Patterned Growth of Large Oriented Organic Semiconductor Single Crystals on Self-Assembled Monolayer Templates

There has been a recent surge of interest in the fabrication of electronic devices from high quality single crystals of organic semiconductors. The importance of these materials stems from the fact that intrinsic charge transport properties are not influenced by grain boundaries and molecular disorder the defects commonly present in polycrystalline organic thin films. Such defects cause low mobilities and therefore reduce the performance of organic thin film transistors (OTFTs). In contrast, mobilities as high as 20 cm2/Vs have been reported for single crystal rubrene transistors and as high as 35 cm2/Vs for ultra pure pentacene single crystals from space charge- limited current measurements.2d,4 Despite the high mobilities reported for single crystal devices, there are many factors limiting their applications. In addition to the difficulties of fabricating good electrical contacts on single crystals, the most challenging task is handling the fragile crystals. Currently, single crystals are handpicked and made into an individual device but this method is impractical for fabricating a high density of devices over a large area. Our long-term goal is to understand the growth behavior of organic semiconductors in order to selectively grow oriented single crystalline organic semiconductors in designated locations directly in a device structure. In this communication we report a method for inducing site-specific growth of large oriented organic semiconductor crystals using micropatterned self-assembled monolayers (SAMs) bearing the regions of oligophenylene thiols as nucleation templates.