Influence of an Applied Electric Field on the Conduction Characteristics of a Bithienyl-Capped Biphenylene and Biphenyl-Capped Oligothiophenes in Organic Field-Effect Transistor Structures

Abstract

ABSTRACTThin films (50 nm) of 2,5-di-4-biphenylthiophene (PPTPP), 5,5´-di-4-biphenylyl-2,2´-bithiophene (PPTTPP) and 4,4´-di-2,2´-bithienylbiphenyl (TTPPTT) were vapor-deposited on microstructured gold (source- and drain-) electrode arrays on thermal SiO2 as gate dielectric with underlying Si serving as gate electrode. The films were studied in their field-effect characteristics during film growth and subsequent to it. A decay of specific conductivity and of charge carrier mobility was observed in subsequent measurements. During annealing without an applied field the films recovered but showed a second decay as soon as an electric field was applied again for repeated characterization. Induced dipoles and subsequent structural changes as well as chemical interactions with the SiO2 interface are discussed as possible origins of these observations.