ZnO is an alternative to TiO2-based dye-sensitized solar cells (DSSCs). Adsorption of cis-ruthenium-bis[2,2′-bipyridine]-bis[4-thiopyridine] onto ZnO nanorods has been studied using X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS). XPS indicates chemisorption with a surface density of ca. 1 × 1015 molecules/cm2, confirming the possibility of using thiol-terminated dyes for ZnO-based DSSC devices. The energy level diagram, based on UPS and absorbance spectroscopy, indicates that the LUMO of this dye is lower in energy than the ZnO conduction band edge, providing minimal enthalpic driving force for photovoltaic electron injection. However, optimization of thiol-functionalized Ru dyes could result in competitive ZnO-based DSSCs.Graphical abstractView high quality image (35K)Research highlights► Ruthenium dyes may be adsorbed onto zinc oxide nanoparticles via the formation of Zn–S bonds. ► The surface density of the adsorbed dyes is similar to alkanethiols self-assembled on Au(1 1 1) surfaces. ► The energy level diagram, for the particular bipyridyl dye studied, indicates that its LUMO is slightly lower in energy than the zinc oxide conduction band edge. This is not optimal for charge transfer. ► Future design of thiol-functionalized Ru dyes could result in photovoltaic devices that compete favorably with titanium dioxide-based ones.