Charge Carrier Doping As Mechanism of Self‐Assembled Monolayers Functionalized Electrodes in Organic Field Effect Transistors

Abstract

Coating electrodes with self‐assembled monolayer (SAM) of polar molecules is known to reduce contact resistance (RC) in organic field effect transistors (OFETs). It is shown that the behavior of SAM in OFETs can be explained by considering a mechanism of interfacial doping in organic semiconductor by electrodes due to charge transfer during interface formation. The enhancement is analyzed in performance of pentacene OFETs with Cu electrodes, by coating Cu with SAM of pentafluorobenzenethiol or perfluorodecanethiol. It is found that application of either SAM leads to an increase in work function of Cu surface. However, work function shift due to SAM does not correlate with trends in RC and OFET drain current. Further, first principle calculations reveal a notable difference in delocalization of frontal orbitals with either SAM, an indicator of the difference in ease of charge transfer across interface. Based on the mechanism of interfacial doping, a semiconductor physics model is developed for estimating interface doping and injection barrier, and for predicting the consequent device characteristics. It is believed that the model and methodology developed in this study can be utilized beyond the SAM and semiconductor system used here.

Enhancing Gating Performance in Organic Molecular Field‐Effect Transistors by Introducing Polar Azulene Components

“…On the other hand, the above charge transport properties are highly related with the charge carrier properties in the NM/AM FET device [56–58] . Therefore, we calculate the reorganization energy ( λ ) for both the isolated NM/AM molecule and the NM/AM FET devices, respectively.…”

“…On the other hand, the above charge transport properties are highly related with the charge carrier properties in the NM/ AM FET device. [56][57][58] Therefore, we calculate the reorganization energy (λ) for both the isolated NM/AM molecule and the NM/ AM FET devices, respectively. The reorganization energy is defined as the energy required for the geometric relaxation during the charge transfer process, and it is inversely proportional to the mobility of charge carrier.…”

Formation and Thermal Stability of Ordered Self-Assembled Monolayers by the Adsorption of Amide-Containing Alkanethiols on Au(111)

“…The surface and interface properties of metal surfaces can be readily tuned by the formation of closely packed and highly ordered self-assembled monolayers (SAMs) derived from organic molecules with chemically active anchoring groups and various backbone structures [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. Hence, SAMs provide a versatile tool for the preparation of functional molecular thin films that can be applied to many practical applications, such as surface passivation [ 16 ], biointerfaces [ 17 ], biosensors [ 18 ], molecular photodiodes [ 19 ], batteries [ 20 ], and molecular electronic devices [ 21 , 22 ]. Among many organic thiols, n -alkanethiols with various alkyl chains are the most popular precursors because they easily form closely packed and well-ordered SAMs on gold with a high reproducibility.…”

Understanding the Microscopic Origin of the Contact Resistance at the Polymer–Electrode Interface

“…It has been shown that orbital interactions at the interface significantly contribute to governing charge transport at the interface. 12,13 Especially, hole injection involves an electron extraction from the highest occupied molecular orbital (HOMO) of the OSC by the electrode. Therefore, the HOMO energy level and distribution are anticipated to be critical in affecting the charge-transfer process.…”