Characterization of Photochromic Dye Solar Cells Using Small-Signal Perturbation Techniques

Photochromic dye-sensitized solar cells (DSSCs) are novel semi-transparent photovoltaic devices that self-adjust their optical properties to the irradiation conditions, a feature that makes them especially suitable for building integrated photovoltaics. These novel solar cells have already achieved efficiencies above 4%, and there are multiple pathways to improve the performance. In this work, we conduct a full characterization of DSSCs with the photochromic dye NPI, combining electrical impedance spectroscopy (EIS) and intensity-modulated photocurrent spectroscopy (IMPS). We argue that the inherent properties of the photochromic dye, which result in a modification of the functioning of the solar cell by the optical excitation that also acts as a probe, pose unique challenges to the interpretation of the results using conventional models. Absorption of light in the visible range significantly increases when the NPI dye is in the activated state; however, the recombination rate also increases, thus limiting the efficiency. We identify and quantify the mechanism of enhanced recombination when the photochromic dye is activated using a combination of EIS and IMPS. From the comparison to a state-of-the-art reference dye (RK1), we were able to detect a new feature in the IMPS spectrum that is associated with the optical activation of the photochromic dye, providing a useful tool for assessing the electronic behavior of the device under different conditions of light excitation. This study provides guidelines to adequate characterization protocols of photochromic solar cells and essential insights on the interfacial electronic processes.Universidad Pablo de Olavide / CEA Grenobl

Microcracking of composites reinforced by stitched multiaxials subjected to cyclical hygrothermal loadings

International audienceMicrocracking of polymer matrix composites reinforced by multiaxial multi-ply stitched carbon preforms submitted to cyclical purely hygrothermal loading is analyzed. The laminates are manufactured by liquid resin infusion (LRI). The stitching induces deviations in fibre layout and creates openings which become resin-rich regions after the resin infusion. The interaction between resin-rich regions and microcracks induced by the hygrothermal cycles was investigated by 2D metallographic micrography and X-ray microtomography. Specific microcracking process was found to occur in this type of material. The occurrence of cracks was quantified and the morphology of the 3D crack network studied. The nature of the stitching yarn and the size of the diamond-shaped resin-rich regions were identified as having a major influence on laminate microcracking after ageing. (C) 2011 Elsevier Ltd. All rights reserved

Introduction à la durabilité des matériaux composites renforcés par nappes unidirectionnelles cousues.

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Role of interface formation versus fibres properties in the mechanical behaviour of bio-based composites manufactured by Liquid Composite Molding processes

The aim of this work was to study the effect of free surface energy modification of flax fibres by a thermal treatment on the mechanical behaviour of bio-based composites. It has been proved that this modification enhances the wettability of flax fibres by liquid epoxy resin and results in a lower porosity amount in composites. Tests to evaluate mechanical properties of elementary fibres, yarns and composites have been performed. The main outcome of this multiscale study, even if elementary fibres and yarns have been embrittled and interface properties have been lowered after thermal treatment, is that the mechanical behaviour of composites manufactured by Liquid Composite Molding (LCM) is better with treated fibres

Vers des éco-composites à base de fibres de lin plus performants et respectueux de l’environnement grâce à la fluoration directe sous F2

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Fluoration de fibres de lin pour la fabrication d’éco-composites.

International audienc

Triisopropylsilylethynyl-functionalized anthracene-based hole transport materials for efficient hybrid lead halide perovskite solar cellsb

International audienceThe development of hole transport materials (HTMs) is a prolific area of research due to the application of these materials in various technologies such as organic lightemitting diodes (OLEDs) or perovskite solar cells (PSCs). HTMs have notably played a crucial role in the development of highperformance PSCs since in these devices, they not only ensure the collection and transport of holes to the counterelectrode but also play an important role on the device stability. In addition to the need for these materials to have good transport properties and to be easy to process, it is also of paramount importance to guarantee that their synthesis costs are reduced to allow them to be used on a large scale. In this work, we show that the use of a 9,10bis[(triisopropylsilyl)-ethynyl]anthracene (TIPS-anthracene) moiety as a $\pi$-conjugated core, in combination with electroactive arylamine moieties, allows us to obtain new efficient HTMs in only 2 or 4 steps after recrystallization. Solar cells fabricated with the hybrid perovskite (Cs$_{0.05}$ FA$_{0.79}$ MA$_{0.16}$ Pb(I$_{0.84}$ Br$_{0.16}$)$_3$ and these new HTMs exhibit power conversion efficiencies of up to 19.3% under AM1.5G solar illumination, which is close to the efficiency obtained with the reference compound 2,2′,7,7′-tetrakis(N,N-di-pmethoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) under the same conditions. Compared to other anthracene-based HTMs reported in recent years and used with perovskites of various compositions, our molecules, which are easy to prepare and purify, are more efficient