Quantum Dot-Sensitized Solar Cells - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 101

Fig. 8 a Schematic illustration of electrospinning set up. The TiO 2 fibrous channels were
directly deposited onto collector (FTO substrates); SEM images of (b) as prepared TiO 2 fibers
and (c) calcinated fibers (An et al. [ 186 ] Reprinted permission from Elsevier)
(D n & 4.6 9 10 -4 cm 2 s -1 ), which is nearly 3 times higher than that of the par-
ticulate electrodes (D n & 1.5 9 10 -4 cm 2 s -1 ) under identical photoexcitation
density. Furthermore, they observed less charge transport resistance and transit time
in the fibrous electrode over the nanoparticle electrode. The high electron diffusive
transport characteristics of fibrous electrodes are fostering as effective photoanodes
for achieving feasible charge collection at QDSCs compared to conventional
nanoparticle electrodes. In addition, fibers have less grain boundary density, which
can overcome the trapping-detrapping loss unlike conventional nanoparticulate
electrodes and beneficial advantages in attenuating the scattering loss [ 98 ]. On the
other hand, the inclusion of nanofibers in conventional nanoparticle electrodes
(composite) substantially improves the light harvesting through promoting the
light-scattering pattern (analogous to antenna lobes) [ 99 ]. The first QDs
(CdS:CdSe)-sensitized solar cells using direct assembled 3-D fibrous electrodes has
been demonstrated by Sudhagar et al. [ 47 ] Followed that significant work has been
developed on fibrous QDSSCs. The schematic structure of electrospinning (ES) set
up is shown in Fig. 8 .
The detailed working principles of ES technique have been explained elsewhere
[ 100 - 102 ]. Briefly a continuous TiO 2 fibrous membrane is directly assembled on a
FTO substrate using the electrospinning technique (Fig. 8 ). The typical solution is
used for spinning: 0.53 g of polyvinyl acetate (PVAc) dissolved in 4.45 g of
dimethyl formamide (DMF). After completely dissolving the PVAc in DMF, 1 g
of titanium(IV) propoxide and 0.5 g of acetic acid were mixed well for 30 minutes.
The resultant solution for spinning is loaded into a syringe driver and connected to
a high-voltage power supply. An electrical potential of 15 kV was applied over a
collection distance of 12 cm. The electrospun fibrous membranes were collected