Good Electron Transport Research Articles

Photocatalytic H2 production of composite one-dimensional TiO2 nanostructures of different morphological structures and crystal phases with graphene

One-dimensional TiO2 nanostructures of different structural phases with graphene composites were employed as photocatalysts for photocatalytic H2 production. Two strategies have been explored for enhancement of photocatalytic reactivity. The first is demonstrated through the use of one-dimensional nanostructures, which feature good vectorial electron transport due to decreased grain boundaries. The second strategy is to form a composite/network with two-dimensional reduced graphene oxide (RGO), which features visible light photosensitization and is an efficient charge transporter and separator. It is noted that other than structural design, it is crucial to attain anatase phase structures and superior interfacial contact between GO and TiO2 nanostructures to enable optimal synergy between one-dimensional TiO2 nanostructures and graphene for enhanced photocatalytic H2 production performance. In this work, hydrothermal synthesis and an in situ solution-based photoreduction method are used owing to their scalability, low temperature, high yield and ease of temperature and reactant concentration control characteristics.

Light emission and current rectification in a molecular device: Experiment and theory

We have investigated optical and transport properties of the molecular structure 2,3,4,5-tetraphenyl-1-phenylethynyl-cyclopenta-2,4-dienol experimentally and theoretically. The optical spectrum was calculated using Hartree-Fock-intermediate neglect of differential overlap-configuration interaction model. The experimental photoluminescence spectrum showed a peak around 470 nm which was very well described by the modeling. Electronic transport measurements showed a diode-like effect with a strong current rectification. A phenomenological microscopic model based on non-equilibrium Green's function technique was proposed and a very good description electronic transport was obtained.

Reducing the thermal conductivity of silicon by nanostructure patterning

Based on molecular dynamics simulations, we propose using nanostructure-patterned silicon for thermoelectric applications. Three typical examples are (i) fractal-like nanoporous Si, (ii) etched Si nanofilm, and (iii) quasi-periodic layered SiGe. All of them can exhibit very low thermal conductivity (less than 1.0 W m−1 K−1) and may be mass produced with standard fabrication techniques such as molecular beam epitaxy or Czochralski process. By maintaining good electronic transport of bulk Si, it is possible to achieve ZT∼5.0 at room temperature.

Synthesis, crystal structures, and photophysical properties of a series of novel tetrahydrobenzodiacridines

Several novel 6,7,14,15-tetrahydro-benzo[1,2-c:4,5-c′]diacridine derivatives (1a–1h) were synthesized in this study. Compounds 1a–1h were thermally robust with high decomposition temperatures (≥359.5°C) and high melting points (223.7°C–452.2°C). On the other hand, compound 1b was crystallized in a triclinic system, containing space groups P-1. Compounds 1a–1h showed UV–vis absorption (λmaxAbs) in the range of 372nm–377nm in chloroform solutions and 381nm–389nm in solid states. They also showed fluorescence (λmaxEm) in the range of 374nm–389nm in chloroform solutions and 421nm–457nm in solid states. Moreover, these compounds exhibited good fluorescence quantum yields ranging from 43.5% to 96.1%. Compounds 1a–1h showed a formal reduction potential in the range of −1.95V to −2.13V (vs. SCE), and their LUMO and HOMO levels were 2.27eV–2.45eV and 4.92eV–6.31eV, respectively. These results demonstrate that novel 6,7,14,15-tetrahydro-benzo[1,2-c:4,5-c′]diacridine derivatives (1a-1h) are promising thermally stable blue light-emitting materials with good electron transport and good hole-blocking properties for organic light-emitting diodes.

Theoretical study of chemosensor for fluoride anion and optical properties of the derivatives of diketopyrrolopyrrole

The interactions between chemosensors, diketopyrrolopyrrole (DPP) derivatives, and different halides (F−, Cl−, and Br−) anions have been theoretically investigated using DFT approaches. Theoretical investigations have been performed to explore the optical, electronic, charge transport, and stability properties of DPP derivatives as charge transport and/or luminescent materials. It turned out that the unique selectivity of DPP derivatives for F− is ascribed to their ability of deprotonating the host sensors. The atoms in molecules theory and natural bond orbitals charge analysis of the complexes consisting of DPP derivatives and X− (X = F, Cl, and Br) confirm that the protons are almost completely abstracted by F−. The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for ratiometric fluorescent fluoride chemosensors as well as chromogenic chemosensors. Furthermore, the derivatives with biphenyl, 2-(thiophen-2-yl)thiophene, and benzo[d]thieno[3,2-b]thiophene fragments are expected to be promising luminescent materials. In addition, derivatives with 2-(thiophen-2-yl)thiophene and 4,9-dihydrothieno[3,4-b]quinoxaline fragments can serve as good electron transport materials for OLEDs as well.

