We report photovoltaic cells based on solution-processed blends using a novel anthradithiophene derivative as the donor and a fullerene derivative as the acceptor. Solvent vapor annealing of these blends leads to the formation of spherulites, which consist of a network of anthradithiophene crystallites dispersed in an amorphous matrix composed primarily of fullerene. We observe a direct correlation between coverage of a device with spherulites and its performance. Devices with 82% spherulite coverage reach a power conversion efficiency of 1%, which makes them one of the highest performing solution-processed small molecule photovoltaic cells to date.