Two carbazole-substituted fullerene derivatives containing mono- and bi-C₆₀ units, (9-butyl-9H-carbazole-3-yl)-C₆₁-butyric acid methyl ester (Cz-C₆₀) and (9-butyl-9H-carbazole-3,6-diyl)-bis(C₆₁-butyric acid methyl ester) (Cz-2C₆₀), were successfully synthesized and characterized by NMR, MS and FT-IR spectroscopy. The photophysical, electrochemical properties and thermal stabilities of the fullerene derivatives were systematically investigated. P3HT-based organic photovoltaic devices were fabricated using Cz-C₆₀ and Cz-2C₆₀ as electron acceptors. The highest power conversion efficiencies (PCEs) of the devices fabricated with Cz-C₆₀ and Cz-2C₆₀ were 3.88 and 3.59%, respectively.