Oxide Catalysts for Rechargeable High‐Capacity Li–O2 Batteries

AbstractNano‐crystalline mixed metal oxides with an expanded pyrochlore structure are synthesized by a chemical precipitation route in alkaline media. The high concentration of surface active sites afforded by their high surface area, intrinsically variable oxidation state and good electron transport lead to promising electrocatalytic properties for oxygen evolution in Li‐O2 cells, yielding rechargeable discharge capacities over 10 000 mAh g−1 and lowering anodic overpotentials significantly. The discharge capacity of the Li‐O2 cell is increased further when a small amount of gold is deposited on the pyrochlore oxide, which serves as a more efficient oxygen reduction catalyst. The amount of catalyst necessary for oxygen evolution performance is reduced to as little as 5 wt% by supporting the highly‐divided pyrochlore oxide crystallites on carbon using in‐situ deposition methods.

Nanoscale investigation on large crystallites in TiO2 nanotube arrays and implications for high-quality hybrid photodiodes

Anodized TiO2 nanotube arrays fabricated on a TiO2 thin film on conducting glass substrates can be readily implemented in diverse applications like hybrid solar cells. In this study, we concentrate on morphologies with inner tube diameter being around 30 nm which is in dimension of the exciton diffusion length of common organic hole conductors. Cross-sectional preparation of the intact tube array in correlation with transmission electron microscopy has been performed to get local information on the TiO2 nanotubes and their arrangements, depending on anodization voltage. Crystallites have been found to be anatase and in size of several hundred nanometers along tube walls with increasing length for increasing anodization voltages. Inter-tube connections with similar crystal orientations of adjacent tubes are found. These give rise to large areas of uniform orientation. Thus, the number of grain boundaries within the film is low compared to the reported values for different TiO2-polymer material systems. Using the arrays, hybrid TiO2 solar cells were fabricated, which show high fill factors indicating good electron transport. The results suggest high electron mobility and are encouraging for a utilization of the nanotube arrays in next generation photovoltaics.

Efficient Triplet Exciton Confinement of Blueand White-Organic Light Emitting Diodes Using a New Host Material

We have demonstrated lower driving voltage and efficient blue phosphorescent organic light emitting diodes (PHOLEDs) using iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate (Flrpic) doped in new host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole (SPC) and 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) as double-emitting layer (D-EML) system. The D-EML was employed to have good electron transportability and exciton confinement. Additionally, we fabricated white organic light-emitting diode (WOLED) using a phosphorescent red emitter; bis(2-phenylquinolinato)-acetylacetonate iridium III (Ir(pq)2acac) doped in SPC and TPBi as D-EML. The properties of white device exhibited a maximum luminous efficiency of 19.03 cd/A, a maximum external quantum efficiency of 9.91%, and a maximum power efficiency of 12.30 lm/W. It also showed white emission with CIE(x,y) coordinates of (x = 0.38, y = 0.37) at 8 V.

Naphthalene Diimide-Based Polymer Semiconductors: Synthesis, Structure–Property Correlations, and n-Channel and Ambipolar Field-Effect Transistors

A series of nine alternating donor–acceptor copolymer semiconductors based on naphthalene diimide (NDI) acceptor and seven different thiophene moieties with varied electron-donating strength and conformations has been synthesized, characterized, and used in n-channel and ambipolar organic field-effect transistors (OFETs). The NDI copolymers had moderate to high molecular weights, and most of them exhibited moderate crystallinity in thin films and fibers. The LUMO energy levels of the NDI copolymers, at −3.9 to −3.8 eV, were constant as the donor moiety was varied. However, the HOMO energy levels could be tuned over a wide range from −5.3 eV in P8 to −5.9 eV in P1 and P3. As semiconductors in n-channel OFETs with gold source/drain electrodes, the NDI copolymers exhibited good electron transport with maximum electron mobility of 0.07 cm2/(V s) in P5. Although head-to-head (HH) linkage induced backbone torsion, polymer P4 showed substantial electron mobility of 0.012 cm2/(V s) in bottom-gate/top-contact devi...

