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Abstract 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 (F4TCNQ). Controlled morphologies are formed by casting blends of regioregular (RR‐P3HT) and regiorandom (RRa‐P3HT) and then subsequently doped with F4TCNQ 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.
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Effects of Counter‐Ion Size on Delocalization of Carriers and Stability of Doped Semiconducting Polymers
Abstract Since doped polymers require a charge‐neutralizing counter‐ion to maintain charge neutrality, tailored and high degrees of doping in organic semiconductors requires an understanding of the coupling between ionic and electronic carrier motion. A method of counter‐ion exchange is utilized using the polymeric semiconductor poly[2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b]thiophene] ‐C14to deconvolute the effects of ionic/polaronic interactions with the electrical properties of doped semiconducting polymers. In particular, exchanging the counter‐ions of the dopant nitrosonium hexafluorophosphate enables investigation into the role of counter‐ion size from 5.2 to 8.2 Å in diameter. The orientational order of the polymeric crystallites is not affected with this exchange process while effectively modifying the counter‐ion distance to the charge carrier. Doped films have electrical conductivities of 320 S cm−1and are not sensitive to an increased ion‐polaron distance. It is posited that other factors dominate the electrical properties at a device scale, such as the morphology and presence of domain boundaries. Interestingly, the temperature stability of the doped film can be drastically improved with the use of counter‐ions containing less labile bonds. This platform serves as a unique way to retain the morphology of polymeric thin films while studying charge interactions at the local scale.
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- Award ID(s):
- 1725797
- PAR ID:
- 10454675
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Electronic Materials
- Volume:
- 6
- Issue:
- 12
- ISSN:
- 2199-160X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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