Page 407 - Polymer-based Nanocomposites for Energy and Environmental Applications

364 Polymer-based Nanocomposites for Energy and Environmental Applications

redox shuttle (route 8) and the nonradiative exciton recombination before charge
injection (route 7) are the other two loss reactions.
In order to reduce the rate of these loss reactions and to obtain highly efficient
DSCs, consistency of electronic energy levels of each component/material is very
important. For effective exciton splitting and injection, the conduction band energy
level of MOS has to be lower than the energy level of the lowest unoccupied molecular
orbital of dye molecules. Furthermore, the increase of energy differences between the
fermi levels of electrons in MOS and the redox potential of electrolyte results higher
open-circuit voltage (V oc ), which is an important parameter for cell performance cal-
culation [10]. The back reaction of electrons can be eliminated by applying additional
thin compact layer between the TCO substrate and the mesoporous MOS layer [11].

13.2.2 Polymeric structures in DSC

In order to improve the efficiency and reduce the cost of DSC, there is a tendency to
replace some of the components with polymers. Although 13% PCEs have already
been achieved for standard rigid and liquid electrolyte-based DSCs [12,13], features
like rigidity, high weight, frangibility of the glass electrode, leakage, and volatility
problems of liquid electrolytes are main drawbacks for some DSCs, especially when
used in portable electronics [14]. Additionally, according to the recent cost and life-
cycle analysis of DSCs, TCO-coated glass accounts for more than 60% of the cost and
55% of global warming effect [15,16].
Polymeric structures can be used as part of several components in DSC, for exam-
ple, flexible substrates, polymer electrolytes, and catalyst materials in order to
improve the device’s cost/performance ratio. Polyethylene terephthalate (PET)- or
polyethylene naphthalate (PEN)-based electrodes can substitute glass electrodes,
improving the flexibility and the impact resistance of a DSC. Polymer electrolytes
can solve the leakage and volatility problems of the liquid electrolytes. Conductive
polymers could also be used as catalyst layer instead of highly expensive platinum.
Additionally, employing plastic materials in DSC allows the production of
flexible DSC.
Usage of polymeric structures in DSCs also enables to produce flexible solar cells
which have received huge attention and fuond wide application areas (from cellular
phones, ID cards, and watches to wearable textiles) in solar market because of their
lightweight and cost-effective (due to the easy handling, installation, shipping, and
being suitable for roll-to-roll (R2R) manufacturing) [17,18]. In this regard, here,
we review polymeric structures used in DSC in terms of materials, deposition
methods, and solar cell performance.

13.2.2.1 Substrates

For flexible DSCs, there are two types of flexible substrates: metal foils like titanium
or stainless steel foils and TCO-coated plastics like ITO-coated PET or PEN.
Depending on the flexible substrates used, three sandwich-type configurations can
be formed: (1) PE on metal and CE on plastic, (2) PE on plastic and CE on metal,