Solution route to large area all-TiO₂ one-dimensional photonic crystals with high reflectivity and different...

In this paper, wafer-scale dense and meosoporous TiO₂ films are fabricated via spin-coating and thermal treatment. A photo-curable resin, acrylated polytitanoxane tetramer (Ti-resin), is synthesized as the precursor of TiO₂ to deposit dense films. The refractive index of TiO₂ films at 500 nm is tuned from 2.17 (dense) to 1.49 (porous) by changing film porosity via adding different amount of polystyrene (PS) to the precursor solvent. A reactive compatibilizer containing one mercapto group and three benzyl rings is synthesized to reduce phase separation and prevent film crack of porous films during the calcinations. The deposition protocol is optimized to prevent infiltration of dense TiO₂ layers into porous TiO₂ layers. Film thicknesses of both dense and porous TiO₂ films can be linearly tuned by changing deposition number. All-TiO₂ 1D photonic crystals with different structural colors are successfully fabricated on quartz and silicon wafers with reflectivity of at least 90%, covering the spectrum from 400 to 800 nm.