In this work we examine small conjugated
molecules bearing a thiol
headgroup as self assembled monolayers (SAM). Functional groups in
the SAM-active molecule shift the work function of gold to n-channel
semiconductor regimes and improve the wettability of the surface.
We examine the effect of the presence of methylene linkers on the
orientation of the molecule within the SAM. 3,4,5-Trimethoxythiophenol
(TMP-SH) and 3,4,5-trimethoxybenzylthiol (TMP-CH<sub>2</sub>-SH) were
first subjected to computational analysis, predicting work function
shifts of −430 and −310 meV. Contact angle measurements
show an increase in the wetting envelope compared to that of pristine
gold. Infrared (IR) measurements show tilt angles of 22 and 63°,
with the methylene-linked molecule (TMP-CH<sub>2</sub>-SH) attaining
a flatter orientation. The actual work function shift as measured
with photoemission spectroscopy (XPS/UPS) is even larger, −600
and −430 meV, respectively. The contact resistance between
gold electrodes and poly[<i>N</i>,<i>N</i>′-bis(2-octyldodecyl)-naphthalene-1,4:5,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene) (Polyera Aktive
Ink, N2200) in n-type OFETs is demonstrated to decrease by 3 orders
of magnitude due to the use of TMP-SH and TMP-CH<sub>2</sub>-SH. The
effective mobility was enhanced by two orders of magnitude, significantly
decreasing the contact resistance to match the mobilities reported
for N2200 with optimized electrodes
