THE ELECTRONIC-STRUCTURE AND ENERGY-LEVEL ALIGNMENT OF PORPHYRIN METAL INTERFACES STUDIED BY ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY/

Electronic structures of 5, 10,15,20-zinctetraphenylporphyrin (ZnTPP)/ metal (Au, Ag, Al, Mg) interfaces prepared in ultrahigh vacuum conditi on were investigated by ultraviolet photoelectron spectroscopy (UPS). We found that the electronic energy levels of ZnTPP align with the vac uum level of substrate metal with a constant energy shift of the vacuu m levels across the interface. These findings cannot be explained by t he concepts of Fermi level alignment nor vacuum level alignment. We al so found that sample exposure to oxygen induces energy level shift in close relation with change of substrate work function at oxygen exposu re. The relation between the observed electronic structure and the ele ctric characteristics of porphyrin/metal interfaces in solar cell is a lso discussed.