Durable radially polatised tubular nanoreactors for catalysis

Rising energy demand and the need to reduce the use of fossil fuels to limit global warming have created an urgent need for clean energy collection technologies. One interesting solution is to use solar energy to produce fuels. Low-cost materials such as semiconductors have been the focus of numerous studies for photocatalytic reactions. Among them, 1D nanostructures are promising because of their interesting properties (high and accessible specific surface areas, confined environments, long-distance electron transport and facilitated charge separation). Imogolite, a natural hollow nanotubes clay, belongs to this category. Its particularity does not lies in its chemical composition (Al, O and Si) but in its intrinsic curvature, which induces a permanent polarization of the wall, effectively separating photo-induced charges. This nanotube belongs to a family sharing the same local structure with different curved morphologies (nanosphere and nanotile). In addition, several modifications of these materials are possible (coupling with metal nanoparticles, functionalization of the internal cavity), enabling their properties to be modulated. These materials are therefore good candidates as nanoreactors for photocatalytic reactions. So far, proof of concept (i.e. nanoreactor for photocatalytic reactions) has only been obtained for the nanotube form. The aim of this thesis is therefore to study the whole family (nanotube, nanosphere and nanotile, with various functionalizations) as nanoreactors for proton and CO2 reduction reactions triggered under illumination.

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).

ClimatSunPV: Study of BIPV components with photonic functionalities, self-cooling capacity and urban heat island mitigation effects.

The integration of PV modules into building envelope or other applications in particular presents different constraints reducing their electrical performance compared to ground installations due to the change in their operating conditions. The objective of this PhD thesis would be the research of a global design method of a BIPV facade or roof in order to optimize its production and its impact on the integration system (building, etc.) by overcoming its constraints: static and mobile shading, temperature gradients due to low albedo, favorable solar radiation especially in cold periods, localized overheating… Different approaches will be considered:
1- Optimize the temperature management of the PV field or the uniformity of the temperature field by forced convection (with air or water as heat transfer fluid): case of a double skin facade (or roof) (extraction or recovery of heat from the rear face of the PV modules through numerical and experimental analysis of natural or forced ventilation paths (air flow) and case of a single wall facade (or roof) (with other cooling methods);
2- Passive cooling of BIPV and PV systems: research from numerical models and experimental studies and validation of simple passive technological solutions (fins, heat sinks, graduated materials, materials with photonic effect, among others).

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.

Survivability of Photovoltaic Assemblies to Hyperveloce Impacts

With the increase of number of space debris and satellites in low-Earth orbit, the vulnerability of the solar panels fitted to these satellites is becoming a major issue. In this context, CEA-Liten is developing new solar panel solutions featuring advanced flexible materials which could be used for Z-folded or rollable photovoltaic Assembly (PVA). The aim of this PhD project is to study the impact and post-impact behaviors of these new solar PVA under hyper-velocity impact of millimeter-sized projectiles. To this end, the IDL and CEA and 3SR laboratories are proposing to develop a strategy based on the following steps: identification of loading-rate and pressure levels through a series of numerical simulations, characterization of the mechanical behavior of materials and interfaces involved in solar PVA by means of high strain-rate testing thanks to Hopkinson bar and plate-impact experiments, identification of equation of states and damage and fracture constitutive models and their implementation in numerical codes, predictions of damage and fracture in PVA subjected to hyper-velocity impact and comparison with experimental data by means of impact tests consider a large range of impact speeds.

Stabilisation of Perovskite photovoltaic devices by passivation with Metal-Organic Frameworks type materials

MOFs are a type of porous organic-inorganic hybrid material with interesting properties in terms of the passivation of defects in the perovskite and its stability, particularly versus light. For example:
- Direct effect of MOF components as passivation agents: Metal ions and organic ligands can passivate defects at the MOF/PK interface.
- Downconversion of incident radiation: Certain metals (such as europium) or ligands (with aromatic groups) can absorb high-energy radiation (typically violet/near-UV), then re-emit this energy in the form of lower-energy radiation or transmit it directly in a non-radiative manner to the perovskite by Förster resonance (or FRET). This protects the perovskite from high-energy photons, and therefore a priori improves light stability, with little energy loss.
The thesis work will focus on
- integrating MOFs into the perovskite layer, either as a surface treatment or as a mixture of suspensions
- Materials studies (in particular advanced studies using XPS and UPS)
- Favrication of single-junction devices and then tandem devices with silicon sub-cells
- Study of lifetime under illumination (continuous, cycling) with associated characterisations (electrical measurements, photoluminescence, etc.).

Melt grafting of polyolefin applied to reparable and recyclable photovoltaic panels

Solar panels are multi-materials assemblies constituted of photovoltaic cells that contains numerous precious metals (metal silicon, silver), high quality and therefore costly-to-manufacture glass that protects the cells, and a polymer film acting as binder, called encapsulant. These encapsulants are mostly thermoplastics that are reticulated during the manufacture of photovoltaic panels, which makes their dismantling and recycling difficult today.
CEA develops new materials to bring recyclability to renewable energy production systems, such as photovoltaic panels. The thesis revolves around the development of new encapsulants that allow improved recyclability of photovoltaic panels through a reversible reticulation system. In a first step, the melt grafting (extrusion, internal mixer) of polyolefins with molecules of interest will be studied in terms of grafting efficiency and kinetics, and impact on polyolefins properties such as thermal, optical, and structural properties. In a second step, a reversible reticulation will be triggered using the firstly grafted molecules. The impacts of this reticulation on the material thermal, mechanical, optical properties will be characterized. The application of the material as encapsulants will be the final aim of the thesis, and small demonstrators of photovoltaic modules using the material will be performed.

Nanodiamond-based porous electrodes: towards photoelectrocatalytic production of solar fuels

Among nanoscale semiconductors, nanodiamonds (ND) have not been really considered yet for photoelectrocatalytic reactions in the energy-related field. This originates from the confusion with ideal monocrystalline diamond featuring a wide bandgap (5.5 eV) that requires a deep UV illumination to initiate photoreactivity. At the nanoscale, ND enclose native defects (sp2 carbon, chemical impurities such as nitrogen) that can create energetic states in the diamond’s bandgap decreasing the light energy needed to initiate the charge separation. In addition, the diamond electronic structure can be strongly modified (over several eV) playing on its surface terminations (oxidized, hydrogenated, aminated) which can open the door to optimized band alignments with the species to be reduced or oxidized. Combining these assets, ND becomes competitive with other semiconductors toward photoreactions. The aim of this PhD is to investigate the ability of nanodiamonds in reducing CO2 through photoelectrocatalysis. To achieve this goal, electrodes will be made from nanodiamonds with different surface chemistries (oxidized, hydrogenated and aminated), either using a conventional ink-type approach or a more innovative one that results in a porous material including nanodiamonds and a PVD-deposited matrix. Then, the (photo)electrocatalytic performances under visible illumination of these nanodiamond-based electrodes toward CO2 reduction will be investigated in terms of production rate and selectivity, in presence or not of a transition metal macrocyclic molecular co-catalyst.

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