Engineering the intermediate band states in amorphous Ti³⁺-doped TiO₂ for hybrid dye-sensitized solar cell applications

Ti³⁺-doped amorphous TiO₂ nanoparticles (a-TiO₂:Ti³⁺), which are an intermediate band semiconductor, were fabricated by high intensity ultraviolet pulsed laser ablation in water. The absorption band of a-TiO₂:Ti³⁺ nanoparticles, which appears between the visible and infrared regions, is much wider than that of the rutile TiO₂ nanoparticles. The intermediate band, which has a recombination lifetime of 0.71 μs, is found to be 1.61 eV above the valence band (VB) top of TiO₂. It can be shown that the a-TiO₂:Ti³⁺/TiO₂ nanotube hybrid dye-sensitized solar cells (DSSCs) not only have a high fill factor and large open circuit voltage, but also have high photovoltaic conversion efficiency as compared to TiO₂ nanotube DSSCs. Considering that most of the current solar cells use only a single photoelectric conversion material (PCM), our results will promote the research on multi-PCM hybrid solar cells.