Good Electron Transport Research Articles

Synthesis and research of a kind of perylene imide discoid molecule

Discotic liquid crystal molecules are excellent organic semiconductor materials due to their high carrier mobility. Dibenzocoronene derivatives obtained by nuclear expansion with perylene diimide as a matrix are one of the discotic molecules. The key factor for the application of this type of molecule is that it can form stable and long-range ordered organic nano-scale thin films. It can be used as an efficient carrier transport channel. This paper intends to use the “channel effect” to obtain the corresponding long-range orderly ideal film. The “channeling effect” referred to in this article is to bond functional discoid molecules on the substrate firstly, than generate the corresponding self-assembled monomolecular membranes (SAMs) to form an ordered channel on the surface which strongly induces and restricts the discoid molecules that arranged in parallel and orderly with each other along the “channels” created on the surface of the SAMs. Perylene diimide derivatives are a kind of good electron transport materials, which are characterized by high carrier mobility, low processing cost, and good thermal stability. However, it has the large rigid core and the melting point is relatively high. In this paper, a monobenzocoperylene diimide derivative is designed and synthesized, which will have a strong effect on the surface of the silicon substrate, and reduce the molecular melting point by reducing the size of the perylene imide discotic molecular core expansion.

A process for developing spherical graphite from coal tar as high performing carbon anode for Li-ion batteries

A new cost-effective method is developed to synthesize crystalline spherical graphite known as mesocarbon microbeads (MCMB) by the heat treatment of coal tar without the need of catalysts or additives and tested for its performance as anode material in Lithium-ion batteries (LIB). Two types of MCMB samples with varying morphological properties were prepared by the heat treatment of coal tar. The resulting MCMB samples were graphitized at 2350οC and were tested for their electrochemical performance as an anode for LIBs. Both MCMB electrodes show high specific capacity and good cycling stability for over 60 cycles and high-rate capability. The porous nature of MCMB with spherical morphology provides large surface area and electrolyte percolation while the high conductivity originating from highly graphitized structure could facilitate good electron transport throughout the MCMB surface. Therefore, MCMB synthesized by this additive free synthesis approach can be used for the cost-effective development of high-performing MCMB based electrode for LIBs.

Thermoelectric performance in the binary semiconductor compound A2Se2(A = K, Rb) with host-guest structure

The host-guest structure compounds are potential candidates for high-efficiency thermoelectric (TE) materials because of their good electronic transport combined with ultralow thermal conductivity. In this paper, we theoretically investigate TE transport properties of the hexagonal ${A}_{2}{\mathrm{Se}}_{2}\phantom{\rule{4pt}{0ex}}(A$ = K, Rb) with strongly quartic anharmonicity based on an incorporation of first-principles calculations with self-consistent phonon theory and Boltzmann transport equations. The calculation results reveal that ${A}_{2}{\mathrm{Se}}_{2}\phantom{\rule{4pt}{0ex}}(A$ = K, Rb) have ultralow lattice thermal conductivities ${\ensuremath{\kappa}}_{L}$, e.g., 0.30--0.$34{\mathrm{W}\phantom{\rule{0.16em}{0ex}}\mathrm{m}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ at room temperature, which are only one third of quartz glass. The calculated results indicate that the coexistence of small phonon lifetime ${\ensuremath{\tau}}_{\mathrm{ph}}$ and phonon group velocity ${\ensuremath{\upsilon}}_{\mathrm{ph}}$ is the reason for the ultralow ${\ensuremath{\kappa}}_{L}$ in these two host-guest structure materials. Additionally, due to the anisotropic electronic structure, that is, the coexistence of high dispersion and flat band edges, these two materials capture a high TE power factor along the $c$ axis. As a consequence, the anomalous high $\mathit{ZT}$ values of 2.95 and 2.17 at 500 K along the $c$-axis direction are captured in $n$-type ${\mathrm{K}}_{2}{\mathrm{Se}}_{2}$ and ${\mathrm{Rb}}_{2}{\mathrm{Se}}_{2}$, which break the long-term record of $\mathit{ZT}\phantom{\rule{4pt}{0ex}}<2$ in most TE materials reported so far. These findings reveal that ${A}_{2}{\mathrm{Se}}_{2}\phantom{\rule{4pt}{0ex}}(A$ = K, Rb) has broad prospects in TE applications.

