TiO2 nanostructures with controlled morphology for improved electrical properties of photoanodes and quantum dot sensitized solar cell characteristics

TiO2 nanostructures were successfully synthesized with different morphologies by sol gel and hydrothermal methods. The hydrothermal growth period was varied as 12, 24 and 48 h. The obtained samples were treated at different temperatures. The effect of synthesis and post treatment conditions on the morphology of TiO2 and its optical and electrical properties were investigated. XRD analysis confirmed the pure anatase phase of sol-gel synthesized TiO2 with tetragonal structure and the presence of mixed phases of anatase and ruffle was observed in the hydrothermally prepared samples. The SEM images show the tubular morphology for the hydrothermal samples whereas spherical morphology was observed for sol-gel synthesized samples. The nanotube formation mechanism has been discussed based on the synthesis conditions and confirmed by Raman and FTIR analysis. Two distinct peaks were observed at 365 and 385 nm in the photoluminescence spectra of hydrothermally prepared samples due to the presence of mixed phases of anatase and ruffle TiO2 whereas a single peak was observed in the absorption spectra of sol-gel synthesised samples. Further, the Hall effect-based measurements confirmed that the hydrothermally prepared TiO2 nanotubes (24 h) shows high electrical conductivity with high mobility compared to sol-gel synthesized nanoparticles. The I-V results demonstrated that the QDSSC with hydrothermally prepared TiO2 nanotubes as photoanode shows better performance with high V-oc, J(sc) and efficiency compared to other samples.