Numerical Investigation of Graphene as a Back Surface Field Layer on the Performance of Cadmium Telluride Solar Cell

This paper numerically explores the possibility of ultrathin layering and high efficiency of graphene as a back surface field (BSF) based on a CdTe solar cell by Personal computer one-dimensional (PC1D) simulation. CdTe solar cells have been characterized and studied by varying the carrier lifetime, doping concentration, thickness, and bandgap of the graphene layer. With simulation results, the highest short-circuit current (I_sc = 2.09 A), power conversion efficiency (η = 15%), and quantum efficiency (QE~85%) were achieved at a carrier lifetime of 1 × 10³ μs and a doping concentration of 1 × 10¹⁷ cm⁻³ of graphene as a BSF layer-based CdTe solar cell. The thickness of the graphene BSF layer (1 μm) was proven the ultrathin, optimal, and obtainable for the fabrication of high-performance CdTe solar cells, confirming the suitability of graphene material as a BSF. This simulation confirmed that a CdTe solar cell with the proposed graphene as the BSF layer might be highly efficient with optimized parameters for fabrication.     

Phenothiazine–BODIPY–Fullerene Triads as Photosynthetic Reaction Center Models: Substitution and Solvent Polarity Effects on Photoinduced Charge Separation and Recombination

Novel photosynthetic reaction center model compounds of the type donor₂–donor₁–acceptor, composed of phenothiazine, BF₂‐chelated dipyrromethene (BODIPY), and fullerene, respectively, have been newly synthesized using multistep synthetic methods. X‐ray structures of three of the phenothiazine‐BODIPY intermediate compounds have been solved to visualize the substitution effect caused by the phenothiazine on the BODIPY macrocycle. Optical absorption and emission, computational, and differential pulse voltammetry studies were systematically performed to establish the molecular integrity of the triads. The N‐substituted phenothiazine was found to be easier to oxidize by 60 mV compared to the C‐substituted analogue. The geometry and electronic structures were obtained by B3LYP/6‐31G(dp) calculations (for H, B, N, and O) and B3LYP/6‐31G(df) calculations (for S) in vacuum, followed by a single‐point calculation in benzonitrile utilizing the polarizable continuum model (PCM). The HOMO?1, HOMO, and LUMO were, respectively, on the BODIPY, phenothiazine and fullerene entities, which agreed well with the site of electron transfer determined from electrochemical studies. The energy‐level diagram deduced from these data helped in elucidating the mechanistic details of the photochemical events. Excitation of BODIPY resulted in ultrafast electron transfer to produce PTZ–BODIPY^.+–C₆₀^.?; subsequent hole shift resulted in PTZ^.+–BODIPY–C₆₀^.? charge‐separated species. The return of the charge‐separated species was found to be solvent dependent. In nonpolar solvents the PTZ^.+–BODIPY–C₆₀^.? species populated the ³C₆₀* prior to returning to the ground state, while in polar solvent no such process was observed due to relative positioning of the energy levels. The ¹BODIPY* generated radical ion‐pair in these triads persisted for few nanoseconds due to electron transfer/hole‐shift mechanism.     

Nickel‐Catalyzed α‐Carbonylalkylarylation of Vinylarenes: Expedient Access to γ,γ‐Diarylcarbonyl and Aryltetralone Derivatives

We report a Ni‐catalyzed regioselective α‐carbonylalkylarylation of vinylarenes with α‐halocarbonyl compounds and arylzinc reagents. The reaction works with primary, secondary, and tertiary α‐halocarbonyl molecules, and electronically varied arylzinc reagents. The reaction generates γ,γ‐diarylcarbonyl derivatives with α‐secondary, tertiary, and quaternary carbon centers. The products can be readily converted to aryltetralones, including a precursor to Zoloft, an antidepressant drug.     

The effect of zinc(II) and some chromium complexes on the constant current chronopotentiometry of insulin

The constant current chronopotentiometry (CCCP) of zinc-free insulin was examined and the effect of additions of zinc(II) or either of two chromium complexes to the zinc-free zinc was studied. The zinc free insulin gave a constant current chronopotentiometric (CCCP) response which indicated that the freeze drying process, which was part of its preparation, may have denatured the insulin. The addition of zinc(II) appeared to reverse this since the response following zinc additions was similar to that of native insulin. Of the two chromium complexes investigated for their influence on insulin electrochemistry tripicolinato chromium(III) had no effect on the CCCP response, trans-Diaquoethylenebis-(salicylideneiminato) chromium(III) had an indirect effect by appearing to restore the native conformation of the insulin following the apparent denaturation caused by the removal of zinc.     

Brain-derived neurotrophic factor modulation of Kv1.3 channel is disregulated by adaptor proteins Grb10 and nShc

Background  

Neurotrophins are important regulators of growth and regeneration, and acutely, they can modulate the activity of voltage-gated ion channels. Previously we have shown that acute brain-derived neurotrophic factor (BDNF) activation of neurotrophin receptor tyrosine kinase B (TrkB) suppresses the Shaker voltage-gated potassium channel (Kv1.3) via phosphorylation of multiple tyrosine residues in the N and C terminal aspects of the channel protein. It is not known how adaptor proteins, which lack catalytic activity, but interact with members of the neurotrophic signaling pathway, might scaffold with ion channels or modulate channel activity.     

