Solar spectral response of photochromic YHO films

Photochromic yttrium oxyhydride, YHO, has excellent properties as a responsive solar control material, in particular due to its color-neutral darkening. In this work, we have investigated YHO’s spectral response to the solar AM 1.5 spectrum to evaluate how the total photon activation flux changes as a function of thickness and wavelength. The calculations are based on ellipsometry measurements in the 240–2000 nm range. Our results show that the UV light absorption saturates at around 400 nm thick film, while blue light (>400 nm) continues to provide photoactivation well beyond 1 μm thickness. Understanding the spectral response and absorption per unit time of activating photons as a function of material thickness is important for evaluating the material or coating for applications.