Camphorsulfonic Acid-Doped Polyaniline Transparent Counter Electrode for Dye-Sensitized Solar Cells

Commercially available polyaniline emeraldine base (PANI-EB) powder was protonated by simple mixing with camphorsulfonic acid (CSA) to form the CSA-doped emeraldine salt form of PANI (PANI-ES). The PANI-ES state was dissolved in m-cresol at various concentrations (4, 2, 1 wt %) and spin-coated onto fluorine-doped tin oxide (FTO) glass to use as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The PANI-based CE exhibited a maximum transmittance of 72.9% in the visible wavelength range, which is equivalent to bare FTO glass. The surface resistivity of CE samples spin-coated with insulating PANI-EB was greater than 109 Ω/square, but the value steeply decreased to 1.3 kΩ/square when the CE was spin-coated with CSA-doped PANI-ES. Although the surface resistivity increased, and therefore fill factor (ff) gradually decreased, with decreasing solid content of the PANI-based coating solution, the charge-transfer resistance (R ct) and short-circuit current (J sc) conversely improved due to increased surface roughness, affording enhanced DSSC performance. Furthermore, the overall power conversion efficiency of a DSSC could be enhanced to a maximum of ∼6.3% by optimizing cell parameters through controlling the preparation conditions of the CE.