ZnO nanorod arrays have been proposed for their application in photovoltaic devices, owing to the ease of growing arrays of high crystalline quality, low cost and low toxicity of ZnO, and well controlled length and shape nanowires. Since ZnO is an n-type semiconductor with a wide bandgap of 3.3 eV, visible light absorption must be provided by an associated p-type semiconductor. In particular, extremely thin absorber (ETA) solar cells could greatly benefit from this nanostructure, because light absorption would occur parallel to the length of the nanorods, but charge separation can occur normal to the nanorods, with increased efficiency. Hybrid photovoltaic devices have been demonstrated using poly (3-hexylthiophene) (P3HT) as light absorber and hole transport phase , and band alignment with ZnO can be achieved with Mg doping of ZnO . Another approach is to design n-core/p-shell structures using a core of ZnO nanowires and a shell of ZnS. Bandgap control is achieved through the staggered type II heterojunction, where the effective bandgap at the junction can be calculated as the difference between the valence band level of ZnS, and the conduction band level of ZnO . ZnO/ZnS core-shell nanorods have been prepared from solution grown ZnO nanorods . ZnO/ZnTe core-shell nanorods have also been prepared by chemical vapor deposition . Here, we will present initial MOCVD growth results of ZnO-ZnS core-shell nanostructures characterized via SEM, XRD and UV-vis spectroscopy. Their efficiency in photovoltaic devices of the type FTO/ZnO-ZnS/Au and FTO/ZnO-ZnS/P3HT/Au will be reported by external quantum efficiency and I-V measurements under simulated sunlight. References: Olson, DC Lee, YJ White, MS Kopidakis, N Shaheen, SE Ginley, DS Voigt, JA Hsu,,J.W.P. Journal of Physical Chemistry C 111, 16640-16645 (2007); J. Piris, N. Kopidakis, DC Olson, SE Shaheen, DS Ginley, and G Rumbles, Adv. Funct. Mater. 17, 3849–3857 (2007); J. Schrier, DO Demchenko, L-W Wang and AP Alivisatos, Nanolett. 7, 2377 (2007); JJ Uhlrich, R Franking, RJ Hamers, and TF Kuech, J. Phys. Chem. C 2009, 113, 21147–21154 21147; HY Chao, JH Cheng, JY Lu, YH Chang, CL Cheng, YF Chen, Superlattices and Microstructures 47, 160-164 (2010).