We report the solution processed graphene oxide (GO), NiO(x) and GO/NiO(x), bi-layer used as an anode interfacial layer in organic bulk-heterojunction solar cells. The bulk-heterojunction solar cells using GO, NiO(x) and GO/NiO(x) bi-layer exhibited the conversion efficiency of 2.33%, 3.10% and 3.48%, respectively. The cell efficiency is correlated with the matching of energy levels between ITO, hole transport layer and P3HT and thus a well-matched stack layer of ITO/GO/NiO(x)/P3HT:PCBM/LiF/Al shows the best cell efficiency of 3.48% with the J(SC) of 8.71 mA/cm(2), V(OC) of 0.602 V and FF of 66.44%. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.