Synthesis and characterization of Nb 2 O 5 mesostructures with tunable morphology and their application in dye-sensitized solar cells
Mesoporous submicrometric particles of orthorhombic Nb2O5 were prepared by a very simple route
consisting in the hydrolysis of niobium ethoxide Nb(OEt)5 in an alcoholic medium containing 1-
hexadecylamine as structure-directing agent followed by a hydrothermal treatment. The effects
related to the variation of the length of the aliphatic chain of the alcohol solvent (C2 to C4) and the
ramification of the alcohol (primary, secondary and tertiary), as well as the reactants to solvent ratio
were analyzed in terms of morphology, crystal structure, specific surface area and porosity. The obtained
solids, once thermally treated to remove the organics, were thoroughly characterized by powder XRD,
UV-Vis spectroscopy (band gap measurement), photovoltage measurements (conduction band edge
determination), BET-BJH surface analysis and FESEM. By simply modifying the solvent and reactants/
solvent ratio, different morphologies spanning from nearly monodisperse beads to peanut-shaped particles,
sintered spheres aggregates, a mix of different morphologies can be achieved. The obtained materials
were tested as photoanodes in dye-sensitized solar cells. After the optimization of the thickness of
the photoanode and of its chemical treatment in order to improve the inter-particle connections, DSSCs
were prepared by using N719 dye and a non-volatile iodide-based electrolyte. The cells were tested by J-V
curves under AM 1.5 G illumination and dark, IPCE measurements and electrochemical impedance
spectroscopy. A remarkable efficiency value of 3.4% under 1 sun illumination was achieved by employing
peanut-shaped particles obtained by using 2-propanol as solvent with the highest used reactant/solvent
ratio.