Facile one-pot synthesis of uniform niobium-doped titanium dioxide microparticles for nanostructured dye-sensitized solar cells

In this study, we present the deposition of uniform sponge-like films using a novel niobium-stabilised TiO₂ gel for dye-sensitized solar cells (DSCs) applications. The introduction of Nb into TiO₂ lattice limits the transformation from anatase to rutile phase, stabilising anatase nanoparticles. The films are composed of uniform spherical particles with diameter around 3 μm, containing small nanoparticles with the average grain size of 40 nm, deposited by dip coating method. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) reveal that Nb⁵⁺ is well incorporated into the titania crystal lattice without forming specific niobium phases. UV–Visible spectra show that the doped-TiO₂ films have lower band gap energy than that of undoped-TiO₂, extending the absorption of TiO₂ into visible region. Diffuse reflectance spectroscopy (DRS) shows that the presence of rutile nanoparticles in photoanodes may improve the photovoltaic performance of solar cells due to better light scattering ability of rutile than anatase phase. The DSC stabilised with 3 at. % Nb (i.e., PN3) had the highest power conversion efficiency of 7.38 % as a result of less recombination, which is demonstrated by electrochemical impedance spectroscopy (EIS).