Electrochemically Synthesized Mesoscopic Nickel Oxide Films as Photocathodes for Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSCs) have been considered as promising and reliable solar energy conversion devices that are suitable for various applications. In general, mesoscopic TiO₂ films are often used as photoanodes in DSCs; however, significant effort has been put into the development of NiO photocathodes with the long-term goal of tandem DSCs for high-voltage output. In this study, we report the preparation of mesoscopic NiO films via electrochemical anodization of Ni foil and their application as photocathodes in p-type DSCs. The anodic NiO had a mesoporous structure composed of ∼10 nm nanoparticles, and to the best of our knowledge, this was the first demonstration of mesoscopic NiO synthesis by anodic oxidation. The performance of the anodic photocathodes was comparable to that of conventional NiO electrodes comprising 20 nm-sized particles, even though the preparation of the anodic oxide film was significantly easier. Additionally, charge transfer kinetics in the NiO films were compared with those in conventional photocathodes using electrochemical impedance analyses, and the feasibility of the anodic NiO photocathodes in tandem DSCs was also demonstrated