In this study, nanostructured TiO 2 electrodes are coated with a NiO x overlayer by reactive direct currrent magnetron sputtering for dye-sensitized solar cells (DSSC). The effects of a 10-min heat treatment at 450 °C in a rapid thermal annealing system under vacuum, TiO 2 /NiO x (vacuum), and under ambient atmosphere, TiO 2 /NiO x (air), has been intensively investigated.For a TiO 2 /NiO x (air) electrode, the cell conversion efficiency (η) can be enhanced substantially due to the 10% increase in amount of N719 dye adsorbed on TiO 2 surface as compared with a bare TiO 2 electrode. The basic NiO x -coated surface favours dye attachment through its carboxylic acid groups since the isoelectric point (IEP) of NiO (pH 10.3) is higher than that of anatase TiO 2 (pH 6.2). Electrochemical impedance spectroscopy analysis (EIS) shows that a NiO x overlayer suppresses the transport of photoelectrons from TiO 2 to the electrolyte. It is proposed that IEP of NiO x (air) is higher than that of NiO x (vacuum). The more basic TiO 2 /NiO x (air) surface leads to an increment in dye adsorption which consequently facilitates the transport of electrons at the TiO 2 /dye interface and results in better light harvesting. For TiO 2 /NiO x (air) electrode, the best η of 7.31% with J sc and V oc of 24.2 mAcm −2 and 0.80 V, respectively are obtained.