Polysilazane-Derived Layer for Enhancing Durability of Yttrium Oxyhydride Photochromic Coatings

Yttrium oxyhydride (YHO) exhibits photochromic properties under ambient conditions, making it a promising material for smart window applications. However, operational challenges including lattice contraction upon illumination, expansion during bleaching, and limited thermal stability introduce mechanical stress and susceptibility to degradation from environmental gases, compromising long-term performance. This study investigates perhydropolysilazane (PHPS)-derived SiO_xN_y coatings as a solution for environmental protection of PHPS. A silicon–nitrogen–hydrogen preceramic polymer was deposited via spin coating and UV-cured on glass substrates, followed by reactive magnetron sputtering of YHO thin films. Three configurations glass/SiO_xN_y/YHO, glass/SiO_xN_y/YHO/SiO_xN_y, and glass/YHO/SiO_xN_y were evaluated under solar simulator illumination, with optical performance characterized by UV–vis spectrophotometry. The results reveal that SiO_xN_y coatings effectively shield YHO from environmental degradation while preserving its photochromic response. Minimal performance loss across coated architectures underscores the potential of PHPS-derived layers as multifunctional barriers, advancing the durability and applicability of YHO-based smart coatings.