A poly(3,3-diethyl-3,4-dihydro-2H-thieno-[3,4-b][1,4]dioxepine) (PProDOT-Et2) counter electrode was incorporated in a plastic dye-sensitized solar cell (DSSC) to substitute for Pt electrode. The surface morphology and I-/I3- redox behaviors based on PProDOT-Et2 and sputtered-Pt electrodes were characterized, and their performances as counter electrodes in the plastic-DSSCs were compared. Cells fabricated with a PProDOT-Et2 counter electrode showed a higher conversion efficiency of 5.20% compared with cell fabricated with sputtered-Pt (5.11%) electrodes under the illumination of 100 mW cm(-2). This enhancement was attributed to the increase in the effective surface area and good catalytic properties of PProDOT-Et2 for I3- reduction.