1 research outputs found
A Planar Cyclopentadithiophene–Benzothiadiazole-Based Copolymer with sp<sup>2</sup>‑Hybridized Bis(alkylsulfanyl)methylene Substituents for Organic Thermoelectric Devices
A semicrystalline
p-type thermoelectric conjugated polymer based
on a polymer backbone of cyclopentadithiophene and benzothiadiazole,
polyÂ[(4,4′-(bisÂ(hexyldecylÂsulfanyl)Âmethylene)ÂcyclopentaÂ[2,1-<i>b</i>:3,4-<i>b</i>′]Âdithiophene)-<i>alt</i>-(benzoÂ[<i>c</i>]Â[1,2,5]Âthiadiazole)] (PCPDTSBT), is designed
and synthesized by replacing normal alkyl side-chains with bisÂ(alkylsulfanyl)Âmethylene
substituents. The sp<sup>2</sup>-hybridized olefinic bisÂ(alkylsulfanyl)Âmethylene
side-chains and the sulfur–sulfur (S–S) chalcogen interactions
extend a chain planarity with strong interchain packing, which is
confirmed by density functional calculations and morphological studies,
i.e., grazing incidence X-ray scattering measurement. The doping,
electrical, morphological, and thermoelectric characteristics of PCPDTSBT
are investigated by comparison with those of polyÂ[(4,4′-bisÂ(2-ethylhexyl)ÂcyclopentaÂ[2,1-<i>b</i>:3,4-<i>b</i>′]Âdithiophene)-<i>alt</i>-(benzoÂ[<i>c</i>]Â[1,2,5]Âthiadiazole)] (PCPDTBT) with ethylhexyl
side-chains. Upon doping with a Lewis acid, BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>, the maximum electrical conductivity (7.47 S cm<sup>–1</sup>) of PCPDTSBT is ∼1 order higher than that
(0.65 S cm<sup>–1</sup>) of PCPDTBT, and the best power factor
is measured to be 7.73 μW m<sup>–1</sup> K<sup>–2</sup> for PCPDTSBT with doping 9 mol % of BÂ(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>. The Seebeck coefficient–electrical conductivity
relation is analyzed by using a charge transport model for polymers,
suggesting that the doped PCPDTSBT film has superb charge transport
property based on a high crystallinity with olefinic side-chains.
This study emphasizes the importance of side-chain engineering by
using the sp<sup>2</sup>-hybridized olefinic substituents to modulate
interchain packing, crystalline morphology, and the resulting electrical
properties