxide@single-walled carbon nanotubes nanocomposite modified glassy carbon electrode

In this work, the multifunctional nanocomposite of zirconium dioxide (ZrO2) nanoparticles and single-walled carbon nanotubes (SCN) was prepared to modify the glassy carbon electrode (GCE) for the fabrication of ZrO2@SCN/GCE sensor. The fabricated nanocomposite electrochemical sensor was successfully used to achieve the efficient and sensitive detection of methyl parathion (MP). For the ZrO2@SCN nanocomposite, ZrO2 nanoparticles could promote the enrichment of MP molecules on the electrode surface of ZrO2@SCN/GCE sensor because of the interplay between Zr-O groups and phosphorus groups of MP molecules; SCN presented efficient one-dimensional charge transport channels, which achieved the excellent conductivity property of carbon material. Moreover, SCN could greatly compensate for the non-conductivity of ZrO2 nanoparticles. The functional combination of ZrO2 nanoparticles and SCN enhanced the electrochemical detection performance of MP. The ZrO2@SCN/GCE sensor exhibited good MP detection property with low limit of detection of 6.15 nM (pH = 7.0, MP concentration: 0.01–10 μM). The fabricated sensor also showed good practical application property for the detection of MP in real samples (Lake water and green tea).

Tuning Oxygen Vacancies in Co3O4 Nanorods through Solvent Reduction Method for Enhanced Oxygen Evolution Activity

Oxygen vacancies can act as active centers for oxygen evolution reaction (OER), thereby enhancing the electrocatalytic activity of the catalyst. Unfortunately, effective methods are rather limited to introducing a high amount of oxygen vacancies on the surface of nanocatalysts. Here, a facile solution reduction method has been demonstrated. By simply tuning the concentration of NaBH4 solution, we fabricate typical spinel Co3O4 nanorods with a reasonable density of oxygen vacancy defects and preserve the nanorod morphology and one-dimensional (1D) charge transport behavior of the starting material. As-prepared defect-rich Co3O4 nanorods show a low overpotential of 378 mV at a current density of 10 mA cm–2 and a small Tafel slope of 58.18 mV dec–1, and at the same time, its double-layer capacitance reaches 25.62 mF cm–2, which is nearly 4 times that of pristine Co3O4. The presence of oxygen vacancies makes the reduced Co3O4 possess excellent OER activity. It is worth noting that it still exhibits high stability even after 20 h of cycles of scanning under OER working conditions. This method is simpler, cheaper, and more environmentally friendly than the existing methods of preparing oxygen vacancies. This mild solution reduction method sheds light on the understanding of defect-based electrocatalysts, opening up a new route for developing highly efficient electrocatalysts for the OER.

Modelling the impact of electrode roughness on net charge density in polyethylene

Predicting the electric field distribution under dc stress within polymeric insulations remains a challenge, as space charge behaviour is still difficult to understand in these materials. Charge generation is often thought to arise from injection at the electrodes. Hence, surface roughness should be taken into account, as it strengthens the electric field locally and therefore promotes charge generation at some points. A charge transport model has been developed in 2D to account for surface roughness. The model is first validated with the help of previous results, obtained with a one-dimensional charge transport model. Then, with simple shapes accounting for roughness, the simulated results show that surface roughness has a significant impact on the net space charge behaviour. The impact of shape, and size of protrusions are presented, as well as a more realistic case where a large surface of the electrode is considered to be rough.

Efficient and tunable one-dimensional charge transport in layered lanthanide metal-organic frameworks.

The emergence of electrically conductive metal-organic frameworks (MOFs) has led to applications in chemical sensing and electrical energy storage, among others. The most conductive MOFs are made from organic ligands and square-planar transition metal ions connected into two-dimensional (2D) sheets stacked on top of each other. Their electrical properties are thought to depend critically on the covalency of the metal-ligand bond, and less importance is given to out-of-plane charge transport. Here, we report a series of lanthanide-based MOFs that allow fine tuning of the sheet stacking. In these materials, the Ln3+ ions lie between the planes of the ligands, thus connecting organic layers into a 3D framework through lanthanide-oxygen chains. Here, efficient charge transport is found to occur primarily perpendicular to the 2D sheets. These results demonstrate that high conductivity in layered MOFs does not necessarily require a metal-ligand bond with highly covalent character, and that interactions between organic ligands alone can produce efficient charge transport pathways.

