Unravelling the structure-property relationship of Cs(Fa)PbI3 3D perovskites

This thesis investigates the structure-property relationships of 3D lead halide perovskites, focusing on the stabilization of photoactive black phases in FA1-xCsxPbI3 and CsPbI3 for applications in solar cells and LEDs. Solid-state NMR is used as primary analytical technique to probe local A-site environments and study phase purity in the mixed cation perovskite. To overcome challenges of low sample yields from thin-film processing, a method for dilution with inert Al2O3 was establish to obtain reliable spectral data. Structural analysis confirms that incorporating Cs+ into FAPbI3 successfully stabilizes the black α-phase at room temperature using cation mixing and halide (Br-) mixing. However, the material remains highly susceptible to rapid degradation into the non-photoactive yellow phase. All-inorganic CsPbI3 nanocrystals are synthesized via hot injection method to investigate their degradation over time. The research optimised their washing process, identifying a 1:4 perovskite to antisolvent ratio as ideal balance between reasonable PLQY and long term stability. Furthermore, B-site doping with 10% La3+ is found to enhance long term stability in terms optical performance, preferring a 1:1 washing ratio. Finally, the successful fabrication of red PeLEDs confirms their potential for optoelectronic devices.