Organic photovoltaic cells based on the multilayers
structure, indium tin oxide
(ITO)/copper-phthalocyanine(CuPc)/fullerene(C60)/aluminium
tris(8-hydroxyquinoline) (Alq3)/aluminium, have been studied. When an
ultra-thin metal layer is deposited onto the surface of the ITO anode the
power conversion efficiency of the cells is significantly improved. The
improvement depends on the ITO used. These differences have been attributed
to the difficulty to control the surface chemistry of ITO. The best result
has been obtained with a gold layer thick of about 0.5 nm. We propose that
the gold ultra-thin film, which is too thin to be continuous, allows to
improve the agreement between the work function of the anode and the highest
occupied molecular orbital (HOMO) of the organic donor CuPc and to passivate
the surface contamination of ITO.