To enhance the performance and understanding of organic photovoltaic devices (OPVs), we have investigated the influence of organic solar cell geometry on power loss and device efficiency using three-dimensional finite element (3-D FE) simulation. To investigate the influence of geometry on power loss, we have proposed a new simple finite element (FE) model of OPV structure. We have checked the characteristics of the voltage drop on the ITO electrode layer and found that this model is suitable for describing the basic operation of an OPV. We have also simulated various geometries using a 3-D FE simulation and discussed these simulations in the paper. The total power loss obtained from the 3-D FE simulation allows us to compute the power conversion efficiencies of the eight OPVs and compare the computations against measured results. Based on these results, we discuss how to minimize resistance losses in the ITO electrode layer of the OPVs and propose a simple method to estimate easily the power losses using an FE simulation. We expect that this work could contribute to enhancing OPV performance to a certain large-area and offer insights into the design. (C) 2011 Elsevier B.V. All rights reserved.