Energy alignment manipulation at the C60/TiO2(110) interface using a blanket molecular dipole approach

Abstract

Modifying the energy alignment between the frontier levels of a chromophore and the band edges of a semiconductor substrate using a “blanket layer” of molecular dipoles is explored. The electronic structure, measured with ultraviolet and x-ray photoemission spectroscopy, of C60 deposited directly onto the TiO2(110) surface is compared with that of C60 deposited onto the surface covered by a blanket layer of the custom-designed helical peptide Z-(Aib)6-Ipa, which has a large dipole moment of 18.6 D oriented along its molecular axis and pointing toward the substrate. The C60 HOMO level is shifted 600 meV to deeper binding energy in the presence of the blanket layer, in good agreement with what is expected from a simple parallel plate capacitor model. These results demonstrate a simple and versatile strategy for controlling energy level alignment at organic/inorganic interfaces.