Niobium pentoxide nanotube powder for efficient dye-sensitized solar cells

In this work, we demonstrate for the first time the fabrication of niobium pentoxide (Nb2O5) nanotube powder using a simple electrochemical anodization method. During the anodization process, the anodic oxide can be continuously and spontaneously released into the electrolyte, and after collection a white powder was obtained. The powder mainly displayed nanotube morphology with the tube length in the range of about 50-100 nm and a diameter of about 20-30 nm. The as-prepared powder was amorphous, and after annealing the powder can be crystallized to the orthorhombic phase. Based on the preparation of the powder, a thick and high quality Nb2O5 film on the transparent conductive substrate was produced, and was further employed as the photoanode in dye-sensitized solar cells (DSSCs). A comparably high efficiency of 3.15% was obtained, with a large open-circuit voltage of 0.738 V, which is among the highest values ever reported for porous Nb2O5 film based DSSCs. Furthermore, the difference in electron behavior of the device as compared to a TiO2 counterpart was studied, which exhibited a significantly reduced recombination rate, beneficial to high efficiency DSSCs.