Dipolar SAMs Reduce Charge Carrier Injection Barriers in n-Channel Organic Field Effect Transistors

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• 作者：Malte Jesper ; Milan Alt ; Janusz Schinke ; Sabina Hillebrandt ; Iva Angelova ; Valentina Rohnacher ; Annemarie Pucci ; Uli Lemmer ; Wolfram Jaegermann ; Wolfgang Kowalsky ; Tobias Glaser ; Eric Mankel ; Robert Lovrincic ; Florian Golling ; Manuel Hamburger ; Uwe H. F. Bunz
• 刊名：Langmuir
• 出版年：2015
• 出版时间：September 22, 2015
• 年：2015
• 卷：31
• 期：37
• 页码：10303-10309
• 全文大小：443K
• ISSN：1520-5827

文摘

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 鈭?30 and 鈭?10 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掳, 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, 鈭?00 and 鈭?30 meV, respectively. The contact resistance between gold electrodes and poly[N,N鈥?bis(2-octyldodecyl)-naphthalene-1,4:5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5鈥?(2,2鈥?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.