Novel fabrication of TiO₂/ZnO nanotube array heterojunction for dye-sensitized solar cells

TiO₂ nanotube arrays (TNTs) were prepared by using an electrochemical anodization method, and then the detached TNTs were successfully transferred onto a fluorine-doped tin oxide glass substrate with the help of a tetrabutyl titanate-containing sol. In order to improve the photoelectric conversion efficiency (PCE) of the as-fabricated dye-sensitized solar cells (DSSCs), an easily-operated immersing method was employed to fabricate a TiO₂/ZnO nanotube array (TNT/ZnO) heterojunction, which has advantages of a high aspect ratio, low recombination rate and high absorption of visible light. The results indicate that under AM 1.5 illumination, the DSSCs based on the TNT/ZnO heterojunction exhibit a better short circuit current density (J_sc) of 8.67 mA cm^-2 and a higher PCE of 3.98%. Electrochemical impedance spectroscopy analysis shows that the TNT/ZnO heterojunction-based DSSCs have optimized properties, such as a longer electron lifetime, lower impedance of electron transport, higher impedance of electron recombination, and electron collecting rate as high as 95.2%.