A novel fullerene derivative, 1,1-bis(4,4′-dodecyloxyphenyl)-(5,6) C₆₁, diphenylmethanofullerene (DPM-12), has been investigated as a possible electron acceptor in photovoltaic devices, in combination with two different conjugated polymers poly[2-methoxy-5-(3′,7′- dimethyloctyloxy)-para-phenylene vinylene] (OC₁C₁₀-PPV) and poly[3-hexyl thiophene-2,5-diyl] (P3HT). High open-circuit voltages, V _OC=0.92 and 0.65 V, have been measured for OC₁C ₁₀-PPV:DPM-12- and P3HT:DPM-12-based devices, respectively, In both cases, V_OC is 100 mV above the values measured on devices using another routinely used fullerene acceptor, [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM). This is somewhat unexpected when taking into account the identical redox potentials of both acceptor materials at room temperature. The temperature-dependent V_OC reveals, however, the same effective bandgap (HOMO_polymer-LUMO_Fullerene; HOMO = highest occupied molecular orbital, LUMO = lowest unoccupied molecular orbital) of 1.15 and 0.9 eV for OC₁C₁₀-PPV and P3HT, respectively, independent of the acceptor used. The higher V_OC at room temperature is explained by different ideality factors in the dark-diode characteristics. Under white-light illumination (80 mW cm^-2), photocurrent densities of 1.3 and 4.7 mA cm^-2 have been obtained in the OC₁C ₁₀-PPV:DPM-12-and P3HT:DPM-12-based devices, respectively. Temperature-dependent current density versus voltage characteristics reveal a thermally activated (shallow trap recombination limited) photocurrent in the case of OC₁C₁₀-PPV:DPM-12, and a nearly temperature-independent current density in P3HT:DPM-12. The latter clearly indicates that charge carriers traverse the active layer without significant recombination, which is due to the higher hole-mobility-lifetime product in P3HT. At the same time, the field-effect electron mobility in pure DPM-12 has been found to be μ_e = 2 × 10^-4 cm² V^-1 s^-1, that is, forty-times lower than the one measured in PCBM (μ_e = 8 × 10^-3 cm² V ^-1 s^-1).