Investigation of Transport and Recombination Properties in Graphene/Titanium Dioxide Nanocomposite for Dye-Sensitized Solar Cell Photoanodes

摘要

In this paper, we present the fabrication and characterization of Dye-Sensitized Solar Cells exploiting graphene/TiO_2 nanocomposite photoanodes produced by in-situ catalytic reduction of graphene oxide. The graphene oxide reduction to graphene was obtained in a solution-based process during the thermal treatment of the composite, catalyzed by the presence of TiO_2 nanoparticles, as confirmed by X-ray photoelectron spectroscopy. The carbon nanostructures act as 2D conductive support path for the photogenerated electrons inside the nanostructured semiconductor electrode, as evidenced by the charge transport properties and recombination kinetics estimated by electrochemical impedance spectroscopy. The presence of graphene sheets led to an increase of the electron lifetime, due to reduction of recombination of charge carriers; moreover, the devices assembled with nanocomposite photoanodes showed an increase of the generated photocurrent, due to the improvement of the transport properties. The optimal value of graphene oxide in TiO_2 was found at a concentration of 0.25 wt%, which corresponds to double photoconversion efficiency with respect to the bare TiO_2-based cells.