Electron and hole transport in ambipolar, thin film pentacene transistors

Abstract

Solution-processed, ambipolar, thin-film pentacene field-effect transistors were employed to study both electron and hole transport simultaneously in a single, organic solid-state device. Electron and hole mobilities were extracted from the respective unipolar saturation regimes and show thermally activated behavior and gate voltage dependence. We fit the gate voltage dependent saturation mobility to a power law to extract the characteristic Meyer-Neldel (MN) energy, a measure of the width of the exponential distribution of localized states extending into the energy gap of the organic semiconductor. The MN energy is ∼78 and ∼28 meV for electrons and holes, respectively, which reflects a greater density of localized tail states for electrons than holes. This is consistent with the lower measured electron than hole mobility. For holes, the well-behaved linear regime allows for four-point probe measurement of the contact resistance independent mobility and separate characterization of the width of the localized density of states, yielding a consistent MN energy of 28 meV.

Small-molecule ambipolar transistors

“…After that, many examples of ambipolar operations have been reported with various conditions of electrodes, dielectrics, device configurations, and molecular orientations (Table 1). 63,66,156–165…”

“…After that, many examples of ambipolar operations have been reported with various conditions of electrodes, dielectrics, device configurations, and molecular orientations (Table 1). 63,66,[156][157][158][159][160][161][162][163][164][165] 6,13-Dicyanopentacene (PCN-2, Fig. 5) has been reported to be an air-stable acene with significantly low-lying HOMO and LUMO by the substitution of the cyano groups.…”