Effects of Electrospun TiO2 Nanowires Mixed in Nanoparticle-Based Electrode for Dye-Sensitized Solar Cells

In this article, we report the improvement of energy conversion efficiency by a simple process for dye-sensitized solar cells (DSSCs). Some previous studies were reported in which TiO2 nanowires were used in the place of TiO2 nanoparticles as a TiO2 electrode because nanowires possess a good electron transport property. However, if larger sizes of nanowires are used for the TiO2 electrode, a large void between nanowires and a decrease in surface area are observed. To solve this problem, we report a TiO2 nanoparticle/nanowire hybrid electrode for DSSCs, which showed both a good electron transport property and dye adsorption. TiO2 nanofibers were fabricated by an electrospinning method and sol–gel techniques. TiO2 nanowires, whose diameters were controlled by varying the polymer concentration in the electrospinning solution, were successfully applied to DSSCs. We examine how TiO2 nanowires can work in the TiO2 electrode. In this study, we demonstrated that this hybrid electrode has an advantage in the efficiency of DSSCs.

A co-immobilized mediator and microorganism mediated method combined pretreatment by TiO2 nanotubes used for BOD measurement

In this paper, we proposed a method by using co-immobilized Escherichia coli (E. coli) as a biocatalyst and neutral red (NR) as an artificial electronic acceptor to modify glassy carbon electrode (GCE) for biochemical oxygen demand (BOD) measurement. Two different modification approaches of GCE were utilized and compared. In one approach, NR was electropolymerized on the surface of GCE, and E. coli cells were mixed with grafting copolymer PVA-g-PVP (briefly gPVP) and covered on NR polymer film to obtain a (gPVP/E. coli)/PNR/GCE. In the second approach, both NR and E. coli cells were mixed with the copolymer gPVP and modified GCE, after drying, which was electrochemically treated similar as above for obtaining a (gPVP/E. coli/NR)p/GCE. Based on the electrochemical evaluation, the performance of the latter was better, which may be caused by that the NR deposited on the surface of E. coli resulting in a good electron transport and permeability of cells membrane. To develop the results obtained at (gPVP/E. coli/NR)p/GCE further, the pretreatment by TiO2 nanotubes arrays (TNTs) was employed, and different effects on samples of GGA, OECD, urea and real wastewater were evaluated. These results suggest that the present method holds a potential application for rapid BOD biosensor.

Enhanced electron field emission properties of high aspect ratio silicon nanowire–zinc oxide core–shell arrays

The enhanced electron field emission (EFE) properties of high aspect ratio, vertically aligned SiNW-ZnO core-shell arrays are presented. These core-shell arrays are prepared by a thin, controlled, highly crystalline and conformal coating of zinc oxide as shell using the plasma assisted-atomic layer deposition (PA-ALD) route on vertically aligned silicon nanowire arrays core. The core-shell nanostuctures are confirmed by HRTEM imaging along with the individual elemental mapping demonstrating the conformal deposition of 10 nm ZnO on the SiNWs. EFE properties of va-SiNW-ZnO core-shell arrays showed a high emission current density of 51 μA cm(-2) and a low turn on field of 7.6 V μm(-1) (defined at a current density of 1 μA cm(-2)) compared to the 3.2 μA cm(-2) emission current density and 9.1 V μm(-1) turn on field for SiNWs. The field enhancement factor (β) of 4227 for the devices demonstrates that these core-shell nanowire arrays are excellent field-emitters. Such an enhancement in the field emission originates from the details of the band structure of this peculiar material combination resulting in good electron transport from SiNW to ZnO as evident from the band diagram of the core-shell material. This is further supported by the conducting AFM studies where lowering in threshold voltage by 1 eV confirms the role of ZnO coating in the enhancement of the emission characteristics.

衬底对PTCDA薄膜结构与电荷输运特性的影响

Perylene-3,4,9,10-tetracarboxylic acid dianhydride(PTCDA) thin films were vacuum evaporated on Au,Al and ITO substrates,their structure and morphology were analysed by X-ray spectroscopy(XRD) and atomic force microscope(AFM).The results show that most of PTCDA molecules don't lie parallel to the substrate,which indicates that electron transport dominates the current conduction in the direction perpendicular to the film plane.PTCDA films grown on ITO and Au arrange regularly.It shows good electronic transport properties perpendicular to the film plane.But the grains of PTCDA film grown on Al arrange disorderly resulting in poor performance of electronic conduction.By the thermionic emission theory at metal-organic interface and space charge limited current conduction theory in the organic bulk and considering the electric field effect on mobility,current density-voltage curves of ITO/PTCDA/Al devices were fitted in different PTCDA film's thickness.The numerical value of electron mobility dependent on electric field was determined for the specific PTCDA film thickness.