Charge transport model to predict dielectric breakdown as a function of voltage, temperature, and thickness

As the minimum pitch in interconnects continues to shrink, dielectric breakdown is becoming increasingly more difficult to qualify for each new technology node. Standard voltage-acceleration models provide quick, but general, assessments of the dielectric quality. Instead, a one-dimensional charge transport model has been developed as a tool to investigate the process of the dielectric breakdown and why it occurs. The model couples Poisson's equation with constitutive equations for mobile electrons, trapped electrons, and defects in the dielectric. Bonds in the dielectric matrix are weakened by the electric field, and broken by energetic electrons, creating defects. Failure occurs when a critical defect density is reached, causing trap-to-trap tunneling and an abrupt increase in the current.The model successfully replicates electrical data for leakage current and dielectric failure as a function of voltage, temperature, and thickness. The activation energy for dielectric failure is shown to increase as the electric field decreases, resulting in much higher activation energies at operating conditions compared to testing conditions. The dielectric strength also increases for decreasing thickness based on a previous theory for planar dielectrics, and is shown to cause the failure vs. field slope to increase for thinner dielectrics.

Single-Walled Carbon Nanotube Short-Channel Transistors Operating at Ultra-Low Voltages

Given that power consumption and short-channel effects exist in a trade-off relationship, there has been much effort to investigate short-channel transistors which enable relative reductions in the operating voltage. Recently, the feasibility of transistors operating at ultra-low voltages with a nanometer-scale channel length has been extensively investigated for future nanoelectronics. Here, we demonstrate solution-processed single-walled carbon nanotubes-based thin-film transistors (SWCNT-TFTs) with a sub-20-nm-channel operating at ultra-low voltages which utilize an electromigration technique that induces a broken bridge of nanoparticles. By employing the post-treatment process of thermal annealing in a vacuum, the charge transport of the short-channel SWCNT-TFTs was improved. The origin of such improvements is presumed to reduce the charge impurities, including organic/inorganic residues as defect states, as well as to improve electric contact between the SWCNT and the metal electrode, which strongly affects the one-dimensional charge transport.

Studies on relation between columnar order and electrical conductivity in HAT6 discotic liquid crystals using temperature-dependent Raman spectroscopy and DFT calculations

ABSTRACTThe vibrational property of 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6) discotic liquid crystal (DLC) material is investigated in this research by using temperature-dependent Raman spectroscopy technique. One-dimensional (1D) charge transport mechanism in the DLC molecules is enabled in the columnar liquid crystalline (Dh) phase. The result indicates a high core-to-core correlation in the liquid crystal columnar phase, which has a ‘memory’ like effect that extends into isotropic phase at femtosecond timescale. This correlation is also confirmed through electrical conductivity measurement of DLCs, in which the electrical conductivity is enhanced in the DLC phase. DFT simulation was also carried out in order to elucidate the basic properties of HAT6 such as the band gap in the light of Raman spectra. An interesting outcome is that a freely unspecified boundary model produces in a more flexible molecule, resulting in a reduced band gap. Thus, this work provides an understanding of relationship between columnar order and electrical conductivity of HAT6 molecule, and potential strategy for design of DLCs in electronics application.

Charge Transport in Hybrid Tunnel Superconductor—Quantum Dot—Superconductor Junctions

We have studied thin-film superconductor - semiconductor (with quantum dots)—superconductor MоRe–Si(W)—MoRe junctions, where electrons are tunneling through a single or several quantum dots within the Si(W) barrier. Current–voltage characteristics (CVCs) of the samples have been measured in a wide voltage range from –900 to 900 mV at temperatures from 4.2 to 8 K. At relatively high tungsten content in the barrier, we have observed emergence of the Josephson effect. Characteristic voltages I $_{c}$ R $_{N}$ , the product of the critical Josephson supercurrent I $_{c}$ and the normal-state resistance R $_{N}$ , of the samples were unusually high. Simultaneously, we have observed large excess quasiparticle currents I exc in the dissipative part of CVCs, which is a strong evidence of intensive electron-to-hole Andreev reflections in the junctions studied. When the W content in the barrier was decreased, the Josephson current disappeared, and we have observed resonant current peaks in the CVCs at bias voltages from 40 to 300 mV, which were symmetrical for positive and negative voltages. In the studied heterostructures, metal clusters inside the barrier behave as quasi-one-dimensional quantum dots; hence, the charge transport can be adequately described by scattering matrices within the quantum model of one-dimensional charge transport.

