Structural, morphological, and optical studies of hydrothermally synthesized Nb-added TiO₂ for DSSC application

Herein, titanium dioxide (TiO₂) nanoparticles doped with various concentrations (0–7 wt %) of niobium (Nb) are hydrothermally synthesized and used effectively as a photoelectrode for application in dye-sensitized solar cells (DSSCs). The rutile-to-anatase phase transition, accompanied by a change in crystallite size from 23.75 to 9.77 nm, is confirmed via X-ray diffraction (XRD) and Fourier transform (FT)-Raman spectroscopy. In addition, the prepared Nb–TiO₂ nanoparticles exhibit a spherical morphology with a mean grain diameter of 43.38–50.69 nm. Further, X-ray photoelectron spectroscopy (XPS) indicates a shift in the Fermi level of the TiO₂ towards the conduction band minimum, and an increase in the bandgap from 2.69 to 2.88 eV, with increasing Nb concentration. The resulting increases in the short-circuit current density (J_SC) and open circuit voltage (V_OC) with the increased injection and conductivity of electrons lead to the enhancement of the DSSC performance. EIS measurements represents the effect of Nb doping on charge transporting and recombination behavior of DSSCs. Moreover, the Nb–TiO₂-based DSSCs provide a better power conversion performance as compared to that of the pristine TiO₂.