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.

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.

Increasing the efficiency of model-based industrial processes requires to improve their uncertainty quantification and numerical optimization. Such issues appear in most of the engineering domains (e.g. energy, transport, agriculture) and scientific fields (e.g. biology, high-energy physics). A major problem comes from the black-box nature of the process/function of interest that is often not directly accessible: in general, the only available information are the outputs of the black-box simulation workflow. In particular, derivative information, which is very valuable in the context of optimization and uncertainty quantification, does not exist or is not available. This is a direct consequence of the increasing complexity and diversity of the industrial problems to be addressed (e.g. coupling of multi-physics or multidisciplinary simulators, creation of economic models, working with more sophisticated machine learning models, handling of uncertainty and non-Euclidean variables). Solving this problem is therefore a major issue with direct and significant industrial benefits. In the two last decades, the field of black-box optimization (BBO) methods – especially, derivative-free optimization and surrogate or metamodel (MM) management frameworks – has experienced major theoretical and practical developments. Nevertheless, despite the growing popularity of these methods, some fundamental limitations remain: in particular, the scale of the problems that can currently be efficiently solved by BBO methods does not exceed a few tens of variables and methods to deal with high-dimensional or categorical variables are limited. In real-world applications, the simulation budget is often very restricted. Moreover, BBO algorithms have become complex tools in themselves, which raises questions about their generality of use (choice of kernels for MM) and the reliability of hyper-parameter learning. The main objectives of the project are, jointly, to develop innovative simulation and surrogate-based optimization methodologies, while pushing back their current limits of performance and applicability, guided by real-world applications. These applications are related to the design and risk assessment of critical and complex systems. Hence, the partners of the project will provide challenging and critical applications in the fields of renewable and low-carbon energies and reduced CO2 air transport domains, in order to demonstrate the relevance and the efficiency of the developed methodologies. More precisely, the partners’ ambition is to solve the four following major challenges: - design MM adapted to large scale problems (typically around 100 input variables) in the context of a limited budget of simulations (around 500); - adapt sequential enrichment strategies to large scale problems for reliability-based design optimization and reliability-based inversion purposes; - design efficient black-box optimization methods capable of handling problems mixing input variables of different types: continuous, ordinal and nominal variables; - increase the performance of the iterative process (optimization and MM building) in case of instabilities, failures or non-physical results of the simulation workflow: the aim will be to learn the hidden constraints and deal with them in the adaptive design procedure. Thus, the project aims at (i) consolidating and extending the existing surrogate-based optimization methods to provide a real improvement of their application to industrial problems, (ii) sharing experiences and methodologies of industrial partners for practical problems, (iii) integrating the resulting methods and methodologies in open-source platforms developed by the partners.

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

Chlorination of seawater is still considered as one of the most effective and least expensive process to control biofilm formation (micro-fouling) that may block the heat exchangers or development of molds (macro-fouling) in industrial pipelines. This process is used in many industrial sites around the world in order to use this water for cooling purposes (petrochemical and steel industries) or for warming (LNG terminals for the liquefaction of gases). This process has also been selected by the International Maritime Organisation as one of the methods to be used for the control and management of ships ballast water before discharge into the sea. Whatever type of industries, whether on land or at sea, chlorination is conducted either by dissolving chlorine gas, or by adding sodium hypochlorite, or -even in the case of use of seawater- by electrolysis at doses between 0.5 and 1.5 mg L-1 (expressed as Cl 2) on water taken from the environment at rates of several hundred m3 /s. It can be conducted in continuous mode at low dose to stop the settlement of larvae, reducing their growth and kill the long term or intermittently then when the heat exchanger fouling reaches a certain threshold. The major concern related to the use of this process is, to some extent, dumping of chlorine in the environment with known impacts on fauna and flora but above potential output of many halogenated compounds formed by complex reactions between the chlorine residual inorganic and organic constituents, natural and man present in the receiving environment. If the formation of chlorination by-products is well studied and referenced in the literature for water intended for human consumption and freshwater, little data exists on the nature and concentration levels and reactivity and fate of these byproducts in coastal waters, mostly based on the knowledge acquired by the reactivity of chlorine with organic matter in freshwater. However, it is known that chlorine (as Cl2 or HClO form) can rapidly react with the bromide ions found in seawater to form instantly hypobromous acid, compound known to be much more reactive than HClO with the organic matter. In marine environments, some research conducted to examine the impact of chlorination on the environment were limited to desalination plants for seawater and nuclear and thermal power plants, and on studies a single discharge point. They also focused on the occurrence of few compounds such as trihalomethanes and haloacetic acids, or even only on the overall toxicity of these releases without even find the nature of the present compounds. They are mainly limited to the measurement and identification of these compounds in the water compartment. FOS-SEA project aims at a better understanding of the nature of the by-products that can be generated during the chlorination processes when seawater is used as makeup water to determine the reaction schemes of their training and their become, to study their transfer in different environmental compartments and their dissemination, and finally to study their toxicity and their metabolites. The results of this research will assess the environmental impacts of releases of chlorinated water at sea and to acquire new knowledge that can help local and national regulatory authorities to formulate control strategies and guidelines for wise use and regulated the chlorination process.