Fluorine-doped tin oxide films for supercapacitor applications
We report the effect of fluorine (F)-doping on the specific capacitance, Cs, of tin oxide (TO). TO films of various doping concentrations (0, 20, 40, and 60 at.%) were deposited on stainless steel substrates at 500°C via the spray pyrolysis method. The appearance of the Eg (488.9 cm-1), A1g (638 cm-1), and B2g (776 cm-1) modes in the Raman spectra verify the presence of TO. The shift and broadening of these fundamental peaks indicate the effective incorporation of F into the TO lattice. The cyclic voltammetry (CV) curves suggest that the electrode films follow a pseudocapacitive mechanism. The highest Cs was calculated from FTO 40% (4855 mF g-1), followed by FT0 20% (1134 mF g-1), FTO 60% (557 mF g-1), and TO (520 mF g-1). The initial increase in Cs is
attributed to the increase in the electrical conductivities of the films as more dopant was added. Upon adding 60 at.% F, TO has already exceeded its saturation point and the excess dopants only caused disorder in the structure, consequently resulting in a decreased electron mobility and electrical conductivity.