Correlating the microstructure of thin films of poly[5,5-bis(3-dodecyl-2-thienyl)-2,2-bithiophene] with charge transport: Effect of dielectric surface energy and thermal annealing

Leslie H. Jimison, Alberto Salleo, Michael L. Chabinyc, David P. Bernstein, and Michael F. Toney
Phys. Rev. B 78, 125319 – Published 16 September 2008

Abstract

Poly[5,5-bis(3-dodecyl-2-thienyl)-2,2-bithiophene] (PQT-12) is a conjugated polymer that shows promising performance (μ>0.1cm2/Vs) as a semiconductor for thin-film electronics. The electrical properties of PQT-12 thin films can vary by over 3 orders of magnitude depending on the chemistry of the substrate onto which they are deposited and on annealing conditions. The highest mobility is obtained in films annealed on a dielectric treated with a self-assembled monolayer of octadecyltrichlorosilane (OTS). Polymeric thin films were processed from either a solution of dissolved PQT-12 molecules in 1,2-dichlorobenzene or from a nanoparticle dispersion of the polymer in the same solvent (nPQT-12). In addition, the substrate surface chemistry was altered by spin coating on a bare SiO2 dielectric or on SiO2 treated with OTS. The microstructure of the two forms of polymer, as characterized using specular and grazing x-ray diffraction in addition to rocking curves, was compared and correlated with the electrical performance of the films as active layers in thin-film transistors. As-spun films of nPQT-12 are always more crystalline than those of PQT-12, independent of substrate chemistry. Consequently, carrier mobility in as-spun films is higher in nPQT-12 than in PQT-12. The presence of the OTS monolayer at the polymer/dielectric interface increases crystallinity of both PQT-12 and nPQT-12, without significantly affecting their texture. After annealing, the mobility in PQT-12 films and nPQT-12 films is comparable. Annealing causes the polymer films on OTS to undergo crystallite growth in the direction normal to the substrate. In nPQT-12, growth of the crystalline coherence length in the ππ stacking direction (i.e., parallel to the substrate and in the direction of charge transport) occurs as well. The mobility increase in nPQT-12 on OTS upon annealing is thus attributed to the higher crystallinity of the film. In PQT-12 films deposited on OTS on the other hand, annealing causes a decrease in the out-of-plane misorientation of neighboring crystallites without any significant grain growth in the plane of the film. The mobility increase in PQT-12 on OTS upon annealing is attributed to a better intergrain connectivity, in agreement with electrical modeling of the transistor characteristics using a mobility edge model.

  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
  • Figure
12 More
  • Received 15 April 2008

DOI:https://doi.org/10.1103/PhysRevB.78.125319

©2008 American Physical Society

Authors & Affiliations

Leslie H. Jimison1, Alberto Salleo1,*, Michael L. Chabinyc3, David P. Bernstein2,4, and Michael F. Toney4

  • 1Department of Materials Science, Stanford University, Stanford, California 94305, USA
  • 2Department of Applied Physics, Stanford University, Stanford, California 94305, USA
  • 3Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, California 94304, USA
  • 4Stanford Synchrotron Radiation Laboratory, Menlo Park, California 94025, USA

  • *Corresponding author; asalleo@stanford.edu

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand
Issue

Vol. 78, Iss. 12 — 15 September 2008

Reuse & Permissions
Access Options
Author publication services for translation and copyediting assistance advertisement

Authorization Required


×
×

Images

×

Sign up to receive regular email alerts from Physical Review B

Log In

Cancel
×

Search


Article Lookup

Paste a citation or DOI

Enter a citation
×