High thermoelectric performance of poly(2,5-dimethoxyphenylenevinylene) and its derivatives

Poly(2,5-dimethoxyphenylenevinylene) (PMeOPV) and a series of copolymers consisting of both 2,5-dimethoxy-substituted phenylenevinylene units and unsubstituted units (P(MeOPV-co-PV)) were evaluated from the viewpoint of their thermoelectric properties. Their conjugated polymer films were prepared by pyrolysis of stretched or unstretched films of sulfonium salt precursor polymers, and subsequently doped with iodine vapor to provide electrical conductivity. The power factors P (=S2σ), indicating thermoelectric performance, were calculated with the measured electrical conductivity σ and Seebeck coefficient S of the doped films. PMeOPV showed a higher power factor of 7.1 μW m−1 K−2 at 313 K than that of a camphorsulfonic acid-doped polyaniline as reference. P(MeOPV-co-PV) precursor polymers with less than 20 mol% of MeOPV unit content in the monomer feed were stretchable, therefore providing stretched P(MeOPV-co-PV) films with low MeOPV unit content. The stretching treatment for P(MeOPV-co-PV) enhanced its electrical conductivity, but kept the Seebeck coefficient at nearly the same level as that of unstretched polymers. Consequently a 4.4-fold stretched copolymer exhibited an electrical conductivity of 183.5 S/cm and a Seebeck coefficient of 43.5 μV/K at 313 K, and thus, its power factor at 313 K was over 30 μW m−1 K−2. To the best of our knowledge, this is the highest thermoelectric performance ever reported among conducting polymers.