A stable organic solar cell with structure of ITO/buffer/donor/acceptor/cathode is presented. A thin layer (5 nm) of MoO3-doped CuPc is adopted as the buffer in CuPc/C-60 organic heterojunction photovoltaic (PV) solar cells, resulting in two times longer lifetime. The surface morphology of buffer layer plays a decisive role in improving the stability. Crown Copyright (C) 2011 Published by Elsevier B. V. All rights reserved.