Wafer-scale single-crystal monolayer graphene grown on sapphire substrate.

The growth of inch-scale high-quality graphene on insulating substrates is desirable for electronic and optoelectronic applications, but remains challenging due to the lack of metal catalysis. Here we demonstrate the wafer-scale synthesis of adlayer-free ultra-flat single-crystal monolayer graphene on sapphire substrates. We converted polycrystalline Cu foil placed on Al2O3(0001) into single-crystal Cu(111) film via annealing, and then achieved epitaxial growth of graphene at the interface between Cu(111) and Al2O3(0001) by multi-cycle plasma etching-assisted-chemical vapour deposition. Immersion in liquid nitrogen followed by rapid heating causes the Cu(111) film to bulge and peel off easily, while the graphene film remains on the sapphire substrate without degradation. Field-effect transistors fabricated on as-grown graphene exhibited good electronic transport properties with high carrier mobilities. This work breaks a bottleneck of synthesizing wafer-scale single-crystal monolayer graphene on insulating substrates and could contribute to next-generation graphene-based nanodevices.

Ultrafast NH3 gas sensor based on phthalocyanine-optimized non-covalent hybrid of carbon nanotubes with pyrrole

The development of innovative methods for optimizing carbon nanotube-based gas sensors for rapid and sensitive detection of ammonia remains challenging. Here, MCNT@PPy/TfmpoPcCo hybrid with a uniform 3-D network were prepared by tightly combining tetra-β-trifluoromethylphenoxyphthalocyanine cobalt (TfmpoPcCo) on the surface of MCNT@PPy through π-π interactions and used to construct NH3 sensor, while the MCNT@PPy were obtained by in-situ polymerization of PPy onto the side wall of MCNT. TfmpoPcCo not only adsorbs on the MCNT@PPy side wall due to its structure advantages, but also acts as a sensor accelerator. MCNT@PPy/TfmpoPcCo sensor show higher NH3 sensing performance than the MCNT, PPy and TfmpoPcCo under same operating conditions, especially in ultrafast response/recovery time (11.7 s/91.8 s to 50 ppm NH3) with low limit-of-detection of 11 ppb at room temperature (20 °C) and excellent gas selectivity. In addition, the MCNT@PPy/TfmpoPcCo sensor preserve superior gas response (26.2% to 50 ppm NH3) as well as outstanding stability over 60 days and humidity resistance. The excellent NH3 sensing properties are attributed to the excellent gas selectivity of TfmpoPcCo, the unique redox characteristics of PPy to ammonia (NH3), and the good electron transport ability and stability of MCNT. The synergistic optimization strategy of ternary materials is of great significance towards the exploration and construction of ideal materials for gas sensor in the future.

Performance-Enhancing Sulfur-Doped TiO2 Photoanodes for Perovskite Solar Cells

High-performance electron transport layer (ETL) anode generally needs to form a uniform dense layer with suitable conduction band position and good electron transport properties. The TiO2 photoanode is primarily applied as the ETL because it is low-cost, has diverse thin-film preparation methods and has good chemical stability. However, pure TiO2 is not an ideal ETL because it lacks several important criteria, such as low conductivity and conduction band mismatch with compositional-tailored perovskite. Thus, TiO2 is an inefficient photo-anode or ETL for high-performance perovskite devices. In this study, sulfur as dopant in the TiO2 photo-anode thin film is used to fabricate solid-state planar perovskite solar cells in relatively high humidity (40–50%). The deposited S-doped thin film improves the power conversion efficiency (PCE) of the device to 6.0%, with the un-doped TiO2 producing a PCE of 5.1% in the best device. Improvement in PCE is due to lower recombination and higher photocurrent density, resulting in 18% increase in PCE (5.1–6.0%).

