The Effect of Ring Expansion in Thienobenzo[b]indacenodithiophene Polymers for Organic Field-Effect Transistors

Garry Rumbles, Bryon Larson, Hu Chen, Andrew Wadsworth, Chun Ma, Alice Nanni, Weimin Zhang, Mark Nikolka, Alexander Luci, Luis Perdigao, Karl Thorley, Camila Cendra, Giovanni Costantini, Thomas Anthopoulos, Alberto Salleo, Henning Sirringhaus, Iain McCulloch

Research output: Contribution to journalArticlepeer-review

44 Scopus Citations

Abstract

A fused donor, thienobenzo[b]indacenodithiophene (TBIDT), was designed and synthesized using a novel acid-promoted cascade ring closure strategy, and then copolymerized with a benzothiadiazole (BT) monomer. The backbone of TBIDT is an expansion of the well-known indacenodithiophene (IDT) unit and was expected to enhance the charge carrier mobility by improving backbone planarity and facilitating short contacts between polymer chains. However, the optimized field-effect transistors demonstrated an average saturation hole mobility of 0.9 cm2 V-1 s-1, lower than the performance of IDT-BT (∼1.5 cm2 V-1 s-1). Mobilities extracted from time-resolved microwave conductivity measurements were consistent with the trend in hole mobilities in organic field-effect transistor devices. Scanning tunneling microscopy measurements and computational modeling illustrated that TBIDT-BT exhibits a less ordered microstructure in comparison to IDT-BT. This reveals that a regular side-chain packing density, independent of conformational isomers, is critical to avoid local free volume due to irregular packing, which can host trapping impurities. DFT calculations indicated that TBIDT-BT, despite containing a larger, planar unit, showed less stabilization of planar backbone geometries in comparison to IDT-BT. This is due to the reduced electrostatic stabilizing interactions between the peripheral thiophene of the fused core and the BT unit, resulting in a reduction of the barrier to rotation around the single bond. These insights provide a greater understanding of the general structure-property relationships required for semiconducting polymer repeat units to ensure optimal backbone planarization, as illustrated with IDT-type units, guiding the design of novel semiconducting polymers with extended fused backbones for high-performance field-effect transistors.

Original languageAmerican English
Pages (from-to)18806-18813
Number of pages8
JournalJournal of the American Chemical Society
Volume141
Issue number47
DOIs
StatePublished - 27 Nov 2019

Bibliographical note

Publisher Copyright:
Copyright © 2019 American Chemical Society.

NREL Publication Number

  • NREL/JA-5F00-74867

Keywords

  • Marcus inverted region
  • microwave conductivity
  • singlet fission
  • solar-photochemistry
  • triplet state dissociation

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