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

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 C-60 deposited directly onto the TiO2(110) surface is compared with that of C-60 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 C-60 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.