Enhancement of Carrier Mobilities of Organic Semiconductors on Sol–Gel Dielectrics: Investigations of Molecular Organization and Interfacial Chemistry Effects

• Published in: Advanced functional materials 2009-02, Vol.19 (3), p.378-385
• Main Authors: Cahyadi, Tommy, Kasim, Johnson, Tan, Huei Shuan, Kulkarni, Shripad R., Ong, Beng S., Wu, Yiliang, Chen, Zhi‐Kuan, Ng, Chee Mang, Shen, Ze‐Xiang, Mhaisalkar, Subodh G.
• Format: Article
• Language: English
• Subjects: fullerene; organic field‐effect transistors; sol–gel silica
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.200800929

The dielectric‐semiconductor interfacial interactions critically influence the morphology and molecular ordering of the organic semiconductor molecules, and hence have a profound influence on mobility, threshold voltage, and other vital device characteristics of organic field‐effect transistors. In this study, p‐channel small molecule/polymer (evaporated pentacene and spin‐coated poly(3,3‴;‐didodecylquarterthiophene) – PQT) and n‐channel fullerene derivative ({6}‐1‐(3‐(2‐thienylethoxycarbonyl)‐propyl)‐{5}‐1‐phenyl‐[5,6]‐C61 – TEPP‐C61) show a significant enhancement in device mobilities ranging from ∼6 to ∼45 times higher for all classes of semiconductors deposited on sol–gel silica gate‐dielectric than on pristine/octyltrichlorosilane (OTS)‐treated thermally grown silica. Atomic force microscopy, synchrotron X‐ray diffraction, photoluminescence/absorption, and Raman spectroscopy studies provide comprehensive evidences that sol–gel silica dielectrics‐induced enhancement in both p‐ and n‐channel organic semiconductors is attributable to better molecular ordering/packing, and hence reduced charge trapping centers due to lesser structural defects at the dielectric‐semiconductor interface. Dielectric‐semiconductor interfacial interactions critically influence morphology and molecular ordering of organic semiconductor molecules, and hence have a profound influence on vital device characteristics of organic field‐effect transistors. Different classes of semiconductors deposited on sol–gel silica gate‐dielectric show significant enhancement in device mobilities, attributable to improved crystal structure, grain size as well as enhanced molecular interactions and ordering.