The effect of the metal and selenium precursors on the properties of NbSe2 and Nb2Se9 nanostructures and their application in dye-sensitized solar cells

Abstract

Herein, we report on the effect of the precursors on the structural, morphological, and optical properties of niobium selenide using the heat-up colloidal method. The metal precursor was varied from the conventional NbCl₅ to NbF₅ whilst Se, SeO₂, and selenourea were used as the selenium precursors. The NbCl₅ and NbF₅ resulted in the formation of NbSe₂ and Nb₂Se₉ respectively. While maintaining the two different metal precursors and varying the selenium precursor from Se, SeO₂ to selenourea, the properties of NbSe₂ and Nb₂Se₉ changed slightly, however the effect of changing the selenium precursor was less pronounced than changing the metal precursors. From the XRD and XPS, the NbSe₂ nanostructures were more susceptible to oxidation than Nb₂Se₉ as Nb₂O₅ was observed in the XRD and the percentage of M–O in the XPS was much higher in NbSe₂. NbSe₂ formed nanoflowers whilst Nb₂Se₉ formed rods with 3.29 eV and 2.43 eV band-gaps, respectively. Also, the band-gaps were red-shifted as the selenium precursors were varied. The NbSe₂ nanoflowers and Nb₂Se₉ nanorods were used as counter electrodes in dye-sensitized solar cells. Two methods were used to fabricate the counter electrodes i.e. spin coating and drop casting. The electrochemical properties of the spin coated counter electrodes were better than the drop casted ones; hence, they were employed in dye-sensitized solar cells. The spin coated NbSe₂ nanoflowers had the highest efficiency of 6.84%, attributed to the nanoflower morphology.