[en] Herein, X-ray photoelectron spectroscopy (XPS) and absorption spectroscopy are used to investigate the band alignment in a vertical graphene/MoS${}_2$/fluorine tin oxide (FTO) heterostructure and its influence on the resulting photoelectric response. The measured conduction band offset (CBO) value (0.65 eV) is found to be identical for both interfaces, whereas the corresponding valence band offset (VBO) values are found to be significantly different: 2.7 eV for MoS${}_2$/FTO interface and 1.0 eV for graphene/MoS${}_2$ interface. The separation of e-h pairs takes place in the built-in electric field between graphene and FTO, across the MoS${}_2$ film. The successful operation of the photodetector, based on this heterostructure, is also demonstrated, and the measured photoresponsivity and external quantum efficiency (EQE) values are found to be about 0.7 A W${}^{-<!--\; ???\; -->1}$ and 0.03, respectively, which indicates the efficient separation of the photogenerated charge carriers. The obtained results demonstrate not only the high potential of XPS diagnostics in the heterostructures preparation with the desired properties but also the good quality of MoS${}_2$ films, obtained by the sulfurization technique. (© 2021 Wiley-VCH GmbH)