Effects of oxidative doping on the thermoelectric performance of polyfluorene derivatives/carbon nanotube composite films

Abstract

The thermoelectric properties of the composite films of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) and single-walled carbon nanotube (SWCNT) were investigated with ferric chloride as oxidative dopant. Ferric chloride had a great influence on the enhancement of electrical conductivity and power factor of the composite films. It was found that the doped composite film with an SWCNT content of 50% (F8BT-FeCl3/50% SWCNT) exhibited a high electrical conductivity of 640.1 S cm−1 at room temperature, which increased fifteen times over the undoped composite film. The power factor of the F8BT-FeCl3/50% SWCNT composite film was 15.7 μW m−1 K−2, also higher than that of the undoped composite film. Additionally, in the temperature range of 20–120 °C, the electrical conductivity of the doped composite films decreased and the power factor increased with the increasing temperature, due to the increase of Seebeck coefficient. The carrier transport behavior was demonstrated to obey the fluctuation-induced tunneling model in the F8BT/SWCNT composite film, but was described by the variable range hopping model after doping, indicating the role of oxidative doping in alternating the electrical transport in the composites.