Synthesis of Ni-poor NiO nanoparticles for DSSC-p applications

International audienceOver the last decade, p-type semiconductors (SC) have known a renewed interest. Indeed these materials may have potentialapplications for light-emitting diodes, transistors, solar cells, etc. Since the achievement of the first Dye Sensitized Solar Cells (DSSC) by Grätzel in 1991 a new generation of solar cells has been developed where the n-type SC is replaced by a p-type one. This leads to the photo-injection of holes instead of electrons in the circuit. To date nickel oxide (NiO) is the reference p-type semiconductor.However yields are still far from those of n-DSSC and many studies aim to replace NiO by other systems such as CuAlO2 , CuGaO2,CuCrO2 or NiCo2O4 nanoparticles. Following our recent synthesis of N doped ZnO with stabilization of p-type charge carriers, wefocus now on the preparation of N doped NiO nanoparticles to improve the p-type conductivity of NiO. We study here the chemicalreactivity of a nickel oxyhydroxide precursor under air and ammonia that conducts to nanostructured Ni-poor NiO

Synthesis of Ni-poor NiO nanoparticles for p-DSSC applications

International audienceTo improve the performances of p-Dye Sensitized Solar Cell (p-DSSC) for the future, the synthesis of modified p-type nickel oxide semiconductor, commonly used as photocathode in such devices, was initiated with Ni3O2(OH)4 as precursor. This specific nickel oxyhydroxide was first characterized by X-ray photo-electron spectroscopy and magnetic susceptibility measurements. Then its thermal decomposition was thoroughly studied in order to control the particles size of the as-prepared NiO nanopowders. Low temperature decomposition in air of this precursor allows the formation of Ni1-xO nanoparticles with a large amount of Ni vacancies and specific surface areas up to 250 m2.g-1. Its ammonolysis at 250°C leads to nanostructured N-doped NiO (NiO:N) materials

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

International audienceNitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO2 substrate from a ZnO colloidal solution. Zinc peroxide (ZnO2) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H2O2 solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250°C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV-Visible transmittance spectroscopy

Size dependence of efficiency of PbS quantum dots in NiO-based dye sensitised solar cells and mechanistic charge transfer investigation

Quantum dots (QDs) are very attractive materials for solar cells due to their high absorption coefficients, size dependence and easy tunability of their optical and electronic properties due to quantum confinement. Particularly interesting are the PbS QDs owing to their broad spectral absorption until the long wavelengths, their easy processability and low cost. Here, we used control of the PbS QDs size to understand charge transfer processes at the interfaces of NiO semiconductor and explain the optimal QDs size in photovoltaic devices. Towards this goal, we have synthesized a series of PbS QDs with different diameters (2.8 A until 4A) and investigated charge transfer dynamics by time resolved spectroscopy and their ability to act as sensitizers in nanocrystalline NiO based solar cells using the cobalt tris(4,4'-diterbutyl-2,2'-bipyridine) complex as redox mediator. We found that PbS QDs with average diameter of 3.0 nm are optimal size in terms of efficient charge transfers and light harvesting efficiency for photovoltaic performances. Our study showed that an hole injection from PbS QDs to NiO valence band (VB) is an efficient process even with low injection driving force (0.3 eV) and occurs in 6-10 ns. Furthermore we found that the direct electrolyte reduction (photoinduced electron transfer to the cobalt redox mediator) also occurs in parallel to the hole injection with rate constant of similar magnitude (10-20 ns). In spite of its large driving force, the rate constant of the oxidative quenching of PbS by Co(III) diminishes more steeply than hole injection on NiO when the diameter of PbS increases. This is understood as the consequence of increasing the trap states that limit electron shift. We believe that our detailed findings will advance the future design of QD sensitized photocathodes. © 2017, Royal Society of Chemistry. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at / https://doi.org/10.1039/C7NR03698

Magnetic structure and ferroelectric polarization of MnWO4 investigated by density functional calculations and classical spin analysis

The ordered magnetic states of MnWO4 at low temperatures were examined by evaluating the spin exchange interactions between the Mn2+ ions of MnWO4 on the basis of first principles density functional calculations and by performing classical spin analysis with the resulting spin exchange parameters. Our work shows that the spin exchange interactions are frustrated within each zigzag chain of Mn2+ ions along the c-direction and between such chains of Mn2+ ions along the a-direction. This explains the occurrence of a spiral-spin order along the c- and a-directions in the incommensurate magnetic state AF2, and that of a uudd spin order along the c- and a-directions in the commensurate magnetic state AF1. The ferroelectric polarization of MnWO4 in the spiral-spin state AF2 was examined by performing Berry phase calculations for a model superstructure to find that the ferroelectric polarization occurs along the b-direction, in agreement with experiment.Comment: 30 pages, 10 figures, 4 figure

Increased risk of left heart valve regurgitation associated with benfluorex use in patients with diabetes mellitus: a multicenter study.

