NOVELTY - Niobium pentoxide (Nb2O5)-doped titanium dioxide (TiO2) nanoparticles (NPs)-containing solution is prepared which involves: (a) preparing a transparent precursor solution containing niobium chloride (NbCl5); (b) treating the transparent precursor solution with UV; (c) centrifuging the UV-treated transparent precursor solution and removing residual water to obtain a polymeric gel containing niobium (Nb) as dopant source; (d) adding a TiO2 slurry into polymeric gel containing corresponding amount of niobium compound; and (e) heat treating homogenously mixed TiO2-Nb composite slurries.    USE - The methods are useful for preparing Nb2O5-doped TiO2 NPs-containing solution, and DSSCs (all claimed).    ADVANTAGE - One-pot synthesis is provided for Nb5+-doped TiO2 NPs with low cost and high efficiency for DSSCs. The NPs exhibit well-crystallized pure anatase TiO2 phase with uniform particle distribution. The incorporation of Nb5+ leads to a stronger and broader light absorption in visible light range and a decrease of band gap with increasing Nb dopant content, which enhances the efficiencies of light-harvesting and electron injection and suppresses the charge recombination. The method provides a simple and cost-effective mass-production route to synthesize n-type metallic ion doped TiO2 NPs as excellent photoanode materials.    DETAILED DESCRIPTION - Niobium pentoxide (Nb2O5)-doped titanium dioxide (TiO2) nanoparticles (NPs)-containing solution is prepared which involves: (a) preparing a transparent precursor solution containing niobium chloride (NbCl5); (b) treating the transparent precursor solution with UV; (c) centrifuging the UV-treated transparent precursor solution and removing the residual water to obtain a polymeric gel containing niobium (Nb) as the dopant source; (d) adding a TiO2 slurry into the polymeric gel containing corresponding amount of niobium compound followed by a high-speed mixing and defoaming to obtain different homogenously mixed TiO2-Nb composite slurries in different molar ratio of Nb/(Nb+TiO2) ranging from 0.5 to 5.0 mol.%; and (e) heat treating the homogenously mixed TiO2-Nb composite slurries for a period of time in order to obtain the Nb2O5-doped TiO2 NPs-containing solution. INDEPENDENT CLAIMS are included for:    (1) a Nb2O5-doped TiO2 NPs-containing solution prepared by the method having a niobium content of 0.5-5.0 mol.%;    (2) a method of preparing dye sensitized solar cells (DSSCs) which involves: (a) providing a clean conductive glass; (b) coating a first film of TiO2 slurry on the conductive glass; (c) coating a second film of the Nb2O5-doped TiO2 NPs-containing solution on the first film in (b) to form a photoanode; (d) sintering the photoanode in (c) at 450 degrees C for 30 minutes to remove the organics and then slowly cooling to room temperature to form a sintered photoanode; (e) immersing the sintered photoanode in a dye solution at room temperature for a period of time to make the Nb2O5-doped TiO2 NPs sufficiently absorb dye molecules to form a dyed photoanode; (f) rinsing the dye-covered photoanode with ethanol and drying in air; (g) providing a counter electrode; (h) sandwiching the counter electrode and the dye-covered photoanode with an electrolyte and a thermal-plastic spacer to form an assembly; and (i) hot sealing the assembly by a cover glass with a hot-melt film as an adhesive under the thin cover glass to form the DSSCs; and    (3) a dye sensitized solar cell prepared by the method having an active area of about 0.16 cm2.