Oxygen induced charge carrier generation and trapping in vacuum deposited phthalocyanine thin films

Investigations of the temperature dependencies of the electrical conductivity and thermo-modulated space charge limited current spectroscopy measurements are carried out on metal-free phthalocyanine (H2PC) thin films, in a gap sample configuration with interdigital gold electrodes in a controlled atmosphere. It was found that the influence of O-2 on the dark conductivity of H2Pc films is a thermally activated process at 360 K. The H2Pc-O-2 interaction is a two-stage process characterized by an activation energy (E-a)=0.36 eV of creation and E-a=0.60 eV of decay of charge transfer complexes and subsequent generation of free charge carriers, increasing the Ohmic current. The dependence of the Ohmic current on the O-2 concentration (for small O-2 concentrations) is linear. An increased concentration of traps, as a result of the oxygen influence upon a trap level of 0.52 eV depth, was observed.