Organic solar cells: multilayer structures

International audienc

Anode buffer layer at the transparent conductive anode/organic electron donor interface in organic solar cells

International audienc

Verdun 1916 : un choix stratégique, une équation logistique

En opposant la conception allemande du choix stratégique raisonné à la position du 3e bureau du GQC français qui refuse de se laisser hypnotiser par Verdun, l’auteur pose les bases de l’équation logistique que les Français auront à résoudre. D’une part, le haut commandement français ne parvient pas, malgré de nombreux indices, à percevoir le danger sur Verdun. Toutefois, contrairement à un certain nombre d’idées reçues, il ne néglige pas complètement l’aménagement des voies de communication de ce front. À l’inverse, les Allemands, qui raisonnant en termes de chemin de fer, considèrent ce secteur, à la valeur hautement symbolique, comme vulnérable. Bien qu’ayant le relatif avantage de pouvoir faire varier les points d’impact des différentes attaques, et donc de disposer ainsi d’une relative liberté de manœuvre, ils ne parviennent pas à annihiler la capacité de résistance des Français. L’observateur attentif ne manquera pas de remarquer, la clairvoyance de Castelnau et la compétence du général Pétain dont le fameux « Courage, on les aura ! » atteste de la réactivité des Français capables désormais de tenir !Verdun 1916: strategic choice, logistical equation. The article sets up the bases of the logistical equation the French had to resolve during the Battle of Verdun by contrasting the strategic conception of the Germans (that of a ‘a rational strategic choice’) with that of the French GQG which ‘refused to let itself be mesmerized by Verdun’. On the one hand, the French high command, in spite of a number of warning-signs, failed to grasp the extent of the danger hanging over their positions at Verdun. Nevertheless, contrary to some of the ‘received wisdom’, they had not completely neglected to improve the communication and re-supply routes behind this part of the French front. In contrast, the Germans, who thought in terms of railway movements, considered this very symbolically important sector to be vulnerable. Although having the advantage of being able to vary the point of impact of their different attacks, and thereby enjoying a relative freedom of operational manoeuvre, the Germans were unable to destroy the French capacity for resistance. The careful observer cannot fail to notice the far-sightedness of General de Castelnau and the professional competence of General Pétain whose famous rallying order –  “Have courage – we’ve get them !” bore witness to the revived ability of the French troops henceforth to hold onto their positions

Le geste divinisé. Regards sur la transe ritualisée au Kumaon (Himalaya occidental)

Cet article traite de la divinisation du geste musical dans le contexte de la possession ritualisée. Il prend appui sur la description du gharau-ka jāgar, une cérémonie domestique de l’Himalaya occidental (Kumaon, Inde du Nord). A travers l’analyse des conduites musicales, comprises comme un savoir céleste, et vécues comme une ascèse par les interprètes, il s’attache plus particulièrement à mettre en lumière la nature des relations entre les représentations symboliques et leurs modalités opératoires. Ici, les techniques vocales, instrumentales et chorégraphiques, mises au service d’une contraction systématique des unités spatio-temporelles du rituel, agissent comme les agents privilégiés d’un passage du temps ordinaire ou linéaire, à un non-temps divin, justifiant aux yeux des bardes, l’appellation gaṇḍharva vidyā, « Savoir des musiciens célestes »

About MoO3 as buffer layer in organic optoelectronic devices, Technology Letters

MoO3 is well known as efficient anode buffer layer in optoelectronic devices. Actually, MoO3 can be easily deposited under vacuum, by sublimation for instance, and also by wet process. So it is known from a long time that the films deposited by sublimation are amorphous and slightly oxygen deficient, which induces a light blue coloration due to oxygen vacancies. These oxygen vacancies imply the presence of Mo4+ and Mo5+ in the films. The presence of oxygen vacancies increases the conductivity from 10-12 to 10-6 (Ωcm)-1, while stoichiometric films are insulating and MoO2 has a metallic like behaviour with s = 2 102 (Ωcm)-1. About the efficiency of MoO3 as buffer layer, recent studies questioned the MoO3 band structure generally admitted. Under ultra high vacuum, the measured ionisation energy, IE, and electron affinity are found to be 9.7 eV and 6.7 eV respectively, while the films are strongly n-type. Its means that the very large IE energy of the MoO3 excludes any hole transport via the valence band, while the energy alignment between the band conduction minimum, CB, of MoO3 and the Highest Occupied Molecular Orbital (HOMO) of the organic material is favourable for electron transfer between the two materials. In the case of organic photovoltaic cells, the photogenerated hole recombines with an electron at the interface between MoO3 and the organic layer. Indeed, the work function, WF, of the molybdenum oxide films depends strongly of its composition, WF decreases when the oxygen deficiency increases, and on the exposition, or not, of its surface to air contamination. This makes that WF varies from 6.9 eV for a layer studied under ultra high vacuum to 5.2 eV for a layer exposed to the air a few hours. However, since the initial value of WF is very high, MoO3 remains effective if the Highest Occupied Molecular Orbital of the organic material is lower than 6 eV. The band structure of MoO3 and the large possible variations of WF make that, for specific conditions of preparation and conditioning, MoO3 can also be used as CBL