Structural and Electrostatic Complexity at a Pentacene/Insulator Interface
Kanan Puntambekar,1 Jinping Dong,2 Greg Haugstad2 and C. Daniel Frisbie1
1Department of Chemical Engineering and Materials
Science, University of Minnesota, 421 Washington Avenue SE, and 2Characterization
Facility, Institute of Technology, University of Minnesota, 100 Union Street SE,
Minneapolis, Minnesota 55455
The properties of organic-semiconductor/insulator (O/I) interfaces are critically important to the operation of organic thin-film transistors (OTFTs) currently being developed for printed flexible electronics. Here we report striking observations of structural defects and correlated electrostatic-potential variations at the interface between the benchmark organic semiconductor pentacene and a common insulator, silicon dioxide. Using an unconventional mode of lateral force microscopy, we generate high-contrast images of the grain-boundary (GB) network in the first pentacene monolayer. Concurrent imaging by Kelvin probe force microscopy reveals localized surface-potential wells at the GBs, indicating that GBs will serve as charge-carrier (hole) traps. Scanning probe microscopy and chemical etching also demonstrate that slightly thicker pentacene films have domains with high line-dislocation densities. These domains produce significant changes in surface potential across the film. The correlation of structural and electrostatic complexity at O/I interfaces has important implications for understanding electrical transport in OTFTs and for defining strategies to improve device performance.