Enhanced Charge Injection Properties of Organic Field‐Effect Transistor by Molecular Implantation Doping

Organic semiconductors (OSCs) have been widely studied due to their merits such as mechanical flexibility, solution processability, and large‐area fabrication. However, OSC devices still have to overcome contact resistance issues for better performances. Because of the Schottky contact at the metal–OSC interfaces, a non‐ideal transfer curve feature often appears in the low‐drain voltage region. To improve the contact properties of OSCs, there have been several methods reported, including interface treatment by self‐assembled monolayers and introducing charge injection layers. Here, a selective contact doping of 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄‐TCNQ) by solid‐state diffusion in poly(2,5‐bis(3‐hexadecylthiophen‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) to enhance carrier injection in bottom‐gate PBTTT organic field‐effect transistors (OFETs) is demonstrated. Furthermore, the effect of post‐doping treatment on diffusion of F₄‐TCNQ molecules in order to improve the device stability is investigated. In addition, the application of the doping technique to the low‐voltage operation of PBTTT OFETs with high‐k gate dielectrics demonstrated a potential for designing scalable and low‐power organic devices by utilizing doping of conjugated polymers.     

A magnetic field simulating device for current measuring instruments testing purpose

In this paper, it presented a device intended to reproduce magnetic fields of differents shapes to help the test or calibration of current measuring instruments based on Ampere's Law (current transformers, current clamps, and Rogowsky probes). In particular, this device can reproduce the effect of uncentered currents without requiring any mechanical displacement of the conductor or the device under test during its operation. Any uncentered or distributed current is approximated by a linear combination of currents flowing along a specific set of conductors. First, the theoretical vectorial analysis is presented, and second, a specific arrangement of conductors is used to illustrate the method. A number of measurements have been taken to check the results. Copyright © 2014 John Wiley & Sons, Ltd.     

Docosahexaenoic acid and traumatic brain injury

Traumatic brain injury (TBI) is becoming increasingly recognised as a major cause of disability, with a significant impact on health costs both in the developed and developing world. At present, there is no effective treatment for this type of acute neurological injury. Docosahexaenoic acid (DHA) is an abundant polyunsaturated fatty acid in the brain, known to have a significant structural role as well as functional roles. Preclinical accumulating evidence indicates that DHA has potential as a restorative therapeutic agent for traumatic brain injury.     

On the performance of microstrip antenna embedded in composite laminated substrates

Fiber‐reinforced composite structures can be tailored to desire mechanical properties and to embed microstrip antenna in aerospace applications. The electromagnetic characteristics of a microstrip antenna on isotropic and uniaxial substrates have been known, but that embedded in composite laminated substrates remain unavailable to date. This work aims at analyzing the performance of microstrip antenna embedded in composite laminated substrates by spectral domain analysis. Parameter studies are conducted to investigate the effects of the substrate's dielectric constants, the fiber directions (the orientation between the antenna and the laminate layers), and the stacking sequence on antenna's resonant frequency and radiation pattern. The antenna size when embedded in composite laminated substrates is larger than that when attached on isotropic substrates, or conversely, the resonant frequency will deviate lower if assuming the substrate as isotropic. The far‐field pattern in composite laminated substrates is more ‘directional’ than that in isotropic substrates. The antenna gain in the substrates of symmetric stacking with ±45° fiber direction is 20 dB better than that in isotropic substrates in some elevations. Copyright © 2014 John Wiley & Sons, Ltd.     

Strengthening effects of sprayed fiber reinforced polymers on concrete

The objectives of this study were twofold. The first was to investigate the compressive and flexural behaviors of small‐sized concrete specimens strengthened with sprayed fiber reinforced polymer (SFRP), considering various fiber lengths, fiber volumes, and concrete strengths. The second was to evaluate the strengthening effects of SFRP on the flexural behaviors of large‐sized reinforced concrete beams. U‐shaped strips and shear keys were applied to the test specimens to improve the interfacial bond resistance between the concrete surface and SFRP. POLYM. COMPOS., 36:722–730, 2015. © 2014 Society of Plastics Engineers     

Synthesis of α‐cellulose/polypyrrole composite for the removal of reactive red dye from aqueous solution: Kinetics and equilibrium modeling

