Effect of Polymer Molecular Weight on Morphology and Charge Transport of Small-Molecular Organic Semiconductors

Abstract

The utilization of polymer additives provides an intriguing pathway to tune the electrical performance of solution-grown, small-molecular organic semiconductors. In this study, we report the effect of different polymer molecular weight on the crystal growth, phase segregation and charge transport of the organic semiconductors. A semicrystalline polymer additive polyethylene oxide (PEO) with 8000 and 100 K molecular weight was blended with a well-known organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene). Distinctively different thin film morphology of the resultant TIPS pentacene/PEO blend film was identified and quantitatively characterized. In particular, PEO with a higher molecular weight of 100 K exerted a stronger effect on enhancing film formation, crystal coverage and likely mechanical properties, whereas PEO with an 8000 molecular weight yielded more superior crystal alignment and larger crystal sizes. Bottom-gate, top-contact TIPS pentacene/PEO OTFTs were fabricated to test the charge transport, which indicated loading the PEO polymer with molecular weight of 8000 demonstrated a five-fold enhancement in the extracted hole mobilities as compared to the 100 K counterpart. This work of using polymer additives with different molecular weight can be used to tune the crystallization of other solution-processed high-mobility small-molecular organic semiconductors.

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Acknowledgements

Z. H. would like to acknowledge support provided from the University of Alabama. S. Bi would like to thank Science and Technology Project of Liaoning Province (20180540006). A part of this research was conducted at the Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, which is a DOE Office of Science User Facility.

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Correspondence to Zhengran He or Jihua Chen.

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He, Z., Zhang, Z., Bi, S. et al. Effect of Polymer Molecular Weight on Morphology and Charge Transport of Small-Molecular Organic Semiconductors. Electron. Mater. Lett. (2020). https://doi.org/10.1007/s13391-020-00227-y

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Keywords

  • Small-molecular semiconductor
  • Polymer additive
  • Molecular weight
  • Thin film morphology
  • Organic thin film transistors