Side-Chain Effects on the Conductivity, Morphology, and Thermoelectric Properties of Self-Doped Narrow-Band-Gap Conjugated Polyelectrolytes

Abstract

This contribution reports a series of anionic narrow-band-gap self-doped conjugated polyelectrolytes (CPEs) with π-conjugated cyclopenta-[2,1-b;3,4-b']-dithiophene-alt-4,7-(2,1,3-benzothiadiazole) backbones, but with different counterions (Na(+), K(+), vs tetrabutylammonium) and lengths of alkyl chains (C4 vs C3). These materials were doped to provide air-stable, water-soluble conductive materials. Solid-state electrical conductivity, thermopower, and thermal conductivity were measured and compared. CPEs with smaller counterions and shorter side chains exhibit higher doping levels and form more ordered films. The smallest countercation (Na(+)) provides thin films with higher electrical conductivity, but a comparable thermopower, compared to those with larger counterions, thereby leading to a higher power factor. Chemical modifications of the pendant side chains do not influence out of plane thermal conductivity. These studies introduce a novel approach to understand thermoelectric performance by structural modifications.

Thermoelectric plastics: from design to synthesis, processing and structure–property relationships

“…A related approach involves self-doping of conjugated polyelectrolytes, where the dopant is covalently bound to the side chain of the semiconductor. 23 …”

Enhancing the n‐Type Conductivity and Thermoelectric Performance of Donor–Acceptor Copolymers through Donor Engineering

“…However, an σ over 1000 S cm −1 has been shown for p‐type polymers, whereas only a handful of n‐type conducting polymers, including the ladder‐type polymers reported by Fabiano et al ., naphthalenedicarboximide (NDI)‐based polymer reported by Takimiya et al ., and benzodifurandione‐based oligo(p‐phenylenevinylene) (BDOPV)‐based polymers reported by us and Katz et al ., are reported to have electrical conductivities approaching or over 1 S cm −1 . Since the Seebeck coefficients of the pre‐eminent p‐ and n‐type polymers are comparable, having values of approximately ± (40–200) µV K −1 at the PF maximum, the low electrical conductivity is thought to be an obstacle for improving the thermoelectric performance of n‐type polymers.…”

High Thermoelectric Power Factor of a Diketopyrrolopyrrole-Based Low Bandgap Polymer via Finely Tuned Doping Engineering

“…For decades, semiconducting polymers have been extensively studied for their application in curved or foldable electronic devices such as the organic light emitting diodes12, thin-film transistors34567, and photovoltaics8910 owing to their flexibility, light-weight, and solution processability. In particular, the current interest in wearable device technology is promoting the development of organic thermoelectric devices that can utilize residual body heat as the power source111213141516171819202122232425.…”

“…By immersing the PEDOT:PSS film in ethylene glycol, the total dopant volume was minimized and as a result, the thermoelectric performance could be maximized. Research efforts on thermoelectric conjugated polymers have been mainly focused on PEDOT18, and only a few other polymer systems showed promise in terms of thermoelectric application;6 Poly(3-hexylthiophene) (P3HT) and poly(2,5 - bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene exhibited PFs of 26 μW m −1 K −2 by doping with a ferric salt of triflimide at room temperature11, and of 25 ± 8 μW m −1 K −2 by treatment of tridecafluoro-1,1,2,2,-tetrahydrooctyl)-trichlorosilane at room temperature14, respectively. Their relatively low thermoelectric performance compared to that of PEDOT systems is expected to be from a lack of research on developing thermoelectric materials and doping processes, thus, in this study, we tried to provide the requirements for high thermoelectric semiconducting polymers and demonstrated their excellent thermoelectric performance under accurately controlled doping levels.…”