Morphology, Optical and AC Electrical Properties of Copper Phthalocyanine Thin Films

AC electrical properties of sandwich devices composed of thermally evaporated thin films of copper phthalocyanine (CuPc) with aluminum and gold electrodes (Al/CuPc/Au) are investigated over frequency (f) range of 10(2)-10(5) Hz and temperature range of 293-453 K. Morphology of the samples was studied via field emission scanning electron microscope images and X-ray diffraction micrographs. The X-ray diffraction micrograph indicates the configuration of alpha-CuPc with the (510) plane as the preferred orientation. UV-Vis absorption spectrum was analyzed and the optical band-gap energy of CuPc thin film was determined to be 2.81 +/- 0.01 eV. Capacitance increased with increasing temperature especially for f = 10(2) Hz. Loss factor decreased considerably with increasing frequency to a minimum value at about f =10(4) Hz and increased afterwards. Capacitance is generally independent of frequency for T <= 413 K; however it decreases remarkably with increasing frequency for T > 413 K. The conductivity increases quite noticeably with increasing frequency particularly for T <= 413 K. The AC electrical characteristics are in good agreement with Goswami and Goswami model. According to our data, at high temperatures, the band theory is applicable in describing the conduction process, whereas hopping mechanism is dominant at low temperatures.