357 research outputs found
Synthèse de nouveaux chromophores pour les cellules photovoltaïques
Date du colloque : 06/2011</p
Miniaturization of molecular conjugated systems for organic solar cells: towards pigmy donors
Organic solar cells with short-circuit current densities and conversion efficiencies of ca. 7.0 mA cm(-2) and 2.0%, respectively, have been fabricated with a very small molecular donor based on substituted triarylamines
Three-dimensional flow instability in a lid-driven isosceles triangular cavity
Linear three-dimensional modal instability of steady laminar two-dimensional states developing in a lid-driven cavity of isosceles triangular cross-section is investigated theoretically and experimentally for the case in which the equal sides form a rectangular corner. An asymmetric steady two-dimensional motion is driven by the steady motion of one of the equal sides. If the side moves away from the rectangular corner, a stationary three-dimensional instability is found. If the motion is directed towards the corner, the instability is oscillatory. The respective critical Reynolds numbers are identified both theoretically and experimentally. The neutral curves pertinent to the two configurations and the properties of the respective leading eigenmodes are documented and analogies to instabilities in rectangular lid-driven cavities are discussed
MoO3/CuI hybrid buffer layer for the optimization of organic solar cells based on a donor-acceptor triphenylamine
We investigate the effect of anode buffer layers (ABLs) on the performances of multi-layer heterojunction solar cells with thienylenevinylene-triphenylamine with peripheral dicyanovinylene groups (TDCV-TPA) as donor material and fullerene C-60 as acceptor. The deposition of a CuI layer between the ITO anode and the electron donor significantly improves the short-circuit current density (J(sc)) and fill factor (FF) but reduces the open-circuit voltage (V-oc). On the other hand, a MoO3 buffer layer increases the V-oc but leads to limited J(sc) and FF values, thus reducing power conversion efficiency (PCE). In this context, we show that the use of a hybrid anode buffer layer MoO3/CuI leads to a considerable improvement of the cells performances and a PCE of 2.50% has been achieved. These results are discussed on the basis of the dual function of MoO3 and CuI. While both of them reduce the hole injection barrier, CuI improves the conductivity of the organic film through an improvement of molecular order while MoO3 prevents leakage current through the diode. Finally the results of a cursory study of the ageing process provide further support to this interpretation of the effects of the various buffer layers. (C) 2012 Elsevier B.V. All rights reserved
Tuning of the Photovoltaic Parameters of Molecular Donors by Covalent Bridging
The synthesis of donor-acceptor molecules involving triarylamines and dicyanovinyl blocks is described. Optical and electrochemical results show that rigidification of the acceptor part of the molecule by a covalent bridge leads to a ca. 0.20 eV increase of the band gap due to a parallel increase of the lowest unoccupied molecular orbital level. A preliminary evaluation of these compounds as donor materials in organic solar cells shows that although this structural modification reduces the light-harvesting properties of the donor molecule, it nevertheless induces an increase of the efficiency of the resulting solar cells due to a simultaneous improvement of the open-circuit voltage and fill factor
Modeling lightning-NOx chemistry on a sub-grid scale in a global chemical transport model
For the first time, a plume-in-grid approach is implemented in a chemical
transport model (CTM) to parameterize the effects of the nonlinear reactions
occurring within high concentrated NO<sub><i>x</i></sub> plumes from lightning NO<sub><i>x</i></sub>
emissions (LNO<sub><i>x</i></sub>) in the upper troposphere. It is characterized by a set
of parameters including the plume lifetime, the effective reaction rate
constant related to NO<sub><i>x</i></sub>–O<sub>3</sub> chemical interactions, and the
fractions of NO<sub><i>x</i></sub> conversion into HNO<sub>3</sub> within the plume. Parameter
estimates were made using the Dynamical Simple Model of Atmospheric Chemical
Complexity (DSMACC) box model, simple plume dispersion simulations, and the
3-D Meso-NH (non-hydrostatic mesoscale atmospheric model). In order to
assess the impact of the LNO<sub><i>x</i></sub> plume approach on the NO<sub><i>x</i></sub> and O<sub>3</sub>
distributions on a large scale, simulations for the year 2006 were
performed using the GEOS-Chem global model with a horizontal resolution of
2° × 2.5°. The implementation of the LNO<sub><i>x</i></sub>
parameterization implies an NO<sub><i>x</i></sub> and O<sub>3</sub> decrease on a large scale
over the region characterized by a strong lightning activity (up to 25 and
8 %, respectively, over central Africa in July) and a relative increase
downwind of LNO<sub><i>x</i></sub> emissions (up to 18 and 2 % for NO<sub><i>x</i></sub> and
O<sub>3</sub>, respectively, in July). The calculated variability in NO<sub><i>x</i></sub> and
O<sub>3</sub> mixing ratios around the mean value according to the known
uncertainties in the parameter estimates is at a maximum over continental
tropical regions with ΔNO<sub><i>x</i></sub> [−33.1, +29.7] ppt and
ΔO<sub>3</sub> [−1.56, +2.16] ppb, in January, and ΔNO<sub><i>x</i></sub> [−14.3, +21] ppt and ΔO<sub>3</sub> [−1.18,
+1.93] ppb, in July, mainly depending on the determination of the
diffusion properties of the atmosphere and the initial NO mixing ratio
injected by lightning. This approach allows us (i) to reproduce a more
realistic lightning NO<sub><i>x</i></sub> chemistry leading to better NO<sub><i>x</i></sub> and O<sub>3</sub>
distributions on the large scale and (ii) to focus on other improvements to
reduce remaining uncertainties from processes related to NO<sub><i>x</i></sub> chemistry
in CTM
One step synthesis of D-A-D chromophores as active materials for organic solar cells by basic condensation
Donor-Acceptor-Donor conjugated systems are synthesized in good yield by double condensation of aromatic aldehydes of triarylamines with 2,3-diaminomaleonitrile under microwave activation with trifluoroacetic acid as catalyst. The electronic properties of the compounds are investigated and discussed and a first evaluation of their potential as donor material in organic photovoltaic cells is presented
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