15 Yet to Be Challenged: TiO 2 as the Photo-Anode Material …
297
to the back-direction, which enhanced the V oc , leading to a maximum efficiency of
0.906% after the H 2 O 2 treatment (Kang et al. 2007).
ZnO as a composite material with TiO 2 has been studied by synthesizing a coaxial
structure (Williams et al. 2012), as a photoanode material for an effective UV-visible
active DSC (Noor et al. 2018), as multilayers (Bhatti et al. 2019) and as a core-shell
nanostructure (Rajamanickam et al. 2019).
SnO 2 is another candidate for applications in DSCs. SnO 2 exhibits a band gap of
3.8 eV, larger than that of TiO 2 , generating much fewer oxidative holes under illumination, therefore improving the long-term stability of the DSSCs and minimizing
the degradation rate of the dye (Qian et al. 2009). Also, electron mobility in SnO 2
is much faster than in TiO 2 . However, SnO 2 has the disadvantages of having poor
dye loading capacity and fast charge recombination, when used in pure form within
DSCs (Gao et al. 2012). These shortcomings can be overcome by the use of a TiO 2
barrier, which has been studied by Huo et al. The overall performance of the DSC
was increased to 6.98%, compared to that of P25 and pure SnO 2 photoelectrodes,
due to the high light scattering effect, fast electron transport due to the 1D structure
and the enhanced dye loading capability (Huo et al. 2014).
Desai et al. has also studied similar hybrid materials using TiO 2 and SnO 2 (Desai
et al. 2013). Further research based on the TiO 2 –SnO 2 composite has been done using
TiO 2 compact layer with nanocrystalline SnO 2 (Yang et al. 2014), using a core-shell
structure (Knauf et al. 2015), by the synthesis of hybrid nanofibers (Wali et al. 2016)
and also by the sol-gel and coprecipitation method (Endarko and Adawiyah 2019).
TiO 2 has also being incorporated with the p-type semiconductor NiO, by Hsu
et al. They have used a flower like structure in order to enhance the light scattering,
trapping for efficient photon harvesting and offering a large surface area for dye
adsorption, thereby improved power conversion efficiency. The p-type component in
TiO 2 –NiO nanoparticles has significantly decreased the charge recombination, but
its photovoltaic efficiency remains below 4% (Hsu et al. 2015).
Maçaira et al. prepared a SiO 2 /TiO 2 composite photoelectrode to overcome the
high number of grain boundaries and morphological defects, that cause recombination reactions, of a usual TiO 2 photoelectrode, while keeping the surface area at an
optimum level. The high efficiency of 9.20% is due to the high surface area, and the
low recombination (Maçaira et al. 2017). A similar study has been done by Cardoso
et al. tuning anatase and rutile phase transition temperature (Cardoso et al. 2019).
More recently, studies have been conducted using gold, SiO 2 and TiO 2 in a core/shell
structure (Fadhilah et al. 2019; Li et al. 2019).
Furthermore, Fe 2 O 3 has also been studied considering the cocktail effect of the
two conduction bands, to prevent electron recombination (Im et al. 2011).
15.3.3 Metal Nitrides
Huang et al. have studied the composite gallium nitride (GaN) with TiO 2 as a photoelectrode material in order to enhance the power conversion. Here a maximum
297
to the back-direction, which enhanced the V oc , leading to a maximum efficiency of
0.906% after the H 2 O 2 treatment (Kang et al. 2007).
ZnO as a composite material with TiO 2 has been studied by synthesizing a coaxial
structure (Williams et al. 2012), as a photoanode material for an effective UV-visible
active DSC (Noor et al. 2018), as multilayers (Bhatti et al. 2019) and as a core-shell
nanostructure (Rajamanickam et al. 2019).
SnO 2 is another candidate for applications in DSCs. SnO 2 exhibits a band gap of
3.8 eV, larger than that of TiO 2 , generating much fewer oxidative holes under illumination, therefore improving the long-term stability of the DSSCs and minimizing
the degradation rate of the dye (Qian et al. 2009). Also, electron mobility in SnO 2
is much faster than in TiO 2 . However, SnO 2 has the disadvantages of having poor
dye loading capacity and fast charge recombination, when used in pure form within
DSCs (Gao et al. 2012). These shortcomings can be overcome by the use of a TiO 2
barrier, which has been studied by Huo et al. The overall performance of the DSC
was increased to 6.98%, compared to that of P25 and pure SnO 2 photoelectrodes,
due to the high light scattering effect, fast electron transport due to the 1D structure
and the enhanced dye loading capability (Huo et al. 2014).
Desai et al. has also studied similar hybrid materials using TiO 2 and SnO 2 (Desai
et al. 2013). Further research based on the TiO 2 –SnO 2 composite has been done using
TiO 2 compact layer with nanocrystalline SnO 2 (Yang et al. 2014), using a core-shell
structure (Knauf et al. 2015), by the synthesis of hybrid nanofibers (Wali et al. 2016)
and also by the sol-gel and coprecipitation method (Endarko and Adawiyah 2019).
TiO 2 has also being incorporated with the p-type semiconductor NiO, by Hsu
et al. They have used a flower like structure in order to enhance the light scattering,
trapping for efficient photon harvesting and offering a large surface area for dye
adsorption, thereby improved power conversion efficiency. The p-type component in
TiO 2 –NiO nanoparticles has significantly decreased the charge recombination, but
its photovoltaic efficiency remains below 4% (Hsu et al. 2015).
Maçaira et al. prepared a SiO 2 /TiO 2 composite photoelectrode to overcome the
high number of grain boundaries and morphological defects, that cause recombination reactions, of a usual TiO 2 photoelectrode, while keeping the surface area at an
optimum level. The high efficiency of 9.20% is due to the high surface area, and the
low recombination (Maçaira et al. 2017). A similar study has been done by Cardoso
et al. tuning anatase and rutile phase transition temperature (Cardoso et al. 2019).
More recently, studies have been conducted using gold, SiO 2 and TiO 2 in a core/shell
structure (Fadhilah et al. 2019; Li et al. 2019).
Furthermore, Fe 2 O 3 has also been studied considering the cocktail effect of the
two conduction bands, to prevent electron recombination (Im et al. 2011).
15.3.3 Metal Nitrides
Huang et al. have studied the composite gallium nitride (GaN) with TiO 2 as a photoelectrode material in order to enhance the power conversion. Here a maximum