Recently it has been shown that the use of [70]PCBM as electron acceptor in polymer solar cells can improve the current output of such devices because C70 derivatives have a stronger and broader absorption compared to C60 ones. In this work we studied the influence of the fullerene on the optical behaviour of the photoactive blend film of a polymer solar cell. We simulated the optical absorption of the active layer inside the device structure and we calculated the maximum achievable short circuit current density with the aim to correlate the variation of the optical constants to the output current of the device. Afterward, we realized several polymer solar cells and we proved the theoretical findings. © 2013 The Authors. Published by Elsevier Ltd.