Inverted small molecule organic solar cells were fabricated with a Ca modified indium tin oxide (ITO) substrates as the cathode and molybdenum trioxide (MoO3) interlayer modified Ag as anode. The Ca and MoO3 layers were found to be critical to the device performance. The insertion of Ca forms Ohmic contact between ITO and fullerene (C-60), significantly enhancing the fill factor and further improvement of efficiency by 65% compared to the device without Ca layer. MoO3 interlayer has multiple functions as anode buffer layer, effectively preventing the exciton quenching and reducing the interfacial resistance. Optimal copper phthalocyanine (CuPc) thickness of 25 nm demonstrates that the balance between light harvesting and charge transport is obtained and a maximum PCE of 0.64% under 100 mW/cm(2) is achieved. Finally, the dependencies of the short-circuit current density and the open-circuit voltage on illumination intensity were investigated. (C) 2010 Elsevier B.V. All rights reserved.