Measurements of Ambipolar Seebeck Coefficients in High-Mobility Diketopyrrolopyrrole Donor-Acceptor Copolymers

The Seebeck coefficient of both electrons and holes in a family of ambipolar diketopyrrolopyrrole copolymers is investigated using field-effect gated measurements. It is found that at high carrier concentrations the magnitude of the Seebeck coefficients is not strongly dependent on the molecular structure of the backbone within this family of polymers. Additionally, the Seebeck coefficients of electrons and holes have very similar magnitudes showing that electrons and holes experience a similar energetic landscape. Subtle differences in the carrier concentration dependence between the polymers are observed, which are interpreted in terms of different degrees of energetic disorder on the basis of molecular dynamics and electronic structure simulations.