“…Several acceptor molecules have been tested in bulk-heterojunction solar cells, among them conjugated polymers, fullerenes, carbon nanotubes, perylenes, and inorganic semiconducting nanoparticles. [90] So far, only derivatives of C 60 and C 70 have been reported to give highly efficient bulkheterojunction devices, despite the fact that the position of the HOMO and LUMO levels and the optical absorption are not ideal for most of the donor polymers. [60] A significant number of other C 60 and C 70 derivatives have been synthesized, to improve the processability, vary the HOMO/ LUMO levels, or influence the morphology in blends with conjugated polymers.…”