Effect of a gate insulator with a long alkyl side chain on the performance of pentacene organic thin-film transistors

Abstract

This paper discusses some recent findings regarding the effect of a long alkyl (C18) group on the performance of organic thin-film transistors (OTFTs). Two different types of polymer gate insulators, BTDA-DACM (PI-1) and BTDA-DACM-DA18IM (PI-2), were prepared by a condensation polymerization. DA18IM with C18 alkyl group was used as a comonomer for the preparation of PI-2. We found that the C18 alkyl group of PI-2 protruded to the surface and made the surface more hydrophobic. The modified surface strongly affects the initial growth mechanism of pentacene on PI-2 and, subsequently, the device performance. The performance of pentacene OTFTs with the PI-2 was superior to that of the OTFTs with the PI-1. The OTFTs with PI-2 exhibited a carrier mobility of 0.4cm2∕Vs, current on/off ratio of 1.5×105, subthreshold slope of 2.1V∕dec. This suggested that the C18 alkyl group over the surface of PI-2 contributed to the better interface formation between PI-2 and pentacene and resulted in more favorable initial growth of pentacene and much improved performance.