Microstructure composite-like Bi2S3 polycrystals with enhanced thermoelectric properties

We have designed a composite-like microstructure to improve the thermoelectric (TE) properties of Bi2S3 polycrystals. The nanosized Bi2S3 powders derived from mechanical alloying (MA) were mixed with [001] oriented single crystalline Bi2S3 nanorods prepared by hydrothermal synthesis (HS), which were densified by spark plasma sintering (SPS) to form a composite-like microstructure bulk with road-like structures consisting of nanorods. Because the nanorods provide good electron transport paths, the carrier mobility of the composite-like Bi2S3 bulk materials was improved by more than two orders of magnitude by mixing 10 wt% nanorods into the MA-derived powders. The electrical resistivity was also reduced from 2.5 × 10−2 to 8.5 × 10−4 Ωm at 323 K, but the thermal conductivity was just slightly increased, resulting in a significantly enhanced ZT value, which was almost two times higher than that of the nanorod-free sample. This study demonstrated the possibility to significantly enhance the ZT value of TE bulks by combining the advantages of single crystals and polycrystals via controlling the microstructure without any chemical doping.

Anthracenedicarboximide-based semiconductors for air-stable, n-channel organic thin-film transistors: materials design, synthesis, and structural characterization

A family of six n-channel organic semiconductors (1–6) based on the N,N′-dialkyl-2,3:6,7-anthracenedicarboximide (ADI) core was synthesized and characterized. These new semiconductors are functionalized with n-octyl (-n-C8H17), 1H,1H-perfluorobutyl (-n-CH2C3F7), cyano (–CN), and bromo (–Br) substituents, which results in wide HOMO and LUMO energy variations (∼1 eV) but negligible optical absorbance (λmax = 418–436 nm) in the visible region of the solar spectrum. Organic thin-film transistors (OTFTs) were fabricated via semiconductor vapor-deposition, and the resulting devices exhibit exclusively electron transport with good carrier mobilities (μe) of 10−3 to 0.06 cm2 V−1 s−1. Within this semiconductor family, cyano core-substitution plays a critical role in properly tuning the LUMO energy to enable good electron transport in ambient conditions while maintaining a low level of ambient doping (i.e., low Ioff). Core-cyanated ADIs 3 and 6 exhibit air-stable TFT device operation with electron mobilities up to 0.04 cm2 V−1 s−1 in air. Very high current on/off ratios of >107 are measured with positive threshold voltages (Vth = 5–15 V) and low off currents (Ioff = 10−9 to 10−12 A). Single-crystal structures of N,N′-1H,1H-perfluorobutyl ADIs 5 and 6 exhibit slipped-stack cofacial crystal packing with close π–π stacking distances of ∼3.2 A. Additionally, close intermolecular interactions between imide-carbonyl oxygen and anthracene core-hydrogen are identified, which lead to the assembly of highly planar lamellar layers. Analysis of the air-stability of 1–6 thin films suggests that air-stability is mainly controlled by the LUMO energetics, and an electrochemical threshold of Ered1 = −0.3 to −0.4 V is estimated to stabilize n-channel transport in this family of materials.

Ultrathin MnO2 nanofibers grown on graphitic carbon spheres as high-performance asymmetric supercapacitor electrodes

Growing MnO2 nanofibers on graphitic hollow carbon spheres (GHCS) is conducted by refluxing GHCS in a KMnO4 aqueous solution aimed to enhance the electrochemically active surface area of MnO2. The stoichiometric redox reaction between GHCS and MnO4− yields GHCS–MnO2 composites with controllable MnO2 content. It is found that these ultrathin MnO2 nanofibers are vertically grown on the external surface of the GHCS, yielding a composite electrode showing good electron transport, rapid ion penetration, fast and reversible Faradic reaction, and excellent rate performance when used as supercapacitor electrode materials. An asymmetric supercapacitor cell with GHCS–MnO2 as the positive electrode and GHCS as the negative electrode can be reversibly charged/discharged at a cell voltage of 2.0 V in a 1.0 mol L−1 Na2SO4 aqueous electrolyte, delivering an energy density of 22.1 Wh kg−1 and a power density of 7.0 kW kg−1. The asymmetric supercapacitor exhibits an excellent electrochemical cycling stability with 99% initial capacitance and 90% coulombic efficiency remained after 1000 continuous cycles measured using the galvanostatic charge–discharge technique.