Conformal field theory out of equilibrium: a review

We provide a pedagogical review of the main ideas and results in non-equilibrium conformal field theory and connected subjects. These concern the understanding of quantum transport and its statistics at and near critical points. Starting with phenomenological considerations, we explain the general framework, illustrated by the example of the Heisenberg quantum chain. We then introduce the main concepts underlying conformal field theory (CFT), the emergence of critical ballistic transport, and the CFT scattering construction of non-equilibrium steady states. Using this we review the theory for energy transport in homogeneous one-dimensional critical systems, including the complete description of its large deviations and the resulting (extended) fluctuation relations. We generalize some of these ideas to one-dimensional critical charge transport and to the presence of defects, as well as beyond one-dimensional criticality. We describe non-equilibrium transport in free-particle models, where connections are made with generalized Gibbs ensembles, and in higher-dimensional and non-integrable quantum field theories, where the use of the powerful hydrodynamic ideas for non-equilibrium steady states is explained. We finish with a list of open questions. The review does not assume any advanced prior knowledge of conformal field theory, large-deviation theory or hydrodynamics.

Dual layer semiconducting nanocomposite of silicon nanowire and polythiophene for organic-based field effect transistors

We investigate a dual layer active channel of random distributed intrinsic silicon nanowires and solution processing semiconducting polythiophene polymers for organic-based field effect transistors. Primary results show that low density silicon nanowire networks could enhance the effective charge carrier mobility of polythiophene transistors by a factor of six, suggesting that these nanowires act as rapid one-dimensional charge transport bridges in the active channel. Moreover, increasing the nanowire loading in the dual layer nanocomposite could further lessen the transistor hysteresis. The lifetime test of nanowire-polythiophene devices is found to be more sustainable with respect to that of pristine polythiophene in ambient air. These results indicate that semiconducting nanowires should be considered as a viable additive to active channel for next-generation organic field effect transistors.

Electrocatalysts: Co–Ni‐Based Nanotubes/Nanosheets as Efficient Water Splitting Electrocatalysts (Adv. Energy Mater. 3/2016)

In article number 1501661, Gengfeng Zheng and co-workers demonstrate nanotube/nanosheet hybrid structures formed by ultrathin nanosheet assembly for electrocatalytic water splitting. These Co-Ni based nanotube/nanosheet hydroxides and nitrides function as efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalysts, respectively, attributed to their high electrochemically active surface area, efficient one-dimensional charge transport and tunable doping.

Double path integral method for obtaining the mobility of the one-dimensional charge transport in molecular chain.

We report on a theoretical investigation concerning the polaronic effect on the transport properties of a charge carrier in a one-dimensional molecular chain. Our technique is based on the Feynman's path integral approach. Analytical expressions for the frequency-dependent mobility and effective mass of the carrier are obtained as functions of electron-phonon coupling. The result exhibits the crossover from a nearly free particle to a heavily trapped particle. We find that the mobility depends on temperature and decreases exponentially with increasing temperature at low temperature. It exhibits large polaronic-like behaviour in the case of weak electron-phonon coupling. These results agree with the phase transition (A.S. Mishchenko et al., Phys. Rev. Lett. 114, 146401 (2015)) of transport phenomena related to polaron motion in the molecular chain.

Bulk Interpenetration Network of Thermoelectric Polymer in Insulating Supporting Matrix

Thermoelectric properties of conjugated polymers are found to improve upon homogeneously distributing conjugated polymer into an insulating supporting matrix. The local one-dimensional charge transport along the interpenetration conductive network simultaneously leads to lower thermal conductivity, higher electrical conductivity without sacrifice of Seebeck coefficient, and thus a higher figure of merit ZT, as compared with neat conjugated polymer.

