High Charge Transport Efficiency Research Articles

Enhanced π–π Stacking between Dipole-Bearing Single Molecules Revealed by Conductance Measurement

Dipoles are widely involved in π-π interactions and are central to many chemical and biological functions, but their influence on the strength of π-π interactions remains unclear. Here, we report a study of π-π interaction between azulene-based, polar single molecules and between naphthalene-based, nonpolar single molecules. By performing scanning tunneling microscopy break junction measurements of single-molecule conductance, we show that the π-stacked dimers formed by the azulene-based, polar aromatic structures feature higher electrical conductivity and mechanical stability than those formed by the naphthalene-based, nonpolar molecules. Mechanical control of π-π interactions in both rotational and translational motion reveals a sensitive dependence of the stacking strength on relative alignment between the dipoles. The antiparallel alignment of the dipoles was found to be the optimal stacking configuration that underpins the observed enhancement of π-π stacking between azulene-based single molecules. Density functional theory calculations further explained the observed enhancement of stacking strength and the corresponding charge transport efficiency. Our experimental and theoretical results show that the antiparallel alignment of the dipole moments significantly enhances the electronic coupling and mechanical stability of π-π stacking. In addition, in the formation of single-molecule junctions, the azulene group was experimentally and theoretically proved to form a Au-π contact with electrodes with high charge transport efficiency. This paper provides evidence and interpretation of the role of dipoles in π-π interactions at the single-molecule level and offers new insights into potential applications in supramolecular devices.

Z-scheme photocatalytic NO removal on a 2D/2D iodine doped BiOIO3/g-C3N4 under visible-light irradiation

We report an unique 2D/2D Iodine doped BiOIO3/g-C3N4 heterojunction was successfully prepared. The iodine doped BiOIO3 was prepared by a simple solvent exchange method and combined with g-C3N4 by solvothermal method. The prepared photocatalyst has potential application value in the future due to its excellent stable cycle property. BiOIO3 nanoplates and g-C3N4 nanosheets form a close interfacial contact directly, so the catalyst has higher charge transport efficiency and wide visible range due to the introduction of iodide ions. Synergistic heterojunction exhibits strong photocatalytic activity for degradation of NO at ppb-level under visible light, of which 30% Iodine doped BiOIO3/g-C3N4 can achieve a maximum removal rate of 57% for NO. According to the experimental results of ESR and other experiments, a more complex Z-scheme photocatalytic mechanism is proposed, which has stronger redox ability than the traditional mechanism.

High-performance tungsten carbide electrocatalysts for the hydrogen evolution reaction

High charge transport efficiency and a large specific surface are two critical factors for the hydrogen evolution reaction.

Ultrathin Co3O4 nanosheets anchored on multi-heteroatom doped porous carbon derived from biowaste for high performance solid-state supercapacitors

Low-cost multi-heteroatom doped porous carbons derived from agricultural waste were prepared as the base material. Then, the cobalt oxides nanosheets were anchored to the surface of the carbon material to obtain the composites. It was found that the adoption of porous carbon is of great significance for the improvement of materials properties. The presence of porous structure derived from carbon materials not only increases the stability of the material, but also facilitates the diffusion and transfer of electrolyte ions. Meanwhile, the flaky Co3O4 endows the material with high energy density and high charge transport efficiency. The resulted composite materials exhibit high specific surface area with low electrochemical impedance. Both aqueous and solid-state SCs were assembled separately. The energy density of aqueous SC can reach up to 42.5 Wh kg−1 at a power density of 746 W kg−1 and even with power density up to 30 kW kg−1 as the energy density still maintained 25 Wh kg−1. As for solid-state SC, the energy density can reach 40.6 μWh cm−2. The retention of solid-state SC can maintain at 87.1% even after 3000 cycle numbers. The excellent performance of composites enables them to be promising electrode materials for energy storage.

Broadband phototransistors realised by incorporating a bi-layer perovskite/NIR light absorbing polymer channel

Broadband phototransistors (PTs) with a bi-layer MAPbI3/NIR light absorbing polymer channel have the advantages of the complementary absorption and high charge transport efficiency of the two materials. The broadband PTs possess simultaneously a specific detectivity (D*) of >109 Jones over the wavelength range from UV to visible light and a high D* of >107 Jones over the NIR light wavelength range.

