121
films mechanical strength and heat stability. Such nanocomposites are just one type
of solid electrolyte under development. Perovskites and copper-based compounds,
such as CuI, which are hole-transporting inorganics, are also showing promise.
However, contact between the electrolyte and sensitizer is more difficult to achieve
in the solid state. A review in 2016 discusses the need for a solid-state electrolyte,
which is key to increasing the stability and lifetime of DSSCs [127].
7.1 Polymer Nanocomposites
Nanostructured surfaces are useful in order to maintain significant contact between
the electrolyte and electrodes, and to prevent electron–hole recombination. Many
examples use the archetypal ion conducting polymer, PEO, and embedded ceramic
composites to prevent crystallization of the matrix. For example, composites of
PEO and titania nanocrystals resulted in an energy conversion efficiency of 4.2% at
65.6 mW cm
−2
, one of the highest values reported at the time (2002). This relatively
high efficiency was attributed to the amorphous nature of the polymer and the
increased contact of the polymer electrolyte with the dye sensitizer [128]. In 2004,
a modification was made to enhance interfacial contact. The polymer chosen was
poly(ethylene oxide dimethyl ether), or PEODME, which penetrates well into the
titania/dye layer. Here, silica nanoparticles were used to prevent crystallization of
the polymer, and the overall system, a composite consisting of PEODME/MI
(M = K
+
, imidazolium
+
) / I 2 / fumed silica nanoparticles, yielded favorable mechanical strength and a solar conversion efficiency of 4.5% at 100 mW cm
−2
[129].
Researchers also demonstrated the use of a hybrid PEO/PVDF/TiO 2 nanoparticle
system as solid-state electrolytes in DSSCs [130]. The iodide/triiodide redox couple
was incorporated into poly(ethylene oxide)/polyaniline (PEO/PANI) solid-state
electrolytes, aiming at expanding the catalytic event of I 3
−
reduction from the electrolyte/counter electrode interface to both the interface and electrolyte system and
shortening the charge diffusion path length. PANi is also responsible for dye regeneration and hole transfer to the counter electrode. The constructed DSSC with the
iodine redox couple incorporated into PEO/1.0 wt% PANi electrolyte yields a maximum efficiency of 6.1% in comparison with 0.8% obtained from a PANi-free
electrolyte- based solar cell and 0.1% for a PANi-based solar cell [131].
This interest in polymer nanocomposites continues today. Armel et al. demonstrated that molecular plastic crystal (succinonitrile)-based solid-state electrolytes
can perform very well in solid-state DSSCs, when combined with a porphyrin sensitizer and inclusion of nanoparticulate SiO 2 [132]. This produced the highest device
efficiency of 5.3% at moderate light intensity. In 2018, a few more publications have
demonstrated the application of polymer nanocomposites for DSSCs. These include
a polymer fibrous membrane electrolyte, whereby an electrospun nanocomposite
polymer (PVDF-HFP + 6 wt% TiO 2 nanofibers fillers) with Li
+
exhibited a conductivity of 1.87 × 10
−2
S cm
−1
at room temperature. However, the function within solar
cells was only suggested, not measured directly [133]. Additionally, PANI-grafted
Polymer Nanocomposites for Ion Transport
films mechanical strength and heat stability. Such nanocomposites are just one type
of solid electrolyte under development. Perovskites and copper-based compounds,
such as CuI, which are hole-transporting inorganics, are also showing promise.
However, contact between the electrolyte and sensitizer is more difficult to achieve
in the solid state. A review in 2016 discusses the need for a solid-state electrolyte,
which is key to increasing the stability and lifetime of DSSCs [127].
7.1 Polymer Nanocomposites
Nanostructured surfaces are useful in order to maintain significant contact between
the electrolyte and electrodes, and to prevent electron–hole recombination. Many
examples use the archetypal ion conducting polymer, PEO, and embedded ceramic
composites to prevent crystallization of the matrix. For example, composites of
PEO and titania nanocrystals resulted in an energy conversion efficiency of 4.2% at
65.6 mW cm
−2
, one of the highest values reported at the time (2002). This relatively
high efficiency was attributed to the amorphous nature of the polymer and the
increased contact of the polymer electrolyte with the dye sensitizer [128]. In 2004,
a modification was made to enhance interfacial contact. The polymer chosen was
poly(ethylene oxide dimethyl ether), or PEODME, which penetrates well into the
titania/dye layer. Here, silica nanoparticles were used to prevent crystallization of
the polymer, and the overall system, a composite consisting of PEODME/MI
(M = K
+
, imidazolium
+
) / I 2 / fumed silica nanoparticles, yielded favorable mechanical strength and a solar conversion efficiency of 4.5% at 100 mW cm
−2
[129].
Researchers also demonstrated the use of a hybrid PEO/PVDF/TiO 2 nanoparticle
system as solid-state electrolytes in DSSCs [130]. The iodide/triiodide redox couple
was incorporated into poly(ethylene oxide)/polyaniline (PEO/PANI) solid-state
electrolytes, aiming at expanding the catalytic event of I 3
−
reduction from the electrolyte/counter electrode interface to both the interface and electrolyte system and
shortening the charge diffusion path length. PANi is also responsible for dye regeneration and hole transfer to the counter electrode. The constructed DSSC with the
iodine redox couple incorporated into PEO/1.0 wt% PANi electrolyte yields a maximum efficiency of 6.1% in comparison with 0.8% obtained from a PANi-free
electrolyte- based solar cell and 0.1% for a PANi-based solar cell [131].
This interest in polymer nanocomposites continues today. Armel et al. demonstrated that molecular plastic crystal (succinonitrile)-based solid-state electrolytes
can perform very well in solid-state DSSCs, when combined with a porphyrin sensitizer and inclusion of nanoparticulate SiO 2 [132]. This produced the highest device
efficiency of 5.3% at moderate light intensity. In 2018, a few more publications have
demonstrated the application of polymer nanocomposites for DSSCs. These include
a polymer fibrous membrane electrolyte, whereby an electrospun nanocomposite
polymer (PVDF-HFP + 6 wt% TiO 2 nanofibers fillers) with Li
+
exhibited a conductivity of 1.87 × 10
−2
S cm
−1
at room temperature. However, the function within solar
cells was only suggested, not measured directly [133]. Additionally, PANI-grafted
Polymer Nanocomposites for Ion Transport