Ultrafast spectroscopy and temperature-dependence of steady-state optoelectronic properties of layered lead halide perovskites

The work presented in this thesis investigates layered metal halide perovskites, which are of high research interest due to their optoelectronic properties and potential applications in light emitters, solar cell encapsulation layers, and other devices. To investigate the fundamental properties of these materials, X-ray diffraction and steadystate and time-resolved spectroscopy techniques were used. These methods were essential for understanding the relationship between structural-functional properties, which could help achieve advancements more quickly through material design instead of relying on trial and error. Metal halide perovskites have attracted significant research interest due to their excellent optoelectronic properties for solar cells, but the lack of long-term stability is an ongoing issue. The more stable counterpart, known as the layered perovskite, has been proposed to resolve this problem via the incorporation of a long organic molecule in the crystal lattice. The introduction of the organic spacer affects the optoelectronic properties of charge carriers via the confinement and the organic-inorganic lattice interactions. The investigation of these actions was carried out in this thesis, which was organised into three separate chapters where materials were studied via different methods. The first study examined temperature-dependent structural and optoelectronic properties across the phase transition. By analysing the X-ray and spectroscopy data, it was shown that the phase transition is accompanied by the change of the octahedral tilting pattern and absorption/photoluminescence emission energy. The second study investigated the exciton recombination and formation dynamics in two samples containing different organic spacers. Finally, the vibrations of the spacers were investigated across a range of layered perovskites using the powerful technique of two-dimensional infrared spectroscopy. This study revealed the importance of the organic cation arrangement with respect to each other and its effects on the vibrational frequencies. Overall, this work contributes to the rational design of the organic spacer in layered perovskite materials.