| This thesis presents an approach to the problem of designing high-mobility organic thin film transistors. The influence of two critical surfaces, the dielectric and the electrode surface on the microstructure and carrier mobility of organic semiconductors, is explored. Modifying the organic/dielectric and the organic/contact interface with self-assembled monolayers enhances the carrier mobility in the channel which is related to measured changes in organic thin film microstructure.;Thiolated (-SH) SAMs modify the work function of gold contacts to reduce the electron injection barrier. Two types of SAMs were used: alkanethiols SAMs with different hydrocarbon chain lengths varying from eight to eighteen methylene groups and a perfluorobenzenethiol (PFBT) SAM. The objective of this study was to match the work function of the contacts to the lowest unoccupied molecular orbital of the channel material, PTCBI. PTCBI deposited on top of the ordered and long chain alkanethiols exhibit (001) and (011) orientations. The short chain and disordered alkanethiols, PFBT and untreated gold exhibit a unit cell orientation of (112¯). To the resolution of these experiments no significant difference in mobility was observed.;In order to passivate the dangling hydroxyl bonds on silicon dioxide (SiO2) dielectric surface, self-assembled monolayers (SAM) have been employed. Ordered and disordered octadecyltrichlorosilane (OTS) SAM treatments were applied, an n-type organic semiconductor 3,4,9,10-perylenetetracarboxylic-bis-benzimidazole (PTCBI) is deposited. A change in the unit cell orientation of PTCBI from (001) to (011) is observed between the two OTS treated and the control untreated SiO2 surfaces, respectively. The observed field effect mobility is surface treatment dependent, with the ordered OTS resulting the largest carrier mobility, followed by the disordered OTS and the untreated SiO 2. |