Tailored anisotropic magnetic conductive film assembled from graphene-encapsulated multifunctional magnetic composite microspheres

Due to the fast electron transportation and good biocompatibility, the use of graphene in biosensors is becoming more and more appealing. But a key challenge is how to obtain well-organized 2D or 3D graphene structures to build larger objects, and the development of methods for controlling the organization of functional objects on a nanometre scale to build larger objects is of fundamental and technological interest. To overcome this problem, we demonstrate a novel strategy for the fabrication of a reduced graphene oxide-encapsulated multifunctional magnetic composite microspheres (rGOE-Ms)-based anisotropic conductive film (ACF). The well-designed rGOE-Ms possess both magnetization and good electron transport properties. Magnetic properties can be detected by their movement in the gel film under an external magnet. Most interestingly, the prepared gel film has displayed the existence of rGOE-Ms alignment and anisotropy in the ACF, and the electrical resistivity of the vertical ACF was almost fifteen times higher than the horizontal. Therefore, the ACF can be extended to various advanced applications, such as chemical/biosensors, nanoelectronics, and so on.

Secondary Branching and Nitrogen Doping of ZnO Nanotetrapods: Building a Highly Active Network for Photoelectrochemical Water Splitting

A photoanode based on ZnO nanotetrapods, which feature good vectorial electron transport and network forming ability, has been developed for efficient photoelectrochemical water splitting. Two strategies have been validated in significantly enhancing light harvesting. The first was demonstrated through a newly developed branch-growth method to achieve secondary and even higher generation branching of the nanotetrapods. Nitrogen-doping represents the second strategy. The pristine ZnO nanotetrapod anode yielded a photocurrent density higher than those of the corresponding nanowire devices reported so far. This photocurrent density was significantly increased for the new photoanode architecture based on the secondary branched ZnO nanotetrapods. After N-doping, the photocurrent density enjoyed an even more dramatic enhancement to 0.99 mA/cm(2) at +0.31 V vs Ag/AgCl. The photocurrent enhancement is attributed to the greatly increased roughness factor for boosting light harvesting associated with the ZnO nanotetrapod branching, and the increased visible light absorption due to the N-doping induced band gap narrowing of ZnO.

Highly sensitive and selective uric acid biosensor based on RF sputtered NiO thin film

Present study highlights the importance of RF sputtered NiO thin film deposited on platinum coated glass substrate (NiO/Pt/Ti/glass) as a potential matrix for the realization of highly sensitive and selective uric acid biosensor. Uricase has been immobilized successfully onto the surface of NiO matrix by physical adsorption technique. The prepared bioelectrode (uricase/NiO/Pt/Ti/glass) is utilized for sensing uric acid using the cyclic voltammetry and UV visible spectroscopy techniques. The bioelectrode is found to exhibit highly efficient sensing response characteristics with high sensitivity of 1278.48 μA/mM; good linearity of 0.05–1.0 mM, and very low Michaelis–Menten constant ( k m ) of 0.17 mM indicating high affinity of uricase towards the analyte. The enhanced response is due to the development of NiO matrix with good electron transport property and nanoporous morphology for effective loading of enzyme with preferred orientation.

Density functional theory study on electron and hole transport properties of organic pentacene derivatives with electron‐withdrawing substituent

Attaching electron-withdrawing substituent to organic conjugated molecules is considered as an effective method to produce n-type and ambipolar transport materials. In this work, we use density functional theory calculations to investigate the electron and hole transport properties of pentacene (PENT) derivatives after substituent and simulate the angular resolution anisotropic mobility for both electron and hole transport. Our results show that adding electron-withdrawing substituents can lower the energy level of lowest unoccupied molecular orbital (LUMO) and increase electron affinity, which are beneficial to the electron injection and ambient stability of the material. Also the LUMO electronic couplings for electron transport in these pentacene derivatives can achieve up to a hundred meV which promises good electron transport mobility, although adding electron-withdrawing groups will introduce the increase of electron transfer reorganization energy. The final results of our angular resolution anisotropic mobility simulations show that the electron mobility of these pentacene derivatives can get to several cm(2) V(-1) s(-1), but it is important to control the orientation of the organic material relative to the device channel to obtain the highest electron mobility. Our investigation provide detailed information to assist in the design of n-type and ambipolar organic electronic materials with high mobility performance.