Microspacing In-Air Sublimation Growth of Ultrathin Organic Single Crystals

Organic single crystals play indispensable roles in high-performance electronic devices because of their completely eliminated or minimized impurities and disorder, wherein ultrathin thickness is a critical prerequisite because charge accumulation in devices occurs within a few molecular monolayers of the semiconductors. The growth of organic crystals through vapor dispels concerns about solubilities and the inclusion of solvents in the final crystals, but achieving an ultrathin thickness for common organic semiconductors is beyond its power. On the basis of our recently invented microspacing in-air sublimation (MAS), the distance between the source and growth position is set to approximate the mean free path of the vaporized molecules. Such a configuration generates a genetic relationship between the morphology of the source materials and that of the grown crystals. By refining the deposition of the source materials using ultrasonic spray, we can obtain ultrathin single crystals with a uniform distribution. We exemplify the strategy through MAS growth of ultrathin DNTT and pentacene single crystals down to five and three molecular monolayers, respectively. Field effect transistors fabricated on the ultrathin crystals exhibited average charge carrier mobilities of 6.08 cm2 V–1 s–1 for DNTT and 2.39 cm2 V–1 s–1 for pentacene, and low threshold voltages (∼83% of the devices within 5 V).