# On the Use of PEDOT as a Catalytic Counter Electrode Material in Dye-Sensitized Solar Cells
## 3 PEDOT in DSSCs
### PEDOT Based Alternative Counter Electrodes in DSSCs
#### 3.2.1. Iodide-Iodine Electrolyte
The authors also explained this effect is due lower conductivity of PEDOT:PSS films (10 S/cm), if compared to PEDOT-TsO of 550 S/cm. [PERSON] et al. later demonstrated that unlike Pt, PEDOT-TsO exhibited no specific interaction with I\({}^{-}\) and I\({}_{3}{}^{-}\). They also observed an improved PCE by increasing PEDOT film thickness. This resulted in enhanced electroactive surface area of the CEs, which improved their catalytic response [51]. It is known that the conductivity of chemically prepared PEDOT:PSS can be strongly increased upon treatment with polar solvents, such as DMSO [52; 53]. It was found that a modified DMSO-PEDOT:PSS mixed with a small amount of carbon black can outperform conventional Pt when used as CE in DSSCs. Indeed, cells assembled with a N3 sensitized photoanode, an iodine/iodide-based electrolyte, and the modified PEDOT:PSS CEs yielded a higher cell efficiency of 5.81% than the equivalent cell assembled with Pt CE (5.66%). This result was explained by the combined action of the DMSO treatment, which was beneficial to enhance the conductivity of the PEDOT:PSS film, with the presence of carbon black, which further increases the surface area of the conductive film, yielding a superior catalytic activity [54]. Following a similar procedure, [PERSON] and co-workers prepared PEDOT:PSS/carbon CEs by adding a small amount of graphite to a commercial solution of PEDOT:PSS. They obtained an overall photovoltaic efficiency of 7.6% by optimizing the annealing temperature of PEDOT:PSS/carbon CEs [55]. Still, the authors of this study claimed that the improved activity of these PEDOT-based composite CEs was mainly due to their larger active surface area compared to the unmodified films, which enhances the electrocatalysis of the I\({}^{-}\)/I\({}_{3}{}^{-}\) couple, together with their increased conductivity. The use of water dispersible and commercially available PEDOT:PSS can be advantageous if the large scale production of DSSC CEs is undertaken. Indeed, starting from commercial PEDOT suspensions, conductive films could be deposited through scalable wet chemical methods, including spin coating, spray coating, or dip coating. On the other hand, electrodeposition methods are also scalable and enable the use of different doping agents, other than polymeric PSS anions, allowing for the fine tuning of the electrochemical properties of PEDOT films. Interestingly, [PERSON] and co-workers electrodeposited PEDOT in the presence of different counter ions, which besides PSS, included perchlorate (ClO\({}_{4}{}^{-}\)) and toylate (TsO\({}^{-}\)) and observed that all electrodeposited PEDOT CEs gave comparable results to that of Pt (Figure 5) [49]. Indeed, a power conversion efficiency near 7.9% was reported for all PEDOT counter electrodes with an iodine-based electrolyte which was almost the same as that observed with a platinized counter electrode under otherwise identical conditions. In a report by [PERSON] et al., PEDOT was electrodeposited in the presence of hydrophobic ionic liquids, and it was pointed out that the fine-tuning of the dopant nature and concentration in the polymer matrix is fundamental to improve the electrochemical performance of the resulting polymer. Following this approach, PEDOT-based counter electrodes in contact with an iodide-based electrolyte performed similarly to platinized counter electrodes yielding cells with a power conversion efficiency of 7.93% [56]. Electrodeposition can be used to prepare composite PEDOT materials in which one or more additives can be included within the polymer matrix during the growth of the PEDOT film. For instance, [PERSON] et al. prepared highly active CEs by electrodeposition PEDOT:TFSI (TFSI = bis(trifluoromentanesulfonyl)imide) in the presence of conductive carbon black [57]. In this way, these authors were able to achieve an overall PCE of 9.8% in iodide/iodine mediated DSSCs. Interestingly, they also reported a PCE of about 7.6% when an alternative thiolate-based redox mediator was adopted.