122
silica nanocomposite-based gel electrolytes for quasi-solid-state dye-sensitized
DSSCs were made, where the silica was again used to prevent crystallization. An
efficiency of 7.15% was measured [134].
7.2 MOFs
Nanocrystalline Solar Cells.
MOFs have only found limited use thus far in DSSCs. Copper-based MOFs have
been employed as the sensitizer in two examples. In the first, HKUST-1 crystals
were doped with iodine to improve the charge transfer across the surfaces of the
DSSC, resulting in a low, but measurable efficiency of 0.26% [135]. Also, a similar
solar cell was constructed with HKUST-1, whereby carbon nanotubes were incorporated with the titania layer for enhanced conversion efficiency, albeit a similarly
low value. With MOFs only, the efficiency was measured at 0.20%, whereas incorporation of nanotubes increased this value to 0.48% [136]. In another example, a
pillared Zn-porphyrin MOF was utilized to study the role of the MOF in a
DSSC. Evidence was shown that clarified the MOF structure is indeed the active
sensitizer in these DSSCs, as care was taken to remove any precursors that may
remain in the MOF pores post-synthesis [137]. ZIF-8 has been grown on the surface
of titania nanocrystals as an intermediate layer before coating with a dye. The
resulting increased open-circuit voltage was ascribed to the inhibition of interfacial
charge recombination by ZIF-8 [108]. Also, MOFs have again been used as decomposition templates to derive metal oxide anode materials with large surface areas for
more surface contact with the sensitizer and electrolyte [138].
Bella et al. reported the first MOF-based polymer nanocomposite for electrolytes
in DSSCs [139]. Here, a polymer composite was formed, containing a Mg-based
MOF (Mg 3 (benzenetricarboxylate) 2 ) mixed with PEG(dicarboxylic acid):
PEG(maleic acid), which was activated by soaking in ionic liquids and utilized as
an electrolyte for quasi-solid solar cells. An efficiency of 4.8% was reported, along
with outstanding long-term durability. The MOFs were shown to interact with the
TiO 2 surface, effectively shielding trap states (electrons get stuck, rather than transferred) of the photoelectrode, resulting in higher photovoltage.
8 Conclusions and Outlook
The scientific community is getting ever closer to developing safer, sustainable,
high-performing compact devices using new, designer materials. All-organic polymers have provided optimism in the construction of solid state (or quasi-solid-state)
devices, having some of the essential features that are in-demand for modern electrochemical solutions. Yet, the limitations were too great to achieve the robustness
that is needed for many applications. Polymer nanocomposites have allowed for the
C. A. Bauer
silica nanocomposite-based gel electrolytes for quasi-solid-state dye-sensitized
DSSCs were made, where the silica was again used to prevent crystallization. An
efficiency of 7.15% was measured [134].
7.2 MOFs
Nanocrystalline Solar Cells.
MOFs have only found limited use thus far in DSSCs. Copper-based MOFs have
been employed as the sensitizer in two examples. In the first, HKUST-1 crystals
were doped with iodine to improve the charge transfer across the surfaces of the
DSSC, resulting in a low, but measurable efficiency of 0.26% [135]. Also, a similar
solar cell was constructed with HKUST-1, whereby carbon nanotubes were incorporated with the titania layer for enhanced conversion efficiency, albeit a similarly
low value. With MOFs only, the efficiency was measured at 0.20%, whereas incorporation of nanotubes increased this value to 0.48% [136]. In another example, a
pillared Zn-porphyrin MOF was utilized to study the role of the MOF in a
DSSC. Evidence was shown that clarified the MOF structure is indeed the active
sensitizer in these DSSCs, as care was taken to remove any precursors that may
remain in the MOF pores post-synthesis [137]. ZIF-8 has been grown on the surface
of titania nanocrystals as an intermediate layer before coating with a dye. The
resulting increased open-circuit voltage was ascribed to the inhibition of interfacial
charge recombination by ZIF-8 [108]. Also, MOFs have again been used as decomposition templates to derive metal oxide anode materials with large surface areas for
more surface contact with the sensitizer and electrolyte [138].
Bella et al. reported the first MOF-based polymer nanocomposite for electrolytes
in DSSCs [139]. Here, a polymer composite was formed, containing a Mg-based
MOF (Mg 3 (benzenetricarboxylate) 2 ) mixed with PEG(dicarboxylic acid):
PEG(maleic acid), which was activated by soaking in ionic liquids and utilized as
an electrolyte for quasi-solid solar cells. An efficiency of 4.8% was reported, along
with outstanding long-term durability. The MOFs were shown to interact with the
TiO 2 surface, effectively shielding trap states (electrons get stuck, rather than transferred) of the photoelectrode, resulting in higher photovoltage.
8 Conclusions and Outlook
The scientific community is getting ever closer to developing safer, sustainable,
high-performing compact devices using new, designer materials. All-organic polymers have provided optimism in the construction of solid state (or quasi-solid-state)
devices, having some of the essential features that are in-demand for modern electrochemical solutions. Yet, the limitations were too great to achieve the robustness
that is needed for many applications. Polymer nanocomposites have allowed for the
C. A. Bauer