Solid-state Organic Solar cells (OSCs) have the potential to be the basis of a renewable energy source that is inexpensive and portable. Current state-of-the-art solution-processed OSC cells are based on the so-called bulk heterojunction (BHJ) architecture, in which phase separation of donors and acceptors is critical to performance. Therefore, understanding the nanoscale morphology and the diffusion mechanism in OSC cells is of great importance, as this directly affects device performance. We plan to build on recent preliminary experiments on LOQ to answer key questions on phase separation in BHJ cells. Specifically, we aim to understand (1) the effect of blend ratio on aggregation, (2) the effect of annealing, (3) why "bilayer" solar cells work as well as they do, and (4) why some materials work well with C70 fullerenes but others don't.