The realization of highly efficient organic solar cells requires the understanding of all optical losses in the solar cell. In this paper, we demonstrate the use of a nano-replicated moth eye anti-reflection coating which functions as an effective medium at the air-substrate interface. We show that the reflection losses of the substrate are compensated, yielding an increase of the peak EQE values by 3.5%. This improvement is valid for a wide range of incidence angles and preserves the insensitivity of organic solar cells against oblique incident light. (c) 2007 Elsevier B.V. All rights reserved.