ZnO/TiO₂ nanohexagon arrays heterojunction photoanode for enhancing power conversion efficiency in dye-sensitized solar cells

TiO₂ nanohexagon arrays (TNHAs) were grown by anodization of Ti foil in an electrolyte containing NH₄F, and then the TNHAs were transferred onto FTO glass by using a drop of sol containing Ti(OBu)₄ for fabricating a front-side illumination cell. In order to improve the power conversion efficiency (PCE) of the as-fabricated dye-sensitized solar cells (DSSCs), ZnO was introduced into the TNHAs by a facile immersing method. The as-obtained ZnO/TiO₂ nanohexagon heterojunction was used as the photoanode for DSSCs, which is expected to have a low recombination rate and high absorption of light. Results indicated that the DSSCs based on the ZnO/TNHAs exhibit an enhanced current density and high PCE of 6.85% under 100 mW cm^-2 illumination. Furthermore, electrochemical impedance spectroscopy showed that the ZnO/TNHAs heterojunction-based DSSCs have optimized electron properties, including longer electron lifetime, lower resistance to electron transport, and smaller probability for electron recombination as compared to the DSSCs fabricated from pure TNHAs as photoanode.