Optoelectronic Properties and Thin-film Studies of Perovskite Structures Passivated by Butylamine Vapours

<p dir="ltr">Perovskite materials with a stoichiometry of ABX3 were well-known for their thermoelectric and piezoelectric properties for decades. The major attraction to perovskite materials was drawn a decade ago in the form of a perovskite co-sensitised solar cell and the exploration of optoelectronic properties of perovskite materials has been a major item ever since. The major perovskite material for this type of emerging photovoltaic applications were hybrid lead halides that come with a mix of metals (such as cesium) and organic molecules (such as methylammonium) in place of A-cation. The B-cation has choices such as lead, tin, etc. but lead-based materials have shown superior photoconversion efficiencies. Alas! The lead halide-based perovskites have a major stability issue that has limited the establishment of perovskite-based photovoltaics as a major commercial or any practical commodity. One way to make use of this wonder photovoltaic material would be its application as a tandem solar cell along with modern silicon solar films. This would reduce the film thickness of traditional silicon solar cells, largely making them less heavy and suitable for compact and modern appliances, at the same time, increasing the efficiency of the devices beyond the maximum efficiency that can be achieved by the silicon solar cells made with thick silicon layers. Reducing the film thickness preserves the benefit of using the perovskite solar cell to some extent.</p><p dir="ltr">This thesis investigates two different solutions to this stability issue, either by a search in the literature for a new perovskite material and experimentally modifying the perovskite film in the photovoltaic device. As a new material, relatively concerning the solar cell application, chalcogenide perovskites promise to be a great replacement for lead halide perovskites or another choice as a tandem solar cell material with silicon. A literature review on chalcogenide perovskites is presented and discussed for their potential in solar cell applications. Then, the material instability of perovskite films in a solar cell is investigated by the application of passivation layers at the top of the perovskite film in vapour-assisted methods. This can be achieved by converting the surface layer of perovskites to hydrophobic using longer chain alkyl ammonium molecules as an A-site cation than most used methyl ammonium molecules. On top of that, the use of vapour-assisted passivation supports the commercialisation through the potential of the use of a chemical vapour deposition for large-scale production.</p>