Effect of LiI/I2 concentration and photoelectrode thickness on the photovoltaic properties of NiO-based p-type dye-sensitized solar cells

ABSTRACTIn this paper, we have studied the effect of LiI and I2 concentrations on the photovoltaic properties of dye-sensitized solar cells (DSSCs) based on NiO. For all concentrations of iodine, the photo-voltage (VOC) and current density (JSC) increased with increasing LiI concentration. The increment in JSC is ascribed to the higher charge transport efficiency of the device. In addition, the effect of NiO film thickness on the efficiency of the as-fabricated DSSCs was investigated, and an optimum efficiency of 0.0587% was obtained for the DSSC with a double-layer NiO film.

Low-Temperature Preparation of Tungsten Oxide Anode Buffer Layer via Ultrasonic Spray Pyrolysis Method for Large-Area Organic Solar Cells.

Tungsten oxide (WO3) is prepared by a low-temperature ultrasonic spray pyrolysis method in air atmosphere, and it is used as an anode buffer layer (ABL) for organic solar cells (OSCs). The properties of the WO3 transition metal oxide material as well as the mechanism of ultrasonic spray pyrolysis processes are investigated. The results show that the ultrasonic spray pyrolysized WO3 ABL exhibits low roughness, matched energy level, and high conductivity, which results in high charge transport efficiency and suppressive recombination in OSCs. As a result, compared to the OSCs based on vacuum thermal evaporated WO3, a higher power conversion efficiency of 3.63% is reached with low-temperature ultrasonic spray pyrolysized WO3 ABL. Furthermore, the mostly spray-coated OSCs with large area was fabricated, which has a power conversion efficiency of ~1%. This work significantly enhances our understanding of the preparation and application of low temperature-processed WO3, and highlights the potential of large area, all spray coated OSCs for sustainable commercial fabrication.

Optimized domain size and enlarged D/A interface by tuning intermolecular interaction in all-polymer ternary solar cells

The selection of sensitizer and its existence in the blend films are important to the performance of all-polymer ternary solar cells. Herein, all-polymer ternary solar cell devices, which used poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′] dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxy-late] (PTB7-Th) as donor, poly[[N,N-bis(2-octyldodecyl)-napthalene-1,4,5,8-bis(dicarboximide)−2,6-diyl]-alt-5, 5′-(2,2′-bithiophene)] (N2200) as acceptor and poly[N−900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole) (PCDTBT) as sensitizer, are successfully demonstrated. The intermolecular interaction between donor PTB7-Th and sensitizer PCDTBT may lead to aggregation of PTB7-Th which decreases domain sizes and enlarges D/A effective interface area. In addition, the PCDTBT molecules also extend light absorption and cascaded energy levels of the ternary blend system. As a result, with 15% PCDTBT we get a power conversion efficiency of 5.11%, almost 20% higher than control device due to more favored exciton dissociation and higher charge transport efficiency. This study reveals a promising way to achieve high efficiency all-polymer solar cells using a low-band gap polymer PCDTBT. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1811–1819

Inter-diffused ordered bulk heterojunction organic photovoltaics: optimized morphology for efficient exciton dissociation and charge transport

Effective control of the morphology can enhance the performance of organic photovoltaics. The morphology of an active layer needs to have a large interfacial area between donors and acceptors for efficient exciton dissociation and continuous, direct charge transport paths to electrodes for high charge transport efficiency. These two requirements are usually contradictory. Here, we propose a morphology that meets these requirements nearly simultaneously, called an inter-diffused ordered bulk heterojunction (IDOBHJ). This novel structure exhibited 9% higher performance based on the Monte Carlo simulation than an optimized disordered bulk heterojunction. The main reasons for superior performance were attributed to the comparable short circuit current density and a higher fill factor. We also implemented the IDOBHJ morphology by the experimental nanoimprint technique combined with thermal annealing process to confirm simulation results. Our experimental results are indeed consistent with the theoretical analysis.

