Surface fluorination of α-Fe2O3 using selectfluor for enhancement in photo electrochemical properties

Fluorinated alpha-Fe2O3 nanostructures are synthesized via a facile hydrothermal route using Selectfluor (TM) (F-TEDA) as a fluorinating as well as growth directing agent. The addition of incrementally increasing amount of F-TEDA to Fe precursor under hydrothermal conditions resulted in preferential growth of alpha-Fe2O3 along (110) orientation with respect to (104) direction by similar to 35%, the former being important for enhanced charge transport. On increasing fluorination, the heirarchical dendritic-type alpha-Fe2O3 changes to a snow-flake type structure (FTEDA-20%) anisotropically growing along the six directions however, at higher F-TEDA concentrations (>= 30%), loosely held particulate aggregates are seen to be formed. The X-Ray Photoelectron Spectroscopy (XPS) suggest the maximum fluorinarion of alpha-Fe2O3 at 1.21 at% in 30% F-TEDA. Further, optical absorption studies reveal reduction in optical band gap from 2.10 eV in case of pristine to 1.95 eV for fluorinated alpha-Fe2O3. A photoanode made by taking 20% fluorinated alpha-Fe2O3 in a ratio of 10:90 with respect to TiO2 (P-25) showed improved performance in dye sensitized solar cells with an increase in efficiency by similar to 16% in comparision to that of pristine Fe2O3 and TiO2. Furthermore, anode consisting of thin films of fluorinated alpha-Fe2O3 on FTO also exhibit enhanced current density on illumination of similar to 100 W/m(2). The increase in photoelectrochemical activity seems to be due to the combination of two factors namely preferential growth of alpha-Fe2O3 along (110) direction resulting in an improved charge transfer efficiency and reduced recombination losses due to the presence of fluorine.