Synthesis and characterization of electrical properties of nanostructured zinc oxide film prepared by spray coated seed layer based hydrothermal method

The aim of study was to investigate the carrier transport properties of seed layer assisted nanostructured ZnO thin film. The structural analysis by XRD showed the predominant peak at 34.63° (2θ) corresponding to <002> plane. From the SEM image, it was found that the particles grown vertical nanoparticles on the glass substrate. The optical bandgap of the material was calculated from UV-Visible absorption spectrum which was found as 3.28 eV. The I-V characteristics showed that the film possess semiconducting nature. The electron mobility was determined as 1.60×102cm2/Vs and the resistivity was around 1.99×10−4 Ω.cm and the carrier concentration of the film was 7.54×1020cm−3 by Hall effect measurement. The seed assisted nanostructured film exhibited good electron transport properties which can be applied in many electrical applications like a solar cells, sensors and optoelectronic devices.

Visible- light responsive PPynt@NH2-MIL-125 nanocomposite for efficient reduction of Cr(VI)

The present investigation aims to remove Cr(VI) by PPynt@NH2-MIL-125 nanocomposite material under visible light irradiation.In this paper, a new photocatalyst material was prepared by using traditional conductive polymer polypyrrole nanotube (PPynt) and MOFs (NH2-MIL-125), and was characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), XPS, ultraviolet-visible diffuse reflectance spectroscopy (UV–VIS/DRS), and transmission electron microscopy (TEM). PPynt is also conducive to the separation and transferring of charge carriers, as well as the improvement of activity because the conductivity of PPynt provides a good electron transport path. The result shows that 5% PPynt@NH2-MIL-125 has superior photocatalytic activity and a 99.02% Cr(VI) reduction. On this basis, we systematically studied the effect of different pH and concentrations on the reduction system.

Hyperdoping of silicon films with titanium via nanosecond-laser melting: Structure evolution, impurity distribution, sub-bandgap formation, and doping mechanism

Hyperdoping of Si films with Ti was achieved via nanosecond (ns)-laser melting of Si/Ti composite films under different film deposition and laser treatment conditions. The structural evolution (from amorphous to nanocrystalline structure), Ti impurity distribution and concentration variation, and sub-bandgap (Ti impurity band) formation in the films, were carefully studied to optimize the hyperdoping process. The results show that the hyperdoping concentration and depth can be manipulated by controlling the Si and Ti co-evaporation speed ratio, Si/Ti composite film thickness together with a matched ns-laser fluence. Furthermore, Ti impurity bands were determined with two sub-bandgaps of energy 385–448 and 759 meV. In addition, the mechanism of ns-laser hyperdoping of Si films was clarified into the heat transfer, material ejection, partial ablation and redeposition, melting, and nanocrystallization (simultaneous hyperdoping) processes. Thus, hyperdoped nanocrystalline films up to the micron-level thickness with a crystallinity of ∼ 70%, an optical absorptance of ∼ 90% from the visible to the long-wavelength near-infrared spectrum, and good electronic transport properties were obtained. These hyperdoped Si films exhibit a high potential in the development of Si-based broad-spectrum tandem or thin film solar cells and room-temperature infrared photodetectors.

Polarizable cesium cations for energy storage from electrolyte characterization to-EDLC application

In the quest for new electrolytes on electrochemical energy storage devices, we present, characterize and test a simple organic electrolyte based on cesium bis (trifluoromethanesulfonyl) imide (CsTFSI) for supercapacitor (SC) application. The physicochemical properties of CsTFSI-based electrolytes in acetonitrile (ACN) and propylene carbonate (PC), alone and mixed with LiTFSI as a co-salt, were characterized under various concentrations and temperatures and revealed a different solution organization system, depending on the solvent and nature of the salt. The solvation radii based on the Jones-Dole-Kaminsky model indicated that ACN forms a single sphere of solvation around the cation Cs+, unlike PC, which does not solvate the large and polarizable Cs cation. The CsTFSI -ACN (1 mol L−1) electrolyte presents a suitable viscosity (<1 mPa•s) and density (36 mS cm−1) for SC application, ionic mobility within an extended temperature range (−40–60 °C), and its molecular level is compatible with the porosity of activated carbon (AC) electrodes. The nanopores of the ACs display good electronic conductivity and ion transport capability, characteristic of electrochemical double-layer capacitors EDLC within an electrochemical window of 3 V and a wide temperature span, i.e., −20–40 °C. In-situ measurements of accumulated gas pressure during typical galvanostatic charge-discharge protocols exposed a minimum pressure at 40 °C (2.6 × 108 Pa for CsTFSI-ACN, 1 mol L−1) compared to standard electrolytes (Et4BF4-ACN, 1 mol L−1) and yielded specific capacitances (Csp) of 115 F g−1 at a normalized current density of 2 A g−1. Standard accelerated aging floating tests confirmed the stability of the SCs (>100 h → 12% decrease on Csp). Finally, the suitability of CsTFSI as a co-salt (with lithium bis(trifluoromethanesulfonyl)imide, LiTFSI) was demonstrated for SC devices, aiming to boost Csp (i.e.,164 F g−1 for equimolar amounts of LiTFSI and CsTFSI). The above results attest to the functionality of CsTFSI as a promising salt for energy storage applications.

