Controlled solution deposition and systematic study of charge-transport anisotropy in single crystal and single-crystal textured TIPS pentacene thin films

In this work, bis-(triisopropylsilylethynyl) pentacene (TIPS pentacene) films were fabricated with a newly designed system for controlled solution casting with adjustable nitrogen flow and deposition temperature, which consequently enabled a systematic examination of crystal orientation-dependent mobilities in single crystal and single-crystal textured TIPS pentacene transistors. One of the two pi-pi stacking directions in TIPS pentacene films was found to be close to [2 1 0] (or the long axis of needle-shaped TIPS pentacene films), with frequent twinning observed between crystalline domains across the (1 (2) over bar 0) planes that are the lateral facets for individual crystallites. The [2 1 0] axes of crystalline TIPS pentacene thin films ran across source-drain channels at different angles, showing a ten-fold hole mobility increase as the [2 1 0] crystallographic axis became parallel to the channel direction. Our results also suggest that the controlled solution casting may be a promising method in fabricating solution-processible small-molecule organic semiconductors with varied morphologies. (C) 2009 Elsevier B.V. All rights reserved.