We fabricated the interdiffused organic photovoltaic devices, which composed of poly (2-methoxy-5-(2'-ethylhexyloxy)-1, 4-phenylenevinylene) (MEH-PPV) and buckminsterfullerene (C(60)), by annealing treatment. After annealing, C60 diffused into the MEH-PPV layer, in consequence, MEH-PPV/C(60) interfacial area was increased and their interface became closer proximity. The results lead to reduce reverse-bias saturation current (J(s)), and increase the open-circuit voltage (V(OC)) and the short-circuit current (J(SC)). Moreover, the increase in conductivity of poly (3, 4-ethylenedioxythiophene)/poly (styrenesulfonate) is also responsible for the performance improvement. Consequently, the power conversion efficiency is improved from 0. 17% to 0.92% combined with the all increase of J(SC), V(OC) and fill factor. (c) 2008 Elsevier B.V. All rights reserved.