Magnetism and candidate muon-probe sites in RBa2Cu3O y

Key results of zero-field (ZF) and transverse-field (TF) muon-spin-relaxation (μSR) experiments on superconducting and insulating RBa₂Cu₃O _y (R123 _y , with R=Eu, Gd, Pr and Pr/Y:y=6, 7) are examined. The chemical behavior of the positive muon probe is addressed, and muon-oxygen bonding is shown to occur in all these cuprates. To explain magnetic fields at muon-probe sites in Pr _x Y_1−x Ba₂Cu₃O _y (0<=x<0.5,y=7 andx=0,y=6) samples, improvements on the reported magnetic structures from neutron diffraction are necessary. Cu magnetism in Pr123y (y=6,7) is observed belowT _N1, which is near RT. The magnetism seen belowT _N2 can be interpreted assuming an additional ordering in the Cutt-O chain layers. Alternatively, Pr ordering is also considered as the cause of the second phase transition. Considering the specific muon-probe location, a more detailed interpretation can be provided for the μSR parameters, measured in the normal and mixed states of these unconventional superconductors.     

Determination of flunitrazepam and nitrazepam in beverage samples by liquid chromatography with dual electrode detection using a carbon fibre veil electrode

Both nitrazepam and flunitrazepam have been determined by high-performance liquid chromatography dual electrode detection (LC-DED) in the reductive–reductive mode, using a carbon fibre veil electrode (CFVE) in conjugation with a glassy carbon electrode. Initial studies were made to optimise the chromatographic conditions. These were found to be 45% acetonitrile-55% acetate buffer (50 mM, pH 4.1) at a flow rate of 1.0 ml/min, employing a Hypersil C18, 5 μm, 250 mm × 4.6 mm column. Cyclic voltammetric studies performed to ascertain the redox behaviour of nitrazepam and flunitrazepam at a CFVE in the optimised mobile phase. Studies showed that similar voltammetric behaviour was obtained to that report at Hg or glassy carbon based electrodes. Further studies were then carried out to identify the optimum conditions required for the LC-DED determination of nitrazepam and flunitrazepam in beverage samples. Hydrodynamic voltammetry was used to optimise the applied potential at the generator and detector cells; these were identified to be −2.40 and −0.25 V, respectively. A linear range of 2.0 to 100 μg ml⁻¹, with a detection limit of 20 ng ml⁻¹ was obtained. A convenient and rapid method for the determination of both nitrazepam and flunitrazepam in beverage sample was developed. Following a simple sample extraction procedure, extracts were examined using the optimised LC-DED procedure. An average percentage recovery of 95.5% (%CV = 4.5%) for nitrazepam and 78.0% (%CV = 8.8%) was achieved for a sample of “Pepsi Max” spiked at 1.0 μg ml⁻¹ nitrazepam, 1.47 μg ml⁻¹ flunitrazepam. Presented at the 4th Annual Meeting of the Great Western Electrochemistry Group, 8th June 2005, University of the West of England, Bristol, UK.     

Resistance transitions detected by analysis of the voltammetry of tetrathiafulvalene microparticles adhered to electrode surfaces under conditions of dynamic resistance compensation

Dynamic resistance compensated cyclic voltammograms have been obtained when solid tetrathiafulvalene (TTF) is converted to a highly conducting TTF⁺ salt. Two resistance transitions were detected, one being related to bulk transformation of solid by nucleation-growth TTF^+/0 processes and the other occurring with negligible detectable current and mass changes in the reversible potential region. The general usefulness of obtaining resistance–potential data and maintaining a linear potential–time (scan rate) relationship by employing dynamic IR_u (I=current, R_u=uncompensatedcellresistance) in mechanistic studies of the voltammetry of solids adhered to electrode surfaces is emphasized.     

Ligand Modifications Produce Two-Step Magnetic Switching in a Cobalt(dioxolene) Complex

Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) Co^III(cat²⁻) and high spin (h.s.) Co^II(sq⋅⁻) forms (cat²⁻=catecholato, and sq⋅⁻=seminquinonato forms of 3,5−di−^tBu-1,2-dioxolene), which reversibly interconvert via temperature-dependent intramolecular electron transfer. Typically, the remaining four coordination sites on cobalt are supported by a tetradentate ligand whose properties influence the temperature at which VT occurs. We report that replacing one chelating pyridyl arm of tris(2-pyridylmethyl)amine (tpa) with a weaker field ortho-anisole moiety facilitates access to a third magnetic state, and examine a series of related complexes. Variable temperature crystallographic, magnetic, calorimetric, and spectroscopic studies support that this third state is consistent with l.s. Co^II(sq⋅⁻). Thus, our ligand modifications not only provide access to the VT transition from l.s. Co^III(cat²⁻) to l.s. Co^II(sq⋅⁻), but at higher temperatures, the complex undergoes spin crossover from l.s. Co^II(sq⋅⁻) to h.s. Co^II(sq⋅⁻), representing the first example of two-step magnetic switching in a mononuclear monodioxolene cobalt complex. We hypothesize that ligand dynamicity may facilitate access to the rarely observed l.s. Co^II(sq⋅⁻) intermediate state, suggesting a new design criterion in the development of stimulus-responsive multi-state molecular switches.