Photoconductivity and oxygen adsorption of Cu-phthalocyanine thin films on cadmium sulphide surfaces

Sandwich structures based on 10 nm thin Cu-phthalocyanine (CuPc) films vacuum deposited on a 500 nm thick cadmium sulphide CdS film surface—deposited onto a glass substrate—demonstrated pronounced photoconductivity at 105 Pa O2 pressure and in vacuum. The photoconductivity transient profiles were measured throughout the spectral range from 300 to 900 nm and the photoconductivity spectra were built on the basis of these data. Two photoconductivity components that had different relaxation time and spectral distribution were registered in the pressure range from 10−6 to 101 Pa. Only the faster photoconductivity component was left after the structure under study was exposed to 105 Pa O2. Formation of an interface layer between CdS and CuPc films, having electronic properties different from each of the films, is suggested. The faster photoconductivity component is attributed to incident light absorption in a CdS subsurface region that is possibly modified by the presence of the CuPc molecules. The slower photoconductivity component is attributed to the processes in the interface layer or in the CuPc film.