Coaxial multi-shelled TiO2nanotube arrays for dye sensitized solar cells

Abstract

The performance of one-dimensional (1D) TiO₂ nanotube based dye-sensitized solar cells (DSCs) was limited by the insufficient surface area of TiO₂ nanotubes. To solve this issue, coaxial multiple-shelled TiO₂ nanotube arrays were successfully synthesized on the transparent conductive oxide (TCO) substrates by using improved ZnO nanorod template assisted layer by layer absorption and reaction (LbL-AR) technique. To fabricate tube-in-tube nanostructures, LbL-AR TiO₂ coatings were successively deposited on the exterior walls of the ZnO nanowires and the sacrificial sol–gel ZnO spacers, which were removed together by selective etching to form the hollow tubal structures. The performance of dye-sensitized solar cells (DSCs) increases with increasing the shell number of multi-shelled TiO₂ nanotube photoanodes, attributed to the increase of the surface area, which was confirmed by N₂ adsorption-desorption isotherms and the dye-loading capacities. A maximum efficiency of 6.2% was achieved for a quintuple shelled TiO₂ nanotube photoanode with a short-circuit current density (J_sc) = 15 mA cm², open-circuit voltage (V_oc) = 0.73 V and fill factor (FF) = 0.57.