Tunable Crystallinity in Regioregular Poly(3-Hexylthiophene) Thin Films and Its Impact on Field Effect Mobility

Authors

  • Avishek R. Aiyar,

    1. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
    Search for more papers by this author
  • Jung-Il Hong,

    1. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
    Search for more papers by this author
  • Rakesh Nambiar,

    1. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
    Current affiliation:
    1. DuPont Central Research and Development, Experimental Station, Wilmington, DE 19880, USA
    Search for more papers by this author
  • David M. Collard,

    1. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
    Search for more papers by this author
  • Elsa Reichmanis

    Corresponding author
    1. School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
    2. School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
    3. School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
    • School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
    Search for more papers by this author

Abstract

The properties of poly(alkylthiophenes) in solution are found to have a profound impact on the self assembly process and thus the microstructural and electrical properties of the resultant thin films. Ordered supramolecular precursors can be formed in regioregular poly(3-hexylthiophene) (P3HT) solutions through the application of low intensity ultrasound. These precursors survive the casting process, resulting in a dramatic increase in the degree of crystallinity of the thin films obtained by spin coating. The crystallinity of the films is tunable, with a continuous evolution of mesoscale structures observed as a function of ultrasonic irradiation time. The photophysical properties of P3HT in solution as well in the solid state suggest that the application of ultrasound leads to a π stacking induced molecular aggregation resulting in field effect mobilities as high as 0.03 cm2 V−1 s−1. A multiphase morphology, comprising short quasi-ordered and larger, ordered nanofibrils embedded in a disordered amorphous phase is formed as a result of irradiation for at least 1 min. Two distinct regions of charge transport are identified, characterized by an initial sharp increase in the field effect mobility by two orders of magnitude due to an increase in crystallinity up to the percolation limit, followed by a gradual saturation where the mobility becomes independent of the thin film microstructure.

Ancillary