Polymeric Conformation of Organic Interlayers as a Determining Parameter for the Charge Transport of Organic Field-Effect Transistors

Abstract

Here, we systematically investigated the effects of different carbon numbers or alkyl chain lengths of organic SAM interlayers on electrical properties of poly (dioctyl-quaterthiophenedioctyl-bithiazole) (PDQDB) organic field-effect transistors (OFETs). Although the end-group functionalities of organic interlayers were chemically identical, the phase state and structural ordering of polymeric chains in the organic SAM interlayers significantly affected the field-effect mobility (µFET) or threshold voltage (Vth). For cases where the PDQDB layer is interfaced with the highly ordered polymeric chains, the average µFETs demonstrated an increase from 0.11 to 0.17 cm2V−1s−1 when the chain length was changed from C8 to C18, respectively, with the Vth variations being negatively shifted. We confirmed that the conformation of polymeric chains in the organic SAM interlayers were not induced by the structural changes in the PDQDB film, which was verified by the crystalline and morphological analyses. Instead, the results could be explained in terms of the variations in the dipole arrangement with changes in the phase state or increased structural ordering of the polymeric alkyl chains in the SAM interlayers.