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Abstract: Mixed 2D/3D perovskite materials are of particular interest to the photovoltaics and light- emitting diode (LED) communities due to their impressive opto-electronic properties alongside improved moisture stability compared to conventional 3D perovskite absorbers. Here, a mixed lead-tin perovskite containing distinct, self-assembled domains of either 3D structures or highly phase-pure Ruddlesden–Popper 2D structures is studied. The complex energy landscape of the material is revealed with ultrafast optical transient absorption measurements. It is shown that charge transfer between these microscale domains only occurs on nanosecond timescales, consistent with the large size of the domains. Using optical pump-terahertz probe spectroscopy, the effective charge-carrier mobility is shown to be an intermediary between analogous pure 2D and 3D perovskites. Furthermore, detailed analysis of the free carrier recombination dynamics is presented. By combining results from a range of excitation wavelengths within a full dynamic model of the photoexcited carrier population, it is shown that the 2D domains in the film exhibit remarkably similar carrier dynamics to the 3D domains, suggesting that long-range charge-transport should not be impeded by the heterogeneous structure of the material.

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Abstract: The recently discovered orthorhombic liquid crystal (LC) phase of symmetry Fddd is proving to be widespread. In this work, a chiral hydroxybutyrate linkage is inserted into the molecular core of hexacatenar rodlike compounds, containing a thienylfluorenone fluorophore. In addition to more usual tools, the methods used include grazing-incidence X-ray scattering, modulated differential scanning calorimetry (DSC), flash DSC with rates up to 6000 K/s, and chiro-optical spectroscopies using Mueller matrix method, plus conformational mapping. Although pure R and S enantiomers form only a strongly chiral hexagonal columnar LC phase (Colh*), the racemic mixture forms a highly ordered Fddd phase with 4 right- and 4 left-handed twisted ribbon-like columns traversing its large unit cell. In that structure, the two enantiomers locally deracemize and self-sort into the columns of their preferred chirality. The twisted ribbons in Fddd, with a 7.54 nm pitch, consist of stacked rafts, each containing ∼2 side-by-side molecules, the successive rafts rotated by 17°. In contrast, an analogous achiral compound forms only the columnar phase. The multiple methods used gave a comprehensive picture and helped in-depth understanding not only of the Fddd phase but also of the “parachiral” Colh* in pure enantiomers with irregular helicity, whose chirality is compared to the magnetization of a paramagnet in a field. Unusual short-range ordering effects are also described. An explanation of these phenomena is proposed based on conformational analysis. Surprisingly, the isotropic–columnar transition is extremely fast, completing within ∼20 ms. A clear effect of phase on UV–vis absorption and emission is observed.

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Abstract: The overall focus of this thesis is investigations into the preferential locations of biomolecules, including membrane proteins, in orientated self-assembled lipid nanostructured materials known as QII phases. The three QII phases, known as the QII G, QII D and QII P , consist of 3 dimensional periodic self-assembled surfaces over which a lipid bilayer is draped. The lipid bilayer in each QII phase consists of regions of flat or high curvature into which it has been hypothesised that guest biomolecules will preferentially partition. Research efforts focus on orientated QII phase domains as more information can be extracted from characteristic Small Angle Scattering (SAS) experiments than from polydomain samples. Different lipid mesophases including the QII phases, were prepared as orientated lipid films and an automated method of 2D Small Angle X-ray Scattering (SAXS) analysis for orientated samples was created. The addition of biomolecules to a QII phase was achieved by co-dissolving with the lipids in an organic solvent before formation of the orientated QII phase, or by addition to an already formed QII phase. Both methods are presented here and the incorporation of various biomolecules into a QII D phase bilayer was monitored in two separate fashions, via SAXS and Raman Spectroscopy. Finally, the addition of biomolecules to orientated QII phases was undertaken and any preferential partitioning into flat or highly curved regions of the bilayer was investigated. It was found via Grazing Incidence Small Angle Neutron Scattering (GISANS) that monopalmitin and cholesterol in a monoolein QII D phase, preferentially partition into the flatter regions of the bilayer. At several instances during my research, variable humidity control was required. Lipid films require particular humidity to maintain specific phase behaviour and for the neutron experiments, the host lipid was contrast matched to a D2O environment. To meet this requirement, two separate humidity control systems were designed and created: the first a low cost, portable, and chamber independent system, the second a fully automated system calibrated to a chamber at Diamond Light Source. A separate study into the relaxed curvature of four lipids, monoolein, monolinolein, phytantriol, and phytantetrol using inverse micelles is also detailed. The relaxed curvature was obtained by calculating the parameters of the neutral surface, or the surface whose area does not change due to bending within a lipid monolayer.

