The development of a new generation of photovoltaic technologies is an important task in order to increase the production of clean energy. Perovskite solar cells, with an exceptionally rapid development over the last decade, have transformed into perhaps the most promising candidate to provide a low-cost alternative to conventional cells. While having excellent efficiency, the most successful category of photovoltaic perovskites, the class of hybrid lead-halide perovskites, suffers from poor stability in ambient conditions and gives rise to potential health concerns due to lead toxicity. Because of these issues, studies yielding a better understanding of lead-based perovskites and investigations of new, lead-free materials are likely meaningful steps towards better and more competitive solar cells. This thesis contains studies about established lead-based perovskites, CH₃NH₃PbI₃ and CH(NH₂)₂PbI₃, as well as the lead-free alternatives AgBi₂I₇ and Cs₂AgBiI₆. The main method employed is electronic structure calculations through density functional theory under periodic boundary conditions including band structure calculations and projected density of states. A particular focus is given to systems with mixed anion and related effects on the electronic structure.