Quantitative analysis of valence photoemission spectra and quasiparticle excitations at chromophore-semiconductor interfaces

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.