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).

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.

Grid-Interface Power Converter with MVAC and MVDC

In this thesis subject, we propose Grid-Interface Power Converter with MVAC and MVDC. GI-PC control strategies to provide system services and facilitate network management and protection will be studied (eg support for the voltage plan, study of resonances, MVRT, etc...). A digital prototype of GI-PC at the MV level will be proposed implementing the control algorithms. The validation of the prototype will include regulation of the MVDC bus according to different scenarios. The GI-PC can contribute for:
• Providing a grid-connected interface for various MVAC systems such as power router
• Providing distribution interface for different levels of DC systems
• Improving power quality of MVAC distribution systems
• Providing a grid-connected interface for high-power DC sources such as electric vehicle charging stations, battery energy storage systems, H2, and PV and wind farms
• Other functionalities: fault support (firewall), imbalance reducing, auto reconfiguration (redundancy), grounding adapting, galvanic isolation …

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.).

Development and characterization of boron doped poly-silicon layers for solar applications

This project of thesis aims at developing technologies facilitating the production of passivated contact silicon solar cells and tandem (perovskite on silicon) cell structures. Both of these cells structures involve doped polycrystalline silicon nano-layers. In the case of boron doped layers, limiting factors such as layer parasitic absorption, contacting issues, and poor passivation properties when deposited on top of textured surfaces, need to be tackled. The main goal of the thesis will be the development , characterization and optimization of such a boron doped poly-Si nano-layer, either by LPCVD or PECVD deposition technique in the purpose of improving both its optical, contacting and passivating properties (700mV on textured surface is a starting target). The different technological bricks developed during the PhD will be used in PV solar devices in order to demonstrate the conversion efficiency gain and potential associated, with a target of > 25% efficient-devices. The results obtained by the PhD student will be presented in the form of scientific articles, patents and oral presentation in international conferences. The PhD student will be given the opportunity to supervise Master internships. The Thesis lasts 3 years, and will be done at the French National Solar Energy Institute (INES), on the Technolac campus, (73355 Bourget du Lac).

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).

Improvement of low impact PV modules through an hybrid experimental/numerical strategy

The global annual photovoltaic (PV) module production has been growing steadily for decades. In 2022, it reached 400 GWc and it should exceed the 1 TWc threshold before 2030. These modules represent massive investments in terms of money, carbon emissions, energy, etc. Since the energy produced by a PV module grows with time, the rationality of these investments increases with their durability and their reliability. In a standard PV module, the cells are embedded in an elastomer, the encapsulant. This inner layer plays several protective roles. Among others: it mitigates the mechanical loadings to which a module is exposed, it is responsible of the mechanical integrity of the module and, consequently, it makes the separation of layers challenging for recycling. Finally, an alternative way to increase the investment rationality is to reduce the investment itself. Regarding environmental costs, this may be done with less matter, materials easier to recycle and/or coming from renewable sources.
In this thesis, the work will focus on the delamination arising during PV module ageing. The conditions in which these critical defaults appear and propagate will be addressed experimentally and theoretically. The impact of the parameters involved will be estimated. This will include the nature of the encapsulant, in connection with the module recyclability, along with the process, the module architecture and the type of ageing. In particular, the impact of the quantity of encapsulant will be assessed. This work will rely on the means and expertise of two laboratories, CEMEF (Sophia Antipolis) and CEA-INES (Bourget-du-Lac).

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