Electron Transport in Soft-Crystalline Thin Films of Perylene Diimide Substituted with Swallow-Tail Terminal Alkyl Chains.

We have examined the structural and electron transport properties of a swallow-tailed N,N'-bis(1-heptyloctyl)-perylene-3,4:9,10-bis(dicarboximide) (PDI-C8,7) in thin films. A comprehensive analysis of material with the use of X-ray scattering methods evidenced the appearance of a new soft-crystalline mesophase that was induced by thermal processing of the swallow-tail PDI derivative. By combining electrical measurements with grazing-incidence wide-angle X-ray scattering (GIWAXS), we show that these morphological changes of thin films boost their charge transport in the organic field-effect transistor (OFET) configuration. The systematic device engineering of OFETs, including device architecture, thermal history, and preparation method of the active layer, resulted in a significant improvement in the electron field-effect mobility and the related performance parameters. In particular, the results demonstrate a strong improvement in the charge transport of PDI-C8,7 films in their soft-crystalline phase, which originates from the N-substitution by swallow-tails. In addition, our study demonstrates that the melt-processing route, a solvent-free and vacuum-free method for the fabrication of organic thin films, represents an efficient strategy for the fabrication of high-performance air-stable n-type OFETs.