Sol-Gel Derived ZnO Nanorod Templated TiO<sub>2</sub> Nanotube Synthesis for Natural Dye Sensitized Solar Cell

Abstract

Natural dye sensitized solar cells (nDSSC) mostly suffer from low solar cell performance, that vertically aligned nanotube TiO2 as the photoanode is expected to increase the performance by providing higher surface area and direct electron transport. Nanostructured TiO2 films have been fabricated on glass substrates employing ZnO nanorod films as the template. First, vertically oriented ZnO nanorod on a glass substrate was prepared hydrothermally. Then, sol-gel dip-coating technique was used to deposit TiO2. The template films were dip-coated into sols of titanium tetraisopropoxide-ethanol-diethanol ammine with withdrawing rate of 2 cm/min for three- (Ti3) and seven-times (Ti7). After drying at 100 °C for 10 min, the films were calcined at 550 °C for 1h and washed with HCl 3% (v/v). The films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). It is observed that different coating cycles resulted in different film morphologies. Nanotube TiO2 with diameter of ~50 nm was identified for Ti3, while Ti7 displayed sheet-like structure. The diffraction patterns confirmed the presence of only anatase crystalline phase with crystallite size of 10.3 nm (Ti3) and 21.7 nm (Ti7). The dye absorption was red-shifted indicating dye monomeric adsorption on TiO2 via chelation. Enhanced absorption of anthocyanin dye extracted from pericarps of mangosteen (Garcinia mangostana l.) fruit on TiO2 nanotube compared to TiO2 nanoparticle (P25) was observed leading to improved photovoltaic performance of the constructed nDSSC.