Development of a new generation of recyclable encapsulation films for photovoltaic modules

In the context of the energy transition, photovoltaic (PV) solar energy represents a growing share of the world's electricity production, and PV itself represents a growing share of the world's energy production. The massive production and deployment of PV modules is putting increasing pressure on the environment. In particular, because of the extraction of the raw materials required for their production and their disposal at the end-of-life. Recycling tackles both of these issues.
PV modules are made of layers of different natures laminated together. In the module central layers, PV cells are embedded in an elastomer, the encapsulant. This material plays several roles: barrier properties, mechanical protection, etc. Currently, the encapsulants used are generally cross-linked EVA copolymers, which makes recycling particularly difficult.
The aim of this thesis is to develop a vitrimer encapsulant for PV applications. Such an encapsulant, with exchangeable bonds, could drastically simplify recycling without compromising the integrity of the module in its lifetime. This work will start with the formulation of the encapsulant. It will go on with the characterization of its properties (thermo-reversibility, rheology and barrier properties), its extrusion into a film and its lamination in a PV module.
This development will be iterative, thus leading to tests under application representative conditions at various stages of development. It will rely on the resources and expertise of three laboratories LCMCP (Sorbonne Université), PIMM (ENSAM) et LITEN (CEA).

Investigate electron and hole transport layers for high temperature stability III-V quantum dot photodiode devices

Colloidal Quantum Dots (QD) are novel building blocks for the fabrication of image sensors with high performance tunable light detection in the SWIR wavelength range but currently exhibit undesired degradation under high thermal stress. Thermal degradation can be significantly improved by optimizing the device materials (contacts, hole transport layer (HTL), electron transport layer (ETL) and encapsulation), film thicknesses, and deposition processes used to make quantum film (QF) photodiode devices. As such, a detailed investigation into many different HTL, ETL and top electrode materials will be pursued to find the best candidates to overcome the current limitations. Materials selection and deposition processes for these layers will be chosen and studied among a variety of existing materials developed at LETI. QD films with tunable absorption from 1-2.5 µm will be prepared by STMicroelectronics and CEA-IRIG in collaboration with other partners. The QD patterning step for the fabrication of the devices and the electro-optical testing will be performed internally at LETI with support from STMicroelectronics.

Ultrasensitive static/dynamic flexible force transducer

In this thesis, the principles and challenges in the development by printing and characterisation of conformable organic piezoelectric matrices for medical use under stress will be examined. A stretchable/conformable piezoelectric sensor, produced on a stretchable substrate, will be developed with materials (PVDF-TrFE type polymer or composite). These developments will make it possible to study the feasibility of using such piezoelectric components in various fields.
The aim of the study carried out to date has been to produce a flexible piezoelectric device based on the principle of a double-sided sensor so as to eliminate the contribution of bending. This sensor must also be stiff enough to be deployed through a 3mm diameter catheter. In this context, the work carried out in this thesis will focus on the development of a flexible piezoelectric sensor capable of converting the mechanical energy of low stresses, coupled with a piezoresistive sensor capable of measuring static stresses. The use of polymers offers greater flexibility, and they are implemented in the form of thin films, making them lightweight and space-saving. In order to achieve these objectives, a dedicated sensor structure guaranteeing redundant measurement (piezoelectric and piezoresistive sensor) will be studied, produced and characterised. The sensor manufacturing process will have to be optimised to increase their efficiency. Optimisation of the architecture of the electrodes and the geometry of the active layers will be tested on a test bench in order to assess their ability to measure static and dynamic stresses simultaneously over the widest possible range of forces. At the same time, fundamental characterisations of the material will be carried out in order to establish correlations between the structure and electrical properties of the sensors.

Modeling of corrosion by the cellular automata method: taking into account diffusion in solution and heat transfer.

