Prolonged lifetime and retarded recombination in dye sensitized solar cells using hydrogenated fluorine doped TiO₂ nanocrystals as a photoanode

Hydrogenated fluorine doped anatase TiO₂ nanoparticles (HF-TiO₂) are synthesized using an annealing method and applied in dye-sensitized solar cells (DSSCs) as an excellent photoanode nanomaterial. An X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure and chemical composition of the material. Scanning electron microscopy (SEM) was applied to characterize the morphology of HF-TiO₂. UV-visible absorption spectroscopy (UV-vis), valence band analysis and Mott-Schottky plots were used to elucidate the electronic band structure. The results show that the HF-TiO₂ samples can positively shift the conduction band of TiO₂, thus enlarging the driving force for efficient electron injection, reducing the interfacial losses from charge recombination and consequently facilitating charge transfer. The conversion efficiency of DSSCs with HF-TiO₂ electrodes is improved from 6.5% to 7.9% and results in a 20% photocurrent enhancement. This work provides a comprehensive explanation of the electronic structure and electron behaviors of HF-TiO₂ samples in DSSCs, like the mechanism of electron injection, transfer and recombination, and a promising strategy to explore high efficiency DSSCs.