Charge transport versus recombination in dye-sensitized solar cells employing nanocrystalline TiO2 and SnO2 films

We report a comparison of charge transport and recombination dynamics in dye-sensitized solar cells (DSSCs) employing nanocrystalline TiO(2) and SnO(2) films and address the impact of these dynamics upon photovoltaic device efficiency. Transient photovoltage studies of electron transport in the metal oxide film are correlated with transient absorption studies of electron recombination with both oxidized sensitizer dyes and the redox couple. For all three processes, the dynamics are observed to be 2-3 orders of magnitude faster for the SnO(2) electrode. The origins of these faster dynamics are addressed by studies correlating the electron recombination dynamics to dye cations with chronoamperometric studies of film electron density. These studies indicate that the faster recombination dynamics for the SnO(2) electrodes result both from a 100-fold higher electron diffusion constant at matched electron densities, consistent with a lower trap density for this metal oxide relative to TiO(2), and from a 300 mV positive shift of the SnO(2) conduction band/trap states density of states relative to TiO(2). The faster recombination to the redox couple results in an increased dark current for DSSCs employing SnO(2) films, limiting the device open-circuit voltage. The faster recombination dynamics to the dye cation result in a significant reduction in the efficiency of regeneration of the dye ground state by the redox couple, as confirmed by transient absorption studies of this reaction, and in a loss of device short-circuit current and fill factor. The importance of this loss pathway was confirmed by nonideal diode equation analyses of device current-voltage data. The addition of MgO blocking layers is shown to be effective at reducing recombination losses to the redox electrolyte but is found to be unable to retard recombination dynamics to the dye cation sufficiently to allow efficient dye regeneration without resulting in concomitant losses of electron injection efficiency. We conclude that such a large acceleration of electron dynamics within the metal oxide films of DSSCs may in general be detrimental to device efficiency due to the limited rate of dye regeneration by the redox couple and discuss the implications of this conclusion for strategies to optimize device performance.     

Sensitive and Low-background Electrochemical Immunosensor Employing Glucose Dehydrogenase and 1,10-Phenanthroline-5,6-dione

We report a sensitive electrochemical immunosensor with a low electrochemical background level, which results from electrochemical-enzymatic (EN) redox cycling based on mediated electrochemical oxidation of an electro-inactive reductant (glucose) at 0.0 V. The EN redox cycling employs flavin adenine dinucleotide-dependent glucose dehydrogenase and 1,10-phenanthroline-5,6-dione (PD). When PD was compared with five common quinone-based electron mediators, PD enabled the highest signal-to-background ratio, due to a very low electrochemical background level. When EN redox cycling was applied to a sandwich-type immunosensor, parathyroid hormone (PTH) in serum could be detected with a very low detection limit of ∼0.1 pg/mL.     

Reducing charge recombination losses in solid state dye sensitized solar cells: the use of donor-acceptor sensitizer dyes

Herein we report the application of supramolecular dyes to control charge recombination between photo-injected electrons and oxidized hole-transporting material, resulting in an enhancement in the performance of dye sensitized solar cell devices based upon such dyes.     

Entanglement entropy in fermionic Laughlin states

We present analytic and numerical calculations on the bipartite entanglement entropy in fractional quantum Hall states of the fermionic Laughlin sequence. The partitioning of the system is done both by dividing Landau-level orbitals and by grouping the fermions themselves. For the case of orbital partitioning, our results can be related to spatial partitioning, enabling us to extract a topological quantity (the "total quantum dimension") characterizing the Laughlin states. For particle partitioning we prove a very close upper bound for the entanglement entropy of a subset of the particles with the rest, and provide an interpretation in terms of exclusion statistics.     

A new analytical technique to find periodic solutions of non-linear systems

Based on the classical harmonic balance method a new technique is presented to determine higher approximate periodic solutions of the non-linear differential equations. The new method is systematic and simple. The solution covers the general initial value problem (i.e., for while the existing solution is determined for a particular case, especially for . The solution is easily transformed to perturbation solution. The method is used in various non-linear problems possessing second and more than second derivatives.     

pH-Dependent Single-Step Rapid Synthesis of CuO Nanoparticles and Their Optical Behavior

This paper reports the pH-dependent growth of copper oxide (CuO) nanoparticles by wet chemical precipitation method using pH value of the samples as the only variable parameter. The phase purity, morphology, optical behavior, and elemental analysis of synthesized nanoparticles are shown to be critically dependent on the pH of the samples. Scanning electron microscope (SEM) results shows that a higher pH results well-defined CuO nanoflakes. X-ray powder diffraction (XRD) results disclosed that the growth of pure CuO with monoclinic structure at higher pH 8, whereas mixed phase was formed at lower pH 7. The average crystallite size of samples prepared at pH 8 to 10 was varying from 23.36 to 25.78 nm. The infrared spectroscopy showed that the O–H stretching peaks become narrow with an increase in the pH value. Optical results revealed the existence of the sharp absorption edges with precise excitonic features and photoluminescence bands both located at visible and near infrared spectral region attributed to the excellent optical behavior and narrow size distribution of particles. The additional near infrared band in photoluminescence spectrum located at 860 nm is attributed the defect-related luminescence. The growth mechanism of CuO nanostructures was discussed in the light of our findings.     

Elastic scattering of electrons and positrons by cadmium atoms

ABSTRACT

The differential, integrated elastic, total and momentum transfer cross sections along with Sherman function for the elastic scattering of electrons and positrons by cadmium atoms have been evaluated from the partial wave solution of the Dirac relativistic scattering equations for a projectile-atom complex potential at the energy range 6.4 eV < E < 1.0 keV. For various scattering quantities, a comparison of our results exhibits better agreement with the experimental data than the other available theoretical values.     

In-situ Observations on Cu-SiO2 and Stainless Steels

Specimens of Cu SiO₂ and of several high purity stainless steels have been observed during deformation in an HVEM. The behaviour of the Cu SiO₂ specimens is dominated by the free surfaces, even in the thickest regions which can be examined, but in the stainless steels it has been found that if the specimen is thicker than about 0.5 μm, bulk behaviour is observed. The formation of ϵ- and α-martensite has been directly observed and essentially identical observations of martensite formation have been made during cooling. It has been shown that ϵ-martensite is always formed in regions where appropriately, but usually irregularly spaced faults, are generated and detailed analyses of isolated and overlapping faults show that these faults contain close-packed planes of the appropriate eph spacing. α-martensite is formed in association with dislocation pile-ups.     

Ratio-dependent predator–prey model of interacting population with delay effect

A system of delay differential equation is proposed to account the effect of delay in the predator?Cprey model of interacting population. In this article, the modified ratio-dependent Bazykin model with delay in predator equation has been considered. The essential mathematical features of the proposed model are analyzed with the help of equilibria, local and global stability analysis, and bifurcation theory. The parametric space under which the system enters into a Hopf-bifurcation has been investigated. Global stability results are obtained by constructing suitable Lyapunov functions. We derive the explicit formulae for determining the stability, direction, and other properties of bifurcating periodic solutions by using normal form and central manifold theory. Using the global Hopf-bifurcation result of Wu (Trans. Am. Math. Soc., 350:4799?C4838, 1998) for functional differential equations, the global existence of periodic solutions has been established. Our analytical findings are supported by numerical experiments. Biological implication of the analytical findings are discussed in the conclusion section.