Increased shaped anisotropy promotes a face-on orientation at the solid interface, and side-on at the vapour. A number of experimental studies have shown that backbone planarisation (induced by fluorination of the backbone, or extending the conjugation of the backbone, such as by adding aromatic components between the backbone and side-chains, both of which can be associated with an increase in shape anisotropy) results in a more face-on orientation at the donor-acceptor interface in OPVs. It should be noted that both of these chemical modifications will also influence the energetics, so an interplay between changes in interaction strength and shape will control the orientation at the interfaces.