Page 426 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer nanocomposites for dye-sensitized solar cells 383

Fig. 13.16 (A) Nyquist plots for the CEs (f-MWCNTs, PPy, PPy/f-MWCNT, and Pt) and
(B) J-V curves of DSCs with f-MWCNTs, PPy, PPy/f-MWCNT, Pt on FTO, and PEN substrates
as CEs. The inset shows photos of Pt (left) and Ppy/f-MWCNT (right) films on FTO substrates.
Reproduced with permission from Peng S, Wu Y, Zhu P, Thavasi V, Mhaisalkar SG,
Ramakrishna S. Facile fabrication of polypyrrole/functionalized multiwalled carbon nanotubes
composite as counter electrodes in low-cost dye-sensitized solar cells. J Photochem Photobiol
A Chem 2011;223:97–102.

to its high surface area, superior conductivity, and low-cost fabrication. However,
carbon-based materials suffer from being insoluble in many solvents. Combining
carbon materials with PEDOT:PSS or PPy into composite structure eliminates the
solubility problem and produces highly porous film structure depending on the used
amount of carbon materials [81,85,86]. For instance, Peng et al. [85] produced
PPy-functionalized multiwall carbon nanotube (f-MWCNT) nanocomposite films
on FTO-glass and ITO-PEN substrates by drop-casting method as CE for DSC. Bare
PPy and bare f-MWCNT-based CE showed higher R ct (at high frequency, Fig. 13.16)
for reducing triiodide ions and higher diffusion impedance (Z w ) (at low frequency,

Fig. 13.16) of the I 3 /I redox couple in the electrolyte. PPy/f-MWCNT composite
structure allowed reduction of both R ct and Z w and gave catalytic performance com-
parable with that of Pt. This effect was attributed to the higher electric conductivity
and superior catalytic activity of PPy/f-MWCNTs electrode obtained as a result of the
high surface area and fast electron-transport channels provided by PPy nanoparticles
and f-MWCNTs, respectively. Performance values of DSCs using these CEs were
found to be proportional to the catalytic activity results in which the usage of compos-
ite structured CE increased the PCE. However, Pt-CE-based DSC still exhibited
higher PCE, Jsc, and FF. This was attributed to the thicker and high photoabsorbing
nature of composite CEs. The ticker film increased the series resistance, and CNT
reduced the reflection of the unabsorbed portion of incident solar light toward the
TiO 2 photoanode.
Additionally, conductive polymer-carbon black composite structure can also give
the possibility to eliminate TCO layer. As mentioned in Section 13.2.2.1, ITO-coated