A highly crystalline Nb3O7F nanostructured photoelectrode: fabrication and photosensitisation

A highly crystalline Nb3O7F nanostructured film composed of a bottom single crystal nanosheet layer with ca. 1.5 mu m thickness and a top microsphere layer with ca. 18.5 mu m thickness has been successfully fabricated on a FTO conducting substrate through a facile and one-pot hydrothermal method. The top Nb3O7F microspheres with 2-5 mu m diameter consist of transparent single crystal nanosheets with 10-40 nm thickness. Without the need for further calcination, the as-synthesised Nb3O7F nanostructured films possess excellent crystallinity and high mechanical stability, which can be directly used as photoanodes for CdS quantum dot-sensitised solar cells (QDSSCs) and dye-sensitised solar cells (DSSCs). The transparent single crystal nanosheets constituting top Nb3O7F microspheres possess exposed (100) and (010) surfaces, which can play an important role in sensitiser loading. The photoelectrochemical measurements indicate that the CdS quantum dot-sensitised Nb3O7F nanostructured photoanode with seven chemical bath deposition (CBD) cycles (NbCdS-7) shows the best performance under visible light irradiation (lambda > 400 nm) due to higher carrier concentration and longer electron lifetime in NbCdS-7. QDSSCs made of NbCdS-7 photoanodes show an overall light conversion efficiency of 1.68%, which is almost 1.4 and 1.9 times of the NbCdS-5 and NbCdS-10 photoanodes, respectively. DSSC measurement indicates that an overall light conversion efficiency of 2.78% can be achieved for the Nb3O7F nanostructured photoanode. This work demonstrates the possibility of direct growth of a highly crystalline metal oxide-based nanostructured film on a FTO conducting substrate as a photoanode material without the need for further calcination for solar energy conversion applications.