Page 429 - Polymer-based Nanocomposites for Energy and Environmental Applications

386 Polymer-based Nanocomposites for Energy and Environmental Applications

In another study, Stergiopoulos et al. [99] investigated the use of TiO 2 nanotubes
(NTs) as nanofillers for PEO-based polymer electrolyte and obtained 18% higher
PCE. This efficiency enhancement was mainly due to the increment in V oc and FF that
are related to the suppressed recombination of the electrons with triiodide ions and to
the decrease of the interfacial resistance between the Pt electrode and the electrolyte,
respectively. Shaheer Akhtar [107] et al. used different amount of TiO 2 NTs in PEG-
LiI-I 2 -based electrolyte system and found that 10 wt% Ti-NTs as optimal amount for
this combination. They obtained 2.95 and 4.43% PCEs from the unfilled and 10 wt%
from the Ti-NT-filled polymer electrolyte-based DSCs, respectively. Additionally,
the presence of Ti-NTs also improved the cell stability up to 30 days.
Apart from the ionic conductivity, another issue related with polymer electrolyte in
DSC is obtaining high level of interfacial contact between electrolyte and dye-
adsorbed photoanode. Due to the viscous nature of the polymer material, penetration
of polymer molecules into the mesopores of TiO 2 layer is generally difficult that
results in high charge-transfer resistance and high recombination rates. Kim et al.
[94] used composite polymer electrolytes consisting of low-molecular-weight
1
poly(ethylene oxide dimethyl ether) (PEODME, 500 g mol ), MI (M K 1+ ,
+
imidazolium )-I 2 as mediator, and fumed silica to achieve high interfacial contact
and ionic conductivity and to get 3D network and mechanical strength for rigid
DSC. In their work, they fixed the silica concentration to 9 wt% of the total polymer
electrolyte and only changed the type of metal salts. They obtained 4.5% as highest
2
PCE (100 mW cm ) from PEODME/MPII/I 2 /fumed silica-based DSC.
Another way to improve the performance of polymer electrolytes is using polymer
blends together. Yang et al. [100] studied the modification of PEO-poly(vinylidene
fluoride) (PVDF) polymer-blend electrolytes with water and ethanol in order to
improve its stability, conductivity, and thermal property. The addition of hydroxyl-
rich additives enabled cross-linked structure that resulted in increased free ion concen-
tration and number of ion transport channels in the electrolyte. As a result, they
obtained higher J sc and PCE records from the modified electrolyte-based DSC. The
efficiency values reported were 2.63%, 3.22%, and 3.9% for unmodified and
3.1 wt% for water- and ethanol-modified cells. In another report of Yang et al.
[108], they added TiO 2 particles into this water-ethanol-modified PEO-PVDF
1
polymer-blend electrolyte and obtained high conductivity (10 3 Scm ) and solar
cell performance (5.8% PCE).
Zhou et al. [101] investigated the influence of the addition of modified SiO 2 in
poly(ether urethane)/poly(ethylene oxide) (PEO/PEUR) polymer electrolyte on the
performance of solid-state DSC. Modification of SiO 2 was done by combining a poly-
mer chain of poly(oxyethylene-co-oxypropylene) monomethyl ether on SiO 2 via a
silane coupling reagent. The results showed that the modified SiO 2 was more uni-
formly dispersed in the PEO/PEUR electrolyte than unmodified ones (Fig. 13.17).
Additionally, surface modification of SiO 2 with polar ethylene oxide/propylene oxide
(EO/PO) polymer chain increased the solvency ability of lithium salts and prevented
possible microphase separation and aggregation of nanofillers in the polymer electro-
lyte. The performance of the DSC was also increased with the addition of modified
SiO 2 up to 10 wt%, exhibiting maximal PCE of 4.86%.