Controlling the morphology of bulk heterojunction (BHJ) films using mixtures of additives: a Neutron Reflectivity study

We have recently demonstrated 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 BHJs, namely through the use of mixtures of additives possessing different affinities towards the polymer and the fullerene which will allow us to tune the affinity of the additive mixture to the polymer and fullerene and therefore to tune and optimize the corresponding morphology and PCE - a strategy we propose to explore on this proposal using neutron reflectivity to study the thermally induced removal of high boiling point solvent additives and vertical composition profiles.