In this thesis, we have developed a reproducible, safe, and scalable sequential thermal vapour deposition (STVD) method for the growth of quality 3D halide perovskite (HaP) thin films. High-quality methylammonium lead tri-bromide (MAPbBr3), methylammonium lead tri-iodide (MAPbI3), and methylammonium lead bromide-iodide (MAPb(I1-xBrx)3) thin films have been optimised using the STVD technique. The structural, optical, morphological, and electrical properties were tuned by varying the thicknesses of the organic (MAI, MABr) and inorganic (PbI2, PbBr2) precursor thin films and post-annealing times of the HaP. X-ray diffractograms confirmed the cubic MAPbBr3 structure with the Pm¯3 m space group, tetragonal MAPbI3 crystal structure with I4/mcm space group, and the tetragonal MAPbI3 structure being transformed to cubic MAPbBr3 system as MAPb(I1-xBrx)3 (x=0.89-0.95) forms. UV-Vis spectra revealed broad absorption bands with a redshift in absorption onset from 540 to 550 nm for MAPbBr3 and 750 to 780 nm for MAPbI3 as the thickness of respective organic precursors increased from 300 to 500 nm. The bandgap of MAPb(I1-xBrx)3 decreased from 2.21 to 2.14 eV as the thicknesses of MABr precursors increased from 300 to 500 nm. The crystallisation of the HaP started within the chamber, and prolonged post-annealing times exceeding 10 min caused the transformation of MAPbI3 to PbI2. Scanning Electron Micrographs show pin-hole-free and densely packed grains with an average size that increases as thicknesses increase. The charge carrier mobility increases while trap density decreases as the thickness of organic precursors increased. Besides, the thesis investigated the growth and stability of thin MAPbBr3 films at metal/MAPbBr3 interfaces. We studied the structure, morphology, and stability of the optimised MAPbBr3 perovskite on aluminium (Al), tin (Sn), silver (Ag), gold-zinc (Au-Zn) and gold (Au) electrodes, immediately and 60 days later. FE-SEM images show an average grain size that increased linearly with the work function from 294 nm for Al to 850 nm for Au. The MAPbBr3 grains remain glued to Sn, Ag, Au-Zn but delaminate quickly on Al. X-ray analysis of MAPbBr3 reveals variable crystallographic texturing for various metals and loss in intensity of prominent peaks at different rates over time. We found that the best thicknesses of 100 nm PbI2 and 500 nm MAI, and 100 nm PbBr2 and 500 nm MABr are needed for the preparation of quality MAPbI3 and MAPbBr3 thin films for solar cells, respectively. Quality thin MAPb(I0.11Br0.89)3 film is formed by inter-diffusion and halide exchange processes when optimised MAPbBr3 is grown on optimised MAPbI3 as a bottom layer. Al speeds up the degradation of MAPbBr3 at Al/MAPbBr3 while MAPbBr3 is relatively stable at Au-Zn/MAPbBr3 interfaces. / Thesis (PhD (Physics))--University of Pretoria, 2020. / University of Pretoria, the National Research Foundation/The World Academy of Sciences (NRF-TWAS), and NRF grant no N0115/115463 of the SARChI / Physics / PhD (Physics) / Restricted

Die Anpassung der Bandlücke und die Herstellung mittels lösungsbasierter Prozesse charakterisieren Metallhalogenid-Perowskite. Sie sind vielversprechend für die Anwendung in optoelektronischen Bauteilen, die die Abscheidung von hochwertigen Dünnschichten erfordern. Deren Qualität hängt stark vom Kristallisationsverhalten ab, welches durch die Komposition der Lösung bestimmt ist. Ziel dieser Arbeit ist es, Korrelationen im Präkursor-Prozess-Eigenschaftsraum von Metallhalogenid-Perowskit zu bewerten und Formierungsprozesse zu rationalisieren. Phasenreinheit, Morphologie und Absorptionseigenschaften zeichnen die Qualität der Perowskit-Dünnschichten aus. Die Optimierung der Herstellung von hochwertigen Filmen über einen breiten Bandlückenbereich wird zuerst beleuchtet. Die Rationalisierung der Formierungsprozesse erweist sich als fundamental, um reproduzierbare Präparationsroutinen für hochwertige Filme zu entwickeln. Anschließend wird ein optischer in-situ Aufbau zur Rationalisierung von Formierungsprozessen vorgestellt. Abhängig vom Halogenidverhältnis in der MAPb(IxBr1-x)3-Reihe werden verschiedene Formierungswege eingeschlagen. Während sich das reine Bromid direkt und Iodid reiche Perowskite über die intermediäre Solvatphase (MA)2(DMSO)2Pb3I8 bilden, bilden sich gemischte Halogenide zwischen 0.1 ≤ x ≤ 0.6 über beide Wege. Die Formierung über konkurrierende Wege erklärt die kompositorische Heterogenität der gemischten Halogenidproben. Zuletzt werden Formierungsprozesse von Bromid-Perowskiten rationalisiert und Abhängigkeiten der Kinetik von der Lösungskonzentration zeigen sich. Niedrige Konzentrationen führen zu einer beschleunigten Kristallisation und Schichtdickenabnahme des Nassfilms. Dieser Trend wird durch geringere Kolloidwechselwirkungen und niedriger koordinierte Blei-Bromid-Komplexe in verdünnten Lösungen erklärt. Die Korrelation im Präkursor-Prozess-Eigenschaftsraum hebt die Herstellung von Perowskiten aus chemischer Sicht zu einem nicht-trivialen Prozess. / Bandgap tunability by ion substitution and the fabrication due to solution-based processes characterize metal halide perovskites. They are promising for application in various thin-film opto-electronic devices, which require the deposition of high-quality thin-films. The quality strongly depends on the crystallization behavior predetermined by the precursors in solution. This thesis aims to evaluate correlations in the vast precursor-process-property space of metal halide perovskite and rationalizes formation processes. Phase purity, morphology, and absorption properties determine the perovskite thin-film quality. The first part focuses on optimizing the perovskite fabrication to obtain high-quality films over a wide bandgap range. From high-quality films, the exciton binding energy is determined. The rationalization of formation processes proves essential to design reproducible preparation routines for high-quality films. The second part presents an optical in-situ setup to rationalize perovskite formation processes. Different formation pathways are taken, depending on the halide ratio in the MAPb(IxBr1-x)3 series. While the pure bromide forms directly and iodide-rich perovskites form via the intermediate solvate phase (MA)2(DMSO)2Pb3I8, mixed halides between 0.1 ≤ x ≤ 0.6 form via both. Such a heterogeneous formation process via two competing pathways rationalizes the compositional heterogeneity of mixed halide samples. The third part focuses on rationalizing the formation process of pure bromide perovskites and reveals a dependency of the formation kinetics on the solution concentration. Lower concentrations lead to accelerated crystallization kinetics and increase wet-film thinning. Lower colloid interaction and lower coordinated lead-bromide complexes in diluted solutions explain this trend. The strong correlation in the precursor-process-property space raises the preparation of perovskites via spin-coating to a non-trivial process from a chemical point of view.