Fine-tuning nano/micro-structural morphologies and their depth studies in small-molecule solar cells are key parameters in elevating device performances. In the current work, we focused on controlling the morphology of a small-molecule organic photovoltaic by treating its active layer film with solvent vapor annealing (SVA). For this project, the devices were made of all-small-molecule p-DTS(FBTTh2)(2):PC71BM heterojunction films processed using different solvents for the vapor annealing. The different solvents resulted in different nano-domain packing structures and segregated phase separation as evidenced by detailed two-dimensional grazing-incidence wide-angle X-ray scattering (2D-GIWAXS) and atomic force microscopy (AFM) analyses. From the data, we demonstrated a correlation between the nanostructural morphology of the active layer film and the performance of the device and found an SVA condition that produced a p-DTS(FBTTh2)(2):PC71BM blend system yielding an improved device performance.