Synthesis and characterization of TiO₂–ZnO core–shell nanograss hetero-structure and its application in dye-sensitized solar cell (DSSC)

TiO₂–ZnO core–shell nanograss (NG) hetero-structure comprising of small nanobranches with sharp edge multiple arms was synthesized via two-step synthesis techniques. Liquid phase deposition and dip-coating technique were employed to prepare the TiO₂ core and ZnO shell, respectively. The effect of the annealing temperature on the properties of TiO₂–ZnO core–shell and the performance of the DSSC has been investigated. The FESEM characterization reveals that at the temperature above 450 °C, NG started to transform into nanoparticle and the particles size increases with temperature. Annealing temperature of 350 °C shows the perfect structure of the TiO₂–ZnO NG. The phase transformation from amorphous to wurzite in the TiO₂–ZnO core–shell occurs at 350 °C. Above 400 °C, the crystallinity degree of the ZnO shell decreases with the temperature. The optical absorption of the sample increases with temperature up to 450 °C and decreases due to the decrease in the thickness of the sample. The device utilizing the sample annealed at 350 °C performs the best J _sc and η of 1.04 mA cm⁻² and 0.204 %, respectively. Annealing temperature of above 350 °C caused the decrease in η and J _sc and it might due to the transformation of NG to nanoparticles and the existence of cracked-structure film.