Quantification and effects of molecular oxygen and water in zinc phthalocyanine layers

Gas effusion measurements on zinc phthalocyanine (ZnPc) layers showed the presence of a significant amount of oxygen and water inside the material during exposure to ambient conditions. Of both species the bulk concentration lay in the range of 10²⁰ molecules per cm³. Temperature-dependent analysis indicated that at 296 K all O₂ molecules, and roughly one half of the H₂O molecules, were mobilized and diffused with diffusion coefficients D_{O₂} of 3 ∗ 10⁻⁸ cm²/s and D_{H₂O} of 1.3 ∗ 10⁻¹⁰ cm²/s. Electrical analysis of ZnPc layers in controlled atmospheres revealed that the electrical properties of the bulk were determined by O₂, whereas H₂O influences the surface conductivity. A space-charge density of (1.6 ± 0.2) ∗ 10¹⁶ O₂⁻ ions per cm³ was measured in atmospheric conditions.