Preparation of dye-sensitized solar cells using template free TiO₂ nanotube arrays for enhanced power conversion

By using the vertically aligned ZnO nanorod arrays (NRAs), TiO₂ nanoparticles attached ZnO nanorods (TiO₂@ZnO) and TiO₂ nanotube arrays (NTAs) were prepared from feasible seed-induced template free sol-gel dip coating method. TiO₂ NTAs were prepared by removing the ZnO nanorod cores using wet-chemical etching. By using TiO₂ NTAs as working electrode, dye-sensitized solar cell with enhanced power conversion efficiency was obtained. To verify the formation of TiO₂ NTAs various characterization techniques such as X-ray diffraction, UV-VIS absorbance spectra, Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive Spectra (EDS), and High-Resolution Transmission Electron Microscopy (HRTEM) have been used. X-ray diffraction patterns of ZnO NRAs and TiO₂@ZnO NRAs indicate that prepared films possess both the ZnO wurtzite (002) and TiO₂ anatase (101) phase. FESEM image clearly shows that vertically aligned ZnO nanorods having the diameter and length of ∼180–240 nm and ∼1.5 μm, respectively, have been formed. The FESEM image also clearly showed that diameter and length of TiO₂@ZnO NRAs are ∼250–320 nm and ∼1.5 μm, respectively. By using UV-VIS absorption spectra, the band gap of vertically aligned ZnO NRAs, TiO₂@ZnO NRAs, and TiO₂ NTAs have been calculated and its values were 3.14, 3.20, and 3.52 eV, respectively. The dye-sensitized solar cell was prepared by using three different working electrodes ZnO NRAs, TiO₂@ZnO, and TiO2 NTAs. The power conversion efficiency of dye-sensitized solar cells prepared using ZnO NRAs, TiO₂@ZnO, and TiO₂ NTAs are 3.53%, 4.04%, and 5.18%, respectively. TiO₂ NTAs with 10 s HCl etching exhibited the highest photoelectric conversion efficiency of 5.18% with short-circuit photocurrent density (J_sc) = 13.34 mA/cm² and open-circuit photovoltage (V_oc) = 0.63 V.