Design, Fabrication, and Modification of Cost-Effective Nanostructured TiO for Solar Energy Applications - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 31

Fig. 11 Schematic diagram
of electrospinning method.
(Reprinted with permission
from Ref. a [ 218 ]. Copyright
Institute of Physics
Publishing)
After the first report of electrospun TiO 2 nanofibers in 2003 [ 221 ], many studies
have been performed for applications in photovoltaic devices and photocatalysis
since the electrospun nanofibers can be fabricated with controllable size, density,
and orientation [ 222 , 223 ]. More importantly, electrospinning is simple, control-
lable, inexpensive, and scalable for industrial production [ 224 ]. For instance, Yang
et al. prepared a bi-layer TiO 2 nanofiber photoanode via combining both small and
large-diameter TiO 2 nanofibers in the nozzleless electrospinning by changing the
applied voltage, electrode separation distance, and electrospinning time. It is
expected that the smaller-diameter nanofiber layer with a high surface-to-volume
ratio can load enough dye molecules and directly transport electrons within the 1D
channels. While the larger-diameter nanofiber layer can serve as a light scattering
layer, further adsorbing more dye molecules, and even providing higher porosity to
facilitate electrolyte diffusion. With the bi-layer photoanode, the efficiency (g)of
DSSCs can be improved from 7.14 % for the single-layer to 8.40 % for the
bi-layer TiO 2 nanofiber photoanode [ 225 ]. As shown in Fig. 12 a, multi-scale
porous TiO 2 nanofibers were fabricated from HF etching of TiO 2 /SiO 2 composite
nanofibers, which were electrospun from a hybrid solution of dissolved SiO 2
colloidal solution, TTIP and PVP, followed by calcination. Such fiber-based
DSSCs showed an g of 8.5% (Fig. 12 b), which is greater than those of conven-
tional photoelectrodes made of TiO 2 nanoparticles (6.0 %) [ 226 ].
Other useful structures, including nanorods [ 227 ], rice-like shapes [ 228 ], and
hollow fibers [ 229 ], have been derived from electrospinning methods. TiO 2
nanorod-based photoelectrodes (Fig. 12 c) were prepared by sintering TiO 2 com-
posite nanofibers that were electrospun from a solution mixture of TiO 2 sol-gel and