High performance graphene for non-metallic contact in perovskite devices

Despite their many positive impacts, PV panels production face threat of sustainability of growth in terms of raw materials, energy, and environment. The PV industry is very dependent on critical raw materials and this dependence is getting worse as the production and consumption of solar panels are increasing considerably.

The main goal of this project is to develop the next generation of transparent/non-transparent conductive layers based on non- critical raw materials. These layers will be used as contact, interconnections in innovative solar panels. Guiding principle of this project is to construct competitive high quality/low-cost conductive line to replace silver contact. Due to these outstanding properties, Graphene could play an essential role in replacing critical material and enhancing electrical conductivity. This Ph-D project will be devoted to the development of low and high temperature conductive graphene inks. These inks will be designed for serigraphy, inkjet, or any suitable low-cost printing deposition techniques to print contact and interconnection. i) Inks properties in terms of composition, viscosity will be tuned. ii) The behavior of printed conductive ink will be investigated after being exposed to different stress (mechanical, temperature, moisture, electrical, light, oxygen….). iii) Finally the focus will be on conductivity characterization as a function of electrode morphology (thickness, porosity, …) and mechanical resistance. The overall aim is to optimize conductivity, mechanical resistance, and durability and finally incorporate these improvement in perovskite solar cells.

Stable tandem perovskite solar cells based on new cross-linked electron transport layers

Perovskite solar cells (PSCs) have become a trending technology in photovoltaic research due to a rapid increase in efficiency in recent years. In 2020, a record efficiency of 25.5% close from Shockley-Queisser theoretical limit of 30% was reported. Tandem solar cells offer an alternative to go beyond but stability still remains an issue.

In our project, we will bring together our complementary expertise in molecular and macromolecular syntheses, thin film morphology tuning and cell device engineering to improve the stability of highly efficient inverted perovskite cells using new electron transport layers (ETL) with high electron mobility and high stability. We will design and synthesize new n-type fullerene free semiconductors. Introduction of cross-linkable groups will lead to stabilized ETLs by thermally-induced cross-linking after film formation. The efficiency and stability of these ETLs will be finally evaluated through their incorporation in tandem configuration.

Development of innovative medical devices from new bacterial polyhydroxyalkanoates (PHA) derivatives.

To address the future challenges of wearable or implanted medical devices (MDs), which are less invasive and increasingly personalized and effective, it is necessary to have a broad range of biocompatible materials with diverse mechanical properties. Preferably, these biomaterials should be of biological origin and employed under mild conditions (preferably in water) to reduce the risk of releasing toxic by-products. Material biodegradability is another key characteristic to master for the development of prostheses and devices with a lifespan adapted to their use. In this context, the ANR PHAMOUS aims to demonstrate the high potential of bacterial polyhydroxyalkanoates (PHA) for designing innovative MDs.
In this framework, the doctoral candidate will initially be responsible for the chemical modification of various PHAs to enhance their water solubility (e.g., pendant PEG groups), introduce photo-crosslinkable groups (e.g., methacrylates), and incorporate specific functions (peptides) to enhance cellular adhesion and antimicrobial properties. The doctoral candidate will then use the different functionalized PHAs to develop two demonstrators implemented through two different processes. Photo-crosslinkable and solvent-soluble PHAs will be formulated to manufacture a prototype of a bronchial stent using "vat polymerization" 3D printing processes. Simultaneously, electrospinning of PHAs will be used to develop micro-structured and porous membranes.

Development of catalysts based on sustainable and non-critical materials for AEMWE

Hydrogen production by electrolysis is the only process that enables hydrogen to be produced without carbon by-products. Electrolysis using anionic membranes is attracting increasing attention, as this technology makes it possible to consider electrodes without noble metals and non-fluorinated membranes.
At the anode, the kinetics of the OER reaction are the most limiting. It occurs under highly basic, high-potential conditions. Carbon is therefore not recommended as a support, as it is susceptible to oxidative degradation at the high potentials applied to the anode, or to nucleophilic OH ions in alkaline media.
The synthesis of non-noble catalysts on conductive supports such as fibers or foams would increase the electrical conductivity of the catalyst as well as the anchoring of the active site in order to increase the electronic active site/support interaction and the durability of the electrode.
On the cathode side, although HER catalysis is faster than that of OER, it remains a major obstacle to electrolysis reactions in alkaline media. Indeed, the overpotential of non-noble materials is on average 100 mV higher than that of platinum. However, our experience suggests that molybdenum-based catalysts hold great promise for the development of PGM-free catalysts. In order to optimize these catalysts, we plan to improve electrical conductivity by using carbonaceous supports and to work on the shape structure of these catalysts to improve HER kinetics.
The aim of this project is to provide the scientific community with new knowledge on materials that could be as efficient as the noble catalysts usually used in anionic electrolysis. The use of manufacturing and shaping processes proven in the field of PEM fuel cells offers a good chance of success. Another major contribution to AEM electrolysis will be the exploration of electrode material degradation mechanisms, about which very little is known at present.

Synthesis and electrochemical characterization of p-type organic electrode materials for anion-ion battery

Nowadays Li-ion batteries use mainly inorganic compounds as electrode materials especially transition metal based ones. Although their performances are satisfying, they present several important drawbacks. Indeed these compounds are expensive and leads to large environmental footprint because they are prepared due to energy-consuming techniques from rare mineral precursors. Moreover, this technology is based on the use of lithium leading to geostrategic issues.

