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 (Jsc) = 13.34 mA/cm2 and open-circuit photovoltage (Voc) = 0.63 V.