We have found that the short-circuit current, J(sc), of polymer/fullerene [RR-P3HT/C(60)] solar cells has a clear dependence on the surface roughness of the ITO/glass substrate. We prepared an ITO surface with an average roughness, R(a), of 0.7-11 nm by chemical etching. At first J(sc) increases with the increase in ITO surface roughness and then gradually decreases. The maximum performance was obtained at R(a) approximate to 4 nm. J(sc) is also high with a very flat surface of R(a) = 0.7 nm. This feature can be attributed to the trade-off between the increase in absorption light path length and film-quality deterioration. (C) 2008 Elsevier B.V. All rights reserved.