Effect of Process-Related Parameters on Band Gap of Electrophoretically Deposited TiO2/Nb2O5 Composite Thin Films

Abstract

Nano-crystalline composite thin films of titanium dioxide and niobium (v) oxide (TiO₂/Nb₂O₅ ) were successfully deposited on fluorine-doped tin oxide (FTO) coated glass substrate using electrophoretic deposition (EPD) technique. The colloidal suspension utilized in EPD cell consisted of mixture of TiO₂ and Nb₂O₅ nanopowders and 2-propanol in a Pyrex glass. Values of potential difference (25 to 60V) were applied across the EPD electrodes placed in a parallel configuration 1.2cm apart and partially immersed in the suspension. The optimization of EPD parameters was achieved from transmittance measurements and band gap energy calculations. Both Nb₂O₅ and TiO₂ nanoparticles were seen in XRD graphs to be present in the composite films in the ratio 1 to 1.78 which confirmed that both type of nanoparticles suspended in 2-propanol developed positive surface charges and were moved towards and deposited on the cathode upon application of an electric field. The band gap energy was evaluated for films deposited from varied EPD process-related parameters namely, concentration, deposition times and applied potential. The maximum values of band gap were obtained for films electrophoretically deposited from particle concentration of 0.01g/40mL (or 0.25g/L), applied voltage of 35V, and deposition time of 90s. These values of EPD process-related parameters formed the optimum values for deposition of crack free films of good porosity. The changes in band gap values are attributed to either energy shift of conduction band or valence band energy levels. The TiO₂/Nb₂O₅ composite thin films, fabricated in this study from optimized parameters of EPD technique had smooth morphology as shown by SEM images. Further work is needed to evaluate the potential of TiO₂/Nb₂O₅ composite films deposited by EPD for dye–sensitized solar cell application.