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. Porous TiO₂ films were prepared by sol-gel method and quartz glass substrate under different process conditions, and 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, and 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 showed that in the spectral range of 300~700 nm, the refractive index of TiO₂ film could be reduced to 1.4960 (wavelength 550 nm) when butyl titanate, hydrochloric acid (20%), deionized water and absolute ethanol were used in the ratio of 3∶1∶10∶8, and the amount of PEG in the solution was 0.03 g·ml⁻¹ and the film was coated twice. The pores of the film layer were evenly distributed, and the porosity was 48.3%. The optical bandgap value of the thin film is 3.77 eV.