Electronic energy levels of organic dyes on silicon:: A photoelectron spectroscopy study of ZnPc, F16ZnPc, and ZnTPP on p-Si(111):H

Alignment of energy levels and chemical interaction of the organic pigments ZnPc, substituted F16ZnPc, and ZnTPP on H-terminated Si(111) have been deduced from valence band and core level photoelectron spectroscopy with high surface sensitivity for coverage below and in the monolayer region. Hydrogen-terminated Si(111) was prepared in UHV. The dyes have been purified by zone sublimation and were deposited at room temperature by PVD. SXPS taken at the synchrotron BESSY shows physisorption of the dye molecules; chemical shifts indicating strong interactions with the substrate have not been observed. The maxima of the HOMO photoemission of ZnPc, F16ZnPc, and ZnTPP are measured at 0.45, 1.55, and 1.0 eV below the Si valence band maximum. These experimental values are compared to theoretical values and are related to the position of the optical gap, the transport gap, and the redox potentials of the ground and excited state.