Switching of Transfer Characteristics of an Organic Field-Effect Transistor by Phase Transitions: Sensitive Response to Molecular Dynamics and Charge Fluctuation

An organic field-effect transistor was fabricated using an anthracene–tetracyanoquinodimethane (AN–TCNQ) single-crystal charge-transfer (CT) complex as the semiconductor material. The CT complex showed molecular dynamics related to reorientational motion of an AN molecule at room temperature. The transfer characteristics drastically changed when the temperature decreased from room temperature to 90 K: n-type → ambipolar-type → p-type → ambipolar-type. From thermal analysis, AN–TCNQ underwent two phase transitions when the temperature decreased from room temperature to 120 K. To clarify the mechanism of the drastic changes of the transfer characteristics, the crystal and electronic structures of AN–TCNQ at various temperatures were investigated by X-ray structure analysis, optical measurements, and magnetic measurements. It was found that the drastic changes of the transfer characteristics originated from changes in the electronic structure accompanied by the molecular dynamics.