TiO2 is a common protection layer on semiconductor electrodes for photoelectrochemical water splitting. We investigate the interface formation of TiO2 on amorphous silicon tandem solar cells by X-ray photoelectron spectroscopy. In order to optimize the contact properties, we prepare TiOx interface layers with various oxygen content by reactive magnetron sputter deposition. We observe, that a TiOx interface layer can reduce the silicon oxide growth during the film deposition on the amorphous silicon, but it forms a non-ohmic contact. The electrochemical investigation shows, that the benefit due to the reduction of the silicon oxide is counteracted by the unfavorable contact formation of TiOx interface layers prepared with low oxygen content. (C) 2016 Elsevier B.V. All rights reserved.