A two-dimensional model accounting for the effect of both the morphology of active layer and the layer configuration of multilayer-structured device on the device performance, is developed to optimize the device parameter for high performance of the bulk-heterojunction organic solar cells. When the photovoltaic properties of poly(3-hexylthiophene)/[6,6]-phenyl C61-butyric acid methyl ester solar cells are calculated as functions of device parameters by using the model, it is found that the optimum thickness of active layer is 80 nm and that the domain size in active layer is about 6 nm. Comparison of simulation with experiment reveals that the simulated short-circuit current as a function of active layer thickness is very consistent with experimental one. (C) 2010 Elsevier B.V. All rights reserved.