Solution Route to Large Area All-TiO2 One-Dimensional Photonic Crystals with High Reflectivity and Different Structural Colors.

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.