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

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