Effect of annealing temperature on nano-crystalline TiO2 for solar cell applications

This study investigates the effect of annealing temperature (AT) on structure, morphology and optical properties of hydrothermally synthesized TiO2 nanocrystals. Selected-Area Diffraction (SAED) confirmed high quality monocrystals. XRD and Raman spectroscopy indicate only anatase and rutile phases. At high temperature, the (101) and (001) are preferred. PL emission peaks appear at 407, 416 and 493 nm, which can be attributed to photo-excited electron-hole pairs, band-edge excitons and oxygen vacancy defects, respectively. UV-Vis spectroscopy indicates that AT over the 200-600 degrees C temperature range causes the band gap to decrease from 3.08 eV to 2.73 eV. Hydrothermal synthesis followed by annealing at 600 degrees C is found to be a good route for high-purity, nanocrystalline anatase-phase TiO2 with the preferred {001} orientation that is thought to enhance solar cell performance.