Some organic redox compounds such as viologen based derivatives can reversibly react with anions. Consequently they appear as an interesting alternative to conventional active materials especially for negative electrode for battery in anion-ion configuration which not use metallic counter ions. Interestingly these organic molecules can be easily prepared using simple organic chemistry techniques from low cost precursors. However their redox potential is too high (~2-2.5V vs Li+/Li) for the development of high energy density batteries.

The work of this thesis will firstly focus on the synthesis of new insoluble structure based on viologen derivatives presenting a redox potential below 2V vs Li+/Li. Some fine characterizations in particular Electron Paramagnetic Resonance (EPR) will be applied in order to better understand their electrochemical mechanisms.

Hyperpolarised, continuous-mode NMR based on parahydrogen and grafted catalysts

Nuclear Nuclear magnetic resonance (NMR) is a robust, non-invasive technique of analysis. It provides valuable information about chemical reactions, which can then be better characterised and optimised. However, NMR is poorly sensitive, and low-concentrated solutes, such as intermediates of reaction, may be unobservable by conventional NMR. One method known to drastically but temporarily increase the sensitivity of NMR is to create a hyperpolarised state in the system of nuclear spins, i.e. a polarisation much greater than that accessible with available magnetic fields. One hyperpolarisation method uses the specific properties of parahydrogen. A catalyst is required to add parahydrogen to a multiple bond or a metal.

The present thesis will investigate the combined contribution of (i) parahydrogen-based hyperpolarisation [1], (ii) the grafting of the appropriate catalyst onto nanoparticles [2], and (iii) a continuous analysis method [3] to detect and identify chemical intermediates, areas in which the laboratory has acquired experience. This subject involves a major investment in instrumentation, as well as skills in synthetic chemistry and NMR.

The thesis will be carried out at NIMBE, a joint CEA/CNRS unit at CEA Saclay. The hyperpolarised NMR and the synthesis will take place under the respective responsibility of Gaspard HUBER, from LSDRM, and Stéphane CAMPIDELLI, from LICSEN. These two NIMBE laboratories are located in nearby buildings.

References:
[1] Barskiy et al, Prog. Nucl. Magn. Reson. Spectrosc. 2019, 33, 114-115,.
[2] Hijazi et al., Org. Biomol. Chem., 2018, 16, 6767-6772.
[3] Carret et al., Anal. Chem. 2018, 90, 11169-11173.

Development of new anode materials for potassium-ion batteries

Classic Li-ion batteries are composed of a graphite anode and a cathode containing a lithiated layered oxide (formula LiNixMnyCozO2). The development and the generalization of the electric automobile market will generate stress on certain chemical elements source, especially for lithium, nickel, cobalt and copper. In addition, the production method consumes a lot of energy (multiple calcinations) and several solvents/products used are not respectful of the environment (NMP, ammonia).
The thesis aims to develop a battery technology based on potassium without using any critical element in order to significantly decrease the ecological footprint.
The insertion of potassium ion inside the graphite structure has been reported as an advantage in front of Na-ion batteries. However, due to the potassium size, the graphite structure expands (60%) and can limit the batterie cycle life.
The final target of the PhD thesis is to solve this issu following two approches : 1/ Find the link beetween graphites specifications and the resulting electrochemical performances in order to select the best graphite grade 2/ Develop new anode materials for K-ion application.

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.

Model development and simulation of coupling between plume migration and chemical perturbations

The fate of chemicals in the environment is of importance in fields, including fuel-cycle or radioecology. Migration models describe the behaviour of radionuclides and relationships with properties: e.g. electrical charge, redox state. In addition, the retention on mineral surfaces strongly delays migration. This later mechanism may be described using various approaches and levels of complexity:
- Non-reactive approach, considering retention (Kd) without species chemistry,
- Reactive-transport, considering speciation in solution and on surfaces,
- Multi-component approaches, specifying diffusion for each compounds, e.g. NO3, EDTA, Th(IV), etc.
- Multi-species approaches, specifying the behaviour of each species for a given compound, e.g. [UO2] 2+, [CaUO2(CO3)3]2-, [Ca2UO2(CO3)3]0.
The work will focus on the development of multi-component and multi-species migration models. Models will be applied to assess more accurately the spread of chemical perturbations in natural barriers (soils, sediments). To this aim, available experimental data will be used as input data. A main objective is to quantify the differences between approaches and potential implications for radionuclide migration & corresponding mitigation strategies.

Novel membranes based on 2D nanosheets

This thesis project aims to exfoliate new nanostructured architectures based on two-dimensional inorganic phases. These nanostructures will be designed for filtration devices and tested using our microfluidic platform. The target application is water purification and the selective separation of metal ions. The doctoral student will interact with chemists, physicists and electrochemists in a real multidisciplinary environment, on a fundamental research subject directly connected to application needs. Thus, during his thesis, the student will be exposed to a multidisciplinary environment and brought to carry out experiments in various fields such as inorganic chemistry, physical chemistry, micro / nano-fabrication and nano-characterization methods. In In this context, this project should potentially lead to significant societal benefits.

For the realization of the latter, he will have access to a very wide and varied range of equipment ranging from optical microscopes to the latest generation synchrotron (ESRF), including field effect or electron microscopes and galvanostats.

This thesis is therefore an excellent opportunity for professional growth, both in terms of your knowledge and your skills.

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