Electrical Properties of Evaporated Thin Films of Copper Phthalocyanine

The electrical properties of evaporated thin films of copper phthalocyanine (CuPc) were investigated by the ac method. The frequency dependence of conductivity and capacitance, and the activation energy for dc conductivity in α- and β-CuPc were determined. No significant variation in the electrical properties was observed with the difference in the phases of CuPc films in vacuo. The frequency dependence of conductivity and capacitance can be explained in terms of the simultaneous hopping and band conduction, viz., σ=σdc+A1·ωn and C=C+A2·ω1−n. The energy gap for α- and β-CuPc in vacuo is 1.80 eV and 1.89 eV, respectively. The adsorbed O2 gas has a great effect on the dc conductivity but little on the ac conductivity of α-CuPc film. The adsorption of oxygen on α-phase GuPc might be the cause of high dc conductivity and low activation energy(0.5–0.7 eV) as compared with those in vacuo.