Synthesis and effects of substrate temperature on ac and dc electrical properties of cobalt phthalocyanine (CoPc) thin films

In this study, 4,4′,4″-[benzene-1,3,5-tryltris(oxy)]tri-9,10, 16,17,23,24-hexa(hexylthio)phthalocyaninatocobalt(II) has been synthesized from 4-[3,5-bis(3,4-dicyano phenoxy)phenoxy]phthalonitrile and 4,5- bishexylthiophthalonitrile with CoCl₂.6H₂O in ethylene glycol at 170-180°C for 6 hours. The effects of substrate temperature (during coating of the films) on the electrical characteristics were investigated. CoPc thin films were prepared by cast coating method at the substrate temperatures of 298, 348, 373, 398 K on interdigital gold electrodes on glass substrate. The dc and ac electrical properties of CoPc films were investigated in the temperature range of 298 - 391 K in dark. The ac electrical properties of CoPc films have been studied in the frequency range from 40 Hz to 100 kHz. All measurements were performed under N₂ flow. The temperature dependence of dc conductivity show typical Arrehenius behavior for all films. As the substrate temperature increases during coating of the films from 298 K to 398 K, the activation energy decreases from 1.04 to 0.96 eV. The ac conductivity of the films is represented by the form ω^s. The temperature dependency of frequency exponent s on temperature suggests a correlated barrier hopping (CBH).