Organic and hybrid solar cells are complex, nanostructured devices, for which an in-depth understanding is required to improve and optimize. Both types of solar cells take advantage of the strong optical absorption of organic chromophores to collect sunlight and have reached maximum efficiencies of around 12% as of the end of 2014. They both also rely on nanostructures and interfaces to balance energy and charge transport. Despite these underlying similarities, organic solar cells and dye sensitized solar cells present different challenges to optimization. We have applied experimental and computational techniques to help explore and understand factors that affect their efficiencies and describe and predict strategies for improving them. We made a comparative study of two isostructural donor molecules and studied the exciton and charge transport in a non-fullerene acceptor molecule in bulk heterojunction organic solar cells. We then wrote a kinetic Monte Carlo simulation to study energy transfer in donor-acceptor systems and applied it to study trapping kinetics in different morphologies, energy relay dyes in dye sensitized solar cells, and energy cascades in bilayer organic solar cells. Based on these simulations, we offer design suggestions for both types of solar cells.