In developing photovoltaic technology for commercial use, it is essential to prioritize low cost, high efficiency, and long-term stability, along with low toxicity and quick energy payback time. Organic-inorganic metal halide perovskites are among the most promising photovoltaic materials due to their exceptional efficiency and cost-effectiveness. However, their practical significance remains unclear due to their notoriously short device operation duration. Mixed-metal tin-lead perovskites are a class of perovskites that have captured researchers' attention due to their unique optoelectronic features, including a small bandgap, making them useful for various applications (tandems, NIR light detection, and imaging e.g.). Still, the low ambient stability of tin-lead perovskites obstructs their commercialization, necessitating extensive research into their underlying breakdown mechanisms. This study aims to better understand these mechanisms and the involvement of halide chemistry, specifically emphasizing the significant role of iodine in perovskite deterioration. Our findings reveal that tin-lead-based perovskites experience cyclic degradation, with iodine and SnI4 as key degradation products that harm the stability of the perovskite. Investigating the impact of iodine is critical because it is a common component of the perovskite material, and its presence has been shown to play a crucial role in the optoelectronic properties of the perovskite. However, the presence of iodine can also lead to the degradation of the perovskite material over time, reducing the efficiency and lifespan of the perovskite solar cells. Therefore, understanding the role of iodine in perovskite deterioration is essential to improve the stability and durability of tin-lead perovskites and bring them closer to commercialization. By gaining insight into the degradation mechanisms of tin-lead perovskites, we can develop effective strategies to mitigate their degradation, enhance their stability and lifespan, and unlock their full potential for use in various photovoltaic applications, contributing to a more sustainable and environmentally conscious future.

Tin halide perovskites are gaining interest as a replacement for lead perovskites for various device applications. However, compared to lead-based perovskites, the understanding of their charge transport properties has received limited attention. In particular, the effect of A-site cation on electronic properties of tin perovskites warrants further attention to design efficient material systems for various applications beyond photovoltaics. In the presented work, leveraging the composition tunability of halide perovskites, we establish a relationship between the A-site composition and electronic properties in tin perovskites (ASnI3). The effect of prototypical A-site cations such as Formamidinium (FA), Methylammonium (MA), Cesium (Cs), and their binary combinations on structure, morphology, and electronic properties are explored. MACs combination offers the highest electrical conductivity owing to enhanced mobility compared to mono-cations MA and Cs, resulting in an impressive electrical conductivity of ∼ 143 Scm−1 and thermoelectric power factor of ∼ 149 μW m−1K−2. The library of properties generated for Sn perovskites in this work will be helpful for their further development as an electronic material.

L' intérêt des phases oxydes à base de terres rares est certes multiple et leurs propriétésont été explorées depuis longtemps: mais nous nous intéressons ici aux comportements de cesphases en tant que phases thermiques, catalytiques ou conductrices ioniques à hautetempérature. Il s'agit en particulier de développer des systèmes innovants de matériauxpouvant intervenir dans la conception de dispositifs pour la microélectronique, pour capteursde gaz ou membranes sélectives ou pour systèmes dépolluants.Les phases de structure pyrochlore ou fluorine de type TR2Ce207 où TR désigne unélément de Terre Rare présentent divers potentiels d' applications: elles ont été considéréescomme des phases pouvant résister à de hautes températures. Les oxydes de structurespérovskites, de formule générale ABO), présentent de multiples applications potentielles,notamment en tant que phases diélectriques pour condensateurs, ou phases conductricesioniques (en ions oxygène ou en protons) pour électrolytes solides, du fait même de leur hautestabilité chimique à haute température.Ce travail a été divisé en deux parties. La première a consisté à élaborer la phase« thermique)} de type pyrochlore TR2Ce20 7 (TR = La, Ce, ... ) en utilisant un minéralcomplexe à base d'allanite-monazite et de silico-aluminates issus de déchets industriels, doncà bas coût.La deuxième partie a consisté à élaborer BaCe03 et à étudier ses propriétéscatalytiques et conductimétriques en fonction de la température. Une nouvelle méthode desynthèse reposant sur l' utilisation du mélange EDTA-citrate a été utilisée afin d'élaborer unprécurseur, qui, traité thermiquement à 950°C, a permis d'élaborer des poudressubmicroniques de la phase BaCe03. L'activité catalytique du composé BaCe03 démarre à450°C pour atteindre la conversion totale à 675°C : dans cette gamme de température,l'efficacité catalytique de la phase BaCe03 est maximale. L'évolution de la conductivité enfonction de la température de pastilles compactées de BaCe03 a révélé l'existence d'une sériede modifications électriques fortement corrélées aux transitions structurales connues pourBaCe03 dans la littérature. À basse température (300 à 450°C), la faible conductivité de laphase orthorhombique, associée à la faible énergie d'activation, peut être liée à la migrationdes défauts extrinsèques (gaz adsorbés). Cependant, au-dessus de 500°C, la conductivité de laseconde phase orthorhombique augmente: ceci pourrait être attribué à une mobilité croissantedes atomes d'oxygène. / Rare earth elements have recently been involved in a range of advanced technologies like microelectronics, membranes for catalytic conversion and applications in gas sensors. In the family of rare earth elements like cerium can play a key role in such industrial applications. However, the high cost of these materials and the control and efficiencies associated processes required for its use in advanced technologies, are a permanent obstacle to its industrial development. In present study was proposed the creation of phases based on rare earth elements that can be used because of its thermal behavior, ionic conduction and catalytic properties. This way were studied two types of structure (ABO3 and A2B2O7), the basis of rare earths, observing their transport properties of ionic and electronic, as well as their catalytic applications in the treatment of methane. For the process of obtaining the first structure, a new synthesis method based on the use of EDTA citrate mixture was used to develop a precursor, which undergone heat treatment at 950 ° C resulted in the development of submicron phase BaCeO3 powders. The catalytic activity of perovskite begins at 450 ° C to achieve complete conversion at 675 ° C, where at this temperature, the catalytic efficiency of the phase is maximum. The evolution of conductivity with temperature for the perovskite phase revealed a series of electrical changes strongly correlated with structural transitions known in the literature. Finally, we can establish a real correlation between the high catalytic activity observed around the temperature of 650 ° C and increasing the oxygen ionic conductivity. For the second structure, showed clearly that it is possible, through chemical processes optimized to separate the rare earth elements and synthesize a pyrochlore phase TR2Ce2O7 particular formula. This "extracted phase" can be obtained directly at low cost, based on complex systems made of natural minerals and tailings, such as monazite. Moreover, this method is applied to matters of "no cost", which is the case of waste, making a preparation method of phases useful for high technology applications. / Elementos terras raras têm sido recentemente envolvido em uma ampla gama de tecnologias avançadas, como a microeletrônica, membranas para a conversão catalítica e aplicações em sensores de gás. Na família de terras raras, elementos como o cério pode desempenhar um papel chave em tais aplicações industriais. No entanto, o alto custo desses materiais e do controle e eficiências dos processos associados necessários para sua utilização em tecnologias avançadas, são um obstáculo permanente ao seu desenvolvimento industrial. No presente trabalho, foi proposto a obtenção de duas fases baseadas em elementos de terras raras que podem ser utilizados devido o seu comportamento térmico, condução iônica e propriedades catalíticas. Desta maneira, foram estudados dois tipos de estrutura (ABO3 e A2B2O7), a base de terras raras, observando suas propriedades de transporte iônico e eletrônico, bem como suas aplicações catalíticas no tratamento do metano. Durante o processo de obtenção da primeira estrutura, um novo método de síntese baseado no uso da mistura EDTA citrato foi usado para desenvolver um precursor, que submetidos a tratamento térmico a 950°C, resultou no desenvolvimento de pós submicrométricos da fase BaCeO3. A atividade catalítica desta perovskita começa a 450°C para alcançar a conversão completa em 675°C, onde nesta temperatura, a eficiência catalítica da fase é máxima. A evolução da condutividade em função da temperatura para a fase perovskita revelou uma série de mudanças elétricas fortemente correlacionada com transições estruturais conhecida na literatura. Finalmente, pode-se estabelecer uma correlação real entre a alta atividade catalítica observada em torno da temperatura de 650°C e o aumento da condutividade iônica de oxigênio. Para a segunda estrutura, mostrou-se claramente que é possível, através de processos químicos otimizados, separar os elementos terras raras e sintetizar uma fase pirocloro específica de fórmula TR2Ce2O7. Esta “fase extraída" pode ser obtida diretamente, de baixo custo, baseado em sistemas complexos feitos de minerais naturais e resíduos, como a monazita. Além disso, este método é aplicado a matérias de "custo zero", que é o caso dos resíduos, tornando um método de preparação de fases útil para aplicações de alta tecnologia.

