Epitaxial Alignment of Organic Semiconductors on 2D Materials Templates

Organic semiconductors are promising candidates for a wide range of electronic and optoelectronic technologies, including solar cells, light-emitting diodes, and thin-film transistors, because of their strong broadband light absorption, efficient light emission, highly tunable structures and properties, and ability to be processed over large areas at low temperatures. However, the development of technologies based on organic semiconductors has been hindered by the inability to control the thin-film orientation, crystallinity, and morphology. Here, we demonstrate that the 2D materials graphene and hexagonal boron nitride (h-BN) can epitaxially align several small-molecule organic semiconductors, including acenes and rylene diimides, into the face-on orientation that is desirable for optoelectronics. GIWAXS, XRD, AFM, and SEM are employed to elucidate the effects of the deposition rate, deposition temperature, and substrate composition on thin-film structure. TA and TRPL are utilized to determine how the film orientation and crystallinity impact exciton dynamics and photophysical mechanisms. Overall, this work provides a route to engineer organic semiconductor thin films with favorable characteristics for high-performance optoelectronics.