High-Performance Supercapacitors Based on ɛ-MnO2/RGO Fiber Electrodes for Wearable Energy Storage.

Hybrid fibers based on MnO2/reduced graphene oxide have been fabricated for flexible energy storage devices. Graphene oxide nanoflakes were reduced in a polytetrafluoroethylene (PTFE) pipeline under the appropriate condition to develop a fiber current collector, which also provides the possibility of weaving. The RGO fiber with the radius of about 35 µm has a resistance of 150 Ω · cm. MnO2 nanoflakes directly grow on the RGO fiber surface acting as the electrode material of the device. The MnO2/RGO hybrid fibers provide excellent energy storage performances. The as-fabricated SC exhibits a high areal capacitance of 1.37 F·cm-2 at the scan rate of 1 mV·s-1, and outstanding long-term cycling stability of 93.75% retention after 5000 cycles. This work demonstrates a cost-effective and versatile strategy for wearable energy storage devices.

Substrate effect on the melting temperature of gold nanoparticles.

Previous experimental, molecular dynamics, and thermodynamic researches on the melting temperature of Au nanoparticles on tungsten substrate provide entirely different results. To account for the substrate effect upon the melting point of nanoparticles, three different substrates were tested by using a thermodynamic model: tungsten, amorphous carbon, and graphite. The results reveal that the melting point suppression of a substrate-supported Au nanoparticle is principally ruled by the free surface-to-volume ratio of the particle or the contact angle between the particle and the substrate. When the contact angle θ is less than 90°, a stronger size-dependent melting point depression compared with those for free nanoparticles is predicted; when the contact angle θ is greater than 90°, the melting temperature of the supported Au nanoparticles are somewhat higher than those for free nanoparticles.

Low-Temperature UVO-Sintered ZnO/SnO2 as Robust Cathode Buffer Layer for Ternary Organic Solar Cells.

The cathode buffer layer (CBL) plays a crucial role in organic solar cells (OSCs), and it has been challenging to obtain high-quality CBL by using simple and reliable processes. In this paper, the bilayer structure consisting of ZnO nanoparticles (NPs) and sol−gel SnO2 was prepared by the low-temperature (<100 °C) UV-ozone (UVO) sintering process and used as the robust CBL for ternary OSCs based on PTB7-Th:PCDTBT:PC70BM. The results show that the insertion of SnO2 can effectively fill the cracks and pores on the surface of the ZnO NP film, thereby improving the overall compactness and flatness of the CBL and reducing the defect density inside the CBL. Furthermore, the insertion of SnO2 slightly improves the transmittance of the CBL to photons with wavelengths in the range of 400−600 nm, and also increases the electron mobility of the CBL thus facilitating the extraction and transport of the electrons. Compared to the devices using UVO-ZnO and UVO-SnO2 CBLs, the devices with UVO-ZnO/SnO2 CBL exhibit exceptional performance advantages, the best power conversion efficiency (PCE) reaches 10.56%. More importantly, the stability of the devices with ZnO/SnO2 CBL is significantly improved, the device (PCE) still maintains 60% of the initial value after 30 days in air. The positive results show that the UVO-ZnO/SnO2 is an ideal CBL for OSCs, and due to the low-temperature process, it has great application potential in flexible OSCs.

Research on Photoelectric Responses of SnO2 Film to Humidity Under UV Light Irradiation.

In this work, to research the photoelectric responses to humidity using a semiconductor film, an ultraviolet (UV) light induced device has been investigated on SnO2 film at room temperature. Screen printing method was used to prepare SnO2 film on the Al2O3 substrate. The crystalline structure and morphology of SnO2 was characterized with XRD and FE-SEM. The UV light induced photoelectric responses of SnO2 to a constant humidity (20% RH) were evaluated firstly under four different bias voltages. At 2 V bias voltage, the photocurrent amplitude reaches 4.58 µA, which is higher than that of 0.2 V bias (0.27 µA). Then the photoelectric responses to different relative humidity conditions (20% RH, 40% RH and 60% RH) were tested. The results display that the photocurrent decreased while the relative humidity increased. To illustrate the anomaly current of SnO2 film at 60% RH, the darkcurrent to different relative humidity conditions (20% RH, 40% RH and 60% RH) were also tested. To make clear these results, corresponding probable illustration was proposed.

UV Light Activated Multi-Cycle Photoelectric Properties of TiO2 and CdS/TiO 2 Films in Formaldehyde.

In this work, UV light activated multi-cycle photoelectric properties of TiO2 and CdS/TiO2 films in formaldehyde were researched. TiO2 film was prepared by screen printing, CdS/TiO2 compounded film was synthesized by SILAR method. XRD and FE-SEM was used to characterize the TiO2 and CdS/TiO2 samples. Multi-cycle photoelectric properties of TiO2 and CdS/TiO2 with uv light on and off were evaluated by testing the photocurrent. On one hand, under the same bias voltage, CdS/TiO 2showed a higher photocurrent than that by TiO2. The reason for this result should be ascribed to the compounded structure in CdS/TiO2, with which the separation and transfer of photogenerated electron-hole pairs could be improved. On the other hand, with the testing cycle number increased, the photocurrent amplitudes of TiO2 and CdS/TiO2 increased. These results suggested that the time to reach a stable photocurrent value for TiO2 and CdS/TiO2 is much longer than one cycle time (300 S). To illustrate the increased photocurrent amplitude value cycle by cycle, the photocurrent of CdS/TiO2 to a much longer time (more than 4000 seconds) was also tested. To explain these results, corresponding possible illustrations were presented.

