# 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
#### 3.2.2 Alternative Redox Electrolytes
In 2011, the group of [PERSON] prepared and studied a series of organic thiolate/disulfide redox couples in DSNCs. Additionally, they compared the catalytic activity of the well-known platinized FTO counter electrodes with PEDOT ones. They found that as an alternative CE material, PEDOT exceeded conventional platinized FTO-type of CE for yielding a PCE efficiency of 6.0% compared to 4.6% for the latter. Authors outlined that the PEDOT films are much more effective than platinum in reducing the charge-transfer resistance at the electrolyte/PEDOT interface, which, in turn, generates higher fill factor (FF), yielding higher PCE [53]. Later on, [PERSON] compared the electrocatalytic activity of conventional platinum, cobalt sulfide (CoS), and PEDOT toward organic thiolate/disulfide (T\({}^{-}\)/T\({}_{2}\)) redox mediators. Remarkably, an unprecedented power conversion efficiency of 7.9% under 100 mW cm\({}^{-2}\) solar irradiation was recorded using a high surface area PEDOT-based counter electrode. In particular, a highly porous structured polymer film with high cat  
Figure 10: Molecular structures and redox equilibrium in T\({}^{-}\)/T\({}_{2}\) organic redox shuttle used as an alternative redox mediator by [PERSON] and co-workers [73]. Figure 9: Best JV curves obtained by reducing the inter-electrode distance in the presence of copper redox mediators. Republished with permission of Royal Society of Chemistry, from Ref. [72]. alytic activity and surface area was obtained by electrochemical oxidation of EDOT in the presence of ionic-liquid medium by the potentiostatic mode [74]. In Table 1, the efficiency of PEDOT-based DSSCs fabricated according to different procedures and with various dyes and redox mediators is summarized. Concerning the stability of PEDOT-based CEs, very recently, [PERSON] et al. reported on the comparative aging tests between electrodeposited PEDOT/SDS and Pt in conjunction with the [Co(bpy)\({}_{3}\)]\({}^{2+/3+}\) redox electrolyte. DSSC devices assembled with Pt CEs exhibited higher stability than those fabricated with PEDOT/SDS. Nevertheless, the degradation mechanism in PEDOT-equipped cells is not completely clear. Indeed, while the reduction in the solar cell efficiency is less pronounced in the case of Pt, the counter electrode \(\mid\) electrolyte interfacial charge-transfer resistance was found to be highly stable for PEDOT. This indicates that PEDOT retains its good electrocatalytic behavior but somehow facilitates the degradation of the electrolyte, presumably due to its higher electroactive surface area, which increases the number of redox cycles of the mediator [77]. A recent study confirmed the long-term stability of PEDOT CEs in DSSCs fabricated with an iodine-based electrolyte. A systematic analysis was conducted to compare PEDOT to Pt under light soaking irradiation conditions. Authors demonstrated that DSSC parameters resulted more stable for devices assembled with PEDOT CES if compared to Pt. This was related to the higher electrochemical stability of PEDOT with respect to Pt in the presence of iodine electrolyte [78]. This also demonstrated that the ability of PEDOT to form charge-transfer complexes with triiodide ions does not represent a key limitation when this polymer is used as CE in solar cells [79]. High photostability was observed by [PERSON]'s group for DSSCs constructed with a new organic dye, a copper-based liquid redox mediator, and PEDOT CEs. In particular, PCE retained 92% of its peak value after 500 h solar light exposure,