Solar cells are among the most promising green technologies for energy production that exist.While currently solar energy production makes up only around 2% of the total energy production in the United States, in order to maintain a livable planet, it will become a necessity for green technologies like solar energy to displace fossil fuels in the coming years. Because our society places great value in economic well-being as well, it is hard to sell the idea of solar cells over their competitors unless the effective dollar per watt is comparable or better. To this end, it is imperative to improve on this figure of merit in any way possible, to help the solar cell industry replace fossil fuels with their much greener alternative. In this dissertation, I show the progress I’ve made on this front from the standpoint of computational condensed matter physics. In the first several chapters, I explore various physical phenomena that greatly affect the efficiency in nanoparticle solar cells, and model various systems to try to better understand one of the great roadblocks for nanoparticle solar technologies, their low carrier mobility, which leads to a low efficiency. In the final chapter, I shift focus to a more proven technology, Heterojunction with Intrinsic Thin layer (HIT) solar cells. HIT solar cells exhibit faster degradation than their crystalline silicon counterparts, and as such, have a higher averaged dollar per watt over their lifetime, despite their out-of-the-box world record holding terrestrial efficiencies. This degradation is not fully understood at a fundamental level, and so, in chapter 6 I show a hierarchical modelling technique that sheds some light on the degradation of these record setting solar cells