Inverted organic photovoltaic (OPV) cells based on poly(3-hexylthiophene) (P3HT) as an electron donor and [6,6]-phenyl-C71-butyric acid methyl ester (PCTIBM) as an electron acceptor, were fabricated and characterized. To improve the photovoltaic performance, interface control using either dense or nano-structured ZnO films as cathode buffer layers for effective electron transport was demonstrated, while an under-stoichiometric transition metal oxide, such as Mob, was employed as the anode buffer layer for efficient hole extraction. Incorporation of a nanostructured ZnO interlayer enhanced electron hole dissociation by enabling a larger interfacial contact with the active layer, that results in increased short-circuit current density (JSC) and eventually contributing to higher power conversion efficiency (PCE).