This paper reports the effects of p-type NiO thin films deposited by magnetron sputtering on performance of organic solar cells (OSCs). The effects of a p-type NiO interfacial layer between indium tin oxide (ITO) and active layer were examined systematically to increase the efficiency and stability of OSCs. Characterization of the sputter-deposited NiO film revealed it to be a p-type semiconductor with a resistivity of 2.7 x 10(-2) Omega cm. Its conduction type was demonstrated by measuring the Seebeck coefficient (+70 mu V/K). The insertion of a 5 nm-thick NiO layer resulted in a power conversion efficiency and a fill factor as high as 2.8 +/- 0.1% and 0.62 +/- 0.02, respectively, which are comparable to OSCs adopting the conventional conducting polymer, PEDOT:PSS. Furthermore, lifetime of the OSCs adopting the NiO layer was 3 times higher than that of the conventional PEDOT:PSS. (C) 2010 Elsevier B.V. All rights reserved.