Electrical properties of TCNQ evaporated thin films

Electroluminescence and electrical conduction in TCNQ (tetracyanoquinodimethane) thin films prepared by the vacuum-evaporation technique were investigated. The electrical properties depended strongly on the thin film deposition conditions, such as deposition rate and/or temperature and substrate temperature. The conduction currents were also affected by the electrode materials. Higher conductivity was observed in the specimen with a Cu anode than in that with Au or Al. The thermally stimulated current showed two peaks, at -120 and -20°C. The trap depths were estimated as 0.10 and 0.22 eV, respectively. X-ray diffraction studies showed that the specimen prepared at 280°C was crystalline, but the one prepared at 180°C was amorphous. An infrared absorption analysis showed that the main chemical composition of TCNQ has been largely preserved in the vacuum-evaporated films