The Role of Ordering on the Thermoelectric Properties of Blends of Regioregular and Regiorandom Poly(3-hexylthiophene)

The thermoelectric properties of semiconducting polymers are influenced by both the carrier concentration and the morphology that sets the pathways for charge transport. A combination of optical, morphological, and electrical characterization is used to assess the effect of the role of disorder on the thermoelectric properties of thin films of poly(3-hexylthiophene) (P3HT) doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F(4)TCNQ). Controlled morphologies are formed by casting blends of regioregular (RR-P3HT) and regiorandom (RRa-P3HT) and then subsequently doped with F(4)TCNQ from the vapor phase. Optical spectroscopy and X-ray scattering show that vapor phase doping induces order in the disordered regions of thin films and increases the long-range connectivity of the film. The thermoelectric properties are assessed as a function of composition and it is shown that while the Seebeck coefficient is affected by structural ordering, the electrical conductivity and power factor are more strongly correlated with the long-range connectivity of ordered domains.