Accelerating charge transfer via nonconjugated polyelectrolyte interlayers toward efficient versatile photoredox catalysis

One of the challenges for high-efficiency single-component-based photoredox catalysts is the low charge transfer and extraction due to the high recombination rate. Here, we demonstrate a strategy to precisely control the charge separation and transport efficiency of the catalytic host by introducing electron or hole extraction interlayers to improve the catalytic efficiency. We use simple and easily available non-conjugated polyelectrolytes (NCPs) (i.e., polyethyleneimine, PEI; poly(allylamine hydrochloride), PAH) to form interlayers, wherein such NCPs consist of the nonconjugated backbone with charge transporting functional groups. Taking CdS as examples, it is shown that although PEI and PAH are insulators and therefore do not have the ability to conduct electricity, they can form good electron or hole transport extraction layers due to the higher charge-transfer kinetics of pendant groups along the backbones, thereby greatly improving the charge transfer capability of CdS. Consequently, the resultant PEI-/PAH-functionalized nanocomposites exhibit significantly enhanced and versatile photoredox catalysis.

The influence of twin boundary on lattice thermal conductivity of thermoelectric InSb

Twin boundaries (TBs) can increase interface scattering to reduce the lattice thermal conductivity. InSb has good electronic transport properties, but its high thermal conductivity constrains its thermoelectric application. In this work, we aim to study the role of TBs on lattice thermal conductivity of InSb. We use non-equilibrium molecular dynamics simulation to investigate how the TB spacing and orientation influence the lattice thermal conductivity of InSb. We find that TBs can hinder the heat flow, leading to decreased temperature gradient and, hence, remarkably reduced lattice thermal conductivity. The relationship between κL and λ can be described by a proportional function. Nanotwinned InSb with TB spacing of 1.1 nm has a lattice thermal conductivity of 12.6 W/m K, a decrease in 22.2% compared with its single crystal (16.2 W/m K). We also find that a minimum lattice thermal conductivity of InSb can be obtained when the TB orientation is perpendicular to the direction of heat flow. These findings provide a theoretical guidance for TBs engineering to reduce the thermal conductivity of thermoelectric materials.

Controllable preparation of N-doped Ni3S2 nanocubes@N-doped graphene-like carbon layers for highly active electrocatalytic overall water splitting

Nickel sulfide (Ni3S2) is a promising electrocatalyst because of its good metal conductivity and stability in alkaline medium. However, the reported catalytic activity of Ni3S2 is still relatively low. N-doped graphene coated N-doped Ni3S2 nanocubes (N-Ni3S2@NG) structure was proposed, which is an effective way to improve the catalytic activity of Ni3S2. Thanks to the unique structural design and functional integration, the OER and HER in alkaline medium provide 238 mV and 100 mV over potential respectively at 10 mA cm−2, and 1.53 V ultra-low operating voltage for overall water splitting. In addition, its super stable catalytic activity is also impressive, and the performance loss is negligible after 70 h durability test. These experimental data and analysis show that, the outstanding catalytic activity of N-Ni3S2@NG is due to its abundant active centers and good electron transport properties. More broadly, this combination of bifunctional concept and nanoscale stereoscopic design is unique and advantageous, especially suitable for the development of highly active and durable electrocatalysts for energy conversion reactions.