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Abstract: High temperature post-deposition annealing of hybrid lead halide perovskite thin films—typically lasting at least 10 min—dramatically limits the maximum roll-to-roll coating speed, which determines solar module manufacturing costs. While several approaches for “annealing-free” perovskite solar cells (PSCs) have been demonstrated, many are of limited feasibility for scalable fabrication. Here, this work has solvent-engineered a high vapor pressure solvent mixture of 2-methoxy ethanol and tetrahydrofuran to deposit highly crystalline perovskite thin-films at room temperature using gas-quenching to remove the volatile solvents. Using this approach, this work demonstrates p-i-n devices with an annealing-free MAPbI3 perovskite layer achieving stabilized power conversion efficiencies (PCEs) of up to 18.0%, compared to 18.4% for devices containing an annealed perovskite layer. This work then explores the deposition of self-assembled molecules as the hole-transporting layer without annealing. This work finally combines the methods to create fully annealing-free devices having stabilized PCEs of up to 17.1%. This represents the state-of-the-art for annealing-free fabrication of PSCs with a process fully compatible with roll-to-roll manufacture.

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Abstract: Materials that undergo a coupled phase transition offer a window into the relationship between electrons, nuclei, and magnetic spins in condensed matter. The development of ultrafast techniques where materials can be probed in the sub-ps time regime have provided the means to provide new insights into the exchanges of energy that occur between these systems. This can be applied to magnetocaloric, memory storage, and spintronics devices. This work investigated the dynamics of the FeRh coupled phase transition, where the magnetic ordering change from Anti-Ferromagnetic (AF) to FerroMagnetic (FM) at temperatures moderately above room temperature. The specific focus of this work is on the structural transformations and the effects of lateral confinement on the transition. An x-ray based probe of anti-parallel Fe spin lattice in the AF phase of FeRh is demonstrated experimentally. Non-resonant x-ray magnetic scattering relies upon long-range spin order being established. We demonstrate the temperature dependence of the long-range ordering and confirm that this order only disappears following complete establishment of the FM moment. As a consequence, it allows for a probe of the mixed AF/FM phase of FeRh. This technique allowed for an estimation of the AF domain size suggesting dimensions are limited by the microstructure of the thin film (~40 nm). Time-resolved X-Ray Diffraction (XRD) studies were carried out at the x-ray Free Electron Laser (x-FEL) at SACLA, Japan. We observed structural changes through the phase transition on a timescale not previously reported and show a fluence dependence that indicates the importance of considering non-equilibrated states in the growth and relaxation dynamics of FeRh. A model is presented which demonstrates that such non-equilibria states can be explained using non-trivial electron-phonon coupling. Complementary heated XRD measurements are consistent with the hypothesis that the paramagnetic phase of FeRh is accessed on ps timescales. The effects of lateral confinement were examined in FeRh nanowire arrays to determine if mesoscale magnetic interactions affect magnetisation dynamics. In order to understand the results obtained, heat dissipation was modelled using finite-element software so as to separate magnetic and thermal contributions. Pump-probe Magneto- Optical Kerr Effect (MOKE) investigations alongside static electrical measurements demonstrate that the orientation of external magnetic fields influences the transition behaviour in FeRh wires. FM stabilisation is observed when the external field is applied along the nanowire length. This orientation dependence was not observed in thin films and is ascribed to the shape anisotropy which may influence the FM domain growth mechanism - shifting the phase transition temperature by up to 10 K at applied magnetic fields of 1 T.