A relationship between a metal work function and a diffusion potential at Schottky barriers in photovoltaic cells based on a molecular semiconductor

A Schottky-Mott rule is examined for the molecular solids of zinc(II) tetraphenylporphyrin (ZnTPP) contacting various metals in order to clarify an influence of surface states on formation of the Schottky barriers. For the same purpose, photocurrents due to the ZnTPP/metal contacts are compared with those observed for the Al/ZnTPP/Au cell biased at different voltages. As a result, the Schottky barrier formation at the contacts is found to be hardly influenced by the surface states, if any, attributable to the ZnTPP solids. It is also found that the Fermi level of the ZnTPP solid lies 4.9 eV below the vacuum level.