Self-assembled monolayers (SAMs) of alkyl silane compounds have been used for modifying gate dielectrics surface
of organic field-effect transistors (OFETs) and they have frequently shown improvement of FET performances. In this
paper we deposited alkyl silane SAMs by simple spin-coating technique onto Si/SiO2 substrates. Spin-cast
octadecyltrimethoxysilane (OTMS) SAMs had ultra smooth crystalline surface and provided an excellent dielectric
surface for OFETs. In fact on the OTMS SAM treated dielectric, pentacene OFETs showed hole mobilities over 2.0
cm2/Vs and electron mobilties over 1.0 and 5.0 cm2/Vs were demonstrated for 3,4:9,10-perylene diimide derivative and
C60, respectively. Fabrication technique and characterizations of the OTMS SAMs is described.
It has been well established that in organic thin film transistors (OTFTs), charge transport occurs within the first few
monolayers of the semiconductor at the semiconductor/dielectric interface. Understanding and engineering the
semiconductor-dielectric is therefore critical. Large discrepancies in performance, even with seemingly identical surface
treatments, indicate that additional surface parameters must be identified and controlled in order to optimize OTFTs.
Here, we used the Langmuir-Blodgett technique to study the effect of an octadecylsilane dielectric modification layer on
OTFT performance. We found a crystalline, dense OTS monolayer promotes two-dimensional growth in a variety of
organic semiconductors. Mobilities as high as 5.3 cm2/Vs and 2.2 cm2/Vs were demonstrated on crystalline OTS for
C60 and pentacene, respectively. Finally, we also developed a simple, scalable spin-coating method to produce crystalline OTS. This work represents a significant step towards a general approach for morphological control of organic
semiconductors which is directly linked to their thin film transistor performance.
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