Solid-state lightings are becoming the popular choice for lightings due to its higher efficiency, improved colour rendering index and the flexibility of various size and shape. Halide perovskite has tunable colour emission, low disorder and is solution processable making it one of a popular choice as emitters. This thesis demonstrates the versatility of using halide perovskite material in light-emitting diodes. We demonstrate the first working perovskite light-emitting diode at room temperature by introducing thin layer of perovskite emitter which is crucial to confine the inherent free carriers in the material. We show that the 3D lead-halide bulk perovskite is bandgap tunable with emission in the green and red visible spectrum. Light-emitting diodes in the visible spectrum are common however near-infrared emission is a rarity. Lead is a heavy metal which is known for its toxicity. We tackled the issue of toxicity by replacing with tin and demonstrate tunable emission in the near-infrared region. Bulk perovskites have large binding energy which makes it difficult to confine the charges and form radiative recombination which is crucial for emission and efficiency of the device. We move into lower dimensionality perovskites by utilising all-inorganic perovskite nanoplatelets and show emission in the blue region.

published_or_final_version / abstract / Physics / Master / Master of Philosophy

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We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.

We quantified the chemical species present at polycrystalline cesium tin bromide perovskite, CsSnBr3 and cesium titanium bromide antifluorite, Cs2TiBr6. For CsSnBr3, experiments utilized the orthogonal reactivity of the Cs+ cation, the Sn2+ cation, and the Br– halide anion. Ambient- pressure exposure to BF3 solutions probed the reactivity of interfacial bromines. Reactions with p-trifluoromethylanilinium chloride probed the exchange reactivity of the Cs+ cation. A complex-forming ligand, 4,4’-bis(trifluoromethyl)-2,2’-bipyridine, probed for interfacial Sn2+- site cations. For Cs2TiBr6, both BF3 and (C6F5)3B probed the reactivity of interfacial bromines. Fluorine features in x-ray photoelectron spectroscopy (XPS) quantified reaction outcomes for each solution-phase species. XPS indicated adsorption of BF3 on CsSnBr3 and (C6F5)3B on Cs2TiBr6 indicating surface-available halide anions on both surfaces. For CsSnBr3, temperature- programmed desorption (TPD) quantified a ~215 kJ mol–1 desorption energy of BF3 on the surface. Adsorption of the fluorinated anilinium cation included no concomitant adsorption of chlorine as revealed by the absence of Cl 2p features within the limits of XPS detection. The bipyridine ligand demonstrated adsorption to CsSnBr3. We discuss the present results in the context of interfacial stability, passivation, and reactivity for solar-energy conversion devices.

Thesis (M.Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.