Surface-Order Mediated Assembly of pi-Conjugated Molecules on Self-Assembled Monolayers with Controlled Grain Structures

Abstract

This study systematically demonstrates the effects of the grain structure of crystalline self-assembled monolayers (SAMs) on the growth of organic semiconductor thin films on such monolayers, as well as the electrical characteristics of the resulting semiconductor films. The grain structure of the octadecyltrichlorosilane (OTS) monolayers could be tailored by constructing the monolayers at three different temperatures: -30 degrees C (-30 degrees C OTS), -5 degrees C (-5 degrees C OTS), and 20 degrees C (20 degrees C OTS). Among the three layers, -30 degrees C OTS exhibited the largest crystalline grains and longest-range homogeneity of alkyl chain arrays. We found that pentacene films deposited on -30 degrees C OTS monolayers show larger crystalline grains with higher degrees of crystallinity and lateral alignment compared to that of films deposited on -5 degrees C OTS or 20 degrees C OTS monolayers, following the surface characteristics of the underlying OTS monolayers. Furthermore, pentacene field-effect transistors fabricated with 30 degrees C OTS monolayers showed lower charge trap densities and higher field-effect mobility values than devices fabricated using 5 or 20 degrees C OTS monolayers. These results are explained in terms of enhanced quasi-epitaxial growth of pentacene films on OTS monolayers with large grains.