Heterojunctions Formed from Phthalocyanine and Perylene Thin Films: Photoelectrochemical Characterization

Bilayer and multilayer structures created from thin films of vanadylphthalocyanine(VOPc) and pe-rylenetetracarboxylic dianhydride(PTCDA) or copper phthalocyanine(CuPc) and PTCDA have been created, and their absorbance spectra and electrochemical/photoelectrochemical properties explored. Vacuum-deposited bilayers of these thin films show rectification in their current-voltage behavior over a narrow potential window. The open-circuit photopotential appears to be determined by the junction potential formed at the Pc/PTCDA interface. The magnitude of this junction is estimated from ultraviolet photoelectron spectroscopy(UPS) of the pure materials and previous electrochemical studies of solutions of comparable molecules. Photocurrent yield spectra, from two different illumination directions, indicated that a narrow region near the VOPc/PTCDA or CuPc/PTCDA interface was responsible for most of the photocurrent production. This was confirmed through the characterization of multilayer assemblies, where it was found that the transient photocurrent(using a modulated light source) was directly proportional to the number of Pc/PTCDA interfaces present.