title: Dipolar SAMs Reduce Charge Carrier Injection Barriers in n-Channel Organic Field Effect Transistors.
abstract: 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-CH2-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-CH2-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[N,N'-bis(2-octyldodecyl)-naphthalene-1,4:5,8-bis(dicarboximide)-2,6-diyl]-alt-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-CH2-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.
authors: Organisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.|InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.
authors: Malte
authors: M
authors: Jesper
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Light Technology Institute, Karlsruhe Institute of Technology , Engesserstraße 13, 76131 Karlsruhe, Germany.|Merck KGaA, Frankfurter Straße 250, 64293 Darmstadt, Germany.
authors: Milan
authors: M
authors: Alt
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Institut für Hochfrequenztechnik, Technische Universität Braunschweig , Schleinitzstraße 22, 38106 Braunschweig, Germany.
authors: Janusz
authors: J
authors: Schinke
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Kirchhoff Institute for Physics, Heidelberg University , Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.
authors: Sabina
authors: S
authors: Hillebrandt
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|BASF SE, Quantum Chemistry Group, GMC/MQ B009, 67056 Ludwigshafen, Germany.
authors: Iva
authors: I
authors: Angelova
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Kirchhoff Institute for Physics, Heidelberg University , Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.
authors: Valentina
authors: V
authors: Rohnacher
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Kirchhoff Institute for Physics, Heidelberg University , Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.|Center for Advanced Materials, Heidelberg University , Im Neuenheimer Feld 225, 69120 Heidelberg, Germany.
authors: Annemarie
authors: A
authors: Pucci
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Light Technology Institute, Karlsruhe Institute of Technology , Engesserstraße 13, 76131 Karlsruhe, Germany.|Institut für Mikrostrukturtechnik, Karlsruhe Institute of Technology , Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors: Uli
authors: U
authors: Lemmer
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Materials Science Department, Surface Science Division, Technische Universität Darmstadt , Jovanka-Bontschits-Straße 2, 64287 Darmstadt, Germany.
authors: Wolfram
authors: W
authors: Jaegermann
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Institut für Hochfrequenztechnik, Technische Universität Braunschweig , Schleinitzstraße 22, 38106 Braunschweig, Germany.|Kirchhoff Institute for Physics, Heidelberg University , Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.
authors: Wolfgang
authors: W
authors: Kowalsky
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Kirchhoff Institute for Physics, Heidelberg University , Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.
authors: Tobias
authors: T
authors: Glaser
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Materials Science Department, Surface Science Division, Technische Universität Darmstadt , Jovanka-Bontschits-Straße 2, 64287 Darmstadt, Germany.
authors: Eric
authors: E
authors: Mankel
authors: InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Institut für Hochfrequenztechnik, Technische Universität Braunschweig , Schleinitzstraße 22, 38106 Braunschweig, Germany.
authors: Robert
authors: R
authors: Lovrincic
authors: Organisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.|InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.
authors: Florian
authors: F
authors: Golling
authors: Organisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.
authors: Manuel
authors: M
authors: Hamburger
authors: Organisch-Chemisches Institut, Universität Heidelberg , Im Neuenheimer Feld 270, 69120 Heidelberg, Germany.|InnovationLab GmbH , Speyerer Straße 4, 69115 Heidelberg, Germany.|Center for Advanced Materials, Heidelberg University , Im Neuenheimer Feld 225, 69120 Heidelberg, Germany.
authors: Uwe H F
authors: UH
authors: Bunz