Poly (3- hexylthiophene) (P3HT)- C-60 organic photovoltaic devices with interpenetrating donor- acceptor interfaces were fabricated by oblique thermal deposition of C-60 into the P3HT nanogratings. The uniformity and step coverage of C-60 infiltration into the P3HT nanostructures, which can determine the device performance, were dependent on the C-60 evaporation angle. It was also observed that the C-60 deposition rate and thickness determine the efficiency. A 50% improvement in power conversion efficiency is observed due to the increased exciton dissociation rate at the larger area P3HT- C-60 interface at optimal C-60 deposition filling. With the proposed technique, a highly efficient organic solar cell using an insoluble acceptor has been fabricated. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3517513]