Nanoimprint lithography (NIL) was carried out on bilayer organic photovoltaics (OPVs) based on regioregular poly (3-hexylthiophene-2,5-diyl) (P3HT) as electron donor and 4,7-bis(2-(1-ethylhexyl-4,5-dicyano-imidazol-2-yl)vinyl)benzo[c]1,2,5-thiadiazole (EV-BT) as electron acceptor. The power conversion efficiency of the devices after nanoimprinting increased from 0.20% to 0.30%, closer to that of the bulk heterojunction device at 0.37%. As a result. NIL proved to be a feasible method for improving the bilayer OPV performance by increasing the donor/acceptor interfacial area. (C) 2009 Published by Elsevier B.V.