Opto-electronic properties of hydrothermally grown rod-like TiO ₂ nanostructures: potential electron transport layer for photovoltaic devices

Abstract This study reports the deposition of compact TiO 2 (c-TiO 2 ) thin films, which serve as seed layers for the growth of TiO 2 nanostructures. Five samples, labeled S 1 , S 2 , S 3 , S 4 , and S 5 , were prepared with 2, 4, 6, 8, and 10 deposition cycles of c-TiO 2 thin films, respectively. Using the hydrothermal method, rod-like TiO 2 nanostructures were successfully grown on these thin films. Field emission scanning electron microscopy images confirmed the formation of rod-like nanostructures with an average length of approximately 0.7 μm, and the number density of the nanorods increased with the seed layer thickness. X-ray diffraction analysis revealed the presence of both anatase and rutile phases of TiO 2 , with the majority of peaks corresponding to the anatase phase. The UV–Vis transmittance ranged from 60–90 % in the 400–700 nm wavelength range for all five films. The optical band gaps for samples S 1 , S 2 , S 3 , S 4 , and S 5 were 3.11, 3.10, 3.07, 3.05, and 3.05 eV, respectively. Based on the overall characterizations, sample S 2 demonstrated the best properties. This study indicates that the TiO 2 nanorod layer on the c-TiO 2 seed layer effectively enhances the electron transport performance of perovskite-based photovoltaic devices.