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(3-5 mm) was shorter than the backbone nanowire (5-9 mm). As the multiple
growth steps can grow backbone ZnO nanowires 40-50 mm long, longer
branches from the backbone nanowire with a weeping willow tree shape
could be grown by repeating the hydrothermal growth steps without polymer
layer removal and seed NP deposition. A weeping willow nanotree structure
with a very long first generation branch can grow up to 12-15 mm. While the
shorter nanotrees grown once show stiff spiny branches, nanotrees grown
multiple times show a weeping willow tree shape with long flaccid branches
that hang down to the substrate. This is because the stiffness drops as the
length of the nanowire increases. The short circuit current density (J
SC
) and
overall light conversion eciency (Z) increase when the branches are
introduced and also as the branches are getting longer by an effective surface
area increase. J
SC
and Z could be significantly increased, just by adding
d
n
3
r
4
n
g
|
9
.
Figure 4.5 Branched TiO
2
nanostructures. (a) Schematic procedure for the format-
ion of the forest-like hierarchical photoanodes and a cartoon of the
presumed preferential electron pathway in the hierarchical photoa-
nodes. (b) J-V characteristics of dye-sensitized solar cells assembled
with different TiO
2
photoanodes.
16
(c) Scanning electron micrographs of
PLD TiO
2
films: (d) J-V characteristics recorded at different light illumin-
ation for PLD films prepared at background oxygen pressures of 20 Pa
with 2 mm thickness.
17
Reproduced with permission from ref. 16. Copyright 2013, American
Chemical Society. Reproduced with permission from ref. 17. Copyright
2013, the Royal Society of Chemistry.
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