Determination of Solvent Systems for Blade Coating Thin Film Photovoltaics

With lab‐scale solution‐processed thin film photovoltaic (TFPV) devices attaining market relevant efficiencies, the demand for environmentally friendly and scalable deposition techniques is increasing. Replacing toxic halogenated solvents is a priority for the industrialization of solution‐processed TFPV. In this work, a generalized five‐step process is presented for fabricating high‐performance devices from nonhalogenated inks. Resulting from this process, several new solvent systems are introduced based on thiophene, tetralin, 1,2,4‐trimethylbenzene, o‐xylene, and anisole for blade coating of three different diketopyrrolopyrrole‐based (pDPP5T‐2, pPDPP5T‐2S, and P390) bulk heterojunctions applied in organic photovoltaic devices. Devices based on pDPP5T‐2S and P390 attain 5.6% and 6.1% efficiency, respectively, greater than the efficiency either material reached when processed from the halogenated solvent system commonly used. These processes are implemented without post‐deposition annealing treatments or additives. The Hansen solubility parameters of the pDPP5T‐2 material are obtained, and are used, along with wettability data on a variety of substrates, to determine optimum solvent combinations and ratios for deposition. This generalized five‐step process results in new nonhalogenated solvent pathways for the scalable deposition of thin film photovoltaic materials.     

Erratum to: Evaluation of the Particle Bonding for Aluminum Sample Produced by Spark Plasma Sintering

Journal of Materials Engineering and Performance -     

Evaluation of the Particle Bonding for Aluminum Sample Produced by Spark Plasma Sintering

Journal of Materials Engineering and Performance - Spark plasma sintering (SPS) is a powder metallurgy process that sinters powder materials within a short time by simultaneous application...     

Silver versus white sheet as a back reflector for microcrystalline silicon solar cells deposited on LPCVD‐ZnO electrodes of various textures

We compare the performance of two back reflector designs on the optoelectrical properties of microcrystalline silicon solar cells. The first one consists of a 5‐µm‐thick low‐pressure chemical vapor deposition (LPCVD)‐ZnO electrode combined with a white sheet; the second one incorporates an Ag reflector deposited on a thin LPCVD‐ZnO layer (with thickness below 200 nm). For this latter design, the optical loss in the nano‐rough Ag reflector can be strongly reduced by smoothing the surface of the thin underlying ZnO layer, by means of an Ar‐plasma treatment. Because of its superior lateral conductivity, the thin‐ZnO/Ag back reflector design provides a higher fill factor than the dielectric back reflector design. When decreasing the roughness of the front electrode with respect to our standard front LPCVD‐ZnO layer, the electrical cell performance is improved; in addition, the implementation of the thin‐ZnO/Ag back reflector leads to a significant relative gain in light trapping. Applying this newly optimized combination of front and back electrodes, the conversion efficiency is improved from 8.9% up to 9.4%, for cells with an active‐layer thickness of only 1.1 µm. We thereby highlight the necessity to optimize simultaneously the front and back electrodes. Copyright © 2014 John Wiley & Sons, Ltd.     

Vertically aligned carbon nanotube‐based composite: Elaboration and monitoring of the nanotubes alignment

We present the different elaboration steps of a composite formed of carbon nanotubes (CNT) carpet embedded in an epoxy polymer. Detailed characterization at each step of the elaboration process is performed. The good alignment of CNT in as‐grown carpets is kept all along the elaboration process of the composite, as it is measured at both macro and microscopic scales by X‐ray scattering. We also ensured by X‐ray fluorescence measurements that the iron‐based catalyst particles used for the synthesis were removed from the carpet after a high temperature post‐annealing treatment. These measurements give valuable information for further applications involving unidirectional nanotube composites and membranes, where CNT alignment is a key parameter. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39730.     

An improved interface model for molten corium-concrete interaction

In the field of research for Severe Accidents of PWRs, calculation results are needed to estimate when corium achieves basemat melt-through. In this framework, knowledge of the heat transfer coefficient as well as the temperature at the interface between the melt and the solid are key issues. It has been previously emphasized that physico-chemistry of the melt (composition) affects the temperature. However, the effect of gas sparging and liquid concrete release on the mechanical stability of the solid layer and on the interface temperature has not been analysed in detail. ARTEMIS 1D tests were launched to analyse the phenomenology at the interface. A general conclusion for all these tests is that a solid medium enriched in refractory species exists at the interface between the pool and the concrete.Tests 2 and 6, which are close to reactor representative conditions, could be well described with the assumption T_interface = T_liquidus. The analysis of tests 3 and 4 revealed that the interfacial medium is thicker by a factor of 4-5 times than calculated with the assumption of pure conduction heat transfer. Detailed analysis leads to the conclusion that the interfacial medium is made of a porous layer of refractory particles embedded in a liquid phase. The liquid density difference, between the porous medium and chimneys, results in recirculation of the liquid in the porous layer. This recirculation is responsible for a convective contribution to heat transfer through the porous layer. The convective heat flux is partly linked to cooling of the recirculating liquid, but also to its partial solidification. The solidification results in gradual plugging and enrichment of the porous layer in refractory species and in the increase of the resistance to heat transfer. The phenomena have been modelled and ARTEMIS tests 3 and 4 are well reproduced. The complete plugging of the porous medium, associated with thermodynamic equilibrium at the interface between the solid medium and the pool leads naturally to the solid crust model implemented in TOLBIAC-ICB. The latter model appears, thus, as a simplification of the porous medium approach described here.Thick interfacial layers, which have composition between refractory and corium mixture, have been observed in ACE and MACE tests with LCS (Limestone-Common Sand) or Limestone concrete and can be explained with the proposed model approach. For siliceous concrete, convection within a porous medium is not possible due to the large viscosity.     

Preparation, electrical conductivity, and magnetic susceptibility of (Ba1 − x Bi x )(Mn0.5 + x/2Nb0.5 − x/2)O3

(Ba_{1 ? x} Bi _x )(Mn_{0.5 + x/2}Nb_{0.5 ? x/2})O₃ perovskite solid solutions have been prepared by solid-state reactions and their physicochemical properties have been investigated. We have studied the influence of bismuth substitution for barium cations on the phase composition of the samples. Their magnetic susceptibility and electrical conductivity have been measured as functions of temperature. The composition dependence of the antiferromagnetic ordering temperature is presented.     

Assigning multiple activities to work shifts

In some companies such as large retail stores, the employees perform different activities (e.g., cashier or clerk in a specific department) to respond to a customer demand for each activity that varies over the planning horizon and must be fulfilled as soon as possible. For a given time period, this demand translates into an ideal number of employees required for the corresponding activity. During a work shift, an employee can be assigned to several activities that are interruptible at any time and subject to operational constraints (required skills, minimum and maximum assignment durations). Given work shifts already assigned to the employees, the multi-activity assignment problem (MAAP) consists of assigning activities to the shifts such that the activity demands are satisfied as best as possible over the planning horizon. In this paper, we propose three integer programming models for the MAAP and develop various heuristics based on mathematical programming techniques. Computational results obtained on randomly generated MAAP instances show that a heuristic column generation method embedded into a rolling horizon procedure provides the best results in general.