Nanoscale Phase Separation in Ternary Organic Solar Cells Based on PTB7:PC70BM:IC70BA.

As a fullerene derivative, IC70BA is widely used in the ternary organic solar cells (TOSCs) to increase the open circuit voltage (Voc) of the devices. Unfortunately, most of the literature shows that IC70BA will lead to a reduction in the short-circuit current density (Jsc) and fill factor (FF). In this work, IC70BA is added to the PTB7:PC70BM binary system to form the ternary system, which is composed of one donor and two fullerene acceptors. Surprisingly, the addition of IC70BA does not immediately lead to a decrease in Jsc and FF. In fact, the appropriate weight ratio of IC70BA in fullerenes can simultaneously increase the Voc, Jsc, and FF of the TOSCs. The synergistic optimization of the surface and bulk morphology of the ternary active layer suppresses the attenuation of Jsc and FF. The smooth surface and suitable phase separation size effectively guarantee the separation, transport and extraction of the charge. Moreover, the addition of IC70BA can significantly improve the hole transport capacity of the active layer, and the optimal hole mobility is 5.13 - 10"4 cm²V-1S-1. Finally, the TOSCs with 10% weight ratio of IC70BA gives the optimal PCE of 9.24% and ideality factor of 2.3.

UV Light Driven Photoelectric Properties of ZnO Film to Humidity.

UV light driven photoelectric properties of ZnO film to humidity were researched. ZnO film was prepared through the method of screen printing sustained on Al2O3 substrate. ZnO was characterized by XRD, FE-SEM and EDX. The time-dependent UV light driven photoelectric properties of ZnO were investigated by exposing it to different bias voltages and different relative humidity (20% RH, 40% RH, 60% RH and 80% RH). On one hand, the photoelectric properties of ZnO increased with the augmenting of bias voltage, which shows that a higher bias causes more separation of carriers. On the other hand, the photocurrent decreased with the increase in relative humidity, which shows that bigger humidity results in smaller photoelectric property. To discuss these results, corresponding possible illustrations for the photoelectric properties under different conditions were proposed.

Electronic Structures of Free-Standing Nanowires made from Indirect Bandgap Semiconductor Gallium Phosphide.

We present a theoretical study of the electronic structures of freestanding nanowires made from gallium phosphide (GaP)-a III-V semiconductor with an indirect bulk bandgap. We consider [001]-oriented GaP nanowires with square and rectangular cross sections, and [111]-oriented GaP nanowires with hexagonal cross sections. Based on tight binding models, both the band structures and wave functions of the nanowires are calculated. For the [001]-oriented GaP nanowires, the bands show anti-crossing structures, while the bands of the [111]-oriented nanowires display crossing structures. Two minima are observed in the conduction bands, while the maximum of the valence bands is always at the Γ-point. Using double group theory, we analyze the symmetry properties of the lowest conduction band states and highest valence band states of GaP nanowires with different sizes and directions. The band state wave functions of the lowest conduction bands and the highest valence bands of the nanowires are evaluated by spatial probability distributions. For practical use, we fit the confinement energies of the electrons and holes in the nanowires to obtain an empirical formula.

Electronic structures of [1 1 1]-oriented free-standing InAs and InP nanowires.

We report on a theoretical study of the electronic structures of the [1 1 1]-oriented, free-standing, zincblende InAs and InP nanowires with hexagonal cross sections by means of an atomistic sp(3)s*, spin-orbit interaction included, nearest-neighbor, tight-binding method. The band structures and the band state wave functions of these nanowires are calculated and the symmetry properties of the bands and band states are analyzed based on the C(3v) double point group. It is shown that all bands of these nanowires are doubly degenerate at the Γ-point and some of these bands will split into non-degenerate bands when the wave vector k moves away from the Γ-point as a manifestation of spin-splitting due to spin-orbit interaction. It is also shown that the lower conduction bands of these nanowires all show simple parabolic dispersion relations, while the top valence bands show complex dispersion relations and band crossings. The band state wave functions are presented by the spatial probability distributions and it is found that all the band states show 2π/3-rotation symmetric probability distributions. The effects of quantum confinement on the band structures of the [1 1 1]-oriented InAs and InP nanowires are also examined and an empirical formula for the description of quantization energies of the lowest conduction band and the highest valence band is presented. The formula can simply be used to estimate the enhancement of the band gaps of the nanowires at different sizes as a result of quantum confinement.

Band-inverted gaps in InAs/GaSb and GaSb/InAs core-shell nanowires.

The [111]-oriented InAs/GaSb and GaSb/InAs core-shell nanowires have been studied by the 8 × 8 Luttinger-Kohn Hamiltonian to search for non-vanishing fundamental gaps between inverted electron and hole bands. We focus on the variations of the band-inverted fundamental gap, the hybridization gap, and the effective gap with the core radius and shell thickness of the nanowires. The evolutions of all the energy gaps with the structural parameters are shown to be dominantly governed by the effect of quantum confinement. With a fixed core radius, a band-inverted fundamental gap exists only at intermediate shell thicknesses. The maximum band-inverted gap found is ~4.4 meV for GaSb/InAs and ~3.5 meV for InAs/GaSb core-shell nanowires, and for the GaSb/InAs core-shell nanowires the gap persists over a wider range of geometrical parameters. The intrinsic reason for these differences between the two types of nanowires is that in the shell the electron-like states of InAs is more delocalized than the hole-like state of GaSb, while in the core the hole-like state of GaSb is more delocalized than the electron-like state of InAs, and both favor a stronger electron-hole hybridization.