We have recently demonstrated, using small angle neutron scattering in combination with other techniques, that in organic photovoltaic devices (OPVs) the additive 1,8-diiodooctane (DIO) largely remains in the film after spin-coating acting as a plasticizer to increase molecular mobility and allowing morphological improvement of the film with a consequent increase in power conversion efficiency (PCE) of the OPV device. This new finding opens new perspectives into the morphology control of OPVs, namely through the use of additives and mixtures of additives possessing different affinities towards the polymer and the acceptor which will allow us to optimize the corresponding morphology and PCE. In this proposal we plan to use this strategy to improve the morphology and PCE of fullerene-free solar cells based on the high efficient system PBDB-T:ITIC which has a reported PCE > 12%.