In order to improve the stability of organic solar cells based on CuPc/C-60 planar heterojunction, an ultrathin layer of Au (similar to 2 nm) is inserted between CuPc and PEDOT:PSS. Although, short circuit current density (J(sc)) and open circuit voltage (V-oc) of the device containing Au layer are less than those of the Au-free one, it has comparable power conversion efficiency (eta(p)) owing to its higher fill factor (FF). In addition, this ultra-thin Au layer enhances the stability of the device significantly. After a month under ambient condition, the device with "indium thin oxide (ITO)/PEDOT:PSS/Au" anode reaches 67% of its initial eta(p) value, while the eta(p) of the cell with "ITO/PEDOT:PSS" anode drops to less than half of its initial value. The improvement in stability is ascribed to the more durable Au/CuPc interface in contrast to the PEDOT:PSS/CuPc interface. (C) 2012 Elsevier B.V. All rights reserved.