Stable Field Electron Emission and Plasma Illumination from Boron and Nitrogen Co‐Doped Edge‐Rich Diamond‐Enhanced Carbon Nanowalls

AbstractSuperior field electron emission (FEE) characteristics are achieved in edge‐rich diamond‐enhanced carbon nanowalls (D‐ECNWs) grown in a single‐step chemical vapor deposition process co‐doped with boron and nitrogen. The structure consists of sharp, highly conductive graphene edges supplied by a solid, diamond‐rich bottom. The Raman and transmission electron microscopy studies reveal a hybrid nature of sp3‐diamond and sp2‐graphene in these nanowalls. The ab‐initio calculations were carried out to support the experimental observations of diamond‐graphene hybrid structure. Finally, this hybrid D‐ECNWs is employed as a cathode in an FEE device resulting in a low turn‐on field of 3.1 V µm−1, a large field enhancement factor, a high FEE Je of 2.6 mA cm−2, and long lifetime stability of 438 min. Such an enhancement in the FEE originates from the unique materials combination, resulting in good electron transport from the graphene phases and efficient FEE of electrons from the sharp edges on the nanowalls. The prospective application of these materials is displayed by employing these hybrids as cathodes in a microplasma device ensuing a low threshold voltage of 160 V and high plasma stability of 140 min, which confirms the role of these hybrid structured nanowalls in the enhancement of electron emission.

Polypyrrole decorated ZnTi hydrotalcite with enhanced adsorption and Cr(VI) photoreduction activity under visible-light

A conjugated polymer polypyrrole (PPy) was used to decorate the ZnTi hydrotalcite (ZnTi-LDH) for constructing an organic–inorganic PPy/ZnTi-LDH composite by a facile in-situ oxidation polymerization. It was found that the as-prepared composite displayed a superior photocatalytic performance and excellent stability under visible light irradiation, which Cr(VI) reduction efficiency (99.72% for 35 min) was around 53 and 12 times higher than those of the pristine ZnTi-LDH and pure PPy, respectively, and still maintained 95.10% even after 5th cycles. The dramatically enhanced photocatalytic performances were attributed to the beneficial combination of the ZnTi-LDH stratified structure and conductive PPy, which effectively facilitated charge transfer, restrained recombination, and increased visible-light absorption. Particularly, PPy as a remarkable conductive polymer, played a crucial role in the Cr(VI) reduction, which not only was a light acceptor to produce photo-generated charge carriers but also provided a good electron transport path to accelerate the separation and migration of electron-hole pairs to improve the photoreduction performances. Finally, possible photocatalytic reaction mechanism of the PPy/ZnTi-LDH was also proposed.

Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

Summary Discovering novel materials and attaining higher performance are the eternal pursuit of thermoelectric materials research. Here, we report a material series, (Cu1−xAgx)2(Te1−ySy) (0.16 ≤ x ≤ 0.24, 0.16 ≤ y ≤ 0.24), which adopts a complex orthorhombic structure differing from any known crystal structure of (Cu/Ag)2(S/Te). This material series is featured by the crystal-amorphicity duality induced by the large anionic size mismatch: a crystalline sublattice of highly size-mismatched anions Te/S coexists with an amorphous-like sublattice of cations Cu/Ag. In the context of structure-property correlation, the crystal-amorphicity duality gave rise to not only interesting electrical properties but also exceptionally low lattice thermal conductivities from 300 to 1,000 K. A state-of-the-art figure of merit zT of 2.0 is obtained in the x = y = 0.22 sample at 1,000 K. These results give insights into crystal-amorphicity duality as a paradigm-shifting materials design approach to develop high-performance thermoelectric materials.

Enhanced electrochemical behaviour of FeCo2O4/PANI electrode material for supercapacitors

Conducting polymers incorporated with binary metal oxides are the upcoming pseudocapacitive materials, which are in high demand owing to their impressive electrochemical performance. In the current study, we describe the synthesis of FeCo2O4/PANI by in-situ polymerization method and its applicability as electrode in supercapacitors. The as-prepared FeCo2O4/PANI was characterized via various physico-chemical techniques. The electrochemical behavior of FeCo2O4/PANI was analysed by Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD) and Electrochemical Impedance Spectroscopic (EIS) methods. The studies revealed pronounced specific capacity (Csp) value of 940 C g−1 at the current density of 1 A g−1 by GCD. Moreover, the elevated capacitive behavior was mainly due to its very porous nanorod like structure with a huge number of active sites, which substantially resulted in good ion and electron transport. The high specific capacity of FeCo2O4/PANI and the simple one-step fabrication process depicted its potential and promising applicability as electrode material for advanced energy storage devices.

