Hollow microflower arrays of PEDOT and their application for the counter electrode of a dye-sensitized solar cell

Hollow microflower arrays (HMFAs) of poly(3,4-ethylenedioxythiophene) (PEDOT) with several two dimensional hollow nanopetals on each microflower are fabricated on a conducting glass by using ZnO microflower arrays as the template. Various charges are applied for the electrodeposition of the film of PEDOT-HMFAs, intending to investigate their effect on the film's morphology. A morphological variation is observed due to the swelling of PEDOT during the removal of the ZnO template. Cyclic voltammetry (CV) is used to optimize the charges for the deposition of the films of both a flat PEDOT and the PEDOT-HMFAs. Long-term stability of the films in an I^-/I ₃^- electrolyte is studied by CV. The PEDOT-HMFA film shows a better stability than those of the films of flat PEDOT and sputtered Pt. The PEDOT-HMFA film is employed as the catalytic material on the counter electrode (CE) of a dye-sensitized solar cell (DSSC). A power conversion efficiency of 7.20% is achieved, at 100 mW cm^-2 for the DSSC with the film of PEDOT-HMFAs, which is much higher than that of the cell with the flat PEDOT (6.39%) and comparable to that of the cell with a sputtered Pt film on its CE (7.61%). Electrochemical impedance spectroscopy is used to substantiate the photovoltaic parameters. "Hemispherical diffusion of ions" occurs on each PEDOT hollow microflower of the CE with PEDOT-HMFAs in the DSSC, as against the linear diffusion occurring on the CE with flat PEDOT or sputtered Pt. This type of "hemispherical diffusion of ions" is explained to result in a smaller diffusion resistance of ions and thereby in a much higher fill factor for the DSSC using the CE with PEDOT-HMFAs.