Showing papers by "Yeong Don Park published in 2007"

Solution-processable pentacene microcrystal arrays for high performance organic field-effect transistors

Abstract: The authors report the fabrication of one-dimensional crystal arrays of triisopropylsilylethynyl pentacene (TIPS PEN) via simple drop casting on a tilted substrate. By pinning a solution droplet on the tilted substrate, an array of ribbon-shaped crystals aligned in the tilted direction was formed on the substrate. X-ray diffraction analysis revealed that these crystals were oriented in the crystal growth direction. A thin film transistor based on such an array of TIPS PEN crystals was found to have a high field-effect mobility of 0.3cm2∕Vs, which results from the directed organization of the π-conjugated molecules.

Effects of the permanent dipoles of self-assembled monolayer-treated insulator surfaces on the field-effect mobility of a pentacene thin-film transistor

Abstract: In order to investigate the effects of permanent dipoles on insulator surfaces on the electrical properties of organic thin-film transistors, the authors fabricated insulators with various self-assembled monolayers and similar surface energies. Surprisingly, they found that the field-effect mobility of pentacene thin-film transistors increases by a factor of approximately 20 for insulators with an electron-withdrawing group. This remarkable increase in the field-effect mobility is due to the increase in the hole density of the insulator surface that arises from the increased band bending of the insulator/semiconductor interface.

Energy‐Level Alignment at Interfaces between Gold and Poly(3‐hexylthiophene) Films with two Different Molecular Structures

Abstract: The electronic structures of the interfaces between Au and poly(3‐hexylthiophene) (P3HT) films with two different molecular orientations and orderings were investigated using synchrotron radiation photoemission spectroscopy. We found that, depending on whether thermal treatment was used, the P3HT thin film adopts two different molecular orientations—parallel and perpendicular to the silicon substrate—which result in different values of the vacuum level shift and hole‐injection barrier. Thus the molecular orientation and ordering of the P3HT material strongly affect the energy level alignment at the P3HT/Au interface.

Ink-jet printing of self-aligned soluble-pentacene crystals for high-performance organic field-effect transistors

Abstract: We have reported the fabrication of the self-organized 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS_PEN) crystals with highly ordered molecular structures by using evaporation-induced flows in a solution process. The one-dimensional microcrystal arrays of TIPS_PEN were fabricated by simple solution casting on a tilted substrate. By pinning a solution droplet on the tilted substrate, an array of ribbon-shaped crystals aligned in the tilted direction was formed on the substrate. In particular, self-aligned TIPS_PEN crystals with highly ordered crystalline structures via inkjet printing were successfully produced by controlling the evaporation-induced flow using solvent mixture, and arise when there is a recirculation flow in a inkjet printed droplet that is induced by a Marangoni flow (surface-tension-driven flow) in the direction opposite to the outward convective flow. The field-effect transistors fabricated with these self-aligned TIPS_PEN crystals via drop casting and inkjet printing exhibit significantly improved electrical performance. These results demonstrate that control of evaporation-induced flow in a solution process of organic semiconductor can be an excellent method for the production of organic semiconductor films with uniform morphology and desired molecular orientation for the direct-write fabrication of high-performance OFETs.