Dye-sensitized solar cells (DSCs) are promising candidates for building integrated photovoltaics. The use of multiple dyes simultaneously, co-sensitization, promises improved efficiency and stability using combinations of new or existing dyes. Understanding how co-sensitization influences the dyes/TiO2 interface of working electrodes at the molecular level informs the use and rational design of compatible co-sensitizers since this interface governs the optoelectronic and photovoltaic properties of the device. To this end, we propose to investigate the influence of co-sensitization on the interfacial structure (dye adsorption modes, interdye separation and dye/TiO2 tilt angles) of N749 and D131 dyes on TiO2 using In situ neutron reflectometry with systematic contrast matching. Results will help produce new molecular design rules for engineering superior DSC dyes.