In this paper, the synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) by cyclic voltammetry (CV) electrochemical deposition and its application in the counter electrode of solid-state dye-sensitized solar cells were studied. The influence of cycle times (10~50 times) on the morphology, thickness and optical properties of PEDOT films were explored by Fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM), scanning electron microscope (SEM) and ultraviolet-visible spectroscopy (UV-Vis). The photoelectrochemical properties of solid-state dye-sensitized solar cells based on PEDOT transparent counter electrode were characterized by J-V, electrochemical impedance spectroscopy (EIS), intensity modulated photocurrent spectrum/photovoltage spectrum (IMPS/VS) and Tafel analysis. The results showed that an un-uniform film with the thickness of 0.5 μm and light transmittance of 80% was formed when CV cycle times was 10, where the PEDOT film was not completely covered on the substrate. When the CV cycles reached 30~40, a uniform and dense transparent film was obtained and the highest photoelectric conversion efficiency of the corresponding solid-state dye-sensitized solar cells reached 5.34%. This is because uniform and dense surface, good optical properties and high photo-electric catalysis properties (J₀=2.51×10^-3 A·cm^-2) for I₃^- in the electrolyte, made the device obtain larger diffusion coefficient (D_n=28.80 μm²·ms^-1) and carrier diffusion length (L=21.41 μm), which were favorable for charge transfer. When the number of CV cycles was further increased to 50 times, showing greater roughness, the PEDOT film was no longer growing uniformly. The PEDOT film deposited on the FTO surface underwent some dissolution and desorption, the PEDOT film became uneven, and the catalytic activity of PEDOT electrode to I₃^- in electrolyte was reduced. The device with PEDOT transparent counter electrode film deposited by cyclic voltammetry could also achieve double-side illumination with good catalytic activity to the electrolyte. Under the condition of double-side illumination, the photoelectric performance of the device using electrodeposited PEDOT as transparent counter electrode was improved by about 20%. The improvement of the photoelectric performance of the device is mainly due to the increase in the absorption of photons by the double-sided illumination.

Key words: solid-state dye-sensitized solar cells, PEDOT, transparent counter electrode, conductive polymers, cyclic voltammetry method