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.