Nanostructural, optical and electrical properties of vacuum evaporated films of an azo-calix[4]arene derivative

The nanomorphology, optical and electrical properties of vacuum-deposited azo-calix[4]arene thin films have been investigated. The nanostructured films exhibit absorption spectra with a resolved electronic structure in the UV-vis and a blue photoluminescence emission at about 430 nm independent of the excitation wavelength. The current-voltage (I-V) characteristics of ITO/azo-calix[4]arene/Au devices have been studied. The I-V dependence follows a power law, I ∝ Vm, which is typical of a space-charge-limited current. Moreover, from the I-V measurements, we have estimated the effective hole mobility of ∼7.5 × 10−6 cm2/V s in the vacuum-deposited azo-calix[4]arene thin films. Using impedance spectroscopy over a broad frequency range, i.e. 100 Hz to 10 MHz, it is found that the ac behavior of an ITO/azo-calix[4]arene/Au device shows several features, described by the simple RC circuit representing an undepleted bulk region. Values of the electrical circuit parameters deduced from fitting experimental data to the model have given a dielectric relaxation time in the millisecond range.