One possible reason for the low photovoltage in this system could be due to a large conduction band offset at the Sb2S3/TiO2 heterointerface. To assess the band offset between Sb2S3 and TiO2, an XPS interface experiment was carried out. The band alignment was determined from the photoemission spectra, following a commonly practiced procedure as described in the literature. The valence band maximum (VBM) and core level (CL) binding energies (BE) for Sb2S3 and TiO2 were determined through measurements on thick layers of each material. XPS measurements of Sb2S3 show an energetic distance of the fermi level EF to the valence band maximum EVBM of ∼1 eV, indicating that it is nearly intrinsic and even weakly n-type (Figure ). For the determination of the band alignment, the peak positions of the substrate (Sb2S3) as well as the film (TiO2) specific photoemission lines need to be considered. The evolution of the CL BEs for all discussed interface experiments is given in Figure . The CL BEs are referenced to the VBM at the free surface of Sb2S3 or TiO2, respectively, and plotted over TiO2 film thickness.