Hierarchically Structured Microfibers of “Single Stack” Perylene Bisimide and Quaterthiophene Nanowires

Organic nanowires and microfibers are excellent model systems for charge transport in organic semiconductors under nanoscopic confinement and may be relevant for future nanoelectronic devices. For this purpose, however, the preparation of well-ordered organic nanowires with uniform lateral dimensions remains a challenge to achieve. Here, we used the self-assembly of oligopeptide-substituted perylene bisimides and quaterthiophenes to obtain well-ordered nanofibrils. The individual nanofibrils were investigated by spectroscopic and imaging methods, and the preparation of hierarchically structured microfibers of aligned nanofibrils allowed for a comprehensive structural characterization on all length scales with molecular level precision. Thus, we showed that the molecular chirality resulted in supramolecular helicity, which supposedly serves to suppress lateral aggregation. We also proved that, as a result, the individual nanofibrils comprised a single stack of the π-conjugated molecules at their core. Moreover, the conformational flexibility between the hydrogen-bonded oligopeptides and the π-π stacked chromophores gave rise to synergistically enhanced strong π-π interactions and hydrogen-bonding. The result is a remarkably tight π-π stacking inside the nanofibrils, irrespective of the electronic nature of the employed chromophores, which may render them suitable nanowire models to investigate one-dimensional charge transport along defined π-π stacks of p-type or n-type semiconductors.

Using Nanowires To Extract Excitons from a Nanocrystal Solid

Synthetic methods yielding highly uniform colloidal semiconductor nanocrystals with controlled shapes and sizes are now available for many materials. These methods have enabled geometrical control of optical properties, which are difficult or impossible to achieve in conventional bulk solids. However, incorporating nanocrystals efficiently into photodetectors remains challenging because of the low charge carrier mobilities typical of nanocrystal solids. Here we present an approach based on exciton energy transfer from CdSe/CdS core/shell nanocrystals to embedded CdSe nanowires. By combining the wide electronic tunability of nanocrystals with the excellent one-dimensional charge transport characteristics obtainable in nanowires, we are able to increase photocurrent extraction from a nanocrystal solid by 2-3 orders of magnitude. Furthermore, we correlate local device morphology with optoelectronic functionality by measuring the local photocurrent response in a scanning confocal microscope. We also discuss how nancocrystal/nanowire hybrid devices could be used in particle detector systems.

Ultrafast Photoconductivity in Organic Semiconductors

ABSTRACTWe present comprehensive study of ultrafast charge carrier dynamics in a variety of organic molecular crystals. In all samples, we observed sub-picosecond charge photogeneration and band-like transport, characterized by (i) an increase in charge carrier mobility as the temperature decreases in a wide temperature range of at least 20 K – 300 K and (ii) mobility anisotropy in the a-b plane of the crystals. The temperature dependence of the decay dynamics of the transient photoconductivity reveals the presence of shallow trapping sites in herring-bone-type-structured crystals (such as pentacene (Pc), tetracene (Tc), and rubrene (Rub)), while such traps are apparently absent in “brick-wall”-type crystals (such as functionalized pentacene (FPc)). We also report on the measurements of the charge carrier mobility anisotropy in the a-b plane of two types of FPc single crystals. Anisotropies of approximately 3.5 and 11.6 were obtained in the crystals characterized by crystal structures favoring two-dimensional and one-dimensional charge transport, respectively, consistent with the degree of π-overlap along different directions in the crystals.

Electronic Raman scattering through a stripe ordering transition in La2−xSrxNiO4

We describe the results of electronic Raman scattering experiments in two differently doped single crystals of La2−xSrxNiO4 (x=0.225 and 1/3). In B1g symmetry a crossover from weakly interacting to pseudogap-like behavior is observed at a charge-ordering temperature Tco. In B2g symmetry a redistribution of electronic continua with decreasing temperature is accompanied by a loss of spectral weight below Tco in the low-frequency region due to opening of a pseudogap. The slope of the Raman response at vanishing frequencies is investigated, too. Its temperature behavior in B2g symmetry, which predominantly selects charge carriers with momenta along the diagonals of the NiO2 bonds, provides clear evidence for one-dimensional charge transport in the charge-ordered phase.

Hall coefficient of the oxygen-intercalated La214 superconductor in the low hole concentration region

The temperature dependence of the Hall coefficient ( R H) of La 2CuO 4+ δ was studied in the low oxygen concentration range δ=0.015–0.030 where the phase separation into the antiferromagnetic and the superconducting states has been observed. The Hall number derived from the R H at room temperature agreed with the hole concentration of 0.03–0.06/Cu in the system, which is similar to the La 2− x Sr x CuO 4. However, in the lowest hole concentration region, the R H increased rapidly below around 250 K with lowering the temperature to 90 K where the R H started to decrease on further cooling. The drop in the R H below 90 K indicates a development of the one-dimensional charge transport in the system. The results are quite different from those observed in the similarly low-doped La 2− x Sr x CuO 4 system and discussed in terms of the phase separation, staging and charged-stripe formation.