This　manuscript　reports　the　impact　of　fullerene　structure　on　the　morphology　and　miscibility　of　small　molecules　via　a　fullerene　bulk　heterojunction　solar　cell.　The　small　angle　neutron　scattering　and　neutron　reflectometry　measurements　were　analyzed　to　provide　quantifiable　measures　of　the　morphology　of　the　resultant　mixtures,　offering　miscibility,　domain　sizes,　interfacial　area　between　the　small　molecule　and　fullerene,　and　depth　profiles　in　the　mixtures.　These　results　indicate　that　the　bis-adduct　fullerenes　exhibit　lower　miscibility　in　small　molecules.　Correlation　of　miscibility　and　morphology　to　photovoltaic　properties　indicates　that　small　molecule/fullerene　miscibility　is　crucial　to　rationally　optimize　the　design　of　fullerenes　for　use　in　small　molecule　organic　photovoltaics.　A　higher　open　circuit　voltage　was　obtained　for　bis-adduct　fullerene　devices　which,　however,　does　not　translate　to　an　increased　power　conversion　efficiency.　This　decrease　in　performance　is　associated　with　the　lower　miscibility　of　bis-fullerene,　which　decreases　the　probability　of　the　dissociation　of　excitons　and　enhances　charge　recombination　rate　in　the　miscible　region.　A　quantitative　analysis　shows　that　an　increase　in　the　average　separation　of　fullerenes　in　the　miscible　region　is　detrimental　to　electron　transport　in　the　miscible　region,　especially　for　a　distance　greater　than　11　Å.　©　2016　American　Chemical　Society.