Page 559 - Polymer-based Nanocomposites for Energy and Environmental Applications

512 Polymer-based Nanocomposites for Energy and Environmental Applications

Different from ZnO and TiO 2 , molybdenum trioxide (MoO 3 ) is a hole-transporting
material and commonly used for the construction of optoelectronic devices. In partic-
ular, MoO 3 owns several advantages such as low toxicity, high stability, and its ability
to facilitate hole injection. MoO 3 nanocrystals have been mixed with poly(3,
4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT/PSS) aqueous solution,
sonicated, and spincast into nanocomposite film with enhanced hole-transporting
properties [17,18].
Several cadmium (Cd)-containing semiconducting compounds have been
proposed to fabricate organic-inorganic hybrid composites. CdS is an electron-
transporting material that can serve as electron acceptor to replace a fullerene deriv-
ative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in conventional organic
photovoltaics (OPVs). The incorporation of CdS into electron donor polymers such
as MEH-PPV and P3HT exhibits high yields of charge photogeneration and improves
the PCE. CdS nanorods were mixed with MEH-PPV in pyridine under stirring and
spincoated into hybrid films [19]. In addition to nanorods, CdS nanoparticle-dispersed
polymer composites have been reported [20,21]. The precursor material
Cd(S 2 COEt) 2 (C 5 H 4 N) 2 containing the xanthate groups was blended with P3HT and
cast into thin films by spincoating. The as-spun films were subsequently annealed
at 150°C to decompose the xanthate species to generate CdS/P3HT nanocomposite
films. The usage of inorganic cadmium selenide (CdSe) nanocrystals in polymer-
based optoelectronics enables good charge transport and augments device perfor-
mance. CdSe nanocrystals were reported to codissolve with P3HT in a mixture of
4–12 vol% pyridine-chloroform solution [22]. Core-shell CdSe(ZnS) nanocrystals
were also mixed with MEH-PPV in toluene and cast into nanocomposite films by spin-
coating [23]. An alternative way is to separately dissolve polymers and CdSe in dif-
ferent solvents and then mix two solutions together under sonication. P3HT and CdSe
were dissolved independently in anhydrous chlorobenzene and chloroform, respec-
tively [24]. The two solutions were then mixed with a volume ratio of 1:9 to form
a blend solution and then spincast into thin films with uniform dispersion of CdSe
nanoparticles in P3HT. A special type of CdSe tetrapods has also been blended with
0
a low-bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b ]
dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] to form nanocomposite layers by spin-
coating from their trichlorobenzene solution [25]. Cadmium telluride (CdTe) is con-
sidered as a promising material due to its high-absorption coefficient and high-carrier
mobility. Surfactant-free CdTe nanoparticles and MEH-PPV were reported to dis-
solve in a mixed 1–8 vol% pyridine-chloroform solution and then spincast into thin
films [26].
There are still some special semiconducting materials to be mentioned as follows.
The absorption cutoff of lead selenide (PbSe) nanocrystals is size tunable and spans
from 1000 to 2500 nm, which is complementary to the light absorption of most poly-
mer materials in solar energy spectrum [27]. The solution mixture of PbSe nano-
crystals and P3HT was spincast into nanocomposite films that were used as
harvester for solar energy. Cobalt sulfide (CoS) offers a synergistic effect on catalytic

performance toward triiodide (I 3 ) reduction for dye-sensitized solar cells (DSSCs).
Besides, CoS owns an additional advantage for large-scale production as it is much