Thioalkyl-substituted benzothiadiazole acceptors: Copolymerization with carbazole affords polymers with large stokes shifts and high solar cell voltages

Abby Casey, Raja Ashraf, Zhuping Fei, Martin Heeney*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

57 Scopus citations

Abstract

Copolymers of carbazole and 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (dTBT) incorporating thioalkyl (-SR) and alkoxy (-OR) solubilizing groups on the 2,1,3-benzothiazdiazole (BT) unit are synthesized and compared. The introduction of -SR and -OR groups onto the BT unit of the polymer was found to have different effects on the electronic properties of the polymers as well as the conformation of the polymer backbone. Large conformational changes between the ground state (GS) and excited state (ES) geometries of the polymers with -SR groups led to very large Stokes shifts of up to 224 nm. The polymer with -OR groups was found to have approximately double the photovoltaic efficiency at ∼4% compared to the polymers with -SR groups (PCE ∼ 2%). However, polymers with -SR groups were found to give very high open circuit voltages (VOC) of over 1 V. Changing the -SR chain length from ethyl to dodecyl was found to have little influence on the solar cell performance of the polymer or the magnitude of the Stokes shift.

Original languageEnglish (US)
Pages (from-to)2279-2288
Number of pages10
JournalMacromolecules
Volume47
Issue number7
DOIs
StatePublished - Apr 8 2014

ASJC Scopus subject areas

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

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