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CZTSSe nanocrystals, liquid processed films and solar cells
No full textCu2ZnSnSSe4 (CZTSSe) est un matériau prometteur comme absorbant de cellules photovoltaïques. Le développement à grande échelle de cellules solaires CZTSSe est conditionné au développement de procédés bas coût et soucieux de l'environnement. Dans ce contexte, le développement de films de CZTSSe à partir d'encres tout aqueuses de nanoparticules de CZTS constitue un challenge intéressant. Une stratégie haute température en présence d'un agent texturant gaz a été définie pour synthétiser des nanocristaux de CZTS présentant des surfaces polaires. Notre procédé agent texturant gaz met en œuvre la formation simultanée de nucléis de CZTS et de bulles de gaz. Nous montrons que la production en conditions de forte sursaturation d'une très forte concentration de nucléis de CZTS en association à un très grand nombre de petites bulles de gaz représente les conditions optimales de formation de nanocristaux. Par une étude électrocinétique, une condensation régulée par la taille de l'ion alcalin est observée dans la série des alcalins Li+ < Na+ < K+ < Rb+ < Cs+, démontrant la stabilité chimique des surfaces de Cu2ZnSnS4 en dispersion toute aqueuse. Par mise en œuvre des dispersions tout aqueuses, nous avons réalisé l'acquisition de données de base permettant de produire une preuve de concept de la formation d'un film sans fissures. Un autre point important à considérer lors de l'utilisation de matières premières bas coût est l'élimination des impuretés inhibitrices de la croissance des grains. Un profil spécifique de recuit des films est proposé mettant en œuvre une purification haute température pour l'élimination du carbone. En effet, notre stratégie met en œuvre la décomposition des domaines amorphes en carbone sp2 qui est ultérieurement éliminé via la formation de CSe2 gazeux. Finalement, des cellules solaires ont été fabriquées avec succès à partir d'encres tout aqueuses avec des rendements de conversion préliminaires jusqu'à 2,6 %.Recently more attention is devoted to Cu2ZnSnS4 (CZTSSe) for photovoltaic applications due to their non-toxic, earth-abundant components and good optoelectronic properties. Large scale fabrication of CZTSSe solar cells will rely on the development of low-cost and environmentally-friendly approach. In this context, development of CZTSSe films from all-aqueous CZTS nanocrystals inks represents an interesting challenge. A high temperature, gas-templating strategy has been defined to synthesize highly crystallized CZTS nanocrystals displaying polar surfaces. Our gas-templating process involves the simultaneous formation of CZTS nucleis and gas bubbles. We demonstrate that production of a high rate of small gas bubbles, as well as a high concentration of nucleis, depict optimal conditions for nanocrystal synthesis. By an electrokinetic investigation, a condensation regulation by the alkali ion size is observed in the alkali series Li+ < Na+ < K+ < Rb+ < Cs+, demonstrating the chemical stability of CZTS surfaces in aqueous basic dispersions. By using all-aqueous chalcogenide nanocrystals dispersions, we determined a critical cracking thickness of 250 nm and an average thickness of 100 nm to fabricate micron crack-free films using a multilayer procedure. Having in mind these results, we give the proof of concept of crack-free film formation from all aqueous CZTS nanocrystals inks. Another important consideration, when employing low-cost materials, is the removal of impurities, inhibitors of grain growth. A specific annealing profile is proposed involving a high temperature purification step in order to remove carbon. Indeed, our strategy involves the decomposition of amorphous domains into sp2 carbon which will be further removed via the CSe2gas formation. Finally, CZTSSe solar cells are successfully fabricated from all-aqueous CZTS inks with preliminary devices efficiencies up of 2.6%
2D TMDC Materials for hydrogen evolution through solar water splitting
No full textLe stockage de l'énergie solaire en énergie chimique est une approche hautement souhaitable pour résoudre le défi énergétique. Les cellules photo-électrochimiques combinent la collecte de l'énergie solaire et la décomposition de l'eau. Les nanofeuillets semiconducteur 2D de di-chalcogenures de métaux de transition (TMDC) sont considérés comme des matériaux attrayants pour l'élaboration de photocatalyseur efficace pour la conversion de l'énergie solaire en hydrogène. Malgré les propriétés optoélectroniques uniques des TMDC, la passivation de défauts de surface présents en concentration élevée est un défi important pour le développement de cette classe de matériaux. Dans ce contexte, le présent travail a concerné l'élaboration d'un photocatalyseur 2D TMDC pour la photo-décomposition de l'eau. Le développement de photocatalyseurs de haute performance a été examiné suivant deux axes principaux. Un premier axe de recherche consiste à passiver les défauts de surface des nanofeuillets 2D p-WSe2 à l'aide de complexes Mo-S pour diminuer la recombinaison des porteurs de charge photo-générés et améliorer l'activité photocatalytique. Nous avons démontré que des couches ultra minces de complexes thio et oxo-thio-Mo moléculaires représentent une classe idéale de catalyseurs, bien adaptée pour fonctionnaliser les matériaux 2D car ils sont stables dans des environnements