Poly3- (4-fluorophenylthiophene), which can be both n- and p-doped, has been chemically synthesized by using FeCl3 as an oxidant and is used as an electrode-active material in composite electrodes. To fabricate an all-solid-state electrochemical capacitor, a liquid electrolyte solution was replaced by a gel polymer electrolyte. Then the laminated capacitor was electrochemically characterized by cyclic voltammetry, a frequency response analyzer, and a charge-discharge instrument. The proposed device was charged at a constant current of 250 muA/cm(2) up to 2.7 V and discharged at the same current up to 0 V demonstrating an energy density of 1.64 Wh/kg and a power density of 268.36 W/kg based on the total weight of active materials in a unit cell at the 1000th cycle. Furthermore, the interfacial resistance decreases from 18 Omega (or 72 Omega cm(2)) to 8 Omega (or 32 Omega cm(2)) after 10,000 charge/ discharge cycles.