Interfaces are inherent in and essential to organic electronic devices. At every interface, both organic/organic and organic/inorganic, the potential to utilize nanostructuring to control device performance is very high. In this paper, we focus on one example of nanostructuring at the donor/acceptor heterojunction in organic photovoltaics, with the purpose of modifing efficiency by four orders of magnitude. We show that the length of the exciton dissociating interface can be tuned by changing the substrate temperature for small molecule heterojunction photodiodes based on crystalline DIP/C60 mixtures. Due to the tuneable interface morphology, the performance of such devices can be changed from poor performing planar heterojunctions to higher efficiency ordered nanoscale bulk heterojunction structures. In this way, highly crystalline DIP can be thought of as a natural “bulk” heterojunction.