Charge transient spectroscopy study of dipolar effects in copper phthalocyanine

Copper phthalocyanine (CuPc) thin films were deposited in UHV on chemically treated Indium-Tin-Oxide (ITO) substrates by organic beam deposition from Knudsen's cells. Ag/CuPc/ITO Schottky diodes were prepared via vacuum deposition of circular Ag dots. Transient behavior of the devices in response to negative bias pulse applied to ITO was explored using charge transient spectroscopy (QTS). The QTS-spectrometer, acting as a filter of time constants, provided maximum of the throughput (Delta Q) when the time constant t of the transient charge Q(t) approached the selected time window t(1). The experimental Delta Q-log(10)(t(1)) spectra taken at room temperature have been fitted in terms of a Gaussian distribution of electron states characterized by a variance of energy sigma(d) approximate to 0.048 eV. Adopting the model of polar molecules embedded in a non-polar matrix, the fraction of the molecules possessing a dipole moment represents about 17% of the calculated total number of molecules. The value of the variance sigma(d) coincides fairly with those reported for molecular glasses.