In this work, a composite from α‐cellulose coated with conducting polypyrrole by in situ polymerization using potassium persulfate as oxidant was obtained. The composite was characterized by fourier transform infrared (FTIR) spectroscopy, cyclic voltammetry, UV/Vis spectroscopy, and scanning electron microscopy (SEM) analysis showed homogeneous coating of α‐cellulose with polypyrrole (PPy) to produce a composite with a conductivity of 3.5 × 10⁻⁵ S/m. Batch aqueous adsorption experiments of the reactive red 120 (RR120) dye onto the synthesized material were conducted. The results showed that this composite is an efficient adsorbent for RR120 dye removal. For the adsorption experiments set to an initial pH of 3.9, the adsorption capacity was 15.6 mg of dye/g of composite for an equilibrium concentration (in the liquid) of RR120 dye equal to 1,000 mg/L, whereas a value of 96.1 mg of dye/g of composite was obtained when the solution pH was set to 2.0 for the same equilibrium concentration. When performing adsorption experiments using pure α‐cellulose, dye adsorption was insignificant at any pH value. Adsorption isotherm for RR120 was described by a typical Freundlich model. The transient adsorption of RR120 on the synthesized composite was described by a general three‐resistance model that includes the transport on the film that surrounds the composite particles, diffusion inside the particles, and adsorption on the surface of the particles. A fitting of the uptake curves was performed allowing the estimation of values for the effective diffusivity, D₀, and the adsorption rate coefficient, k₁. For the adsorption experiments with an initial pH value set to 3.9, D₀ was estimated as 1.05 × 10⁻¹⁰ m²/s, whereas k₁ was 1.65 × 10⁻⁴ Lⁿ/g mg^{n − 1} s; the corresponding values of k₁ at pH = 2 and 9.0 were 3.18 × 10⁻⁴ and 5.16 × 10⁻⁵, respectively. POLYM. COMPOS., 36:312–321, 2015. © 2014 Society of Plastics Engineers     

Temperature accelerated life test on commercial concentrator III–V triple‐junction solar cells and reliability analysis as a function of the operating temperature

A temperature accelerated life test on commercial concentrator lattice‐matched GaInP/GaInAs/Ge triple‐junction solar cells has been carried out. The acceleration of the aging has been accomplished by subjecting the solar cells at temperatures markedly higher than the nominal working temperature inside a concentrator, and the nominal photo‐current condition (820 X) has been emulated by injecting current in darkness. Three tests at different temperatures have been carried out. The failure distributions across the three test temperatures have been fitted to an Arrhenius–Weibull model. An Arrhenius activation energy of 1.59 eV was determined from the fit. The reliability functions and parameters of these solar cells at two nominal working conditions (80 and 100 °C) have been obtained. In both cases, the instantaneous failure rate function monotonically increases, that is, the failures are of the wear‐out kind. We have also observed that the reliability data are very sensitive to the nominal temperature condition. In fact, at a nominal working condition of 820 X and 80 °C, assuming that the concentration module works 5 h per day, the warranty time obtained for a failure population of 5% has been 113 years. However, for a nominal working condition of 820 X and 100 °C, the warranty time obtained for a failure population of 5% has been 7 years. Therefore, in order to offer a long‐term warranty, the working temperature could be a key factor in the design of the concentration photovoltaic systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Failure analysis of Cu(In,Ga)Se2 photovoltaic modules: degradation mechanism of Cu(In,Ga)Se2 solar cells under harsh environmental conditions

High‐temperature‐induced and humidity‐induced degradation behaviors were investigated through the failure analysis of encapsulated Cu(In,Ga)Se₂ (CIGS) modules and non‐encapsulated CIGS cells. After being exposed to high temperature (85 °C) for 1000 h, the efficiency loss of CIGS modules and the resistivities of the aluminum‐doped zinc oxide (AZO) layer, CIGS layer, and Mo layer were slightly increased. After damp heat (DH) testing (85 °C/85% RH), the efficiency of some modules decreased significantly accompanied by discoloration, and in these areas, the resistivity of the AZO layers increased markedly. The causes of degradation of CIGS cells after high temperature and DH tests were suggested through X‐ray photoelectron spectroscopy analysis. The high‐temperature‐induced degradation behaviors were revealed to be increases in series resistance of the CIGS cells, due to the adsorption of oxygen on the AZO, CIGS, and Mo layers. The degradation behavior after DH (85 °C/85% RH) exposure was caused by the adsorption of oxygen, as well as the generation of Zn(OH)₂ due to water molecules. In particular, the humidity‐induced degradation behavior in discolored CIGS modules was ascribed to the generation of Zn(OH)₂ and carboxylic acids in the AZO layer, due to a chemical reaction between the AZO, ethylene‐vinyl acetate copolymer, and water. Copyright © 2014 John Wiley & Sons, Ltd.