Page 427 - Polymer-based Nanocomposites for Energy and Environmental Applications

384 Polymer-based Nanocomposites for Energy and Environmental Applications

PET or PEN substrates are widely used in flexible DSCs. However, due to the inor-
ganic and brittle nature of ITO layer, it tends to deform and to increase the sheet resis-
tance when bent. Additionally, the production of TCO layers onto glass or plastic
substrates requires high-cost vacuum processes; thus, the development of new
TCO-free conductive substrates is needed to reduce the cost of the solar cells. Lin
et al. [49] reported a study on flexible, TCO-free CE fabrication. In their work, they
used plasma-etched carbon nanotube/polypropylene (ECP) composite plate as con-
ductive substrate and PEDOT film on this substrate to further improve the
electrocatalytic activity of the layer. The resultant PEDOT-ECP CE displayed excel-
lent electric conductivity, electrocatalytic activity, and flexibility. They observed
6.82% PCE from DSC with PEDOT-ECP-based CE that was only 5.5% less PCE
than obtained Pt-CE-based DSC (7.2%).
Sun et al. [90] produced flexible polyaniline/carbon composite CE by in situ chem-
ical polymerization of PANI onto flexible graphite (FG) layer, at room temperature.
They also investigated the effects of oxidation state, doping acids, and thickness of
PANI film on the performance of CE and DSC. They reported that 0.3 M initial mono-
mer concentration and 60 min reaction time are optimal conditions for obtaining
330 nm-thick PANI film CEs and did not observe any differences between the doping
with sulfuric acid and perchloric acid. The obtained PCE from PANI/FG composite
CE-based DSC was 7.36%, which was very close to the one obtained from Pt-CE-
based DSC (7.45%).
Chen et al. [91] developed flexible CE with very low charge-transfer and series
resistance by electrochemical deposition of polyaniline nanofibers on graphitized
polyimide (GPI) carbon film. PANI NFs and GPI carbon provided high catalytic
activity and high electric conductivity, respectively. They obtained 6.85% PCE from
the electropolymerized PANI (by 10 cycles of CV scanning) on GPI-CE based
DSC. The obtained result was higher than bare GPI (2.49%), PANI-FTO (6.31%),
or Pt-FTO (6.44%) CE-based DSCs.

13.2.2.4 Electrolytes
Electrolyte materials in DSCs are responsible for the inner charge carrier transporta-
tion between CE and the dye and for the continuous regeneration of dye molecules.
Similarly to the other DSC components, the electrochemical, optical, and physical
properties of the electrolyte directly affect the performance and the long-term stability
of DSCs. Additionally, physical properties of each component limit the process and
cell design parameters. Leakage and volatilization of organic solvents from the liquid
electrolyte solution require perfect sealing that limits the shape and stability of
the cells. Besides, problems like electrolyte-related corrosion of CEs or charge recom-
bination between semiconductor-liquid electrolyte interfaces move the focus
toward research on how to substitute liquid electrolytes by solid or gel electrolytes.
Polymer electrolytes, polymer gel electrolytes (PGEs), and organic/inorganic hole
conductors are some of the suggested alternative solutions for these problems in
DSC applications [20,92].