The validity of conventional circuit model for interpreting results obtained using organic solar cells is examined. It is shown that the central assumption in the model that photo-generated current remains constant from short-circuit to open-circuit condition may not hold for organic cells. An improved model based on the photovoltaic response of organic solar cells is proposed and a method of extracting the parameters of the model is presented. (c) 2005 Elsevier B.V. All rights reserved.