title: Threshold-Voltage Shifts in Organic Transistors Due to Self-Assembled Monolayers at the Dielectric: Evidence for Electronic Coupling and Dipolar Effects.
abstract: The mechanisms behind the threshold-voltage shift in organic transistors due to functionalizing of the gate dielectric with self-assembled monolayers (SAMs) are still under debate. We address the mechanisms by which SAMs determine the threshold voltage, by analyzing whether the threshold voltage depends on the gate-dielectric capacitance. We have investigated transistors based on five oxide thicknesses and two SAMs with rather diverse chemical properties, using the benchmark organic semiconductor dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene. Unlike several previous studies, we have found that the dependence of the threshold voltage on the gate-dielectric capacitance is completely different for the two SAMs. In transistors with an alkyl SAM, the threshold voltage does not depend on the gate-dielectric capacitance and is determined mainly by the dipolar character of the SAM, whereas in transistors with a fluoroalkyl SAM the threshold voltages exhibit a linear dependence on the inverse of the gate-dielectric capacitance. Kelvin probe force microscopy measurements indicate this behavior is attributed to an electronic coupling between the fluoroalkyl SAM and the organic semiconductor.
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstr.1, 70569, Stuttgart, Germany.
authors.forename: Mahdieh
authors.initials: M
authors.lastname: Aghamohammadi
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstr.1, 70569, Stuttgart, Germany.
authors.forename: Reinhold
authors.initials: R
authors.lastname: Rödel
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstr.1, 70569, Stuttgart, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Zschieschang
authors.affiliation: Instituto de Ciencia de Materiales de Barcelona (ICMAB-CSIC) , Campus de la UAB, 08193 Bellaterra, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Ocal
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstr.1, 70569, Stuttgart, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Boschker
authors.affiliation: BASF SE , GVE/T - J542s, 67056 Ludwigshafen, Germany.|Innovation Lab GmbH , Speyerer Str. 4, 69115 Heidelberg, Germany.
authors.forename: R Thomas
authors.initials: RT
authors.lastname: Weitz
authors.affiliation: Instituto de Ciencia de Materiales de Barcelona (ICMAB-CSIC) , Campus de la UAB, 08193 Bellaterra, Spain.
authors.forename: Esther
authors.initials: E
authors.lastname: Barrena
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstr.1, 70569, Stuttgart, Germany.
authors.forename: Hagen
authors.initials: H
authors.lastname: Klauk
keywords: Kelvin probe force microscopy; gate-dielectric capacitance; organic transistors; self-assembled monolayers; threshold-voltage shift