INDEX will study efficient incremental solutions to combinatorial optimisation problems occurring in design of computer experiments. Modern industrial processes often resort to simulation models of huge computational costs. Use of the original numerical codes for engineering tasks such as design optimisation and performance assessment, which require an intensive exploration of the model input space, would then require unrealistic amount of time. The current trend is to substitute the original numerical codes by a surrogate model of much lesser complexity, often a semi-parametric interpolator of a finite set of its outputs. The quality of the surrogate model depends on the set of simulation inputs (the design) used for this construction, and, obviously, it increases with design size. Classical approaches to design of experiments consider the design size N as a fixed parameter and try to optimise the information in the overall set of N points. However, in many situations the model simulations are progressively integrated, and a decision to stop the learning process is done on-line, based either on the estimated quality of the surrogate model already built or, more pragmatically, because the available (time, cost) budget has been totally consumed. In this context, it is important that the order of execution of the design points be well chosen, such that for all n

Engineered alpine rivers are often characterised by alternated bar systems and substantial sediment transport, particularly of fine sediments (clay, silts and sands). A current problem is the gravel bar aggradation due to successive deposits of fine materials and the growth of riparian vegetation. Such evolution can increase the flood risk in mid and long-term. Many restoration projects were recently financed but they are often limited to mechanical operations and reprofiling of gravel bars. Such projects are very expensive and their sustainability is not guaranteed. The purpose of this project is to study the fine sediment dynamics (erosion and deposition) for typical hydrological events. In particular, we will try to quantify which part of the stocks in the riverbed or in the watershed contributes predominantly on the fluxes measured downstream. Specifically on the river stocks, we will differentiate surface deposits that can be directly resuspended by the flow from stocks infiltrated in the bed matrix that can be resuspended thanks to bank erosion or mobilisation of the armoured layer. The impact of hydrology will be studied by differentiating dam flushing event, natural floods, and the snow-melt period. A major effort will be made on the effects of gravel bar geometry and their different features on the fine sediment dynamics. The study will be carried out at different temporal and spatial scales, from local (instantaneous processes), to a few kilometer reach (processes on the event scale) to the whole river system (long-term processes, i.e. decades), coupling field and laboratory experiments with the use of 1D and 2D numerical modelling. The final objective is to be able to reproduce and predict in mid and long terms the fine sediments dynamics including effects of vegetation, unsteady flow (bar covering and uncovering). Thanks to this project, tools and recommendations will be suggested for a better management of alpine rivers and to limit the fine sediment deposits on gravel bars. This project will be carried out with the help of two academic partners (Irstea and IGE) and an industrial partner (EDF) with the support of local river managers (SPM, SISARC, SIMBHI).

Transient, buoyancy-affected turbulent flows play a major role in many industrial and environmental applications, in particular for the sectors of the two industrial partners, automotive and nuclear industries. Therefore, the present project focuses on configurations representative of a wide range of systems, in order to develop innovative models that will make possible the use of CFD for such very challenging configurations in the daily practice of engineers, which is not possible nowadays. The objective of the project is thus to incorporate buoyancy effects in a range of turbulence models, in order to provide engineers with efficient, robust and accurate tools for the prediction of flows in the mixed or natural convection regimes. The prediction of transient phenomena due to the influence of buoyancy constitutes the main barrier that must be overcome during the project, such that a particular effort will be devoted to the development of hybrid RANS/LES methods, with the objective of demonstrating their potential for buoyancy dominated flows.

