Electrochemical Assessment
of the Band-Edge Positioning
in Shape-Tailored TiO<sub>2</sub>‑Nanorod-Based Photoelectrodes
for Dye Solar Cells
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Abstract
Three families of linear shaped TiO<sub>2</sub> anatase
nanocrystals
with variable aspect ratio (4, 8, 16) and two sets of branched TiO<sub>2</sub> 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 branched-nanorod 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