Size-controlled synthesis of mesoporous Nb₂O₅ microspheres for dye sensitized solar cells

Mesoporous Nb₂O₅ microspheres assembled by nanoparticles are successfully synthesized through a simple solvothermal process and subsequently annealing treatment, free of any template or catalyst. By controlling the reactant NbCl₅ concentration, we could easily tune the diameter of the Nb₂O₅ spheres from 200 to 900 nm, which were also used to fabricate dye-sensitized solar cells. Studies found that dye-sensitized solar cells based on Nb₂O₅ with sizes of around 480 nm show a highest power conversion efficiency of 2.97% with a relatively high short current density (J_sc) of 6.8 mA cm^-2 and an open circuit voltage (V_oc) of 0.738 V, which benefits from its higher specific surface area for adsorbing more dye molecules, superior light scattering capacity for boosting the light-harvesting efficiency, and modest electron transport properties.