Charge separation versus recombination in dye-sensitized nanocrystalline solar cells: the minimization of kinetic redundancy

In this paper we focus upon the electron injection dynamics in complete dye-sensitized nanocrystalline metal oxide solar cells (DSSCs). Electron injection dynamics are studied by transient absorption and emission studies of DSSCs and correlated with device photovoltaic performance and charge recombination dynamics. We find that the electron injection dynamics are dependent upon the composition of the redox electrolyte employed in the device. In a device with an electrolyte composition yielding optimum photovoltaic device efficiency, electron injection kinetics exhibit a half time of 150 ps. This half time is 20 times slower than that for control dye-sensitized films covered in inert organic liquids. This retardation is shown to result from the influence of the electrolyte upon the conduction band energetics of the TiO2 electrode. We conclude that optimum DSSC device performance is obtained when the charge separation kinetics are just fast enough to compete successfully with the dye excited-state decay. These conditions allow a high injection yield while minimizing interfacial charge recombination losses, thereby minimizing "kinetic redundancy" in the device. We show furthermore that the nonexponential nature of the injection dynamics can be simulated by a simple inhomogeneous disorder model and discuss the relevance of our findings to the optimization of both dye-sensitized and polymer based photovoltaic devices.     

Mixed micelles formed by n-octyl-beta-D-glucopyranoside and tetradecyltrimethylammonium bromide in aqueous media

Speed of sound, density, conductivity, and fluorescence spectroscopy experiments were run to analyze the mixed aggregation process of a nonionic-cationic surfactant system in aqueous media at 298.15 K. The mixed system comprises a nonionic surfactant, n-octyl-beta-D-glucopyranoside (OBG), and a cationic surfactant, tetradecyltrimethylammonium bromide (C14TAB), with 8 and 14 carbon atoms on the hydrophobic tails, respectively. From these data, the total and partial critical micellar concentrations, the total and partial aggregation numbers, apparent molar volumes and isentropic compressibilities, hydration numbers, and the corresponding changes in the latest properties due to the mixed aggregation process were determined. Pure and mixed micelles were analyzed from a geometrical point of view by determining the packing parameter of the aggregates. Furthermore, the experimental characterization of both the monomeric and micellar phases was completed with a theoretical study of the mixed micellization phenomena studied herein, by means of some of the most relevant theoretical models.     

Fast atom bombardment mass spectrometric analysis of the partial ozonolysis products of poly(isoprene) and poly(chloroprene)

The low molecular weight compounds formed by partial ozonolysis of poly(isoprene) and poly(chloroprene) were analyzed by fast atom bombardment mass spectrometry (FABMS). In the poly(chloroprene) case, the ozonized mixtures were treated with piperidine before the MS analysis to transform in amide end groups the reactive acyl chlorides formed by the cleavage of double bonds along the main chain. Only one family of compounds having carboxyl and ketone or carboxyl and amide end groups were obtained from the ozonolysis of poly(isoprene) and poly(chloroprene), respectively. The assigned structures were confirmed by FAB-MS analysis of the GPC separation fractions [poly(chloroprene)] or by FAB-MS of the KOH-doped ozonolysis mixtures [poly(isoprene)]. It has been also ascertained, by GPC experiments, that poly(chloroprene) decomposes more rapidly than poly(isoprene) and poly(butadiene).     

Design of ordered bimetallic complexes,Part 2:Trans-1,2-cyclohexanediaminetetraacetate bimetallates

Summary Knowledge of the kinetic and thermodynamic behaviour of aqueous solutions containing two divalent cations andtrans-1,2-cyclohexanediaminetetraacetate has been used to design synthetic pathways to ordered bimetallic complexesPart 1: E. Escriva, A. Fuertes and D. Beltran,Transition Met. Chem.,9, 184 (1984).     

On-line multidimensional chromatography using packed capillary liquid chromatography and capillary gas chromatography

The introduction of selected fractions from a liquid chromatograph into a gas chromatograph has been described; however, analyses were performed by off-line experiments requiring collection and reinjection of the separate fractions or by on-line procedures where disadvantageously, only a fraction of the separated peak or a well resolved component in a mixture could be introduced into a gas chromatograph. This disadvantage is overcome by the apparatus and method described in this paper, which utilizes a multidimensional chromatography system employing a high efficiency, packed capillary LC column coupled on-line to a capillary gas chromatograph. The liquid chromatograph (so designed) can act as a highly efficient clean-up or chemical class fractionation step prior to introduction into the gas chromatograph, significantly reducing sample preparation times in many applications. Thus minor components in a complex matrix can be determined without prior sample clean-up, an example of which is the determination of polychlorinated biphenyls in a complex hydrocarbon matrix.     

Covalent-ionic nature of the potential energy surface of the Li-CO2 complex

Unrestricted Hartree-Fock calculations with large basis sets, including d-functions, and the estimation of the correlation energy, show that the potential energy surface for the Li-CO₂ complex is built from the crossing of two states, each of them corresponding to a different electron arrangement. One has a strong ionic character and the other is of van der Waals type. Each portion of the energy surface presents a minimum, which is stable in respect to the dissociation limit.     

The state of conservation of painted surfaces in the presence of accelerated ageing processes monitored by use of FT-Raman spectroscopy and multivariate control charts

A new method has been developed for monitoring the degradation of paintings. Two inorganic pigments (ultramarine blue and red ochre) were blended with linseed oil and spread on canvas. Each canvas was subjected to simulated accelerated ageing in the presence of typical degradation agents (UV radiation and acidic solution). Periodically the painted surfaces were analysed by FT-Raman, to investigate the status of the surface. The data obtained were analysed by principal component analysis (PCA). Finally the Shewhart and cumulative sum control charts based on the relevant principal components (PC) and the so called scores monitoring and residuals tracking (SMART) charts were built. The method based on the use of PC to describe the process was found to enable identification of the presence of relevant modification occurring on the surface of the samples studied.Electronic supplementary material Supplementary material is available for this article at     

ANVAS: Artificial Neural Variables Adaptation System for descriptor selection

A new algorithm model-oriented for variable selection is presented in this study. It is based on the combination of genetic algorithms (GA) for hyperspace exploration, and counterpropagation artificial neural network (CP ANN) for deriving the fitness score. The proposed method performed very well on both well defined synthetic data sets and real academic data sets.     

Nuclear-related analytical techniques: Literature retrieval from the INIS database

The applicability of the INIS database for literature retrieval on nuclear-related analytical techniques [e.g. neutron activation analysis (NAA), X-ray fluorescence (XRF), particle-induced X-ray emission (PIXE)] has been studied. There exist about 9700 documents on NAA and other forms of activation analysis, about 3500 documents on XRF and about 1200 documents on PIXE in the database collected from 1976 until July 1988. They cover a variety of elements and matrices in the fields of biology, geochemistry and the physical sciences. Some technical notes and comments on the practical use of this database are also included.