Studies On The Modification Of TiO₂ Thin Films And Its Impact On The Optical Characterization

In order to solve the gradually worsening energy crisis, solar energy as a kind of clean energy has been paid much attention. As a low cost, non-toxic and highly chemical stable semiconductor, titanium dioxide becomes the hotspot as the energy conversion parts of solar cell. Unfortunately, the band gap of TiO₂ is wide, which causes low conversion efficiency. Therefore, different elements were doped into TiO₂ to narrow the band gap and enhance the absorption of solar energy.In this paper, pristine TiO₂ thin films were synthesized by sol-gel method and magnetron sputtering systems. Modifications were followed by sol-gel and ion implantation methods respectively. Ge was doped into TiO₂ films by sol-gel method. Fe and Cr were implanted separately and then co-implanted. In the TiO₂ films prepared by magnetron sputtering, Ge and Si were implanted separately and together. The impact of this doping methods and different ions were researched on the crystallization, surface chemical states and optical characterization.The results showed that the absorption of original TiO₂ films prepared by magnetron sputtering was better than the films prepared by sol-gel method. According to XRD and XPS, the different absorption results from the difference of surface chemical states and bonds of these two kinds of films.Certain improvement was achieved by Ge doped TiO₂ films synthesized by sol-gel method. In comparison to the pristine TiO₂ films, the doped films (Ti:Ge = 7:3) had high crystallinity, and the majority of Ge was element. The absorption edge of the doped films was red shift and the band gap decreased. Fe/Cr co-implanted films showed lower crystallinity than the pure TiO₂ films, and in the co-doped films, Fe and Cr existed in the form of element and oxides based on XPS spectra. The interaction of Fe and Cr lowered the valid ion concentration, which made the absorption of the co-implanted films worse than Fe doped but better than non-doped. Unlike the Fe/Cr co-doped films, the new phase of Ge and Si in the Ge/Si co-implanted films improved the optical properties.