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Abstract Theoretical analysis of the interaction between concentrated solar radiation and a honeycomb matrix or a bed of particles cooled by a gas is presented. The computation and the experimental results show evidence of overheating of the solid near the irradiated surface. To prevent the upper surface from this phenomenon and to reduce the radiative heat losses, we propose to use selective semi-transparent porous absorbers. The first results about coatings on silica are presented.

Abstract Novel proton-conducting electrolytes were prepared from the sol–gel precursor 1-[3-(trimethoxy-λ4-silyl)propyl]imidazole with the addition of either trifluoroacetic or acetic acid. The presence of trimethoxysilyl groups enabled the solvolysis and condensation reactions of silsesquioxane species. IR spectroscopy revealed that more cube-like species formed in the electrolyte prepared from trifluoroacetic acid, while cube- and ladder-like silsesquioxanes were present in the electrolyte with acetic acid. This assignation was independently confirmed by 29Si NMR analyses revealing the T3 signals of trisiloxane bonding. IR spectroscopy also pointed to the formation of hydrogen bonding in the latter electrolyte, since the frequencies of the observed bands at 1710, 1409, and 1272 cm−1 approached those of acetic acid. In contrast, the IR bands at 1662, 1204, and 1130 cm−1 confirmed the existence of trifluoroacetate anions in the case when the electrolyte was prepared from trifluoroacetic acid. The presence of free trifluoroacetate anions contributed to the moderately higher specific conductivity of this electrolyte (4.6×10−5 S/cm) compared to that of acetic acid (1.6×10−5 S/cm). The specific conductivity of the electrolytes could be further increased by the addition of a lithium salt. All electrolytes were employed in electrochromic devices with optically active WO3 and various inorganic counter-electrodes (CeVO4, V2O5, Ti/V-oxide). Photopic transmittance changes from 30% to 40% were achieved.

Abstract The present work aimed to find the answer how does the isomerization of the Ru based dyes affect the overall photon-to-current efficiency of the DSSCs and to explain the charge transfer phenomenon occurring on the dye/nanosemiconductor interface. Therefore, electronic and optical properties of three bipyridine derivatives anchored on the TiO2 electrode were investigated by computational simulations based on quantum chemistry codes performed on a cluster model and the predictions compared with experimental responses. The quantum chemical calculations carried out for the para-, meta- and ortho-isomers has given the possibility to explain the role of an anchor group position in the DSSC devices design. An in-depth analysis of the obtained data shows that the nature of the bonding between the anchor groups and the semiconducting nanoparticles affects the charge transfer at the interfaces. The electronic properties obtained for the hybrid systems and their components indicate that solar cells with the para-derivatives of the Ru based dyes as sensitizers exhibit the highest photo conversion efficiency. The observed phenomenon was explained based on the photogenerated excitons in the organic groups and their dissociation at the dye/semiconductor interfaces to ensure the free charge carriers.

AbstractRenewable energy sources and electric automotive transportation are popular topics in our belated energy‐conscious society, placing electrochemical energy management as one of the major technological developments for this new century. Besides efficiency, any new storage technologies will have to provide advantages in terms of cost and environmental footprint and thus rely on sustainable materials that can be processed at low temperature. To meet such challenges future devices will require inspiration from living organisms and rely on either bio‐inspired or biomimetic approaches.

AbstractThe thermodynamic and kinetic data obtained for the electrochemical lithium intercalation into sol‐gel derived β‐Na0.33V2O5 are in agreement with the scheme suggested for the filling of available M sites of the β‐structure by Li+.

Abstract This paper is focusing on a numerical investigation of hydrogen Active Magnetic Regenerative Liquefier (AMRL). For this purpose, two-dimensional transient numerical modeling with finite volume method has been developed (i.e. CFD method) to simulate the parallel plane plate (PPP) AMRL regenerators type in order to predict and investigate its thermal performances. The resulting mathematical model has been implanted in ANSYS-Fluent software to overcome the complexity of the Active Magnetic Regenerative (AMR) cycle. To run the simulations, a six cascade-stages hydrogen AMRL cycle has been proposed. From the first to the last stage, the regenerators are made of the following magnetic materials: Gd, Tb, Dy, Ho, Er and Tm respectively. The validity of the proposed model has been performed through Cristal2 AMR demonstrator built to operate at room temperature. Good agreements have been found between experimental and numerical results. Then, simulations of the proposed multistage hydrogen AMRL have been carried out for applied magnetic induction up to 7 T. It has been shown that a mass flow rate of 100 mg s−1 of hydrogen initially at 300 K and 1 atm can be cooled down to 57 K. Thus, the capability of the proposed CFD method for predicting consistent results has been demonstrated.

Abstract A study on the optimisation of front contacts of n-type multicrystalline silicon solar cells is presented. In this study the same cell processing was applied to two types of wafers: electronic grade (EG-Si) and metallurgic grade (MG-Si) silicon. The contact firing temperature was optimised, by measuring the contact resistivity of the front and back contacts for different firing temperatures. The front contacts were improved by deposing silver using an electrochemical process. The solar cells were characterised before and after the silver deposition. For all cells processed the line resistance was reduced by over 90% after the silver deposition. After the contact improvement, EG-Si cells showed an absolute efficiency improvement of 2.6%, but MG-Si cells suffered a reduction on the cell efficiency, an effect related to parasitic shunting existent in these cells.

In this article, the effect of the various processing steps during the fabrication of c-Si/SiOx/SiCx fired passivating contacts on the silicon bulk lifetime is studied, and the kinetics of defect deactivation by hydrogenation is investigated. It is found that the firing step at 800 degrees C induces shallow bulk defects in float-zone silicon wafers, which can subsequently be passivated with hydrogen provided by an a-SiNx:H/D reservoir layer upon annealing at 450 degrees C. Experimental results and numerical data treatment indicate a rapid passivation of the surface within less than 1 min, followed by a slower passivation of the shallow bulk defects. In situ lifetime measurements are consistent with a slow bulk lifetime improvement by showing similar lifetime evolutions for both p-type and n-type SiCx layers. The kinetics of the hydrogenation process seems to be limited by the available hydrogen supply at the c-Si/SiOx interface, rather than by its diffusion within the bulk of the wafer. Moreover, it is affected by the bulk doping as well as the SiCx layer thickness. Finally, it is shown that hydrogenation is also possible with an a-SiNx:H/D reservoir layer deposited on one side of the wafer only, although resulting in a lower passivation level (s similar to 700 mu s compared to similar to 1300 mu s for symmetrical samples), and slower kinetics (similar to 5 min compared to similar to 0.8 min).

Abstract Different anhydrous potassium ion conducting polymer electrolytes have been studied: (POE)nKTFSI (trifluorosulfonimide), plasticized (POE)nKTFSI, (PEM)nKTFSI and (POE-ACETAL)nKTFSI. DSC and conductivity measurements have been used to characterize these electrolytes. Several solutions to avoid crystallization have been examined. The best conductivity has been obtained with (POE-acetal)nKTFSI. This electroylte exhibits good transmission in the VIS-IR region. The time response of cells using these electrolytes and Prussian blue and KxWO3 as electrodes has been measured and compared. The influence of H2O on cycling is also presented and discussed.