Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction

Use of efficient anode cathode buffer layer (CBL) is crucial to improve the efficiency of organic photovoltaic cells. Here we show that using a double CBL, Ca/Alq3, allows improving significantly cell performances. The insertion of Ca layer facilitates electron harvesting and blocks hole collection, leading to improved charge selectivity and reduced leakage current, whereas Alq3 blocks excitons. After optimisation of this Ca/Alq3 CBL using CuPc as electron donor, it is shown that it is also efficient when SubPc is substituted to CuPc in the cells. In that case we show that the morphology of the SubPc layer, and therefore the efficiency of the cells, strongly depends on the deposition rate of the SubPc film. It is necessary to deposit slowly (0.02 nm/s) the SubPc films because at higher deposition rate (0.06 nm/s) the films are porous, which induces leakage currents and deterioration of the cell performances. The SubPc layers whose formations are kinetically driven at low deposition rates are more uniform, whereas those deposited faster exhibit high densities of pinholes

Intérêt de l'étude par diffraction des rayons X et microscopie électronique à transmission d'un catalyseur composite à base de fer et de cobalt

Des matériaux à base d'alliage Co-Fe et de ferrite de cobalt ont été préparés par chimie douce dans une solution de potasse concentrée, et cela pour différents rapports Co/Fe. Ces matériaux ont montré de bons comportements catalytiques pour l'hydrogénation du monoxyde de carbone (synthèse Fischer-Tropsch) en vue de produire des oléfines légères C2-C4. Si l'analyse par diffraction des rayons X (DRX) nous permet d'obtenir de nombreux renseignements concernant la composition de ces catalyseurs avant et après les tests catalytiques, elle ne nous renseigne pas sur leur microstructure. C'est pourquoi, cette technique a été couplée à la microscopie électronique à transmission (MET) afin de voir les liens entre la phase métallique et la phase oxyde, ainsi que les transformations de la morphologie des grains avant et après la synthèse Fischer-Tropsch.(Co-Fe) alloy/cobalt ferrite have been prepared in high potassic media for different Co/Fe ratio. These materials have shown very good catalytic behaviours for the hydrogenation of carbon monoxyde (Fischer-Tropsch synthesis) to produce light olefins (C2-C4). X-Ray diffraction (XRD) provides us a lot of informations about the composition of the catalysts, but is inefficient to give informations about the microstructure of the catalysts. So that, X-Ray diffraction has been coupled with transmission electron microscopy (TEM) to view the links between the different phases and what kind of transformation occured during the Fischer-Trospch synthesis

Magnetic structure and magnetic properties of synthetic lindgrenite, Cu-3(OH)(2)(MoO4)(2)

International audienceSynthetic Cu3(OH)2(MoO4)2 consists of Cu3(OH)2 brucite ribbons of edge-sharing copper octahedra connected by MoO4 into a 3D network as in the mineral, lindgrenite, for all temperatures between 1.5 and 300 K. Each ribbon consists of a triangular connection between two different types of copper atom (Cu(1) and 2 Cu(2)) via í3-OH. The MoO4 acts both as one- and three-atom bridges to connect six Cu atoms belonging to three adjacent ribbons. The magnetic properties are consistent with those of ferrimagnetic chains, and the resulting moment of each chain is parallel below the long-range magnetic ordering at 13 K. The Curie constant is 0.468(1) emu K mol-1 of Cu; the Weiss temperature is -14.2(2) K, and the saturation magnetization at 2 K in 50 kOe is 0.41 N íB mol-1 of Cu. Analyses of the neutron powder diffraction reveal an ordered magnetic state where the moment of Cu(1) is antiparallel to those of the two Cu(2); all of them point along the a axis without any sign of geometrical frustration. Any degeneracy that may be present because of the triangular topology of the Cu atoms (s ) 1/2) appears to be lifted by the distortion from an ideal equilateral geometry of the triangle. The entropy, estimated from the heat capacity measurements, attains 50% of the total of 17.7 J K-1 mol-1, close to that expected for three Cu atoms (3R ln 2), up to the long range ordering temperature, and the remaining is associated with the low dimensionality of the material

Microstructure and Photocatalytic Properties of TiO2–Reduced Graphene Oxide Nanocomposites Prepared by Solvothermal Method

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Nuclear and magnetic structures and magnetic properties of the layered cobalt hydroxysulfate Co-5(OH)(6)(SO4)(2)(H2O)(4) and its deuterated analogue, Co-5(OD)(6)(SO4)(2)(D2O)

International audienceThe structures (nuclear and magnetic), magnetic properties (2-300 K, 1-104 bar), and heat capacity of the layered ferromagnet Co5(OH)6(SO4)2(H2O)4 are reported. The crystal structure consists of brucite-like MII-OH layers of edge-sharing octahedra, but having two different Co sites, which are pillared by âââO3SO-Co(H2O)4-OSO3âââ. The absorption spectrum confirms the presence of divalent Co, and by comparison of the two isotopic materials, the assignment of the vibrational spectra is proposed. The magnetic properties are those of a ferromagnet with a Curie temperature of 14 K. Temperature and field dependence magnetization data taken on an aligned sample suggest an easy-plane magnet. The Curie temperature increases linearly with pressure at a rate of +0.12 K/kbar, suggesting small progressive and uniform modifications of the Co-Co exchange interactions. Rietveld refinement of the neutron powder diffraction data and consideration of a group analysis reveal the direction of the moments of the Co within the layer to be along the b-axis, with a maximum moment of 3.33 íB per cobalt. Those of the pillars remain random. Estimation of the entropy from the heat capacity data accounts for the presence of four ordered moments of Co with spin 1/2 at the long-range ordering temperature, while the moment of the pillaring Co contributes only at lower temperature due to the increase of the internal field as the temperature is lowered. The purely 2D-magnetic ordering in an easy-plane magnet, evidenced by neutron diffraction and heat capacity, challenges the existing theories and is a rare example of a single-layer magne

Study of different microorganism and organic compound photocatalytic degradation on TiO2 thin films

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