High-efficient dye-sensitized solar cell based on highly conducting and thermally stable PEDOT:PSS/glass counter electrode

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.