A novel photoelectrochromic device (PECD) with dual application was studied using an electrochromic polymer thin film, poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDot-Et2), and an organic photosensitive dye, FL dye1, which was adsorbed on a TiO2 electrode. In the presence of the redox couple, the electron transfer reaction at the electrolyte/PProDot-Et2 conducting polymer interface was found to determine the electrochromism of the PECD. The rate constants of the electron transfer (k0) for different redox couples at the PProDot-Et2 film were obtained by using electrochemical impedance spectroscopy (EIS) and were correlated with the coloration depth of the thin film. Since I−/I3− and Br−/Br3− couples possess the highest and the lowest k0 value, respectively, the PECD was investigated using these two redox couples under constant light illumination of 50mWcm−2. The I−/I3− couple provided a higher short circuit current density (JSC) when acting as a dye-sensitized solar cell (DSSC), thus the switching response upon coloration (ca. 3s) was much faster than that of the PECD using the Br−/Br3− couple (ca. 2min). On the contrary, the PECD using Br−/Br3− exhibited a larger transmittance attenuation of ca. 33.7%, in comparison to that using I−/I3− (ca. 14.1%).