Annealing temperature effect on structural, morphological and optical parameters of mesoporous TiO₂ film photoanode for dye-sensitized solar cell application

Use of Degussa P25 titanium-dioxide nanopowder in dye-sensitized solar cell (DSSC) photoanode improves efficiency of the DSSC cell. Annealing of titanium dioxide is required for fabrication of crystalline mesoporous thin film photoanode on transparent conducting glass using doctor blade method. Different annealing temperatures provide different structural, morphological, and optical properties of the photoanode, which may influence the efficiency of the cell. In this paper, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and UV-Vis-NIR spectroscopicanalysis have been carried out to investigate annealing temperature effect on various structural parameters, mole-fraction, phase-content, and optical bandgap of the TiO₂ film photoanode. It was observed that depending on annealing temperature, theratio of polymorphs of Degussa P25 changed substantially. For the change in annealing temperature from 350 °C to 600 °C, variations occurred in crystallite size from 11.9 nm to 24.9 nm, strain from 0.006 to 0.014, specific surface area from 62.77 m²·g^-1 to 125.74 m²·g^-1, morphology index from 0.49 to 0.64, dislocation density from 5 × 10¹³ line/m² to 8 × 10¹⁵ line/m², crystallite per unit surface area from 2 × 10¹³ m^-2 to 2.5 × 10¹⁴ m^-2, and optical bandgap from 2.4 eV to 3.1 eV.