International audienceBACKGROUND: Benfluorex was withdrawn from European markets in June 2010 after reports of an association with heart valve lesions. The link between benfluorex and valve regurgitations was based on small observational studies and retrospective estimations. We therefore designed an echocardiography-based multicenter study to compare the frequency of left heart valve regurgitations in diabetic patients exposed to benfluorex for at least 3 months and in diabetic control subjects never exposed to the drug. METHODS AND RESULTS: This reader-blinded, controlled study conducted in 10 centers in France between February 2010 and September 2011 prospectively included 376 diabetic subjects previously exposed to benfluorex who were referred by primary care physicians for echocardiography and 376 diabetic control subjects. Through the use of propensity scores, 293 patients and 293 control subjects were matched for age, sex, body mass index, smoking, dyslipidemia, hypertension, and coronary artery disease. The main outcome measure was the frequency of mild or greater left heart valve regurgitations. In the matched sample, the frequency and relative risk (odds ratio) of mild or greater left heart valve regurgitations were significantly increased in benfluorex patients compared with control subjects: 31.0% versus 12.9% (odds ratio, 3.55; 95% confidence interval, 2.03-6.21) for aortic and/or mitral regurgitation, 19.8% versus 4.7% (odds ratio, 5.29; 95% confidence interval, 2.46-11.4) for aortic regurgitation, and 19.4% versus 9.6% (odds ratio, 2.38; 95% confidence interval, 1.27-4.45) for mitral regurgitation. CONCLUSIONS: Our results indicate that the use of benfluorex is associated with a significant increase in the frequency of left heart valve regurgitations in diabetic patients. The natural history of benfluorex-induced valve abnormalities needs further research

Étude de matériaux hybrides organique-inorganique photochromiques à base de polyoxomolybdates

Un matériau photochromique change de couleur sous excitation lumineuse (UV et visible). Ce comportement, réversible ou non, est bien connu dans de nombreux matériaux organiques (spirooxazines, diaryléthènes, ), ou purement inorganiques (AgX: Cu, TiO2:Fe, MoO3, WO3 ). Depuis quelques dizaines d années, des matériaux hybrides organique-inorganique photochromes voient le jour. Parmi eux, les assemblages de polyoxomolydates avec des cations organoamonium présentent de nombreux avantages. De par la remarquable diversité topologique des anions (0D, 1D ou 2D) et le large choix d alkylamonium, ils conduisent à une chimie structurale riche. La connaissance précise de leur structure cristalline est indispensable pour comprendre le mécanisme du photochromisme. Lors de la synthèse, les alkylamonium agissent non seulement comme contre-cations structurants mais ils orientent également la condensation inorganique. Nous montrons comment le pH, la concentration, le rapport cation/anion ainsi que la température sont autant de paramètres déterminants pour la synthèse de ces composés. Par ailleurs, grâce à des études comparatives du comportement optique de nos composés, nous avons pu mettre en avant des clés du contrôle du photochromisme. En effet, la couleur est directement liée à la topologie de la partie minérale, tandis que la vitesse de coloration est fortement influencée par la nature du cation organique. L interface est également primordiale puisque la présence de liaisons hydrogène entre les cations et les anions est une condition nécessaire au photochromisme. Les tendances décrites permettent d accorder le photochromisme de ce type de composés à façon.Investigations on photochromic materials, compounds that undergo a significant color change upon UV-vis irradiation, have been extensive over the last century. This stems from their potential application as ophtalmic lenses, printing, cosmetics, switches and sensors, optical data storage While pure organic and inorganic photochromic materials have been known for a long time, hybrid organic-inorganic materials receive much attention only recently. Hybrid organic-inorganic materials based on structurally well-defined polyoxomolybdates (Mo-POMs) and organoammonium cations are potential photochromic materials, when the building blocks are linked via hydrogen bonds interaction. These compounds exhibit a high degree of organization, which favors the characterization of the organic-inorganic interface. The topological versatility of both organoammonium cations and Mo-POMs blocks enables a large range of original hybrid self-assembled frameworks with tunable dimensionality and photochromic properties. Namely, the mineral entity can be designed by playing with the nature of the countercation, the pH, the temperature, the cation/molybdate ratio, , as we discuss for the HDBU+, H2DABCO2+ and H2pipz2+ containing systems. Moreover, we evidence that the photogenerated color of the material strongly depends on the inorganic anions, while the kinetics of the coloration change is influenced by the nature of the organoammonium cation. The topology of the hydrogen-bond subnetwork will determine the material ability to transit towards a photogenerated state under illuminationNANTES-BU Sciences (441092104) / SudocSudocFranceF

