Electrical mobility in organic thin-film transistors determined by noise spectroscopy

Organic field-effect transistors (OFET) based on both n-type (perylene derivative) and p-type (alpha-sexithiophene and pentacene) organic thin films are characterized using low-frequency noise spectroscopy to estimate the charge carrier mobility. The power spectral density shows that the exposure of OFET to air affects the thermal noise fluctuations and that the thermal noise RMS value depends on gate voltage. The power spectral density noise proves that the carrier mobility is gate-voltage dependent. Unlike the I-V measurements, the noise spectroscopy analysis demonstrates the dependence of the mobility on the carrier polarity. We discuss the charge mobility and transport mechanism of a pentacene device with and without electrodes functionalized by an octanethiol chain. The results show that in the functionalized device the carrier mobility is improved and does not depend on the high gate voltage. (C) 2011 American Institute of Physics. [doi:10.1063/1.3658846]