Transport mechanism and trap distribution in ITO/azo-calix[4]arene derivative/Al diode structure

Electrical measurements have been performed on spin-coated azo-calix[4]arene derivative on pre-cleaned indium thin oxide (ITO) substrates using current versus voltage, capacitance versus voltage and impedance spectroscopy measurements. The nature of trap states in single layer ITO/azo-calix[4]arene derivative/Al organic diodes has also been investigated. The energy band gap of the thin film containing calixarene derivative has been measured by UV–Vis absorption spectroscopy and is about 2.77 eV. The current–voltage characteristics have shown ohmic behavior at low voltages. At high applied bias the I–V characteristics can be successfully modeled by space-charge limited current (SCLC) theory. The impedance dependence of bias and frequency is discussed in terms of the presence of a depletion layer in the bulk. The device is accurately modeled, in a range of frequency between 100 Hz and 1 MHz, as a single parallel resistor and capacitor network placed in series with a resistance. Their values deduced from fitting experimental data to the model have given a dielectric relaxation time in the ms range and an exponential trap distribution.