Mono/bidentate thiol oligoarylene-based self-assembled monolayers (SAMs) for interface engineering

A new set of linear oligoarylene thiol molecules, namely (40-(Thiophen-2-yl)Biphenyl-3,5-diyl) Dimethanethiol (TBD), (40-(Thiophen-2-yl)Biphenyl-4-yl)Methanethiol (TBM) and ([1,10;40,100] Terphenyl-3,5-diyl)Dimethanethiol (TD), were synthesized and used for functionalizing the polycrystalline gold electrodes. Such molecules differ for the number of anchoring groups (TBM vs. TBD) and the terminal rings (TD vs. TBD). As shown by electrochemical measurements, they form homogeneous and pinholes-free self-assembly monolayers (SAMs) when deposited on the gold electrode. Moreover, the wettability of the functionalized surface and the morphological changes of pentacene films grown on SAMs were investigated by contact angle and atomic force microscopy, respectively. OTFT has been used as organic gauge for investigating the metal-SAM-organic semiconductor structure. Charge carriers mobility, threshold voltage, contact resistance were measured in both air and vacuum to assess the influence of the anchoring groups and the terminal rings to the transistor performance. Although these SAMs do not show an improvement of mobility due to an increase of contact resistance, they allow a better modulation of the current flowing across the electrode-organic semiconductor (OS) interface, pointing out the structural differences between the three SAMs in terms of resistance drop combined with the critical voltage.