Metal-based flexible TiO2 photoanode with titanium oxide nanotubes as the underlayer for enhancement of performance of a dye-sensitized solar cell

A flexible photoanode was prepared for a dye-sensitized solar cell (DSSC), using a titanium (Ti) foil as the substrate, titanium oxide nanotubes (TNTs) as the underlayer, and TiO2 nanoparticles (TNPs) as the overlayer; the TNTs were intended to provide one-dimensional (1-D) electron transfer paths at the interface of the Ti foil and the TNPs. The Ti foil was subjected to anodization at a constant applied potential to obtain the TNTs. Scanning electron microscopic (SEM) images show a steady increase in the diameters of the TNTs with the increase of the anodization potential from 20 to 50 V. X-ray diffraction (XRD) patterns indicate anatase (1 0 1) crystal plane for all the TNTs. The DSSCs with the TNTs as the underlayer show higher short-circuit current density (jSC) and higher light-to-electricity conversion efficiency (η), compared to those of a DSSC without TNTs. An efficiency of 6.68% was achieved for the DSSC with TNTs as the underlayer, which is 20.4% higher than that obtained for a cell with only a film of TNPs. This efficiency is also one of the best for a back-illuminated DSSC with Ti foil as the substrate. Charge transfer resistances of the cells were investigated by electrochemical impedance spectroscopy (EIS). Laser-induced photo-potential transient and photo-current transient techniques were respectively used to calculate the electron lifetime and electron diffusion coefficient in Ti/TNTs/TNPs films.

► Flexible Ti/TiO2 photoanodes, with TiO2 nanotubes (TNTs) as the underlayer and TiO2 nanocrystals as the overlayer, were proposed for DSSCs.
► SEM images show steady increases in the diameters of TNTs with the anodization potential increasing from 20 to 50 V.
► The DSSC with a TNTs underlayer shows an efficiency of 6.68%, which is 20.4% higher than that without such layer.
► The enhanced performance of the DSSC with a TNTs underlayer is attributed to the improved electron lifetime and electron diffusivity.