Alternating current measurements of thermally evaporated triclinic lead phthalocyanine thin films

Electronic properties of thermally evaporated thin films of triclinic lead phthalocyanine were investigated employing symmetric gold ohmic electrodes in the frequency range of 100–20 kHz. At low temperatures, ac conductivity was identified to be via a hopping type mechanism whereas at higher temperatures, the free-band model is considered to be the major cause for electronic transitions. Measurements on the dependence of capacitance on frequency (100–20 kHz) indicates that the capacitance is strongly frequency dependent, decreasing with increasing frequency at low frequency and less rapidly at higher frequencies. This is quantitatively interpreted using an equivalent circuit model. Oxygen doping was found to increase the capacitance of PbPc. The phenomenon was understood in terms of a reduction in the value of device internal resistance induced by oxygen absorption.