Modeling hybrid halide perovskites for solar cell applications : Simulations of electronic structure and X-ray spectroscopy

Abstract: Over the past 13 years, perovskites have become a very promising candidate in the search for cheap and effective photovoltaic materials for solar cells.  Perovskite solar cell power conversion efficiency has increased from 3.8% in 2009 to over 25% by late 2022, rivaling that of crystalline silicon cells, and there are a variety of potential chemical compositions that provide a range of materials to investigate.  However, there are still questions about the specific role of all the different chemical components in the material and how they influence its efficiency.  This thesis aims to investigate the effect of material composition and structure through electronic structure calculations and theoretical X-ray absorption and X-ray photoelectron spectroscopy, with comparison to experimental spectra.  Herein, studies on the prototypical hybrid halide perovskite methylammonium lead triiodide (CH3NH3PbI3) are presented and compared among materials with various differences: structural/elemental changes in the case of its precursor methylammonium iodide (CH3NH3I), halide substitution in the case of methylammonium lead tribromide (CH3NH3PbBr3), or organic cation substitution in the case of formamidinium lead triiodide (CH(NH2)2PbI3).