The materials’ degradations caused by corrosion is a major issue in industry. Their experimental study in the laboratory, necessary in most cases, often proves difficult to perform. It also has its limits, because the processes involved generally take place over long periods of time and in complex environments, which are therefore difficult to reproduce. In this context, modeling is a powerful and complementary approach to the experimental approach, insofar as it is likely to lead to the development of predictive numerical tools and/or interpretation aids.
Modeling by the cellular automata (CA) method, proposed in this thesis, is used in fields as varied as physics, biology, chemistry and social sciences.
It consists of paving a space with a network of identical cells, each being characterized at time t by a state (which is part of a predefined set of possible states) whose temporal evolution is calculated by means of rules of transition which take into account the states of neighboring cells. Its main asset is to explore the spatio-temporal dynamics of simplified representations of systems likely to be very complex in reality.
Significant advances in corrosion modeling using the CA method have been made over the past ten years at CEA/DPC/SCCME/LECA. 3D extension of existing 2D models has in particular been successfully achieved, as well as the coupling of spatially separated anodic and cathodic reactions. This made it possible to study with the same model the competition between generalized corrosion and different types of localized corrosion. 3D models of intergranular corrosion have also been developed.
In the thesis proposed here, it will be a question of developing a CA model allowing the study of corrosion processes in which the diffusion of corrosive species in solution and/or a temperature that is both variable in time and inhomogeneous in space may prove to be dimensioning (pitting and crevice corrosion, evolution of macroscopic defects). We will take advantage of two main features: firstly the equations governing diffusive transport and heat transfers are similar (they will be simulated using 3D random walks), secondly the AC method is particularly suitable for the study of phenomena involving time-dependent interfaces/boundaries.
The model developed will be implemented in C language and CUDA, in order to perform simulations on mixed CPU/GPU computers (parallel programming on graphics cards). Code development will therefore be the main activity, with simulations being performed on dedicated CEA and ENSCP machines. In order to validate the results provided by the model, reference will be made to experimental results selected from the literature and from SCCME/LECA data.

Development of a predictive power model for a photovoltaic device under spatial constraints

CEA is developing new cell and module architectures and simulation tools to assess the electrical performance of photovoltaic (PV) systems in their operating environment. One of these models, called CTMod (Cell To Module), takes into account not only the different materials making up the module, but also the different cell architectures. For space applications, the community wants to use terrestrial silicon-based technologies that can be integrated on flexible PVAs (Photovoltaic Assembly). The space environment imposes severe constraints. A relevant evaluation of performance at the start and end of a mission is therefore essential for their dimensioning.
The aim of this thesis is to correlate physical models of radiation-matter degradation in space with electrical models of photovoltaic cells. Performance degradations linked to the various electron, proton and ultraviolet (UV) irradiations of the space environment will be evaluated and validated experimentally. Linked to the CTMod Model, this new approach, never seen in the literature, will able to get a more accurate understanding of interactions between radiations and PVAs. These degradations result from non-ionizing energy deposition phenomena, quantified by the defect dose per displacement, and ionizing ones quantified by the total ionizing dose for protons and electrons. In the case of UV, the excitation of electrons in matter generates chain breaks in organic materials and colored centers in inorganic materials. Initially, the solar cell used in the model will be a Silicon cell, but the model can be extended to include other types of solar cell under development, such as perovskite-based cells.

Develoment of lithium mediated ammonia electrolyzer

Recent developments in electrochemical ammonia (NH3) synthesis using lithium (Li) metal deposition in THF-based electrolytes in the presence of protic species, reinvigorated the research interest in direct NH3 electrolyzes technology thanks to its surprisingly high performance in terms of synthesis rate and faradaic efficiency. However, the main drawback is poor energy efficiency due to minimum voltage requirements associated to Li metal deposition and H2 oxidation reactions on the opposite electrodes. In this project, we propose to study the nitridation reaction of Li-alloy forming metals that can enable the decrease in electolyzer voltage. This study will be performed using a 3-electrode electrochemical pressure cell and differential scanning calorimetry – thermogravimetric analysis under N2, H2 pressures. The goal here is to couple existing knowledge in chemical looping synthesis of ammonia with electrochemical synthesis. Porous (carbon or steel tissue) electrodes will be developed with nanoparticles of Li-alloy forming metals and their performance will be studied in an electrolyzer. The assumed 3-step reaction mechanism to form NH3 is as follows: Li deposition > nitridation > protonation. This mechanism is already a subject of discussion for pure Li metal which will be further complicated with the use of alloy forming metals. Therefore, we propose an in-depth study using x-ray photoemission spectroscopy. The ultimate objective of the project is to accelerate the direct NH3 electrolysis technology and address the Power-to-X needs of renewable electricity sources.

