Mesoporous SnO2 Spheres Synthesized by Electrochemical Anodization and Their Application in CdSe-Sensitized Solar Cells

Mesoporous SnO2 spheres of tunable particle size were synthesized for the first time by facile electrochemical anodization of tin foil in alkaline media. As the anodization process involves no sophisticated reactor or toxic chemicals, and proceeds continuously under ambient conditions, it provides an economic way of synthesizing nanostructured SnO2 on a large scale. Structural characterization indicates that these spherical particles consist of an agglomeration of SnO2 nanocrystals, resulting in a high internal surface area. This makes them a promising photoanode material for use in semiconductor-sensitized solar cells (SSCs). By using the successive ionic-layer adsorption and reaction method, a thin layer of CdSe was conformally coated on the surface of SnO2 nanocrystals, which were previously treated with aqueous TiCl4 solution. Efficient charge separation was observed by photoluminescence spectroscopy. After deposition of a ZnS passivation layer onto the CdSe light-harvesting layer, a power conversion efficiency of similar to 1.91% was achieved in a regenerative photoelectrochemical cell. Factors dictating interfacial charge recombination and charge separation are discussed and compared to those in its molecular dye-sensitized counterpart. This study represents the first attempt so far of using mesoscopic SnO2 as a photoanode in a SSC device, and characterizing it under simulated AM 1.5, 100 mW cm(-2) illumination. The results are a step toward development of highly efficient SSCs employing novel electron transport materials and sensitizers, such as infrared light absorbers PbS. CuInSe2, etc.