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Review
. 2023 Sep 15;6(5):2909-2916.
doi: 10.1021/acsaelm.3c00936. eCollection 2024 May 28.

Impact of Oligoether Side-Chain Length on the Thermoelectric Properties of a Polar Polythiophene

Mariavittoria Craighero  1 , Jiali Guo  2 , Sepideh Zokaei  1 , Sophie Griggs  3 , Junfu Tian  3 , Jesika Asatryan  4 , Joost Kimpel  1 , Renee Kroon  5 , Kai Xu  2 , Juan Sebastian Reparaz  2 , Jaime Martín  4   6 , Iain McCulloch  3 , Mariano Campoy-Quiles  2 , Christian Müller  1
Affiliations
Review

Impact of Oligoether Side-Chain Length on the Thermoelectric Properties of a Polar Polythiophene

Mariavittoria Craighero et al. ACS Appl Electron Mater. .

Abstract

Conjugated polymers with oligoether side chains make up a promising class of thermoelectric materials. In this work, the impact of the side-chain length on the thermoelectric and mechanical properties of polythiophenes is investigated. Polymers with tri-, tetra-, or hexaethylene glycol side chains are compared, and the shortest length is found to result in thin films with the highest degree of order upon doping with the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). As a result, a stiff material with an electrical conductivity of up to 830 ± 15 S cm-1 is obtained, resulting in a thermoelectric power factor of about 21 μW m-1 K-2 in the case of as-cast films. Aging at ambient conditions results in an initial decrease in thermoelectric properties but then yields a highly stable performance for at least 3 months, with values of about 200 S cm-1 and 5 μW m-1 K-2. Evidently, identification of the optimal side-chain length is an important criterion for the design of conjugated polymers for organic thermoelectrics.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Maximum electrical conductivity values reported for polythiophenes and thienothiophene-based copolymers doped with F4TCNQ,,−,− (black circles), and values obtained in this study (red diamonds).
Figure 2
Figure 2
Molecular structures of p(gx2T-T) and F4TCNQ.
Figure 3
Figure 3
UV–vis (a) and transmission FTIR (b) absorbance spectra, with the absorbance A normalized by the film thickness d, of p(g32T-T) before (light green) and after coprocessing with 20 mol % F4TCNQ (dark green).
Figure 4
Figure 4
Electrical conductivity σ, Seebeck coefficient α, and power factor α2σ versus aging time of p(g32T-T) coprocessed with 20 mol % of F4TCNQ at ambient conditions; error bars represent the standard deviation of five measurements on the same sample.
Figure 5
Figure 5
(a) In-plane (light green) and out-of-plane (dark green) GIWAXS diffractograms of neat p(g32T-T) and coprocessed with 20 mol % of F4TCNQ. (b) Out-of-plane GIWAXS diffractograms of p(gx2T-T) polymers coprocessed with 20 mol % of F4TCNQ.
Figure 6
Figure 6
DMA thermograms of the storage and loss modulus, E′ and E″, and tan δ of (a) neat p(g32T-T) and (b) p(g32T-T) coprocessed with 20 mol % of F4TCNQ. (c) Stress–strain curves recorded by tensile deformation of free-standing films of neat p(g32T-T) (light green) and p(g32T-T) doped with 20 mol % F4TCNQ (dark green).
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