Electronic and Molecular Surface Structure of a Polyene-Diphenylaniline Dye Adsorbed from Solution onto Nanoporous TiO2

The surface electronic and mol. structure of a new org. chromophore useful for dye-sensitized nanostructured solar cells was studied by electron spectroscopy. Initially the use of a simple mol. system contg. the polyene-diphenylaniline chromophore in a solar cell device was verified. The electronic and mol. surface structure of the functional dye-sensitized interface was then studied in detail by a combination of core level spectroscopy, valence level spectroscopy, x-ray absorption spectroscopy, and resonant photoemission spectroscopy. The results indicate a dominating orientation of the mol. at the surface, having the diphenylaniline moiety pointing out from the surface. Valence level spectroscopy, x-ray absorption spectroscopy, and resonant photoemission spectroscopy were used to exptl. delineate the frontier electronic structure of the mol., and the exptl. spectra were analyzed against theor. spectra, based on d. functional theory. Together the study gives insight into energy matching of the mol. electronic states with respect to the TiO2 substrate as well as the localization of the frontier electronic states and the direction of the charge-transfer absorption process with regards to the TiO2 surface.