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Elaboration de films de perovskites hybrides par coévaporation pour des applications photovoltaïques.

Abstract : Hybrid perovskites celebrate this year their 10-year anniversary in the photovoltaic field. Besides the unprecedented rise in solar cells efficiencies, perovskite materials have tunable optical properties and can be manufactured at low cost, making them very promising candidates for the high efficiency, multijunction solar cells strategy. Perovskite crystal structure offers a relative degree of freedom, allowing the partial integration of multiple cations and halide ions. This chemical composition tuning translates into a bandgap tuning. Through fine chemical engineering, the 1.7 eV requirement for a c-Si-based tandem device can be achieved. Perovskite thin films can be prepared by a large variety of deposition techniques, from low cost precursors (CH3NH3I and PbI2 for instance), through low-temperature processes. While most of the reported works on perovskite thin films are based on the basic wet-process spincoating technique, this latter hardly allows large scale, homogeneous and reproducible deposition. With the future challenge of industrialization and the increasing interest for the Silicon/Perovskite tandem approach, solvent-free methods appear more suitable. Already widely implemented in the OLED industry, coevaporation stands as a viable option for perovskites’ future. Reported for the first time in 2013, coevaporated perovskites are still scarcely studied compared to wet-based techniques, requiring more expensive set ups. In the present thesis, we implemented and developed the coevaporation process to fabricate perovskite thin films for solar cells applications.Starting off on a proof-of-concept reactor to assess the feasibility of the technique, we got accustomed to the perovskite precursors behaviour and identify very early on the organic precursor to be hardly manageable, as reported in the literature. In six months, we were nonetheless able to obtain nice perovskite films leading to 9% efficient photovoltaic devices, unfortunately with a poor reproducibility that we think to be partially due to the cloud vapour behaviour of CH3NH3I. We eventually found ourselves missing some features on the equipment, preventing us from accurately get a grasp on the process. From this feedback we then designed, hand in hand with the manufacturer, a dedicated semi-industrial equipment for perovskite coevaporation. Following its implementation, we then focused on establishing the reproducibility of the method, trying to mitigate the parasitic effect of the organic compound. Even though the efficiencies in solar cells were still slightly lower for coevaporated perovskites, with respect to classical spincoated ones, we expected the material homogeneity to be in favour of the vacuum-based process. We then eventually integrated to this thesis a comparative study between wet- and dry-processed perovskite films using a Synchrotron-based X-ray spectromicroscopy technique.
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Chloe Dindault. Elaboration de films de perovskites hybrides par coévaporation pour des applications photovoltaïques.. Material chemistry. Université Paris-Saclay, 2019. English. ⟨NNT : 2019SACLX079⟩. ⟨tel-02441820⟩

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