Design of experiment optimization of aligned polymer thermoelectrics doped by ion-exchange

Yuxuan Huang, Dionisius Hardjo Lukito Tjhe, Ian Jacobs, Xuechen Jiao, Qiao He, Martin Statz, Xinglong Ren, Xinyi Huang, Iain McCulloch, Martin Heeney, Christopher R. McNeill, Henning Sirringhaus

Research output: Contribution to journalArticlepeer-review

Abstract

Organic thermoelectrics offer the potential to deliver flexible, low-cost devices that can directly convert heat to electricity. Previous studies have reported high conductivity and thermoelectric power factor in the conjugated polymer poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT). Here, we investigate the thermoelectric properties of PBTTT films in which the polymer chains were aligned uniaxially by mechanical rubbing, and the films were doped by a recently developed ion exchange technique that provides a choice over the counterions incorporated into the film, allowing for more optimized morphology and better stability than conventional charge transfer doping. To optimize the polymer alignment process, we took advantage of two Design of Experiment (DOE) techniques: regular two-level factorial design and central composite design. Rubbing temperature Trub and post-alignment annealing temperature Tanneal were the two factors that were most strongly correlated with conductivity. We were able to achieve high polymer alignment with a dichroic ratio >15 and high electrical conductivities of up to 4345 S/cm for transport parallel to the polymer chains, demonstrating that the ion exchange method can achieve conductivities comparable/higher than conventional charge transfer doping. While the conductivity of aligned films increased by a factor of 4 compared to unaligned films, the Seebeck coefficient (S) remained nearly unchanged. The combination of DOE methodology, high-temperature rubbing, and ion exchange doping provides a systematic, controllable strategy to tune structure–thermoelectric property relationships in semiconducting polymers
Original languageEnglish (US)
Pages (from-to)111903
JournalApplied Physics Letters
Volume119
Issue number11
DOIs
StatePublished - Sep 13 2021

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)

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