Plasma Reduction of Nanostructured TiO2 Electrode to Improve Photovoltaic Efficiency of Dye-Sensitized Solar Cells

Abstract

This study first reports the surface modification of nanostructured TiO2 film on an FTO glass substrate using plasma reduction; we also report the application of this film to a working electrode for enhancement of the efficiency of dye-sensitized solar cells. The change in the electronic structure of the TiO2 films was confirmed by XPS measurements. IMPS and IMVS studies showed that the plasma reduction induced increases of the electron diffusion coefficient and the electron recombination lifetime. The longer electron diffusion length prevents the charge recombination with oxidized redox, which is controlled by trap-limited electron diffusion in the TiO2. These results can be explained by the increase of number of the Ti3+ valence states (electron traps) and their occupancy, induced by plasma reduction. The obtained data are consistent with the remarkable increase in the values of FF and Jsc. Plasma reduction facilitated charge transport in sensitized TiO2 due to the increase in the charge collection efficiency. The higher Voc value was ascribed to the upward moving of the quasi-Fermi level due to the increase in the density of the Ti3+ valence states and their occupancy. Thus, we achieved an enhancement in efficiency of 11.6% for 6 hours of dye adsorption.