  We calculate from first principles the O1s core-level shifts for a variety of
atomistic models of the interface between TiO2 and the dye N3 found in
dye-sensitized solar cells. A systematic comparison between our calculations
and published photoemission data shows that only interface models incorporating
hydrogen bonding between the dyes are compatible with experiment. Based on our
analysis we propose that at the TiO2/N3 interface the dyes are arranged in
supramolecular assemblies. Our work opens a new direction in the modeling of
semiconductor/dye interfaces and bears on the design of more efficient
nanostructured solar cells.