Quantification of strategic binary compounds by hard X-ray photoemission (HAXPES) and combined surface analysis

The main objective of the thesis is to provide reliable support to the processing of front-end materials for advanced FD-SOI technologies. To achieve this, methodologies for elemental quantification focused on the use of hard X-ray photoelectron spectroscopy (HAXPES) will be developed and validated through a collaborative framework at multiple levels, both internal and industrial.
These collaborations will enable to pool upstream work aimed at a better understanding of quantification in HAXPES at all levels (intensity measurement, types of sensitivity factors used, measurement reproducibility).
In a second step, the protocols will be applied to the targeted technological materials and then optimized. The targeted materials are primarily silicon and germanium compounds contributing to the optimization of the channels of advanced FD-SOI transistors, such as Si:P, SiGe, and their derivatives (GeSn, SiGe:B). A combined analytical approach involving other nanoscale characterization techniques will be strengthened by identifying the most appropriate techniques to produce reference data (ToF-SIMS, RBS, etc.).
In a third step, multi-scale aspects will be developed. In particular, they will aim to investigate to what extent the composition measured by HAXPES on a material developed upstream of transistor integration steps (for process deposition optimization) compares to that determined by other techniques (atom probe tomography, TEM-EDX, TEM-EELS) at the end of nanometric device integration.

Synthesis and post-synthesis treatments of ultra-light weight mesoporous metals obtained by plasma electrolysis for laser targets fabrication

For fundamental physics experiments conducted on the Megajoule Laser, the CEA must develop mesoporous metal materials with very low apparent density. Based on the discovery by CEA researchers of a new reactive mechanism between plasma and liquid, CEA has developed a unique electrolytic plasma synthesis process in the world. This technology converts thousands of flashes into as many metallic nano-filaments in seconds to form metals in the form of a nano-structured, ultra-light sponge.
The understanding of the physico-chemical mechanisms that govern the synthesis of these foams is crucial to optimize the properties of synthetic raw materials. A first part of the thesis will consist in continuing the studies already carried out and completing the innovative phenomenological model in the field of electrolytic plasmas.
In a second step, the influence of a heat treatment on the crystallization of these materials and their mechanical resistance will be conducted in order to optimize their subsequent shaping by laser or ultra-precision mechanical machining.

Realization of MOSFET gates at the sub-10nm node on FD-SOI

As part of the NextGen project and the European ChipACT to ensure the sovereignty and competitiveness of France and Europe in terms of electronic nano-components, CEA-LETI is launching the design of new FD-SOI chips. Already present daily in the automotive or connected object areas, 28-18nm FD-SOI transistors are produced in large volumes by microelectronics founders such as STMicroelectronics. This technology is based on an innovative architecture allowing the production of transistors that are faster, more reliable, and less energy-consuming than transistors on massive substrates. The move to the 10nm node will improve the performance of this technology while being compatible with the issues of energy efficiency and the challenges of miniaturization.
The Field-Effect Transistor (FET) at the 10nm node requires a complex silicon/high-k insulator/metal gate stack. The addition of the high-k dielectric enables to reduce the leakage currents of the gate, but its use coupled with the miniaturization of the components induces new difficulties in the electrical behavior of the FET related to the heterogeneity of the materials constituting the gate stack. To try to resolve these difficulties, this doctorate focuses on an assembly including the deposition of extremely thin metal films on high-k and allowing adjustment of the threshold voltage of the transistors. To study these layers and carry out metallic deposits, CEA-LETI is equipped with PVD equipment for multi-cathode co-sputtering on 300mm silicon wafers. It will make it possible to produce complex alloys and metallic layers adjusted in composition with thickness control at the atomic scale.

Role of cement paste and fine aggregates in the triaxial behavior of concrete