Electronic Structures and Charge Transport of Stacked Annelated β-Trithiophenes

Density functional theory (DFT) calculations were performed using a MPWB1K functional to interpret the charge transport (CT) properties of stacked annelated β-trithiophene molecules. The goal was to help understand how the chemical composition, face-to-face stacking, intra- and intermolecular correlations, and the applied electric field affect the CT properties of this organic semiconductor compared with those of the edge-to-face "herringbone" motif. The variations in the frontier molecular orbitals, energy gap, nonadiabatic electron attachment energies (EAE), and vertical detachment energies (VDE) were investigated under an external electric field as a function of the number of stacked layers (n). Two possible CT pathways, monomer-to-monomer (MM) and dimer-to-dimer (DD) transports, were postulated to determine the charge carrier conductivities of these molecules. The results highlight that the intermolecular electronic couplings and electrostatic interactions can significantly affect the stacking geometry, even in more extended structures; displaced stacks with smaller interlayer spacing resulted in more compact stacking and, thus, higher CT efficiency; face-to-face stacking geometries can help to reduce the energy gap and VDE. Despite the fact that common thiophene-based oligomers adopting edge-to-face herringbone motifs exhibited p-type (hole-transporting) characters, the face-to-face stacked models based on annelated β-trithiophenes exhibited remarkably increased n-type (electron-transporting) performances. The electric field in the z-direction produced a small influence on the DD charge transport, whereas both electron and hole mobilities decreased dramatically in the MM case. More importantly, in MM charge transport, the electric field increases the hole mobility so that it is higher than that of the electron.

Hyperbranched Ferrocenyl Polymer Film with High Charge Transport Efficiency

The electrochemical behaviors of hyperbranched poly(ferrocenyl-methylsilane) (HPFMS) and linear oligo(ferrocenyldimethylsilane) (LOFS) films were studied systematically by cyclic voltammetry and chronocoulometry under different polymer coverage and solvents. Both poly(ferrocenylsilanes) show stable cyclic voltammographs in LiClO 4 solutions. Compared with LOFS films, HPFMS films exhibit higher charge transport efficiency because of their hyperbranched structure: peak current ( i p) and apparent diffusion coefficient ( D app) for HPFMS films are larger than those for LOFS films, especially at high polymer coverage (3.8 x 10 (-11) vs 3.9 x 10 (-12) cm2/s for HPFMS and LOFS film at the coverage of 2.1 x 10 (-6) mol Fc/cm2). The conceptual models of electrode processes for HPFMS and LOFS films were proposed to account for higher charge transport efficiency of HPFMS films. It is also found that a solvent with the appropriate solubility parameter and polarity, lower viscosity, and higher dielectric constant is in favor of charge transport through polymer films, which is consistent with the proposed model of electrode process for HPFMS films. These results imply that hyperbranched ferrocenyl polymers have the potential to be excellent chemical sensor materials with convenient synthesis and high sensitivity.

Electronic Conduction through Single Molecule of New π-Conjugated System Measured by Scanning Tunneling Microscopy

In recent years, π-conjugated organic compounds have become a widely investigated class of advanced materials as they exhibit a variety of interesting electronic properties. One of the most attractive properties is their small highest occupied molecular orbital-lowest unoccupied molecular orbital gap, which results in the very high charge transport efficiency of the π-conjugated compounds as compared with that of saturated compounds. A new π-conjugated compound was synthesized by a recently developed method. We investigated electronic conduction through an isolated single molecule of the π-conjugated compound by scanning tunneling microscopy (STM) and self-assembly techniques.

Protein charge transport in gas phase

We propose a local heating method via molecular dynamic simulation to investigate the charge transport efficiency along a polypeptide chain in the gas phase. In the protein charge transfer process, the carbonyl groups next to a C α -hinge collide with each other. Within a critical contact distance between OO atoms, charge starts to transfer otherwise the charge being at rest. This is termed a bifunctional model. In the gas phase and in the low temperature limit, the rotational energy can be transferred with very high efficiency and hence one obtains high charge transport efficiency.

A Novel Electrochemical Method for Enhancing the Conductivity of Polyaniline Solid Matrices in Preformed Films

A fast, simple, and environmentally friendly new electrochemical method capable of enhancing the conductivity of a preformed polyaniline film has been found. Utilizing this method of electrochemical forcing pretreatment at a certain effective voltage, a polyaniline solid matrix can be made more conductive. For example, the conductivity of a preformed polyaniline film (as thick as 10 μm) can be easily enhanced by about an order of magnitude within a pretreatment time of only ca. 5 min. The UV−vis−NIR and ESR spectroscopic evidences indicated that the charge carriers in the polyaniline matrix are more delocalized after such electrochemical pretreatments. The results of CV studies indicated that the resultant polyaniline film has higher charge transport efficiency and a greater redox rate. Such phenomenon may be linked with a possible backbone conformational change, as induced by this novel electrochemical pretreatment, within the solid matrix of polyaniline film.