P3HT:PCBM polymer solar cells with a very small amount of TiO₂ nanotube aggregates (0.002 mol per 100 mL) in the active layer have been fabricated. Although in dye-sensitized solar cells nanotube aggregates have been shown to increase light absorption of devices, it was found that TiO₂ nanotube aggregates reduced the absorbance of the active layer in our case. However, its positive role on the charge collection and transportation maintained the EQE the same as a conventional P3HT:PCBM device and improved the electron mobility from 5.71 × 10⁻⁵ cm² V⁻¹ s⁻¹ to 7.22 × 10⁻⁵ cm² V⁻¹ s⁻¹. The final devices showed a 15% increase in power conversion efficiency compared to conventional P3HT:PCBM devices. The effects of TiO₂ nanotube aggregates on the morphology of the active layer were studied by AFM.