Bi2MoO6 hierarchical microflowers for electrochemical oxygen evolution reaction

Solvothermal Bi2MoO6 hierarchical microflowers synthesis has been successfully attempted. Methanol, ethanol and isopropanol have been mediated to synthesize three kinds of Bi2MoO6 hierarchical microflowers. Highly oriented (311) plane growth of orthorhombic Bi2MoO6 hierarchical microflowers have been confirmed. Interstitial vacancies and its role on electrochemical activity have been extensively discussed. Electrode fabrication was constructively done by using Ni foam substrate. Half cell arrangement of each electrode in alkaline medium has been designed to measure the electrochemical activity towards water oxidation. High current density of 356 mA/cm2 was afforded by Bi2MoO6 hierarchical microflowers mediated by ethanol solvent during synthesis. Low Tafel slope value of 43 mV/dec has been reported to obtain 10 mA/cm2 current density. Higher conductivity long with very good electron transportation has been achieved and is also adapted for 12 h long time stability test and achieved 86% of retention in its performance. Hence, optimally prepared Bi2MoO6 hierarchical microflowers could be an efficient electrode for clean energy fabrication.

Fabrication, Functionalization, and Application of Carbon Nanotube-Reinforced Polymer Composite: An Overview.

A novel class of carbon nanotube (CNT)-based nanomaterials has been surging since 1991 due to their noticeable mechanical and electrical properties, as well as their good electron transport properties. This is evidence that the development of CNT-reinforced polymer composites could contribute in expanding many areas of use, from energy-related devices to structural components. As a promising material with a wide range of applications, their poor solubility in aqueous and organic solvents has hindered the utilizations of CNTs. The current state of research in CNTs—both single-wall carbon nanotubes (SWCNT) and multiwalled carbon nanotube (MWCNT)-reinforced polymer composites—was reviewed in the context of the presently employed covalent and non-covalent functionalization. As such, this overview intends to provide a critical assessment of a surging class of composite materials and unveil the successful development associated with CNT-incorporated polymer composites. The mechanisms related to the mechanical, thermal, and electrical performance of CNT-reinforced polymer composites is also discussed. It is vital to understand how the addition of CNTs in a polymer composite alters the microstructure at the micro- and nano-scale, as well as how these modifications influence overall structural behavior, not only in its as fabricated form but also its functionalization techniques. The technological superiority gained with CNT addition to polymer composites may be advantageous, but scientific values are here to be critically explored for reliable, sustainable, and structural reliability in different industrial needs.

CsPbBr3-MoS2-GO nanocomposites for boosting photocatalytic degradation performance

In order to address the main challenge of weak photocatalytic performance of pure metal halide perovskite materials, we innovatively introduced MoS2-graphene oxide (GO) composite structure and synthesized CsPbBr3-MoS2-GO nanocomposites by a two-step method. XRD and Raman results show that the three components are well combined to form a new CsPbBr3-MoS2-GO nanocomposite. TEM results show that MoS2 nanoribbons and CsPbBr3 quantum dots (QDs) are uniformly dispersed on the GO sheet. The photocatalytic activity of nanocomposites was evaluated by studying the photodegradation of Sudan Red III under xenon lamp irradiation. Benefiting from abundant active interfaces, the nanocomposites show much excellent photocatalytic degradation performance compared with pure CsPbBr3 QDs. The degradation rate of Sudan Red III by CsPbBr3-MoS2-GO nanocomposites is 3.1 times of that of pure perovskite QDs. Sudan Red III was completely photocatalytic degraded in 100 min. We believe that GO, with suitable band structure, high conductivity and good dispersibility, can bridge well MoS2 and CsPbBr3, act as a good electron transport channel, reduce carrier recombination and ultimately boost photocatalytic performance.