Dye sensitized solar cells (DSSCs) based on TiO2/MWCNTs composite with varying concentrations of CNTs (0, 0.03, 0.06, 0.09, 0.15, and 0.21 wt%), fabricated using N3 dye as a sensitizer. Transmission electron microscopy was used to confirm the dispersion of carbon nanotubes in TiO2. UV-visible absorption spectroscopy, photocurrent-voltage characteristics, and electrochemical impedance spectroscopic measurements were conducted to characterize the DSSCs. The results show that the photo conversion efficiency is highly dependent on the concentration of CNTs in the photoanode. A solar cell based on a photoanode containing 0.03 wt% MWCNTs has a power conversion efficiency which is about 30% greater than that of the unmodified photoanode. A quantum modeling technique based on the density functional theory was used to investigate the thermodynamic aspects of the charge transport processes in DSSCs. Simulation results support the experimental data. (C) 2015 Elsevier B.V. All rights reserved.