Peculiar perovskites: Unraveling the unique optical response of hybrid organic-inorganic perovskites from first principles

Hybrid organic-inorganic perovskite (HOP) materials and their layered analogs (LHOP) have been extensively applied to optoelectronic applications including solar cells, light-emitting diodes, optical detectors, and spintronics due to their unique atomic, electronic, and optical properties. HOPs and LHOPs are hosts to fascinating microscopic interactions that influence their macroscopic optical and electronic properties. Researchers still debate how interactions between optically excited charge carriers, free-carriers, lattice vibrations, and atomic geometry influence the measured optical response of HOPs. First principles simulations provide a window to examine how these atomic-scale interactions contribute piece-by-piece to the measurable optical properties of materials. In this PhD thesis, I apply and develop first principles optical calculations based on density functional theory and many-body perturbation theory to determine how the optical response and excitonic properties of HOPs and LHOPs are influenced by the presence of free-carriers, polar lattice vibrations, and layer stoichiometry. In order to describe polar lattice screening, I extend the lattice screened Coulomb interaction in the Fan-Migdal self energy to the electron-hole interaction by the Shindo approximation and subsequently construct model screening functions from the generalized and simple Frohlich models for the electron-phonon vertex. Additionally, I apply optical response calculations to predict how the choice of organic spacer layers in LHOPs can be used to design novel triplet light-emitting materials with emission wavelengths spanning the visible range