De l'esquisse à l'optimisation d'un élément de paroi multicritère (proposition d'une méthodologie)

Cette étude a pour objet de proposer une méthode de conception allant de la définition des besoins à l'esquisse puis à l'optimisation et l'évaluation d'un élément de façade en terme d'ambiance. La méthode proposée est appliquée au développement d'un élément de paroi multicritère répondant simultanément aux paramètres d'ambiance lumineux, thermique, aéraulique et acoustique au niveau physique, sensible, réglementaire et esthétique. L'optimisation du dimensionnement de l'élément de paroi et l'évaluation des performances de celui-ci sont réalisés en appliquant plusieurs méthodes, chacune d'elles étant relative à un paramètre d'ambiance (c'est le cas des facteurs d'ambiance lumineux et acoustique) ou relative à deux paramètres d'ambiance (c'est les cas des facteurs d'ambiance thermique et aéraulique qui sont traités simultanément). L'application de la méthode à un élément de paroi multicritère permet de montrer en quoi et comment la méthode a permis de faire évoluer la conception de cet élément de paroi.NANTES-BU Sciences (441092104) / SudocNANTES-Ecole Centrale (441092306) / SudocLA ROCHELLE-BU (173002101) / SudocSudocFranceF

Synthèse, caractérisation et étude cinétique de coloration de composés hybrides organiques-inorganiques photochromes à base de polyoxomolybdates

Le groupe MIOPS (Matériaux Innovants Organiques pour l'Optique et le Stockage) étudie des matériaux hybrides organiques-inorganiques photochromes, composés présentant une transition réversible de couleur sous l'effet d'un rayonnement. Il s'agit de polyoxométallates (ou POM), notamment des oxydes de molybdène à haut degré d'oxydation (Movi).Ils sont obtenus par chimie douce via une condensation acido-basique (synthèse hydrothermale sous pression autogène, co-précipitation, métathèse, ) en solution aqueuse et en présence de cations organiques de types alkylammonium. Ces derniers agissent lors de la synthèse non seulement comme contre-cations structurants mais ils ont un rôle clé sur la photochromisme. Cette propriété trouve son origine dans la redistribution du nuage électronique sous l'effet d'une stimulation lumineuse, rayonnement UV, et dans le piègeage dans leur état excité des électrons ainsi promus, conduisant à une nouvelle configuration électronique métastable, responsable de la coloration, due à une modification des transitions optiques associées. Les propriétés optiques des composés hybrides sont liées à la charpente minérale (couleur photogénére) et à la nature des cations organiques (vitesse de coloration dépendant de l'espèce organique en interaction hydrogène avec le polyoxomolybdate). De nombreux polyoxomolybdates hybrides ont été synthétisés avec, à chaque fois, une optimisation des synthèses et une caractérisation par diffraction des rayons X sur poudre ou monocristaux, et optique. Des simulations par calcul DFT des densités d'état (DOS) des composés hybrides ont été effectuées pour montrer l'accord entre calcul et mesures optiques. Un mécanisme a été proposé pour rendre compte de l'importance de la partie organique quant à la vitesse de coloration.The MIOPS group study photochromic materials, i.e., compounds that undergo a light-induced reversible color change. Self-assembled organic-inorganic hybrid materials based on polyoxomolybdates (POM's) and organoammonium cations are considered as promising photochromic materials with a high degree of tunability in optical property. In general, the photogenerated colors of these compounds depend upon the chemical composition and topology of the POM's, while the coloration and fading kinetics of these compounds are related to the nature of the organoammonium cations and their N+-H...O hydrogen bonds with the POM's at the organic-inorganic interface.The kinetics of photoinduced coloration in a lot of compounds under UV-visible illumination was analyzed, and the mechanism of photochromism was discussed on the basis of density functional theory (DFT) calculations.NANTES-BU Sciences (441092104) / SudocSudocFranceF