Tuning of Ag work functions by self-assembled monolayers of aromatic thiols for an efficient hole injection for solution processed triisopropylsilylethynyl pentacene organic thin film transistors

We demonstrate tuning of hole injection barriers in bottom contact triisopropylsilylethynyl pentacene (TIPS-pentacene) organic thin film transistors (OTFTs) by forming the self-assembled monolayers (SAMs) of thiophenol, 4-fluorothiophenol, or pentafluorothiophenol on the pristine Ag electrode. The work functions of SAM-treated Ag electrodes are measured by Kelvin probe method. The TIPS-pentacene OTFT devices were fabricated by a drop-cast method with a micropipette like an inkjet printing. The OTFTs with pentafluorothiophenol-Ag electrodes as source and drain exhibit carrier mobility of 0.17 cm(2)/V s and on/off current ratio of 10(5) because of almost no hole injection barrier to TIPS pentacenes. The SAM-treated Ag electrodes are robust over repeated electrical scans of 100 cycles. (C) 2008 American Institute of Physics.