aqueux, bon marché, respectueux de l'environnement. Des densités de courant de -2 mA cm-2 à -0.2 V par rapport à l'électrode d'hydrogène (NHE) ont été obtenues pour la nouvelle photocathode p-WSe2/ MoxSy. En plus d'offrir une activité électro-catalytique élevée, les films complexes Mo se sont révélés capables de guérir les défauts de surface. Les contributions respectives aux effets catalytiques et cicatrisants observées expérimentalement pour les divers complexes moléculaires de Mo impliquaient la forte adsorption sur les défauts ponctuels du substrat 2D WSe2 de complexes de Mo tels que (MoS4)2-, (MoOS3)2- et (Mo2S6O2)2-. Il a été démontré que ces couches de co-catalyseur Mo-S formés à un pH bien défini présentent un comportement n-semi-conducteur et l'ingénierie des bandes formées avec p-WSe2 s'est révélée appropriée pour assurer la séparation des charges et la migration efficace des électrons photo-induits pour la RDH, représentant un exemple de couche de passivation multi-composant avec de multiples propriétés. Un deuxième axe de travail concerne l'optimisation de la nanostructure du film de WSe2 comme objectif l'obtention d'une surface spécifique élevée et des parois de pores composées de quelques monofeuillets. Des films de WSe2 nanostructurés de haute surface et à bonne collecte de porteurs de charge ont été obtenus par co-assemblage des nanofeuillets de WSe2 et des nanofeuillets d'oxyde de graphène réduit (rGO) avec un rapport de nanofeuillets rGO/WSe2 optimal.[...]Collecting and storing solar energy in chemical energy is a highly desirable approach to solve energy challenge. The great potential of a photoelectrochemical cell technology combines the harvesting of solar energy with the water splitting into a single device. 2D semiconducting nanosheets of Transition Metal Di-Chalcogenides (TMDC) are seen as an attractive material to design an efficient photocatalyst for the conversion of solar energy into hydrogen. Despite the unique optoelectronic properties of the TMDCs, the passivation of surface defects in high concentration is a remaining challenge for the development of this class of materials. In this context, the present work has aimed the elaboration of thin 2D TMDC photocatalyst for solar water splitting. The development of high performance photocatalysts was evaluated following two main axis. A first strategy consists in the surface defects passivation of 2D p-WSe2 nanosheets using Mo-S complexes to decrease the photogenerated charge carrier recombination and improve photocatalytic activity. We demonstrated these Mo thio and oxo-thio- molecular complexes films as an ideal class of catalysts, well-suited to functionalize 2D materials since they are stable in aqueous environments, cheap and environmentally benign. Current densities of -2 mA cm-2 at -0.2 V vs NHE electrode were obtained for the new p-WSe2/MoxSy photocathode. Besides developing high electro-catalytic activity, the Mo complexes films were shown to display ability to heal surface defects. The respective contributions in catalytic and healing effects observed experimentally for the various molecular Mo complexes involved strong adsorption on point defects of the 2D WSe2 substrate of Mo complexes such as (MoS4)2-, (MoOS3)2-and (Mo2S6O2)2-. The Mo complexes films spontaneously formed at well-defined pH were demonstrated to present n-semi-conducting behaviour and band engineering formed with p-WSe2 showed to be suitable for ensuring charge separation and efficient migration of the photo-induced electrons for the Hydrogen Evolution Reaction, thus representing an example of multicomponent passivation layer exhibiting multiple properties. A second strategy focus in the nanostructure optimization of WSe2 with high specific surface area and pore walls composed of few layers. Nanostructured WSe2 films of high surface area and good charge carrier collection were obtained by co-assembling WSe2 nanosheets and reduced graphene oxide (rGO) nanosheets with an optimal rGO/WSe2 nanosheet ratio. After deposition of co-catalyst thin layer, the new layered nanojunctions of rGO-WSe2/MoxSy exhibited photocurrents up to -5 mA cm-2 at -0.2V vs NHE. Incident-photon-to-current efficiency conversion of 10% were achieved for WSe2 nanoflakes of 70 nm thickness in presence of rGO and MoxSy co-catalyst.[...
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Utilisation de materiaux a base d'oxyde de cerium pour des applications photovoltaiques
No full textFecha de presentación internacional: 09.07.2004. - Titulares: Consejo Superior de Investigaciones Científicas (CSIC). - Rhodia
Chimie. - Universidad Politécnica de Valencia[EN] The invention concerns the use of cerium oxide materials, as photovoltaic materials, and in particular the use of said materials for constituting photoreceptor electrodes for collecting current carriers in photovoltaic devices, in particular in solar cells. The invention also concerns said photovoltaic devices.[FR] La présente invention conceme l'utilisation de matériaux à base d'oxyde de cérium, à titre de matériaux photovoltaiques, et en particulier l'utilisation de ces matériaux pour la constitution d'électrodes photoréceptrices collectrices de porteurs de charges dans des dispositifs photovoltalques, en particulier dans des cellules solaires. L'invention conceme également les dispositifs photovoltaiques précités.Peer reviewe
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