Two fulleropyrrolidine derivatives with the benzophenone moiety were synthesized based on a molecular design that suppresses their crystallization. The organic photovoltaic devices using the fulleropyrrolidine derivatives showed higher thermal stability than the devices using [6,6]-phenyl C-61-butyric acid methyl ester. Solid-state nuclear magnetic resonance studies revealed that the benzophenone moiety reduced the domain sizes of the fullerene derivatives in the bulk heterojunction.