Rose bengal-sensitized nanocrystalline ceria photoanode for dye-sensitized solar cell application

For efficient charge injection and transportation, wide bandgap nanostructured metal oxide semiconductors with dye adsorption surface and higher electron mobility are essential properties for photoanode in dye-sensitized solar cells (DSSCs). TiO2-based DSSCs are well established and so far have demonstrated maximum power conversion efficiency when sensitized with ruthenium-based dyes. Quest for new materials and/or methods is continuous process in scientific investigation, for getting desired comparative results. The conduction band (CB) position of CeO2 photoanode lies below lowest unoccupied molecular orbital level (LUMO) of rose bengal (RB) dye. Due to this, faster electron transfer from LUMO level of RB dye to CB of CeO2 is facilitated. Recombination rate of electrons is less in CeO2 photoanode than that of TiO2 photoanode. Hence, the lifetime of electrons is more in CeO2 photoanode. Therefore, we have replaced TiO2 by ceria (CeO2) and expensive ruthenium-based dye by a low cost RB dye. In this study, we have synthesized CeO2 nanoparticles. X-ray diffraction (XRD) analysis confirms the formation of CeO2 with particle size similar to 7 nm by Scherrer formula. The bandgap of 2.93 eV is calculated using UV-visible absorption data. The scanning electron microscopy (SEM) images show formation of porous structure of photoanode, which is useful for dye adsorption. The energy dispersive spectroscopy is in confirmation with XRD results, confirming the presence of Ce and O in the ratio of 1:2. UV-visible absorption under diffused reflectance spectra of dye-loaded photoanode confirms the successful dye loading. UV-visible transmission spectrum of CeO2 photoanode confirms the transparency of photoanode in visible region. The electrochemical impedance spectroscopy analysis confirms less recombination rate and more electron lifetime in RB-sensitized CeO2 than TiO2 photoanode. We found that CeO2 also showed with considerable difference between dark and light DSSCs performance, when loaded with RB dye. The working mechanism of solar cells with fluorine-doped tin oxide (FTO)/CeO2/RB dye/carbon-coated FTO is discussed. These solar cells show V (OC) similar to 360 mV, J (SC) similar to 0.25 mA cm (-2) and fill factor similar to 63% with efficiency of 0.23%. These results are better as compared to costly ruthenium dye-sensitized CeO2 photoanode.