Contact resistance and electrode material dependence of air-stable n-channel organic field-effect transistors using dimethyldicyanoquinonediimine (DMDCNQI)

N-channel organic field-effect transistors with stable performance at ambient conditions are fabricated on the basis of an electron-accepting molecule, dimethyldicyanoquinone diimine (DMDCNQI). The transistors are investigated by varying source and drain electrode materials: Au, Ag, Cu, and a highly conducting organic charge-transfer salt, (tetrathiafulvalene)(tetracyanoquinodimethane) [(TTF)(TCNQ)]. The devices with the Au electrode show lowest contact resistance and highest electron mobility (0.011 cm²V⁻¹ s⁻¹ for bottom-contact configuration), and the performance decreases in the order of Au > (TTF)(TCNQ) > Ag > Cu. This order does not seem related to the metal work functions, but is attributed to the organic–metal interfacial potentials. DMDCNQI forms highly conducting charge-transfer complexes with Ag and Cu, but the complex layer increases the interfacial potential as well as the electron-injection barrier and also increases the off-current for short channel devices. The air stability is not determined solely by the organic semiconductor but is considerably influenced by the electrode materials.