A Planar Cyclopentadithiophene-Benzothiadiazole-Based Copolymer with sp2-Hybridized Bis(alkylsulfanyl)methylene Substituents for Organic Thermoelectric Devices

Jiae Lee, Jaeyun Kim, Thanh Luan Nguyen, Miso Kim, Juhyung Park, Yeran Lee, Sungu Hwang, Young Wan Kwon, Jeonghun Kwak, Han Young Woo

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

A semicrystalline p-type thermoelectric conjugated polymer based on a polymer backbone of cyclopentadithiophene and benzothiadiazole, poly[(4,4′-(bis(hexyldecylsulfanyl)methylene)cyclopenta[2,1-b:3,4-b′]dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTSBT), is designed and synthesized by replacing normal alkyl side-chains with bis(alkylsulfanyl)methylene substituents. The sp2-hybridized olefinic bis(alkylsulfanyl)methylene 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 poly[(4,4′-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b′]dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTBT) with ethylhexyl side-chains. Upon doping with a Lewis acid, B(C6F5)3, the maximum electrical conductivity (7.47 S cm-1) of PCPDTSBT is ∼1 order higher than that (0.65 S cm-1) of PCPDTBT, and the best power factor is measured to be 7.73 μW m-1 K-2 for PCPDTSBT with doping 9 mol % of B(C6F5)3. 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 sp2-hybridized olefinic substituents to modulate interchain packing, crystalline morphology, and the resulting electrical properties.

Original languageEnglish
Pages (from-to)3360-3368
Number of pages9
JournalMacromolecules
Volume51
Issue number9
DOIs
Publication statusPublished - 2018 May 8

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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