Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers

Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers

The Journal of Physical Chemistry B

10.1021/acs.jpcb.2c00303

http://dx.doi.org/10.1021/acs.jpcb.2c00303

Teck Lip Dexter Tam, Akshay Moudgil, Wei Jie Teh, Zicong Marvin Wong, Albertus Denny Handoko, Sheau Wei Chien, Shuo-Wang Yang, Boon Siang Yeo, Wei Lin Leong, Jianwei Xu

Physical and Theoretical Chemistry, Surfaces, Coatings and Films, Materials Chemistry

24 February 2022

Dexter Tam, T. L., Moudgil, A., Teh, W. J., Wong, Z. M., Handoko, A. D., Chien, S. W., Yang, S.-W., Yeo, B. S., Leong, W. L., & Xu, J. (2022). Polaron Delocalization Dependence of the Conductivity and the Seebeck Coefficient in Doped Conjugated Polymers. The Journal of Physical Chemistry B, 126(9), 2073–2085. https://doi.org/10.1021/acs.jpcb.2c00303

Conjugated polymers are promising materials for thermoelectrics as they offer good performances at near ambient temperatures. The current focus on polymer thermoelectric research mainly targets a higher power factor (PF; a product of the conductivity and square of the Seebeck coefficient) through improving the charge mobility. This is usually accomplished via structural modification in conjugated polymers using different processing techniques and doping. As a result, the structure–charge transport relationship in conjugated polymers is generally well-established. In contrast, the relationship between the structure and the Seebeck coefficient is poorly understood due to its complex nature. A theoretical framework by David Emin (Phys. Rev. B, 1999,59, 6205–6210) suggests that the Seebeck coefficient can be enhanced via carrier-induced vibrational softening, whose magnitude is governed by the size of the polaron. In this work, we seek to unravel this relationship in conjugated polymers using a series of highly identical pro-quinoid polymers. These polymers are ideal to test Emin’s framework experimentally as the quinoid character and polaron delocalization in these polymers can be well controlled even by small atomic differences (<10 at. % per repeating unit). By increasing the polaron delocalization, that is, the polaron size, we demonstrate that both the conductivity and the Seebeck coefficient (and hence PF) can be increased simultaneously, and the latter is due to the increase in the polaron’s vibrational entropy. By using literature data, we also show that this phenomenon can be observed in two closely related diketopyrrolopyrrole-conjugated polymers as well as in p-doped P3HT and PANI systems with an increasing molecular order.

Publisher Copyright

This research / project is supported by the A*STAR - SERC Thermoelectric Materials Programme
Grant Reference no. : 1527200019

This research / project is supported by the A*STAR - SERC Thermoelectric Materials Programme
Grant Reference no. : 1527200021

This research / project is supported by the A*STAR - SERC Agritech Program
Grant Reference no. : A19D9a0096

This research / project is supported by the Nanyang Technological University (NTU) - NTU start-up grant
Grant Reference no. : M4081866

This research / project is supported by the Ministry of Education (MOE) - Tier 2 grant
Grant Reference no. : 2018-T2-1-075

This research / project is supported by the A*STAR - AME Young Individual Research Grant
Grant Reference no. : A1784c019

This research / project is supported by the National University of Singapore (NUS) - Faculty research grant
Grant Reference no. : R143-000-B52-114

This document is the Accepted Manuscript version of a Published Work that appeared in final form in The Journal of Physical Chemistry B, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jpcb.2c00303

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