  Investigating quasiparticle excitations of molecules on surfaces through
photoemission spectroscopy forms a major part of nanotechnology research.
Resolving spectral features at these interfaces requires a comprehensive theory
of electron removal and addition processes in molecules and solids which
captures the complex interplay of image charges, thermal effects and
configurational disorder. We here develop such a theory and calculate the
quasiparticle energy-level alignment and the valence photoemission spectrum for
the prototype biomimetic solar cell interface between anatase TiO2 and the N3
chromophore. By directly matching our calculated photoemission spectrum to
experimental data we clarify the atomistic origin of the chromophore peak at
low binding energy. This case study sets a new standard in the interpretation
of photoemission spectroscopy at complex chromophore/semiconductor interfaces.
