Photochromism of amorphous molybdenum oxide films with different initial Mo5+ relative concentrations

► The effect of defects on optical properties of virgin and photo-colored MoO3 thin films ► Raman spectroscopy was used to confirm that the results of XPS were consistent with the bulk of the films. ► The absorption coefficient of as-deposited films increases with Mo5+ content. ► The temporal evolutions of absorption coefficients for all the films show initial fast rise. ► Mo5+ content of the films increases after UV irradiation except for the film with the highest initial Mo5+ content.