The conductivity and thermal stability of PEDOT:PSS film can be enhanced by adding some organic solvents such as EG (ethylene glycol) and HFIP (hexafluoro-isopropyl alcohol) in PEDOT:PSS aqueous solution. The amphiphilic HFIP has the hydrophobic CF3 groups to interact with the hydrophobic PEDOT chains, while the hydrophilic OH group preferentially interacts with the hydrophilic PSS chains in the solution. M-PEDOT:PSS film spin coated (or casted) from the PEDOT:PSS/H2O/EG/HFIP mixed-solvent solution thus is highly conducting and thermally stable. Compared to PEDOT:PSS film made from PEDOT:PSS/H2O aqueous solution, M-PEDOT:PSS film has a denser packing, better ordered and clearer phase (PEDOT and PSS) segregation as revealed with AFM and X-ray diffraction data. M-PEDOT:PSS film (4 μm in thickness), with a sheet resistant of 1.3 Ω sq-1, can be used to replace FTO as a counter electrode in dye-sensitized solar cell (DSC). Furthermore taking the advantage of the difference in solubility but good compatibility between PEDOT:PSS and PEDOT, a layer of PEDOT can be casted on top of M-PEDOT:PSS to be a redox catalyst. DSC based on PEDOT/M-PEDOT:PSS counter electrode, N719 sensitizer, and I-/I3- liquid electrolyte has an efficiency of 7.29% which is close to that (7.62%) for DSC based on thermal-Pt/FTO counter electrode assembled under the same conditions.
- Dye-sensitized solar cell