Renewable energy sources are the only sustainable solutions that can address the increasing worldwide demand for energy without significantly furthering anthropogenic climate change and damage to our environment. Photovoltaics are able to harness the massive amount of solar radiation onto the earth each day through direct conversion to electricity, however have historically been expensive to produce and deploy on a large scale. In this thesis, we examine some of the challenges facing current photovoltaic technologies and how recently-developed materials, such as the inorganic-organic lead halide perovskites, have inspired the search for materials that may be used to provide highly-efficient, yet also cheap, mass-producible and flexible solar cells. Through ab initio density functional theory, we examine three families of compounds and, through the calculation of their electronic, optical and defect properties, are able to assess their suitability and potential as absorbers within photovoltaic devices. The caesium silver bismuth halides are lead-free analogues of the lead halide perovskites, however our calculations demonstrate that they are limited in comparison to their lead counterparts due to a mismatch in orbital angular momentum in their electronic structure, weakening their absorption. The silver copper sulfides have also shown recent promise as solar absorber materials, although we show that consideration of the optical properties is essential in successfully predicting the potential of such emergent materials. Finally, our survey of the lead bismuth sulfides predicts a promising compound for solar absorption, including the cell architecture that would be necessary to produce high device efficiencies. Through this study, we can accurately calculate properties of these materials but also hope to provide guidance in the future search for new photovoltaic technologies at the atomic scale
