Page 415 - Polymer-based Nanocomposites for Energy and Environmental Applications

372 Polymer-based Nanocomposites for Energy and Environmental Applications

Fig. 13.7 Dependence of J sc and V oc of 7 0.8
DSCs on reaction time of UV
V oc
irradiation treatment of TiO 2 6 J
nanocrystalline layers on ITO-PET sc 0.75
electrode.
Reproduced with permission from 5
Murakami TN, Kijitori Y, Kawashima J sc (mA cm −2 ) 0.7 V oc (V)
N, Miyasaka T. Low temperature 4
preparation of mesoporous TiO2 films
for efficient dye-sensitized 0.65
photoelectrode by chemical vapor 3
deposition combined with UV light
irradiation. J Photochem Photobiol
2 0.6
A Chem 2004;164:187–91. 0 5 10 15 20 25
Treatment time (min)

1
10 V cm . After EPD process, they dried the samples at 140°C and subsequently
compressed them under the pressure of 50 MPa. The results showed that, despite
the increase of the film thickness with increasing deposition time, more and wider
cracks were formed in the structure. However, after mechanical compression, all
cracks were eliminated. By studying the effect of deposition time and composition
of EPD bath, they obtained 5.23% as maximum PCE (by deposition of P25 for
80 s and P25/ST41 mixture for 160 s). Nonetheless, they did not give any information
about the flexibility-dependent performance and stability of DSC.
A further improvement of the low-temperature DSC can be obtained by UV irra-
diation or UV-O 3 treatment of the TiO 2 film. Decomposition of organic contaminants
adsorbed on the TiO 2 surfaces by UV light directly or via photocatalytic reactions of
TiO 2 is thought to be the mechanism for this improvement. Hilleringmann et al. [43]
applied UV irradiation on TiO 2 film in order to activate the TiO 2 NP surfaces by
removing organic residues from the structure. The increase of the number of activated
particles provides higher amount of dye attached to the surface and hence an increase
of J sc and PCE. Yamaguchi et al. [40] applied UV-O 3 treatment on TiO 2 -based flexi-
ble photoanode and obtained a slight increment in the efficiency from 7.1% to 7.4%
for a flexible DSC. Murakami et al. [46] also studied UV irradiation on low-
temperature TiO 2 photoanode and obtained slight improvements of both V oc and
J sc (Fig. 13.7).

13.2.2.3 Counter electrodes
The counter electrode (CE) is one of the most important components in DSCs. The
main function of the CE is to efficiently transport the charge from the external circuit
to the electrolyte by reduction of iodide/triiodide redox couples in liquid-state DSCs
or the collection of the holes from the hole-transport material in solid-state DSCs
[47,48]. Low charge-transport resistance, high catalytic activity, high surface area
with porous nature, optimal thickness, and good adhesion with TCO substrate are
some of the highly needed properties in order to obtain fast reduction of the oxidized