Ultrathin films serving as a light-harvesting and hole-transporting material were fabricated by layer-by-layer deposition of a water-soluble phthalocyanine derivative, copper(II) phthalocyanine-3,4',4 '',4 '''-tetrasulfonic acid tetrasodium salt (CuPcTS), and poly(diallyldimethylammonium chloride). The blue-shift of absorption peak and the absorption dichroism of the Q band indicated that CuPcTS molecules in the layer-by-layer films form cofacial dimers or oligomers and that their molecular planes take a three- or two-dimensional orientation in a direction parallel to the substrate depending oil a drying process of the film during the deposition. The diffusion constant of hole carriers among CuPcTS molecules ill the film was evaluated to be 6.5 x 10(-11) cm(2) s(-1) in an acetonitrile Solution from potential step chronoamperometry measurement. Solution-processed thin-film organic solar cells with a triple-layered structure were developed by combining a hole-transporting layer made of poly(3.4-ethylenedioxythiophene) oxidized with poly(4-styrenesulfonate), a light-harvesting layer of CuPcTS, and all electron-transporting layer of fullerene, in this sequence. Photovoltaic properties of the cells strongly depended oil the thickness of CuPcTS films and call be maximized by controlling the thickness at ca. 10 nm. (C) 2008 Elsevier B.V. All lights reserved.