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Dans le contexte énergétique actuel, le développement de technologies de production d’énergies renouvelables, telles que les panneaux photovoltaïques, est une nécessité. Dans ce mémoire, l’attention s’est portée sur les cellules photovoltaïques à base de pérovskite et plus précisément sur les composés MAPbI3, MAPbI3-xClx et RbCsMAFAPbI3-xBrx (MA = CH3NH3+, FA= CH(NH2)2+). Ces matériaux ont été déposés par spray pyrolyse ultrasonique (USP), assemblés en cellules et leur efficacité a été comparée aux cellules obtenues par spin coating, technique de dépôt de films généralement utilisée dans la littérature, l’objectif du mémoire étant de valider la transposabilité de fabrication des cellules photovoltaïques à base de pérovskite vers des techniques de mise en œuvre compatibles avec une production à l’échelle industrielle en roll-to-roll Le dépôt de pérovskite par USP a été optimisé en jouant sur différents paramètres comme la concentration en précurseurs, le débit de solution, la température du substrat, la température de stabilisation ou encore le lissage par un anti-solvant après dépôt. Si le lissage anti-solvant a prouvé son utilité en spin-coating afin d’améliorer l’efficacité des cellules, il n'a pu être transféré avec succès en USP. A l’issue de cette campagne d’optimisations, les cellules photovoltaïques constituées des meilleurs films pérovskite par USP (sans lissage) ont donné une efficacité de conversion moyenne de 3% pour MAPbI3 (cellule champion : 4,2%) et 7,4% pour RbCsMAFAPbI3-xBrx (cellule champion : 8,9%). La pérovskite MAPbI3-xClx a donné des efficacités proches de 0%. A titre de comparaison, les dépôts par spin coating (avec lissage) ont donné des performances photovoltaïques moyennes de 4,5% pour MAPbI3 (cellule champion : 7,1%), 12,7% pour RbCsMAFAPbI3-xBrx (cellule champion : 14,9%) et 2,5% pour MAPbI3-xClx (cellule champion : 3,5%). Le dépôt de la pérovskite par spray pyrolyse ultrasonique ne permet donc pas, avec nos optimisations actuelles, d’égaler les efficacités de cellules préparées par spin coating mais est en bonne voie pour aboutir à terme à une production industrielle des panneaux photovoltaïques à base de pérovskite. In the current energy context, the development of renewable energy technologies, such as photovoltaic panels, is necessary. In this master thesis, a special attention was paid on perovskite-based photovoltaic cells and more specifically on MAPbI3, MAPbI3-xClx and RbCsMAFAPbI3-xBrx (MA = CH3NH3+, FA = CH(NH2)2+). These compounds were deposited by ultrasonic spray pyrolysis (USP), assembled in cells and their efficiency was compared to cells obtained by spin coating, usually used in the literature. The goal of this work is to validate the manufacturing process transposition towards roll-to-roll industrial production. The perovskite deposition by USP has been optimized by varying different parameters such as the precursor concentration, the solution flow, the substrate temperature, the stabilization temperature or the smoothing with an anti-solvent after deposition. If anti-solvent smoothing has proven to improve the cell efficiency by spin coating, it could not be successfully transferred to USP process. From our optimization work, the best photovoltaic cells by USP (without smoothing) gave an average conversion efficiency of 3% for MAPbI3 (champion cell: 4.2%) and 7.4 % for RbCsMAFAPbI3-xBrx (champion cell: 8.9%). The MAPbI3-xClx perovskite gave efficiencies close to 0%. In comparison, the best cells by spin coating (with smoothing) gave average photovoltaic efficiency of 4.5% for MAPbI3 (champion cell: 7.1%), 12.7% for RbCsMAFAPbI3-xBrx (champion cell: 14,9%) and 2.5% for MAPbI3-xClx (champion cell: 3.5%). At this stage, the perovskite deposition by ultrasonic spray pyrolysis, therefore, does not allow to reach the efficiencies of cells prepared by spin coating but is on track to achieve large-scale production of perovskite solar cells.

pérovskite --- USP --- cellule photovoltaïque --- multi-cations --- anti-solvant --- Physique, chimie, mathématiques & sciences de la terre > Chimie

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Since their emergence about ten years ago, perovskite solar cells show great promise. Indeed, they have achieved performances comparable to those of silicon cells and have good flexibility properties. However, their transparent conductive electrodes - transparent conductive oxides -, are not only composed of scarce elements but are also quite fragile. In the present work, silver nanowire networks will be suggested as a more viable alternative. For this purpose, the production process of perovskite solar cells will be analyzed step by step, allowing the identification of the stresses experienced by the cells. Similarly, silver nanowire networks will
be produced and characterized in order to determine what stresses they can withstand. It will be found that in the case of replacement, two main factors can cause problems: the high production temperatures of the cells and the low adhesion of the nanowire networks. Various solutions will be proposed for successful replacement.

perovskite --- solar --- cell --- transparent --- conductive --- material --- silver --- nanowire --- network --- TCM --- PSC --- TCO --- AgNW --- nanomaterial --- Physique, chimie, mathématiques & sciences de la terre > Physique

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Ce mémoire tente de répondre à la question: existe-t-il un équivalent granulaire de la poussée
d’Archimède ?

Physique, chimie, mathématiques & sciences de la terre > Physique

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Superconductivity at room temperature is a hundred year old problem of condensed matter physics. Since the recent discovery of SH3 (200~GPa) and LaH10 (300~GPa), conventional superconductors under pressure play a major role in solid state physics. These BCS-superconductors can be described by theoretical tools and can be more and more synthesized experimentally with strenuous efforts. These classes of materials are especially interesting for they display outstanding parameters influencing the critical temperature. The extreme pressures they are synthesized in lead to completely new materials that would otherwise not spontaneously form in ambient pressures.cite{main2} The following work is investigating possible superconducting properties of novel metal-nitrides that can be obtained via high-temperature and high-pressure synthesis techniques. They can be recovered at ambient temperatures with interesting parameters, making them versatile for industrial use. 
A focus is put on binary transition metal nitrides with the nitrogen to metal ratio 3:2, while a close look is taken on Group 5 metals. This material class does not only display superconductivity but also interesting mechanical properties. For all compounds, structural, electronic and vibrational properties are predicted and they are found to be in good agreement with literature. Firstly, the previously synthesized eta-Ta2N3 compound is investigated and its experimentally found critical temperature of ~3K is theoretically confirmed in this work. Similar superconductive parameter are found for the same material at 26.065 GPa. We compare the calculation of superconductive parameters from the software Abinit, which is used to obtain all results, with previous results from Quantum Espresso for the tetragonal Ta2N3 and it is found that the superconductive parameters, especially the logarithmic frequency, are generally underestimated with Abinit. It is proposed to calculate the critical temperature with the help of the more accurately calculated Debye-temperature. The tetragonal Ta2N3 is predicted to be a very low critical temperature superconductor, while it still might display no superconductivity at all. Furthermore, the orthorhombic Nb2N3 is investigated further, its electronic and vibrational parameters are found and it is predicted to have a very high electron phonon coupling that could potentially lead to a superconductivity at 30K. The last Group 5 metal nitride in question is the V2N3. Previously, the instability of the orthorhombic V2N3 was found, which is confirmed by us through calculating the phonon dispersion and finding various imaginary frequencies. Its stable trigonal form is investigated, its electronic structure and vibrational properties are discussed in the following. Superconductivity is either not present in this compound or it can be found at very low critical temperatures.

Physique, chimie, mathématiques & sciences de la terre > Physique