Ionic liquid-doped poly(3,4-ethylenedioxythiophene) counter electrodes for dye-sensitized solar cells: Cationic and anionic effects on the photovoltaic performance

Composite films of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with various functional ionic liquids were obtained by electro-polymerization process on indium-doped tin oxide (ITO) conducting glasses. The ITO glasses coated with the composite films were used as the counter electrodes in dye-sensitized solar cells (DSSCs). Various imidazolium cations with different alkyl chains (-C₂H₅, -C₆H₁₃, -C₁₀H₂₁) and anions (BF4-,PF6-,SO3CF3-,TFSI-) were used as the ionic liquids. The films of PEDOT doped with the ionic liquids render for their DSSCs enhanced power conversion efficiencies (η), compared to that of the cell with bare PEDOT counter electrode. The DSSC with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMITFSI)-doped PEDOT counter electrode shows a high η of 8.87±0.11, while the DSSCs with bare PEDOT and platinum counter electrodes show the ηs of 6.19±0.09 and 8.09±0.06, respectively. X-ray photoelectron spectroscopy, scanning electron microscopy, and contact angle data were used to characterize the ionic liquid-doped PEDOT films. Cyclic voltammetry, rotating disk electrode, Tafel polarization plots, electrochemical impedance spectroscopy, and incident photon-to-current conversion efficiency curves were used to substantiate the photovoltaic performance.