Electrochemical Assessment of the Band-Edge Positioning in Shape-Tailored TiO2-Nanorod-Based Photoelectrodes for Dye Solar Cells

Three families of linear shaped TiO2 anatase nanocrystals with variable aspect ratio (4, 8, 16) and two sets of branched TiO2 anatase nanocrystals (in the form of open-framework sheaf-like nanorods and compact braid-like nanorod bundles, respectively) were employed to fabricate high-quality mesoporous photoelectrodes and then implemented into dye-sensitized solar cells to elucidate the intrinsic correlation holding between the photovoltaic performances and the structure of the nanocrystal building blocks. To this aim, the chemical capacitance and the charge-transfer resistance of the photoelectrodes were extrapolated from electrochemical impedance spectroscopy measurements and used to draw a quantitative energy diagram of the dye-sensitized solar cells realized, on the basis of which their photovoltaic performances have been discussed. It has thus been revealed that photoanodes made from braid-like branchednanorod bundles exhibited the most favorable conditions to minimize recombination at the interface with the electrolyte due to their deep distribution of trap states, whereas linear-shaped nanorods with higher aspect-ratios result in more remarkable downshift of the conduction band edge.