Temperature dependent carrier mobility in organic field-effect transistors: The role of dielectrics

Abstract

It has been shown that the use of a ferroelectric dielectric in 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) field-effect transistors (FETs) results in a negative coefficient of carrier mobility, a signature of a band-like transport, above a certain temperature [A. Laudari and S. Guha, Phys. Rev. Appl. 6, 044007 (2016)]. Along with spontaneous polarization, polymer ferroelectric dielectrics offer a platform for tuning interfacial transport in FETs as their dielectric constant may vary nearly by an order of magnitude with temperature. In this work, we explore a variety of organic and inorganic dielectrics with varying dielectric constants on the temperature-dependent transport properties of TIPS-pentacene organic FETs to obtain a comprehensive insight into the role of energetic disorder and trap states. In particular, a high κ dielectric, Al2O3, shows an activated transport throughout the temperature regime, whereas the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE), with comparable and even higher values of κ compared to Al2O3, above 200 K shows a very different behavior. Additionally, the external poling condition of the PVDF-TrFE dielectric plays a role. We attribute the band-like negative coefficient of carrier mobility, observed at high temperatures, in TIPS-pentacene FETs with unpoled PVDF-TrFE to a polarization fluctuation process and explore this phenomenon using the concept of transport energy.