Today, single junction silicon technology dominates the photovoltaic (PV) market, with more than 90% of market share. However, the power conversion efficiency of silicon solar cells is now close to the theoretical limit. Indeed, the record has been pushed to 26.7 %, which is close to the silicon single junction theoretical limit of approximately 29% when the unavoidable Auger recombination is taken into account. To increase solar cell efficiency above 30% while keeping the abundant, cheap and stable silicon material as a basis, one solution is to couple silicon with another semiconductor having a larger bandgap in a tandem cell configuration. Currently, silicon based tandem technology follows two paths: the monolithic two terminals tandem (2TT) where the top and the bottom sub-cells are electrically and optically connected, and the four terminals tandem (4TT) where the two sub-cells are electrically independent. However, the 2TT architecture needs to manage photocurrent matching and to optimize the tunnel junction charges transport mechanisms between the top and the bottom sub-cells, while the 4TT device has to deal with issues related to the buried contacts shadowing and access and losses induced by the adhesive interconnection. The THESIS proposal aims at developing an original 3 terminals tandem solar cell (3TT). The approach is threefold: - To propose a new solar cell technology with 3 terminals. This allows us to suppress the constraint of photo-current matching for the two cells constituting the tandem cell. Furthermore, a 3-terminal tandem cell does not need a tunneling junction. - To facilitate the access to the different contacts of the top and bottom cells without the need for etching and without having to align buried contact grids, - To combine the advantages of reliable and mastered silicon technology with those of emerging technologies, allowing the creation of a heterojunction stack with the silicon. This new 3-terminals tandem cell technology we have patented is made possible in an innovative and simple way by using a silicon PV cell with interdigitated back contacts (IBC) on the rear face as a bottom sub-cell and depositing a larger bandgap semiconductor on top of the c-Si surface with a selective band offset barrier (BOB) at the interface in order to form a front heterojunction stack (FHS) realizing a top heterojunction sub-cell. This barrier is chosen so that the heterojunction allows a separation of the operation of the two cells. In the THESIS project, we propose to focus on the emerging perovskites as the absorber of the p-type FHS. The interface between the perovskite and silicon will be actively studied in the project and will need deep investigations to improve the interface quality and device operation. We plan to use also p/i a-Si:H stack as the FHS, forming a (p) a-Si:H/ (i) a-Si:H/ (n) c-Si vertical front subcell. Of course, we do not expect the best photovoltaic performances with this subcell due to the limited transport properties of a-Si:H. However, the growth of device quality a-Si:H for the top subcell, and the c-Si IBC technology are already well mastered in the consortium, so this will allow us to fabricate a proof of concept device for this innovative 3TT architecture. This will be a breakthrough in the PV world, since the 3TT architecture has never been demonstrated so far.

The aim of the project is to provide low-cost and high efficiency tandem cells grown on crystalline silicon (c-Si) substrates, with merging both the monocristalline Si approach with the high-efficiency monocristalline multijunction approach based on III-V materials. These CPV cells will be used under natural lighting and under low light concentrators (100 suns) developed by IRDEP-CNRS, and benchmarked under medium concentration by Heliotrop sas. The PV cells efficiency is one of the most important parameters for the final cost of electricity, since it impacts directly the ratio between produced energy and production cost. With 22% efficiency modules based on c-Si, the technology seems to reach its limits. To increase further the efficiency of c-Si cells and modules, going to multijunction devices (association of two different absorbing layers in the same cell) seems to be the obvious choice. While many projects tend to focus on all silicon technology, best high bandgap cells are yet based on III-V compounds. This project proposes to demonstrate the proof-of-concept for a monolithic integration of high efficiency multijunction CPV device on a low cost monocristalline silicon substrate upon which a III-V lattice-matched material will be grown using molecular beam Epitaxy (MBE). This Lattice-Matched heterostructure with its very low structural defect densities (Dislocations, AntiPhase Domains, point defects) will be capable of sustaining III-V high performing PV devices onto silicon with long life-time. This novel route overcomes the problems of high cost substrates (as compared to Ge or III-V substrates used currently for this kind of CPV), the killer structural defect formation and reliability issues of lattice mismatched systems (metamorphic approach) and the low reliability and low lifetime of hybrid techniques (such as wafer bonding). The integration of photovoltaic functions onto a single silicon substrate will also achieve a reduction in the use of III-V based semiconducting materials in high-efficiency multijunction CPVs. The two main scientific and technologic objectives of the project are : 1) The achievement of GaAsPN (1.7 eV) single cell on Si (with a 15% efficiency under low concentration, i.e. 100 sun). 2) The demonstration of a high efficiency and low cost multi-junction solar cell: GaAsPN pn cell at 1.7 eV on Si pn cell at 1.1 eV (25% efficiency under low concentration, i.e. 100 sun, as a first step towards very high-efficiencies >30%) Lattice-matched layers and slightly tilted substrates are used to overcome the two main difficulties faced by the growth of III-V materials on silicon substrates: misfit dislocations and antiphase lattice defects, in order to obtain defect-free III-V materials and to get large minority carrier diffusion lengths for the PV applications. The PV devices will consist in high efficiency tandem cells III-V/Si double-pn-junctions separated with a Buried Tunnel Junction. The final structure will include a first bottom Si pn (1.1eV low gap) grown on the Si substrate, then a thin GaP layers is grown by MBE to prevent structural defects formation, a top cell GaAsPN pn (1.7eV large gap) junction is then grown on top of it. The project relies on a high quality consortium which brings together six french partners, and an associated European partner, with high, established competence and complementary methodology and expertise in their fields and leading appropriate workpackages: FOTON (growth of III-V materials), INL (Si-based PV technology), CEMES-CNRS (structural characterizations), IRDEP-CNRS (research in PV development), EDF R&D (a European leader in the Energy sector), HELIOTROP (French manufacturer of high concentration photovoltaic modules (HCPV)) and AALTO (a Finnish associated academic partner specialised in point defects analysis). The partners are active in European research consortia and in networks of excellence and they drive many projects on the national and international level.