Flexible thermoelectric films with high power factor made of non-oxidized graphene flakes

Abstract

Films made from exfoliated graphene flakes have great potential in flexible thermoelectric devices, but are generally limited by the poor quality of flakes and the lack of effective n-doping strategies. The oxidative exfoliation routes typically employed to make reduced graphene oxide (rGO) reduce electrical conductivity because of defects in the basal plane, and typically creates p-type flakes because of the many remaining oxygenous groups. Here, an alternative synthesis strategy using non-oxidative intercalation and molecular adsorption is employed to create high-quality n-type graphene films. A film produced from these non-oxidized graphene flakes (NOGF) showed a Seebeck coefficient of -45.3 µV K-1 and electrical conductivity of 3280 S cm-1 at room temperature, both of which are significantly better than previously reported graphene thermoelectric films. This resulted in an extremely high power factor of 673 µW m-1 K-2, the highest ever reported from a film made of any 2D material. The films were also shown to be extremely robust under bending conditions, with less than 3% electrical conductivity loss after 1000 bending cycles at a bending radius of 3 mm. Finally, the practicality of the films was demonstrated with a flexible thermoelectric device that generated 2.2 mV using only body heat.