Interfacial structure and dynamics in molecular solar cells

A novel approach to studying interfacial processes in dye-sensitized solar cells is presented. In order to reduce the complexities of heterogeneity at the heterojunction in such cells, charge transfer is investigated from single fluorescent molecules (alkyl-perylene bisimide) to a highly defined single-crystalline wide-bandgap semiconductor (GaN) using confocal fluorescence microscopy under ultrahigh vacuum conditions. We report detailed studies on the energy level alignment between the perylene bisimide and GaN, characterize the nature of the surfaces involved and demonstrate confocal fluorescence microscopy in an ultrahigh vacuum set-up. The results reported here indicate that the excited state in the chromophore lies at 0 = 100 meV with respect to the bulk conduction band minimum of GaN.