Relation between substrate surface morphology and microcrystalline silicon solar cell performance

In the present paper, the structural and electrical performances of microcrystalline silicon (μc-Si:H) single junction solar cells co-deposited on a series of substrates having different surface morphologies varying from V-shaped to U-shaped valleys, are analyzed. Transmission electron microscopy (TEM) is used to quantify the density of cracks within the cells deposited on the various substrates. Standard 1 sun, variable illumination measurements (VIM) and Dark J(V) measurements are performed to evaluate the electrical performances of the devices. A marked increase of the reverse saturation current density (J₀) is observed for increasing crack densities. By introducing a novel equivalent circuit taking into account such cracks as non-linear shunts, the authors are able to relate the magnitude of the decrease of V_oc and FF to the increasing density of cracks.     

Efficient synthesis of isogranulatimide C, an analogue of the marine G2 checkpoint inhibitor alkaloid isogranulatimide

A three-step procedure to isogranulatimide C starting with the thermal condensation of 3-chloroindole with imidazole and proceeding in 41% yield is described.     

Evolution of glass properties during a substitution of S by Se in Ge28Sb12S60 −xSex glass network

In this paper, a detailed study to examine the influence of chalcogen S/Se mole % in the Ge₂₈Sb₁₂S_60 ?xSe_x glass system, with x = 0, 15, 30, 45 and 60, is presented that provides insight into the effect of chalcogen content on the glass network and properties. Specifically, we report results of a systematic study to evaluate the relationship between compositional variation, glass properties and dominant bonding configurations. These materials are important to applications in optics manufacturing where correlation of physical and optical properties is required to predict fabrication behavior and ultimate material performance. It has been found that the dominant bonds in the glass system change upon reaching a specific molar ratio (percentage, %) of chalcogen substitution, between 30 < x < 45 mol%, changing from Ge―Se to Sb―Se bonds as the dominant bond type. This singularity has been observed using micro-Raman spectroscopy and X-ray photoelectron spectroscopy. This effect of the dominant bond configurational change was also shown to impart changes in important physical properties including micro-hardness, thermal properties, and the glass' viscometric behavior. Results indicate that the observed dominant bond change was responsible for a constant value in the evolution of both the micro-hardness and calorimetric glass transition temperature. The viscosity was also affected by the change in dominant bond type, breaking the monotony of the viscosity evolution during the S substitution, due to the total strength of the vitreous system which does not linearly increase.     

13C NMR discrimination of regioisomeric bispyrroloquinone/bispyrroloiminoquinone ring systems

The structural assignment of bispyrroloquinone and bispyrroloiminoquinone regioisomers was achieved using ¹³C NMR spectral data. In the case of bispyrroloiminoquinones, the carbonyl group in the regioisomer possessing a nitrogen atom in both α‐positions was systematically less deshielded than the carbonyl group in the other regioisomer. In the case of bispyrroloquinones, the most deshielded carbonyl group in the regioisomer with a nitrogen atom in both α‐positions was more deshielded than the same carbonyl group in the other regioisomer. Copyright © 2009 John Wiley & Sons, Ltd.     

Efficient Pd‐Catalyzed Allene Synthesis from Alkynes and Aryl Bromides through an Intramolecular Base‐Assisted Deprotonation (iBAD) Mechanism

An optimized ligand‐controlled palladium‐catalyzed allene synthesis starting from alkynes and aryl bromides giving rise to allene products in a simple and direct manner is described. The methodology is performed in an inter‐ and intramolecular fashion with unprecedented scope and excellent yields. Based on mechanistic investigations and on DFT calculations, the role played by the carboxylic additive (i.e., PivOH) in controlling the selectivity of the reaction is discussed, allowing us to propose an intramolecular base‐assisted deprotonation (iBAD) mechanism for this process.     

Highly Enantioselective Rhodium(I)‐Catalyzed Activation of Enantiotopic Cyclobutanone CC Bonds

The selective functionalization of carbon–carbon σ bonds is a synthetic strategy that offers uncommon retrosynthetic disconnections. Despite progress in C? C activation and its great importance, the development of asymmetric reactions lags behind. Rhodium(I)‐catalyzed selective oxidative additions into enantiotopic C? C bonds in cyclobutanones are reported. Even operating at a reaction temperature of 130 °C, the process is characterized by outstanding enantioselectivity with the e.r. generally greater than 99.5:0.5. The intermediate rhodacycle is shown to react with a wide variety of tethered olefins to deliver complex bicyclic ketones in high yields.     

New Synthesis of l-Ribofuranose Derivatives from l-Xylose

Abstract

Since l-nucleosides and 2-deoxy l-nucleosides are finding more and more applications for the preparation of nucleases resistant “antisense” oligonucleotides¹ as well as for preparation of modified nucleosides as potential inhibitors of HIV,² efficient preparation of l-ribofuranose derivatives is needed. Although l-ribose was obtained by inversion of d-ribono-1,4-lactone followed by reduction,³ epimerization at C-2 of l-arabinose⁴ and inversion of configuration at C-2 of l-arabinose or at C-3 of l-xylose by displacement of a sulfonate group⁵ were also evaluated, but were found to be not very satisfactory. We recently published a preparation of l-ribofuranose derivatives from l-arabinose in which the configuration at C-2 was inverted by an oxidation-reduction sequence after suitable protection of O-3 and O-5.⁶ Although a high overall yield was obtained, upscaling was difficult because none of the intermediates were obtained in crystalline form. Therefore we decided to evaluate the same methodology starting from l-xylofuranose and we report herein our results.     

Diffusion coefficients of solids in supercritical carbon dioxide: Modelling of near critical behaviour

Most of the models proposed in literature for binary diffusion coefficients of solids in supercritical fluids are restricted to infinite dilution; this can be explained by the fact that most of experimental data are performed in the dilute range. However some industrial processes, such as supercritical fluid separation, operate at finite concentration for complex mixtures. In this case, the concentration dependence of diffusion coefficients must be considered, especially near the upper critical endpoint (UCEP) where a strong decrease of diffusion coefficients was experimentally observed. In order to represent this slowing down, a modified version of the Darken equation was proposed in literature for naphthalene in supercritical carbon dioxide. In this paper, the conditions of application of such a modelling are investigated. In particular, we focus on the order of magnitude of the solubility of the solid and on the vicinity of the critical endpoint. Various equations proposed in literature for the modelling of the infinite dilution diffusion coefficients of the solutes are also compared. Ten binary mixtures of solids with supercritical carbon dioxide were considered for this purpose.