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Perovskite solar cells (PSCs) offer an efficient, inexpensive alternative to current photovoltaic technologies, with the potential for manufacture via high-throughput coating methods. However, challenges for commercial-scale solution-processing of metal-halide perovskites include the use of harmful solvents, the expense of maintaining controlled atmospheric conditions, and the inherent instabilities of PSCs under operation. Here, we address these challenges by introducing a high volatility, low toxicity, biorenewable solvent system to fabricate a range of 2D perovskites, which we use as highly effective precursor phases for subsequent transformation to α-formamidinium lead triiodide (α-FAPbI 3 ), fully processed under ambient conditions. PSCs utilising our α-FAPbI 3 reproducibly show remarkable stability under illumination and elevated temperature (ISOS-L-2) and “damp heat” (ISOS-D-3) stressing, surpassing other state-of-the-art perovskite compositions. We determine that this enhancement is a consequence of the 2D precursor phase crystallisation route, which simultaneously avoids retention of residual low-volatility solvents (such as DMF and DMSO) and reduces the rate of degradation of FA + in the material. Our findings highlight both the critical role of the initial crystallisation process in determining the operational stability of perovskite materials, and that neat FA + -based perovskites can be competitively stable despite the inherent metastability of the α-phase. The use of harmful solvents to fabricate stable devices hampers the commercialization of perovskite solar cells. Here, the authors introduce a biorenewable solvent system and precursor-phase engineering to realize stable formamidinium lead triiodide-based solar cells.

The scanning transmission electron microscope (STEM) is an extraordinarily powerful tool for materials characterisation. The wealth of signals available in the microscope mean that chemical and structural details may be probed simultaneously, and often at the atomic scale. Recent developments in quantitative STEM methods have brought about new capabilities for acquiring mass and compositional information. In particular, advances in the measurement of the high-angle annular dark-field (HAADF) signal means it is now possible to count atoms within individual nanostructures with extremely high precision. In parallel, new approaches for quantifying energy-dispersive x-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) data afford new opportunities for the determination of elemental composition on an absolute scale. Thus far, many of these emergent methods have seen little application outwith inorganic samples. This thesis aims to explore to what extent these advances can be applied in complex biological environments, with a particular focus on the measurement of intracellular elemental distributions. High-resolution imaging is first used to elucidate the nanoscale structure of two platinum-based chemotherapeutics. Similar methods are then used to identify single heavy atoms inside the cell bodies of dorsal root ganglia following Pt-drug administration. The use of quantitative HAADF STEM allows experimental measurements of atomic scattering cross- sections to be directly compared with those predicted from simulation. This ultimately confirms that the single atoms observed are indeed platinum, and allows the masses of small atomic clusters visualised in the cells to be measured. In later chapters, it is further shown that quantitative STEM imaging may be combined with spectroscopy to measure EDX and EELS partial scattering cross-sections. These are acquired for several elements of biological significance, including calcium, sodium and potassium. Finally, spectroscopic cross-sections are applied in samples of peripheral nerve to quantify aggregations of calcium in the mitochondria, and to measure changes in intra-axonal sodium and potassium levels following treatment with a chemotherapeutic agent.