Effects of different preparation parameters on optical properties of porous TiO₂ thin films

The preparation process of porous thin films is an important part of their optical properties. The porous TiO₂ films were prepared by sol-gel method and quartz glass substrate under different process conditions, the optical properties of the films were characterized and analyzed by ellipsometer, spectrophotometer and white light interferometer, and the effects of raw material ratio, hydrochloric acid concentration, the addition of porous agent (polyethylene glycol, PEG) and other process parameters on the refractive index, porosity, transmittance and surface morphology of porous TiO₂ films were studied. Finally, the optimal process parameters for the preparation of porous TiO₂ films were determined. The results show that in the spectral range of 300 nm~700 nm, the refractive index of TiO₂ film can be reduced to 1.496 0 (wavelength 550 nm) when butyl titanate, hydrochloric acid (20%), deionized water and absolute ethanol are used in the ratio of 3∶1∶10∶8, the amount of PEG in the solution is 0.03 g·ml⁻¹, and the film is coated twice. The pores of the film layer are evenly distributed, and the porosity is 48.3%. The optical bandgap value of the thin film is 3.77 eV.