A highly crystalline Nb3O7F nanostructured photoelectrode: fabrication and photosensitisation

Abstract

A highly crystalline Nb₃O₇F nanostructured film composed of a bottom single crystal nanosheet layer with ca. 1.5 μm thickness and a top microsphere layer with ca. 18.5 μm 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 μm 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 (λ > 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.