We synthesized pyrrolidinofullerenes functionalized with an electron donor or acceptor group via Prato reaction. Their structures were studied using H-1-NMR, FT-IR and MALDI-TOF mass spectrometry. The electronic energy levels were calculated using quantum chemical calculation based on the density functional theory, showing that the lowest unoccupied molecular orbitals were in the range of -3.7 and -3.9 eV. The electron mobility of one of the fullerene derivatives was as high as 0.05 cm(2)/(V s), suggesting that pyrrolidinofullerenes can be promising n-type semiconductors. The fullerene derivatives were also blended with P3HT to fabricate bulk heterojunction polymer solar cells, and the performance of solar cells as a function of structural variations of the fullerene derivatives was investigated.