Page 189 - Multifunctional Photocatalytic Materials for Energy

Metal-based semiconductor nanomaterials for thin-film solar cells 175

method to grow oriented, single-crystalline rutile TiO 2 NR films on transparent con-
ductive fluorine-doped tin oxide (FTO) substrates [82]. The small lattice mismatch
between the FTO substrate and the rutile TiO 2 played a key role in driving the nucle-
ation and growth of the rutile TiO 2 NRs on the FTO substrates. However, only ~3%
PCE was obtained by using such rutile TiO 2 NRs as photoanodes. The low PCE can
be attributed to the limited length (only 3–5 μm long) of such NRs, which resulted in
low surface areas. Further improvements in the cell efficiency should increase the sur-
face area. Several strategies have been developed to address this problem. As shown
in Fig. 8.17, Lv and colleagues [83] first fabricated ultra-long, porous rutile TiO 2 NR
arrays (~30 μm) onto FTO glass substrates to enhance the performance of DSSCs.
Such TiO 2 NR arrays were prepared by a repeated hydrothermal method and further
etched into porous NR arrays by HCl under a high temperature. The porous TiO 2 NR
arrays showed much higher dye loading compared to the original TiO 2 NRs, yielding
2
an improved PCE of 7.91% with J sc of 20.49 mA/cm .
To further enhance the performance of DSSCs, hybrid electrodes including zero-
dimensional (0D), 1D, and 3D nanostructured materials were incorporated into various

Fig. 8.17 Fabrication of ultra-long rutile TiO 2 NWs on FTO glass: (A) schematic
representation of the processes for fabricating 1D porous rutile TiO 2 NWs; (B) SEM images of
the morphological development of the 1D rutile TiO 2 NWs before and after etching treatment;
(C) J-V characteristics of DSSCs based on rutile TiO 2 NWs with different etching duration and
P25 TiO 2 NP film.
Reprinted with permission from M. Lv et al., Optimized porous rutile TiO 2 nanorod arrays
for enhancing the efficiency of dye-sensitized solar cells. Energy Environ. Sci. 6 (2013)
1615–1622.