Page 424 - Polymer-based Nanocomposites for Energy and Environmental Applications

Polymer nanocomposites for dye-sensitized solar cells 381

Another extensively investigated conducting polymer as CE for DSCs is poly(3,
4-ethylenedioxythiophene) (PEDOT). CEs with PEDOT have high room-temperature
conductivity, electrochemical reversibility, and remarkable thermal and chemical
stabilities. Additionally, doping with polyanions like polystyrene sulfonate (PSS)
improves PEDOT’s compatibility with polar group polymers and the performance
of the device in aqueous electrolytes [48]. It was reported that among all the con-
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ducting polymers, PEDOT has the highest electrocatalytic activity toward I /I
redox couple in DSCs [75]. The performance of DSCs with PEDOT-based CEs
strongly depends on the polymerization method and time [76–78], the type of electro-
lytes used [77,79], annealing temperature [80], and physical or chemical treatment
[80,81]. It is also possible to use hybrid polymer films as CEs in order to enhance
the catalytic activity and performance of DSC [82,83].
Gao et al. [76] synthesized PEDOT film on FTO-glass substrates via aqueous
galvanostatic polymerization technique. They controlled the surface morphologies
of PEDOT film by varying the polymerization time. Increase in polymerization time
resulted in higher catalytic activity and lower R ct , which had positive effects on both
V oc and J sc of the DSC. They obtained 6.46% PCE with PEDOT-based CE that is
0.13% higher than the one based on Pt-CE (6.33%).
Saito et al. [77] reported chemically polymerized p-toluenesulfonate-doped
PEDOT (PEDOT-TsO) as CE for DSC and compared the result with sputtered
Pt-CEs. According to their results, the surface of PEDOT-TsO film became more
porous with increasing reaction time and hence reduces the R ct and increases the per-
formance of DSC. DSC with the thicker PEDOT-TsO CE ( 2 μm) showed higher
V OC ( 0.605 V), FF ( 0.67), and PCE ( 3.65%) than the cell with PEDOT-TsO
CE ( 50 nm) and Pt-CE ( 70 nm) when ionic liquid was used as electrolyte. In case
of organic liquid electrolyte, they could not observe any obvious differences between
PEDOT- and Pt-CE-based DSCs [84].
Park et al. [80] investigated the effect of thermal annealing of PEDOT:PSS-based
CEs on the performance of DSC. They fabricated PEDOT:PSS CEs by spin coating of
commercial PEDOT:PSS solution and subsequent annealing at temperatures between
45°C and 120°C for 20–720 min. The reported PCE values showed an increase from
2.49% for untreated to 3.22% for annealed PEDOT:PSS-CE at 45°C for 720 min. This
effect was attributed to the increase of the surface area and crystallinity of the PEDOT:
PSS film.
Modifying PEDOT:PSS with different organic solvents such as dimethyl sulfoxide
(DMSO), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and
dichloromethane (DMC) or addition of inorganic fillers like carbon black (CB) can
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enhanced the conductivity (2 0.05 S cm ) and surface roughness of PEDOT/
PSS-based film. Chen et al. [81] investigated the effect of these modifications on
the performance of PEDOT:PSS-CE based DSC. They prepared PEDOT:PSS films
on FTO-glass by simple dip-coating method from aqueous PEDOT:PSS solutions
in which certain amount of these solvents were added individually. They found that
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DMSO-treated PEDOT:PSS exhibits the highest conductivity (85 15 S cm ) and
that the addition of carbon as conductive filler further increased the conductivity
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(350 15 S cm ) and also the surface roughness of the DMSO-PEDOT:PSS