Effect of mixed valence state of titanium on reduced recombination for natural dye-sensitized solar cell applications

Nanocrystalline TiO₂ was prepared using water-assisted hydrothermal technique. X-ray diffraction pattern confirms the formation of tetragonal anatase phase, and it was further confirmed with Raman results. Williamson-Hall (W-H) plot reveals an induced strain in the sample and the calculated crystallite size of 15 nm is in accordance with the XRD results. Strain induced in the sample is due to creation of oxygen vacancies (defect), and it is responsible for the mixed valence state of Ti atom (Ti³⁺ and Ti⁴⁺) which is confirmed by X-ray photoelectron spectroscopy. Impedance studies result in increased conductivity of oxygen defect-based TiO₂ due to its fast electron hopping between the mixed valence states. High-resolution scanning electron microscopic (HR-SEM) image shows a well-agglomerated spherical-shaped nanoparticle with high surface area of 152 m²/g. Here, we report for the first time the effect of mono and co-sensitization of natural dyes on the prepared TiO₂ photoanode for dye-sensitized solar cell (DSSC) applications. The interfacial charge transfer resistance, chemical capacitance and electron recombination lifetime of the devices were examined using electrochemical impedance spectroscopy (EIS) analysis, and the performance of the best photoanode was studied using standard solar simulator at 1 Sun intensity (AM 1.5 G).