Ferrocene-Based Organic Semiconductors: Evaluating Intermolecular Transfer Integrals and Transistor Properties

Ferrocene, with its unique redox properties and stability,
offers
promising potential for use in semiconductor layers of organic transistors.
However, it has not previously been applied due to its high vapor
pressure and inability to form thin films. We have successfully fabricated
thin-film transistors by introducing appropriate substituents into
ferrocene and increasing the molecular weight, thereby suppressing
its sublimation properties. Based on the crystal structures at room
temperature, we have calculated the intermolecular transfer integrals
using density functional theory. We have evaluated the carrier-path
anisotropy (dimensionality of the electronic structure), as well as
thin-film transistor properties. Ferrocene derivatives having small
substituents such as phenyl groups form herringbone-like molecular
arrangements, realizing two-dimensional carrier paths. In contrast,
ferrocene derivatives with bulky substituents such as anthryl groups
form one-dimensional uniform stacks, though the transfer integrals
of all ferrocene derivatives are relatively small below 10 meV. Our
evaluation have confirmed the switching of the drain currents in the
forward-back scan of the gate voltage during transistor operations,
indicating that the reversible redox property of Fc/Fc+ in the ferrocene units are realized even in the solid state.