17 Conducting Polymers as Cost Effective Counter Electrode …
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due to favourable characteristics such as low charge transfer resistance, promising
electrical conductivity, high surface area and corrosion resistance. The applicability
of Pt composite materials as CE in DSCs has also been studied (Xu et al. 2008; Yen
et al. 2012). Although platinum based CEs yields high photovoltaic performances,
platinum is an expensive noble metal and its usage in DSCs makes it one of the most
expensive components in a DSC. In addition to its expensiveness, Pt is corrosive when
used with electrolytes consisting of the redox mediator I
−
3 /I
− . It has been discovered
that Pt decomposes into PtI 4 in the presence of redox mediator I
−
3 /I
− which would
result in an adverse impact on the long term stability of the CE (Xiao et al. 2014).
The high cost and corrosion susceptibility has led to the exploration of substitute materials in place of Pt as a CE material. Hence carbon based material such as
graphene (Xu et al. 2014a, b), conducting polymer-graphene nanocomposites (Huang
et al. 2011), metal organic frameworks (MOFs) (Sun et al. 2016), conducting polymers and polymer hybrid composites (Rahman et al. 2016) have been investigated as
alternative CE materials and they have shown favourable photovoltaic performances.
Carbon is used as a promising counter electrode material due to favourable properties such as high conductivity, appreciable catalytic activity towards many redox
mediators, corrosion resistivity and cost effectiveness. The use of carbon based materials such as carbon black, graphene, mesoporous carbon, carbon nanotubes and
graphene based composite materials; as CE material has been explored. The use of
carbon black as a CE material was investigated and it yielded an efficiency around 9%
(Murakami et al. 2006). The highest efficiency achieved with the use of a graphene
CE was reported by Kakiage et al., in which an efficiency of 14.7% was yielded with
the use of a graphene/gold CE (Kakiage et al. 2015).
The applicability of MOFs as CE materials has been explored. The use of CoS 2
embedded within carbon nanocages synthesized using ZIF-67 template achieved an
efficiency of 8.2% (Cui et al. 2016). An outstanding efficiency of 8.69% was yielded
by the use of CE material ZnSe embedded N-doped carbon cubes synthesized using
MOFs with Zn nodes and benzimidazole linkers (Jiang et al. 2018).
17.2 Conducting Polymers as CE Material
Conducting polymers are organic polymers that possess an orbital system that assures
the mobility of charge carriers. These polymers show extensive conjugation with
overlapping π orbitals along the polymer backbone of sp
2 hybridized carbons. As
a result of the delocalization of the π electrons these polymers reveal appreciable
conductivity that ranges from 10
−8 to 10
5 S/cm (Rahman et al. 2016). Conducting
polymers are considered as favourable candidates for CE materials in DSCs due to
characteristics such as efficient catalytic activity, promising conductivity and superior
stability. Moreover the usage of conducting polymers is further favoured due to high
surface area associated with the porous nature of the material thus enhancing catalytic
activity and their facile cost effective synthesis. Various conducting polymers such
as polypyrrole, polyaniline, polythiophene, poly(3,4-ethylenedioxythiphene) and
351
due to favourable characteristics such as low charge transfer resistance, promising
electrical conductivity, high surface area and corrosion resistance. The applicability
of Pt composite materials as CE in DSCs has also been studied (Xu et al. 2008; Yen
et al. 2012). Although platinum based CEs yields high photovoltaic performances,
platinum is an expensive noble metal and its usage in DSCs makes it one of the most
expensive components in a DSC. In addition to its expensiveness, Pt is corrosive when
used with electrolytes consisting of the redox mediator I
−
3 /I
− . It has been discovered
that Pt decomposes into PtI 4 in the presence of redox mediator I
−
3 /I
− which would
result in an adverse impact on the long term stability of the CE (Xiao et al. 2014).
The high cost and corrosion susceptibility has led to the exploration of substitute materials in place of Pt as a CE material. Hence carbon based material such as
graphene (Xu et al. 2014a, b), conducting polymer-graphene nanocomposites (Huang
et al. 2011), metal organic frameworks (MOFs) (Sun et al. 2016), conducting polymers and polymer hybrid composites (Rahman et al. 2016) have been investigated as
alternative CE materials and they have shown favourable photovoltaic performances.
Carbon is used as a promising counter electrode material due to favourable properties such as high conductivity, appreciable catalytic activity towards many redox
mediators, corrosion resistivity and cost effectiveness. The use of carbon based materials such as carbon black, graphene, mesoporous carbon, carbon nanotubes and
graphene based composite materials; as CE material has been explored. The use of
carbon black as a CE material was investigated and it yielded an efficiency around 9%
(Murakami et al. 2006). The highest efficiency achieved with the use of a graphene
CE was reported by Kakiage et al., in which an efficiency of 14.7% was yielded with
the use of a graphene/gold CE (Kakiage et al. 2015).
The applicability of MOFs as CE materials has been explored. The use of CoS 2
embedded within carbon nanocages synthesized using ZIF-67 template achieved an
efficiency of 8.2% (Cui et al. 2016). An outstanding efficiency of 8.69% was yielded
by the use of CE material ZnSe embedded N-doped carbon cubes synthesized using
MOFs with Zn nodes and benzimidazole linkers (Jiang et al. 2018).
17.2 Conducting Polymers as CE Material
Conducting polymers are organic polymers that possess an orbital system that assures
the mobility of charge carriers. These polymers show extensive conjugation with
overlapping π orbitals along the polymer backbone of sp
2 hybridized carbons. As
a result of the delocalization of the π electrons these polymers reveal appreciable
conductivity that ranges from 10
−8 to 10
5 S/cm (Rahman et al. 2016). Conducting
polymers are considered as favourable candidates for CE materials in DSCs due to
characteristics such as efficient catalytic activity, promising conductivity and superior
stability. Moreover the usage of conducting polymers is further favoured due to high
surface area associated with the porous nature of the material thus enhancing catalytic
activity and their facile cost effective synthesis. Various conducting polymers such
as polypyrrole, polyaniline, polythiophene, poly(3,4-ethylenedioxythiphene) and