Thermal and mechanical cracking in bis(triisopropylsilyiethnyl) pentacene thin films

Bis(triisopropylsilylethnyl) pentacene (TIPS pentacene) was synthesized to increase its solubility in common liquid solvents and, at the same time, enhance the pi-pi stacking between neighboring acenes in the crystallized state in comparison with unmodified pentacene. Hot-stage microscopy experiments revealed that during heating voids develop along the long axis of the TIPS pentacene films {along the [210] direction/parallel to the (126) planes and crystals overlap along the short axis {along the [120] direction/parallel to the (210) planes}. From molecular mechanics simulations, the predominant twin boundaries of (120) and commonly observed cracking planes of (120), (120), and (210) had relatively low surface energies in comparison with planes with similar Miller indices. Organic thin-film transistors with TIPS pentacene as the active layer were fabricated, and the mobility values decreased from 0.4-1.0 cm(2)/V s before cracking to similar to 0.2 cm(2)/N s after cracking. To maintain the high charge carrier mobility of TIPS pentacene devices, these cracks should be avoided. (c) 2006 Wiley Periodicals, Inc.