Photovoltaic cells, with a conducting polymer/fullerene (C-60) interpenetrating heterojunction structure fabricated by spin-coating a conducting polymer onto a C-60 thin film, have been investigated and demonstrated a high efficiency as solar cells based on organic materials. The photovoltaic properties of the solar cells with a structure of indium-tin-oxide (ITO)/C-60/poly(3-hexylthiophene) (PAT6)/Au have been improved by the insertion of a molybdenum trioxide (VI) (MoO3) layer as a cathode buffer layer. In the solar cells with the structure Of ITO/C-60/PAT6/MoO3/Au, the energy conversion efficiency has been improved to 1.15% under AM1.5 (100 mW/cm(2)) illumination. (C) 2009 Elsevier B.V. All rights reserved.